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Palomar Electronics Max-Mod. Spoiler alert!

Now if only someone could crack the original type number that they scraped off their "ERF7530" MOSFET, that would be really cool!

And Eric, if you read this feel free to chime in and contradict me if you like. No hard feelings.

73

I have done some quirky search typos to see if 7530 even comes up...

References to ERF are there, but there's something more - did anyone try using letters?

Try AN75n30 and see what comes up

It's way outdated....but it appears to have been used initially for Automotive Spark Plug applications...

The newer stuff can't match that - too slow of recovery times...

See the Littlefuse PDF below and compare.....
 

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  • OnSemiFETFDA59N30-D.pdf
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  • 13N10Replacement.pdf
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  • Littelfuse_LSIC1MO120E0080-1148188.pdf
    1.8 MB · Views: 2
I just figured that "7530" number was simply pulled out of Eric's, er, you know.

Reminds me of the russky sweep tubes with the globby rubber-stamped "8975" number on them. That number was chosen because of a gap in the sequence of officially-registered JEDEC tube-type numbers. Galaxy used it in their base linears and deliberately used a bogus number rather than the original russky "6P45C".

I strongly suspect that the original manufacturer's type number for the 7530 or the newer 9530 does not contain those four digits at all.

73
 
You're prolly' right (as always (y)(y) ... )

I just figured that "7530" number was simply pulled out of Eric's, er, you know.
... [...] ...
I strongly suspect that the original manufacturer's type number for the 7530 or the newer 9530 does not contain those four digits at all.

73

I'm quoting you on it...:D

Just in my searches, the MOSFET series' "set" ID's crossed over to having to use the "N"

Like 12N8 or 13N10 - found these and tried variants and located the PDF's above but from the various manufacturers.

Don't need to go into it, but I started this research project back in the CB Tricks days WAY-BACK when...

So you're not the only one that is trying to find sources for the dead boxes left behind after these kids tend to blow them up looking for that "Radioactivity"....
 
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Gee that's wonderful and makes me feel warm and fuzzy inside that they were able to do some mathematical calculations.
Unfortunately those calculations are completely useless since the tip 36 95% of the time when it fails will always send line voltage directly to the finals causing them to detonate and when the max mod fails it always results in an open circuit which protects the finals. Unfortunately mathematical calculations are no substitute for Real World experience

The scenario you've described is rare. The average radio operator stops talking once they realize the radio is only producing a carrier after the series pass modulator shorts out. This does not cause the finals to self destruct instantly. Many radios apply the full 12 volts to the driver and final in SSB with AB bias on. The only difference here is the presence of carrier and that will take time to heat and fail. 25 years ago I modified a 148 to run 12 volts of modulated DC in the final, working the final much harder than just 12 volts. The mod has been copied thousands of times with success since then. You'll change 10 pass transistors before you find one that needs a final too. That was the guy who kept right on talking with no response, long after the mod transistor shorted. When that happens, the final is usually the weaker 2SC1969 and not the better 2SC2312.
 
The scenario you've described is rare. The average radio operator stops talking once they realize the radio is only producing a carrier after the series pass modulator shorts out. This does not cause the finals to self destruct instantly. Many radios apply the full 12 volts to the driver and final in SSB with AB bias on. The only difference here is the presence of carrier and that will take time to heat and fail. 25 years ago I modified a 148 to run 12 volts of modulated DC in the final, working the final much harder than just 12 volts. The mod has been copied thousands of times with success since then. You'll change 10 pass transistors before you find one that needs a final too. That was the guy who kept right on talking with no response, long after the mod transistor shorted. When that happens, the final is usually the weaker 2SC1969 and not the better 2SC2312.
 
LMAO, I bet Bog boss still running that same 148 today too. Half the guy in nyc city went to the "water hole tech" to get their 148's "volted" and most ran them without issues for many years aside from some heat dissipation issues if they were long winded as some on the bowl can be . Long time Donald, good to see ya still here , im back after 52 months away...Steve
 
LMAO, I bet Bog boss still running that same 148 today too. Half the guy in nyc city went to the "water hole tech" to get their 148's "volted" and most ran them without issues for many years aside from some heat dissipation issues if they were long winded as some on the bowl can be . Long time Donald, good to see ya still here , im back after 52 months away...Steve
Hey Steve, I've wondered when I was going to hear that broadcast audio on the band again? Very few of the other locals utilize my receivers bandwidth as well. As you probably know, Big Boss sells everything at one point or another so that early 148 is long gone. Hope to talk to you soon.
 
Hey Steve, I've wondered when I was going to hear that broadcast audio on the band again? Very few of the other locals utilize my receivers bandwidth as well. As you probably know, Big Boss sells everything at one point or another so that early 148 is long gone. Hope to talk to you soon.
Yes everything is for sale w Pete,lol..I may speak with ya but wont be local GW, Im down in Raleigh Area now, left Ny area when I went away. Be well !!, sorry for thread hijack.
 
Yes everything is for sale w Pete,lol..I may speak with ya but wont be local GW, Im down in Raleigh Area now, left Ny area when I went away. Be well !!, sorry for thread hijack.
Well that is "DXable" from CT. Conditions here have been getting good enough to motivate a water change in the big amp. It's just been sitting for over a year. This time I'll be driving it with a transmitter that has Kahn AM Powerside circuitry installed. The energy of both sidebands is constructively re-phased back into the bandwidth of one. This idea is something I had wanted to talk to Dave about but you're the only one I know that can get a hold of him.
 
First-off., I know I'll be most likely be "stepping on some feet" here :( and to others, just "preaching to the choir".!:D But feel the need produce a somewhat mini-novel length of an "explanatory-rant" concerning a few "pet-peeve" subjects of mine, but will also WELCOME any additions, corrections, dis-likes, or likes.?(y)

It's just that I've always enjoyed doing my best to take-the-time in explaining some basic (and some semi-complex) issues / principals surrounding just some of the MANY "urban-legends" floating-around for SO many years.!! Just ask ANY of my customers, of which I've been known (at times that is..) to "talk the ears off an elephant".!!:eek:


+++++++++++++++++

Pertaining to a "volted" final(s), disabled audio limiters (aka: "NPC" / negative-peak-compression / RF-envelope flat-lining, splatter mod) and Cobra-style "swing-kit" mods:

Well first-off., there's a GOOD reason as to why ALL manufactures (even since the early 1960s.!) of voltage-modulated, transistor-output, AM radios would apply the modulation voltage to BOTH the RF-driver AND the RF final., whether it be via the old-style dual-coil transformer (or single-coil "autotransformer") architecture., or via the new-style, pass-transistor architecture.

Just check-out the oldest of the old, SAM's photofact books going back to the very first transistorized radios.!

Then, add to that., that EVERY volted-final radio that's ever come across my "surgery-table" also had its AMC circuitry (at best.!) trim-pot "cranked-up", or (at worst.!) had a part (or parts.!) "clipped" (cut) out of the AMC / audio-limiter circuitry. I once had an RCI-2950 that had been through 4 different shops before getting to me, and had found four (4) individual places where the AMC "chain" had a part removed or cut.!

I mean., it's like having a steel chain. If someone cuts-out just one individual "link" from it, it's now broken, and if someone (or in this case, each subsequent shop) cuts another "link" (in the chain) it's just as broken as before.! But yet, each "tech".?!, has their own favorite "monkey-see, monkey-do" component (from a CB-trick book or internet-page) that they remove or cut, in believing in (or "justifying" their service-fee for) their customer's "peak & tune" job:mad:

BTW, I just HATE that term., because it's like going to an auto-repair shop, and then having the auto-technician asking the customer: "Sir, would you like to have your vehicle's "front-end" to be "peaked & tuned".? -- Well, it's aptly called an "alignment" for a reason.!(y)

And because of this volted-final modification (especially when combined with a typically "cranked" or "clipped" audio limiter) I've had a number of "blown-final" rigs come-across my bench. But luckily (in the case of the older BJT final rigs) I've still got quite a "stash" of genuine OEM (Mitsubishi) 2SC-1969s.!:D

BTW & FYI., just check the spec-sheets for the OEM Mitsubishi 1969 and the 2312, and although you'll find that both of them are rated at about the same ~18w output, the hFE forward-gain of the 1969 (depending on the suffix letter of X, A, B, C or D., but typically C) has at least a 30-40 point higher rating than a typical 2312, plus the OEM 1969 has that very nice internal reverse-protection diode, which the lower hFE gain 2312 doesn't.!:)

**Anyway., sorry ya'll for me continuing my mini-rant here., but after being the lead-tech for multiple Motorola company-owned, service-centers, which then lead to becoming a self-employed, sole-proprietorship business for 35+ years in servicing virtually only Motorola & GE "professional-grade" FM equipment & control systems, and then because of micro-sized, "surface-mount" components (and SUPER reliability.!) of such professional equipment, bench-servicing basically "dried-up", which left mostly just the "grunt-work" of doing "installs":(

I've now (for 12+ years) become all TOO aware of the almost universal LACK of "electronics-101" knowledge AND the understanding to apply such concepts to actual, real-world "consumer-grade" electronics (radios, RF-amps, guitar / audio amps, inverters, etc) of the wanna-be / self-proclaimed, electronics-technicians "out-there":mad:

But getting back to the 1st subject of this ranting-post (regarding "volting") and about the voltage-modulating of both the driver & final in a transistor transmitter, as opposed to modulating only the RF-final in a tube-type transmitter-chain.

A vacuum-tube is for the most part / cases, a voltage amplifier (measured as mutual-conductance / micomhos / Gm) versus a transistor, which is for the most part / cases is a current-amplifier (measured as beta / current-gain / hFE)

A tube-type, plate-voltage modulated, single RF final transmitter has (in most cases) a "clean-looking", symmetrical, AM-modulated, RF-envelope output. This is mostly because the "modulation-free", RF carrier that's "driving" the control-grid of that RF-final tube, contains virtually NO "power" (barely a few milliwatts.?) because of the extremely high input impedance / resistance of that vacuum "voltage-valve", and so as the plate B+ supply drops (during the negative-going halves, of the plate modulation voltage "swing") there will NOT be seen any "leak-though" (of power) from the non-modulated, RF-carrier / driver stage showing-up in the resulting RF-final output (at the negative-peaks / "mirror-image valleys") of the RF-envelope.

BUT., contrast that with the requirements to "drive" a typical BJT power-transistor, in which there NEEDS to be a relatively large amount of power (~0.5 - ~2.0w) to "drive" that RF-final transistor (depending on the make-up & power output rating of the RF-chain).

In such a typical transistor AM modulated transmitter-chain, if you would ONLY voltage-modulate the RF-final (as is done in tube-type, plate-modulation) meaning that the transistor driver stage would consist of a relatively large amount of un-modulated carrier power (of the driver) could then easily "pass-through" that final stage, even during the negative-going halves of the modulation voltage applied to the RF final's collector, which could / would result in a distortion of the negative-going peaks / valleys of the output RF envelope, by not allowing for the "mirror-image valleys" to drop to zero (which is what equals a 100% modulated "envelope")

Hence., virtually ALL manufacturer-designed voltage-modulated transistor, transmitter-chains have a 2-tiered chain of collector / drain modulation.

This is because, when the final AND driver stages are voltage-modulated together (in phase) the amount of un-modulated RF carrier power required (from the pre-driver) is SO small (~25 - ~100mw) that it should / will not affect the output RF-envelope wave-form "valleys" (near the 100% point) of the voltage modulated RF driver, much less the RF final.!

Sooo, if the RF-final is "volted" (tied to B+) and only the "driver" is modulated, whether it's just an AM-only "class-C" biased RF-chain, or especially in the case of a transmitter-chain with SSB capability ("class AB" biased) because in such RF-chains, there will be a pre-set bias-voltage applied to that RF-final and driver during transmit mode, which makes those transistors even more susceptible to "pass-through" of RF power from the preceding stage, and will result in some amount of that RF power from the modulated driver stage (~0.5 - ~2.0w) to leak-through (and be amplified by) the "volted" final.

Even when the modulated RF driver's collector-voltage is near the RF "cut-off" point (during the negative-going halves of the modulation voltage) some of that driver's RF-power will easily just "push-its-way-through" (and then be amplified by) the RF-final (which now has full B+ applied to it) and will show-up as some form of a distortion in the output of the resultant RF-envelope's, negative-peaks ("valleys")

Also, one must consider that in such a "volted-final" scenario, that each "power-transistor" (driver and final) are now "sitting" at a MUCH different part of their beta / hFE "output-curve", which is caused by the GREATLY differing collector voltages of driver & final during modulation.!

AND it will also do NOTHING to increase the transmitter's output (you're still limited to the spec-sheet, power-rating of that volted-final.!) except that now, it will display itself in the form of some (or a lot of.!) fake / splatter "air-watts" on your watt-meter (no matter HOW expensive someone's watt-meter may be.!)

***A good illustration / analogy that I believe explains this "fake-effect", would be like having a natural-gas meter outside of your house, that measures how many cubic-feet of natural-gas that has passed through it, to heat your house. It measures the total volume of gas (ANY gas or air.!) that passes through it, right.?! Well, what would happen if your gas company added other types of non-flammable (or less-flammable gases) to your supply line.? Simple.! Your gas-meter would now show you're using more cubic-feet (total volume) of gas, for the same amount of heat (or less) generated in your home.!

It's the same principal for RF harmonics & "splatter". They ARE in fact, actual watts, but are on other, much higher frequencies, which are then just simply added together in a / your wattmeter, but they're watts that are totally useless.! And given the fact that they are FAR away from 27Mhz (mostly 54Mhz & 81Mhz and even higher multiples.!) they also then just "add insult to injury", in the fact that all of those higher-frequency watts being produced, are just being "jammed right back down the throat" of your transmitter / amplifier as full-out reflections from your tuned-antenna giving you an SWR of 10+:1 on those other "out-of-the-ballpark" frequencies.!

Then another "add insult to injury" fact (that fools your watt-meter into reading those "air-watts") is that those higher frequency harmonics (2nd, 3rd, 4th, 5th, etc.) AND splatter, will "push" your watt-meter's needle (or digital read-out) MUCH further per-watt produced at those higher frequencies, on your meter, that's been designed / calibrated for ~30 Mhz.!

Meaning in general, that for every watt produced at some of those higher frequency harmonics & splatter can AND will "push" your 30 Mhz designed & calibrated meter (even a PEP modified Bird-43 meter with the proper "slug" inserted.!) will be displayed by as much as 3 or more watts, per 1 watt of that harmonic-splatter.!!

Due to "character-limit"., to be continued in just a moment...:eek:
 
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*** And here's a web-link to a "photo-article" I had produced, concerning a customer's Galaxy DX-95T mobile-radio in the hope to illustrate to others this principal of what I call fake / air-watts, that's got some pretty good "before & after" photos, and showing a side-by-side comparison of an O-scope wave-form, along with both a non-powered / passive analog watt-meter, and a powered / active digital watt-meter, and how EASY it is to "fool" just about ANY watt-meter - see photo #5 - Just click on the FaceBook "F" in the upper right corner of the main-photo below to view the entire 7-photo tech-article directly on my public-page...



But just as another example of "volting", there are a few of the semi-newer "Styker" brand / models (ie: SR-955) in which the two main paralleled / gate-tied output finals are in fact "volted" to B+, BUT, even in those models (as shown in their corresponding schematics), that they are ALWAYS preceded by a 2-tiered stage (pre-driver & driver) of voltage-modulated "devices".!(y)

BTW., but even in the above factory-volted type transceivers, I've always felt a bit "uncomfortable" with the way the resulting RF-envelope appears (slightly mis-shaped "slopes" between their valleys & peaks) when it's compared to the RF-envelope of the more "normal" / common designs of single & dual final, voltage-modulated transmitters that have been around for a looong time.

***One of the other wonderful (NOT.!) "snake-oil mods" is the "Cobra swing-kit" (with or without the variable dead-key control) modification, in which one just simply puts either a fixed or variable resistor in series with the modulated B+ to the RF driver transistor, and then adds an electrolytic capacitor (of various values) across / in parallel with said resistor / control-pot.

And the logic goes like this., that the resistor will limit the voltage to the RF driver (lowering the RF final's output) which because the driver "draws" a small amount of current, even a 1/2w potentiometer will "handle it", in order to make your dead-key variable, and then by adding the electrolytic-capacitor across that resistance, will, when modulated by the AC audio voltage, that the positive-going (higher voltage) halves of the modulation voltage, will just pass through the capacitor, giving one a large / wide, dead-key to forward-swing "ratio" on their watt-meter.

Well actually, all the above IS true, BUT, when the resulting RF-envelope is looked at, one will observe a TERRIBLY shaped RF-envelope, wave-form:(

This manifestation is caused by a two-fold problem that is NOT taken into consideration if one actually understands (not just "knows".!) how capacitor dynamics work.!

Firstly (and quite well known.?) is that as the frequency of the AC audio signal rises, a capacitor will conduct more of that voltage through it, as a result of having a lower impedance / resistance and provides more voltage being applied to that RF-driver at higher voice frequencies, and less at lower voice frequencies.

Secondly (and actually MORE importantly) is remembering "ELI the ICE man".!! -- Is anyone here old enough to remember that one.?!;)

Whereas, E (voltage) leads I (current) by 90* in an inductive (L) circuit (hence ELI) and I (current) leads E (voltage) by 90* in a capacitive (C) circuit, hence ICE. >ELI the ICE man<

This means that when using the above-mentioned resistor & capacitor "swing-kit", whenever you're modulating that radio, not only will the frequency-response by "out-of-wack" (between the driver & final) but more importantly (and REAL easy to see in the resultant RF-envelope) is that the voltage reaching the RF-driver transistor WILL lag-behind the voltage reaching the RF-final transistor by ~90*. -- And what a mess it makes of (and lessens the "clean-watts".!) of what's trying to "leave your antenna".!!

Whew-wee, what a lot of "rant" typing.! Especially for a slow, 2-fingered, hunt & peck typist as myself:( Though hopefully (as verbose / wordy at it is) was at least a bit helpful to some, and NOT irritating to otherso_O

Again., with advance thanks for any likes, additions and / or corrections (even dis-likes.!)

Regards & 73s
Eric (aka: the channel 21 "Radioman")
https://www.facebook.com/radioman55
 
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First-off., I know I'll be most likely be "stepping on some feet" here :( and to others, just "preaching to the choir".!:D But feel the need produce a somewhat mini-novel length of an "explanatory-rant" concerning a few "pet-peeve" subjects of mine, but will also WELCOME any additions, corrections, dis-likes, or likes.?(y)

It's just that I've always enjoyed doing my best to take-the-time in explaining some basic (and some semi-complex) issues / principals surrounding just some of the MANY "urban-legends" floating-around for SO many years.!! Just ask ANY of my customers, of which I've been known (at times that is..) to "talk the ears off an elephant".!!:eek:


+++++++++++++++++

Pertaining to a "volted" final(s), disabled audio limiters (aka: "NPC" / negative-peak-compression / RF-envelope flat-lining, splatter mod) and Cobra-style "swing-kit" mods:

Well first-off., there's a GOOD reason as to why ALL manufactures (even since the early 1960s.!) of voltage-modulated, transistor-output, AM radios would apply the modulation voltage to BOTH the RF-driver AND the RF final., whether it be via the old-style dual-coil transformer (or autotransformer) architecture, or via the new-style, pass-transistor architecture.

Just check-out the oldest of the old, SAM's photofact books going back to the very first transistorized radios.!

Then, add to that., that EVERY volted-final radio that's ever come across my "surgery-table" also had its AMC circuitry (at best.!) trim-pot "cranked-up", or (at worst.!) had a part (or parts.!) "clipped" (cut) out of the AMC / audio-limiter circuitry. I once had an RCI-2950 that had been through 4 different shops before getting to me, and had found four (4) individual places where the AMC "chain" had a part removed or cut.!

I mean., it's like having a steel chain. If someone cuts-out just one individual "link" from it, it's now broken, and if someone (or in this case, each subsequent shop) cuts another "link" (in the chain) it's just as broken as before.! But yet, each "tech".?!, has their own favorite "monkey-see, monkey-do" component (from a CB-trick book or internet-page) that they remove or cut, in believing in (or "justifying" their service-fee for) their customer's "peak & tune" job:mad:

BTW, I just HATE that term., because it's like going to an auto-repair shop, and then having the auto-technician asking the customer: "Sir, would you like to have your vehicle's "front-end" to be "peaked & tuned".? -- Well, it's aptly called an "alignment" for a reason.!(y)

And because of this volted-final modification (especially when combined with a typically "cranked" or "clipped" audio limiter) I've had a number of "blown-final" rigs come-across my bench. But luckily (in the case of the older BJT final rigs) I've still got quite a "stash" of genuine OEM (Mitsubishi) 2SC-1969s.!:D

BTW & FYI., just check the spec-sheets for the OEM Mitsubishi 1969 and the 2312, and although you'll find that both of them are rated at about the same ~18w output, the hFE forward-gain of the 1969 (depending on the suffix letter of X, A, B, C or D., but typically C) has at least a 30-40 point higher rating than a typical 2312, plus the OEM 1969 has that very nice internal reverse-protection diode, which the lower hFE gain 2312 doesn't.!:)

**Anyway., sorry ya'll for me continuing my mini-rant here., but after being the lead-tech for multiple Motorola company-owned, service-centers, which then lead to becoming a self-employed, sole-proprietorship business for 35+ years in servicing virtually only Motorola & GE "professional-grade" FM equipment & control systems, and then because of micro-sized, "surface-mount" components (and SUPER reliability.!) of such professional equipment, bench-servicing basically "dried-up", which left mostly just the "grunt-work" of doing "installs":(

I've now (for 12+ years) become all TOO aware of the almost universal LACK of "electronics-101" knowledge AND the understanding to apply such concepts to actual, real-world "consumer-grade" electronics (radios, RF-amps, guitar / audio amps, inverters, etc) of the wanna-be / self-proclaimed, electronics-technicians "out-there":mad:

But getting back to the 1st subject of this ranting-post (regarding "volting") and about the voltage-modulating of both the driver & final in a transistor transmitter, as opposed to modulating only the RF-final in a tube-type transmitter-chain.

A vacuum-tube is for the most part / cases, a voltage amplifier (measured as mutual-conductance / micomhos / Gm) versus a transistor, which is for the most part / cases is a current-amplifier (measured as beta / current-gain / hFE)

A tube-type, plate-voltage modulated, single RF final transmitter has (in most cases) a "clean-looking", symmetrical, AM-modulated, RF-envelope output. This is mostly because the "modulation-free", RF carrier that's "driving" the control-grid of that RF-final tube, contains virtually NO "power" (barely a few milliwatts.?) because of the extremely high input impedance / resistance of that vacuum "voltage-valve", and so as the plate B+ supply drops (during the negative-going halves, of the plate modulation voltage "swing") there will NOT be seen any "leak-though" (of power) from the non-modulated, RF-carrier / driver stage showing-up in the resulting RF-final output (at the negative-peaks / "mirror-image valleys") of the RF-envelope.

BUT., contrast that with the requirements to "drive" a typical BJT power-transistor, in which there NEEDS to be a relatively large amount of power (~0.5 - ~2.0w) to "drive" that RF-final transistor (depending on the make-up & power output rating of the RF-chain).

In such a typical transistor AM modulated transmitter-chain, if you would ONLY voltage-modulate the RF-final (as is done in tube-type, plate-modulation) meaning that the transistor driver stage would consist of a relatively large amount of un-modulated carrier power (of the driver) could then easily "pass-through" that final stage, even during the negative-going halves of the modulation voltage applied to the RF final's collector, which could / would result in a distortion of the negative-going peaks / valleys of the output RF envelope, by not allowing for the "mirror-image valleys" to drop to zero (which is what equals a 100% modulated "envelope")

Hence., virtually ALL manufacturer-designed voltage-modulated transistor, transmitter-chains have a 2-tiered chain of collector / drain modulation.

This is because, when the final AND driver stages are voltage-modulated together (in phase) the amount of un-modulated RF carrier power required (from the pre-driver) is SO small (~25 - ~100mw) that it should / will not affect the output RF-envelope wave-form "valleys" (near the 100% point) of the voltage modulated RF driver, much less the RF final.!

Sooo, if the RF-final is "volted" (tied to B+) and only the "driver" is modulated, whether it's just an AM-only "class-C" biased RF-chain, or especially in the case of a transmitter-chain with SSB capability ("class AB" biased) because in such RF-chains, there will be a pre-set bias-voltage applied to that RF-final and driver during transmit mode, which makes those transistors even more susceptible to "pass-through" of RF power from the preceding stage, and will result in some amount of that RF power from the modulated driver stage (~0.5 - ~2.0w) to leak-through (and be amplified by) the "volted" final.

Even when the modulated RF driver's collector-voltage is near the RF "cut-off" point (during the negative-going halves of the modulation voltage) some of that driver's RF-power will easily just "push-its-way-through" (and then be amplified by) the RF-final (which now has full B+ applied to it) and will show-up as some form of a distortion in the output of the resultant RF-envelope's, negative-peaks ("valleys")

Also, one must consider that in such a "volted-final" scenario, that each "power-transistor" (driver and final) are now "sitting" at a MUCH different part of their beta / hFE "output-curve", which is caused by the GREATLY differing collector voltages of driver & final during modulation.!

AND it will also do NOTHING to increase the transmitter's output (you're still limited to the spec-sheet, power-rating of that volted-final.!) except that now, it will display itself in the form of some (or a lot of.!) fake / splatter "air-watts" on your watt-meter (no matter HOW expensive someone's watt-meter may be.!)

***A good illustration / analogy that I believe explains this "fake-effect", would be like having a natural-gas meter outside of your house, that measures how many cubic-feet of natural-gas that has passed through it, to heat your house. It measures the total volume of gas (ANY gas or air.!) that passes through it, right.?! Well, what would happen if your gas company added other types of non-flammable (or less-flammable gases) to your supply line.? Simple.! Your gas-meter would now show you're using more cubic-feet (total volume) of gas, for the same amount of heat (or less) generated in your home.!

It's the same principal for RF harmonics & "splatter". They ARE in fact, actual watts, but are on other, much higher frequencies, which are then just simply added together in a / your wattmeter, but they're watts that are totally useless.! And given the fact that they are FAR away from 27Mhz (mostly 54Mhz & 81Mhz and even higher multiples.!) they also then just "add insult to injury", in the fact that all of those higher-frequency watts being produced, are just being "jammed right back down the throat" of your transmitter / amplifier as full-out reflections from your tuned-antenna giving you an SWR of 10+:1 on those other "out-of-the-ballpark" frequencies.!

Then another "add insult to injury" fact (that fools your watt-meter into reading those "air-watts") is that those higher frequency harmonics (2nd, 3rd, 4th, 5th, etc.) AND splatter, will "push" your watt-meter's needle (or digital read-out) MUCH further per-watt produced at those higher frequencies, on your meter, that's been designed / calibrated for ~30 Mhz.!

Meaning in general, that for every watt produced at some of those higher frequency harmonics & splatter can AND will "push" your 30 Mhz designed & calibrated meter (even a PEP modified Bird-43 meter with the proper "slug" inserted.!) will be displayed by as much as 3 or more watts, per 1 watt of that harmonic-splatter.!!

Due to "character-limit"., to be continued in just a moment...:eek:
Radioman56, your knowledge here impressed me and surpasses most that have tried volting a final. Believe it or not this entire thing about volting the final started as a 1986 high school electronics project when we were studying different modulators. Being a CBer, I was comparing this to what was being done inside the 148GTL and the 29LTD. I noticed the 148GTL had a larger final but was only applying modulated 6 volts VCC to the final collector and was essentially wasting the 5 watts of audio output from the TA7222AP, since it was only driving the darlinton pass transistor in AM.

The 29LDT put modulated 12 volts on a smaller final from that chip, through what first appears to be a modulation transformer. Turns out in TX, only one winding was being used as an AF choke to isolate it from the DC supply. All that was needed here was a Radio Shack 10 amp alternator whine choke. And, of course rewiring the mode switch so that the 8 volt bias line only turned on in SSB. Now the pass transistor ran cool only modulating the driver and the final 12 volt VCC was modulated through a coupling cap and choke, from the AF chip.

As I read your second part of the post, you mention very good phasing information when combining two modulated stages. The stock 148GTL takes audio from the TA7222AP and passes it through a coupling cap (90 degree phase shift), through two more transistors where the the phase remains the same as the input to them. The overall change is 90 degrees from the output of the AF chip to the finals. When modded, the final goes through one coupling cap and provides a 90 degree shift. To line the cap charge time up with the driver, the closest common value cap was a 470 uf. Messing this up still made the watt meter happy but produced noticeable distortion in the audio.

Eventually a local (T-Bird) purchased the modification, reverse engineered half of it and sent it into Secrete CB Magazine. He never did figure out you still needed to run the final in class C in order to properly modulate it at 12 volts on AM and every one I've seen done elsewhere left that part out too. Snake one wire into the stock harness and it gets easily missed. That mistake killed a lot of stock finals. If you took the time to bend the pins on an MRF477 to fit the pinout of the 2SC1969 and rematch the lower output impedance, this thing took off with the higher gain but killed internal, base power supplies. Today the mod has been reduced to nothing more than placing 12 volts on the final in most cases. That's just a bad idea all around.
 
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The driver transistor is modulated along with the final transistor because of the way a transistor behaves when the collector supply is shut off.

In a high-level modulated tube-type AM transmitter, only the final tube is modulated. The driver tube is powered from steady DC voltage only.

The reason is the "off" behavior of a tube compared to a bipolar transistor.

The tube won't feed any carrier at all out to the antenna when the modulated B+ feeding it reaches zero.

Zero modulating voltage, zero output.

Bipolar transistors do not behave this way. Even with the collector at zero Volts, a small amount of carrier will leak through from the driver transistor.

Makes it impossible to achieve 100 percent modulation, if the carrier power can't be modulated down to zero output power.

The driver and final transistor are modulated together for the simple purpose of achieving 100% modulation.

At least that's what I remember being told by the ARRL handbook 50 or more years ago. Or maybe it was one of their other ARRL-branded tech books.

A tube just has less "feedthrough" when its supply voltage is cut off.

Not sure why this factoid doesn't get much mention.

For reasons I can't explain, the driver transistor in a typical CB radio will, in fact modulate down to 100 percent negative peaks, even when the final has been "volted", powered from a fixed supply voltage.

Maybe because the drive level feeding into the driver transistor is fairly small?

Maybe.

73
 
The driver transistor is modulated along with the final transistor because of the way a transistor behaves when the collector supply is shut off.

You're spot-on there sir.! (y)
In a high-level modulated tube-type AM transmitter, only the final tube is modulated. The driver tube is powered from steady DC voltage only.

The reason is the "off" behavior of a tube compared to a bipolar transistor.

Correct (x2) again.!! :)
The tube won't feed any carrier at all out to the antenna when the modulated B+ feeding it reaches zero.

Zero modulating voltage, zero output.

You're certainly quite correct with the above two statements, but., a plate-modulated, RF-final tube does not reach 0 volts during the negative going halves of the audio modulation voltage. :oops:

Take for example, a Browning Mk-4. The steady-state (no-modulation / dead-key) plate-voltage on the RF-final during AM operation is about ~250v (and about ~380 in SSB). The factory datasheet of that 7558 RF-final tube shows a MAX plate-voltage of about ~375v, which is more than close enough for safe operation in the SSB mode, as there's no 2-way (up & down) "voltage-swing" (only plate-load, voltage-dropping) while in SSB mode.

BUT., during AM operation (in order to achieve ~100% modulation) the plate voltage must "swing" (change direction EQUALLY., both down AND up.!) from its dead-key, resting-point voltage (~250v in the above case).

This would mean, that if the negative-going halves of the modulation voltage would go to 0 volts., then the positive-going halves of the modulation voltage would have to swing-up to about ~500v (2x250=500), which could easily "pop" that 375 volt rated tube.! :eek:

A vacuum tube (or transistor) does not have to reach zero (0) supply voltage in order for it to go into "RF cut-off" (stop conducting) within an RF "tank-circuit" configuration...

Bipolar transistors do not behave this way. Even with the collector at zero Volts, a small amount of carrier will leak through from the driver transistor.

Yes, you're quite correct again with the above statement (y) But., the same set of standards still apply here. Namely., that when you have a transistor driver & final (let's say in a generic Cobra-29) those two transistors (at a no-modulation, dead-key) are "sitting" at a nominal ~14v (a vehicle's voltage while the engine is running).

If those transistors actually needed to reach 0 volts during the negative going halves of the modulating voltage in order to reach RF cut-off (aka: ~100% modulation) they would then also need to reach about ~28v (2x14=28) during the positive-going halves of the modulation-voltage, which would cause enough amps to flow through those devices to easily let-out some of the "factory-installed smoke".!! :whistle:

Makes it impossible to achieve 100 percent modulation, if the carrier power can't be modulated down to zero output power.

Correct-amundo.! (y)

But., depending on the parts-values of the "support-components" around the RF driver & final(s)., the collector / drain voltage at which the driver and final(s) need to approach the point of RF cut-off (for ~100% modulation) can vary GREATLY.!! :cautious:

As an example, a
transformer-modulated radio (like a generic Cobra) uses the ~14v supply (at dead-key) and has the "support-components" around the transistors / MOSFETS designed to generated a typical ~4 watt dead-key output (~5w DC input to the final) at that approximate ~14v of collector / drain voltage., and then "swings" a plus & minus voltage of about ~5v (~9v to ~19v) to achieve the ~100% modulation., meaning that the circuit is designed so that the driver & final are in fact at or near RF cut-off, at about ~9v.

But a
transistor-modulated radio (like a generic Galaxy) uses a LARGE pass-transistor / "Darlington-pair", voltage-regulator (which also modulates that voltage) in order to bring the nominal ~14v supply all the way DOWN to a nominal (and variable) voltage of about ~3v to ~8v., which then produces a nominal ~1w to ~9w of dead-key output.

In such radios, the architecture of the "support-components" around those transistors / MOSFES are designed to typically produce about a ~4w dead-key with only about ~5v being applied to the collectors / drains.

In other words., the circuit architecture is designed to produce the same watts with less volts (as compared to a generic Cobra)., though of course., requiring more amps (at the lower voltage) in order to equal the same amount of collector / drain watts.!!

From there., the transistor regulator / modulator then "swings" a plus & minus voltage of only about ~2 volts (~3 to ~7v) to achieve the same ~100% modulation.

So in the end., it totally depends on the circuit-design AND the component-values surrounding / supporting the RF amplifying device (whether a tube or transistor.!) that determines not only the amount of voltage needed to produce a determined amount of dead-key wattage., but also at what voltage the amplifying "device" goes into the "cut-off" region to produce the "mirror-image valleys" of the AM modulated RF-envelope...

The driver and final transistor are modulated together for the simple purpose of achieving 100% modulation.

Again., you're correct that both transistors / MOSFETS are modulated together to achieve 100% modulation., where the mirror-image valleys of the RF-envelope just "touch" each other., which is what a ~100% modulated RF-envelope looks like.! (y)

But., it's actually because of the ability for some of the relatively large amount RF energy (from a modulated driver-stage) to leak or "push-through" the final-stage (especially when there's a full & steady Vcc applied to the final) that could easily make it difficult for the final-stage output from producing that zero (~0) watt cut-off "valley" point., which represents a ~100% modulation envelope.!

At least that's what I remember being told by the ARRL handbook 50 or more years ago. Or maybe it was one of their other ARRL-branded tech books.

Yep., the esteemed & respected "ARRL handbook" has always been one of my "go-to" books.!, and even have an antique one (1/8 the size of the present ones.!) that I acquired from the school-library in the 5th-grade, that was printed in my birth-year of 1956.! :rolleyes:
A tube just has less "feedthrough" when its supply voltage is cut off.

As mentioned a number of paragraphs up., an RF final tube., even during the negative-going halves of its modulation voltage will never have its plate voltage drop even close zero...

Its because a plate-modulated RF-final tube has its "steady-state" RF input (from the driver tube) being fed to the RF-final's "control-grid" (G1)., which has a VERY high impedance / resistance., and therefore can NOT add any "power" (perhaps a few milliwatts.?) to the RF-final's "plate" output.!

That's why when you look at a schematic of a tube-type linear-amplifier., the RF input to the first driver tube(s) / stage (being fed from your transmitter)., AND the input to the linear's final output tubes (coming from the output of the linear's driver stage)., is almost ALWAYS applied to the cathodes of all the tubes.

This is because in a "grounded-grid" amplifier (which is just about any tube-type amp I've seen)., uses the typically very low impedance / resistance of the cathodes for the RF power input to not only "match-up" to the input(s) driving them., but also that almost all the power being driven into the cathode of a power-tube will be added-to the output of whatever power is being produced by the amplification factor (Gm / Transconductance) of the tube(s) themselves.!! :D

Not sure why this factoid doesn't get much mention.

See above...
For reasons I can't explain, the driver transistor in a typical CB radio will, in fact modulate down to 100 percent negative peaks, even when the final has been "volted", powered from a fixed supply voltage.

Well normally., the only times I've seen such results (on a properly connected O-scope waveform of the radio's output)., is when the modulation circuit (now only connected to the driver-stage)., has either been adjusted beyond the 100% point, and / or outright "clipped".!

This is because what's considered to be a 100% modulated envelope must actually be limited to about ~98% in order to keep it from creating harmonics / splatter.

And when the RF-driver is "pushed" totally to absolute zero output ("hard cut-off") during the negative going halves of the modulation voltage (which in actuality causes over-mod / splatter generated by the driver.!)., then YES., the "volted" final WILL in fact., "turn-off" completely., giving the effect / look of a fully-modulated RF-envelope.

But that's because
there's absolutely no RF at all being produced by the driver (at those at / or beyond cut-off points) with which to pass / leak through (which would otherwise be also amplified by) the final.!!
Maybe because the drive level feeding into the driver transistor is fairly small?

Yes, yes, yes..!!
Maybe.

73

Actually., all-in-all (although it took quite a bit of time to type all this)., thank you for your input.!, as not only is it all now in my "MSword-doc" files for future use., but it also gave me the incentive to do my best at analyzing AND explaining the best I could.!!

With respectful regards,
Eric (aka: the channel 21 "Radioman")
KY8E
 
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