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"Pill" questions...

steved

Member
Feb 4, 2008
97
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What are the input drives for the common pills like the 1446, 2290, and 2879??

How do you figure the input requirements of multiple pill amps with these pills? Do you multiply the input drive of the pill by the number of pills?
 
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sd1446.pdf
2sc2290.pdf
2sc2879.pdf

multiply the input drive of the device by the number used. study the Pout VS Pin graph while keeping in mind the minimum device gain. max input levels should be avoided for am/ssb operation.

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then Get Foxit PDF Reader Here
 
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So...

A 4-pill box with 1446 transistors should be driven at 28 watts (4 units at 7 input watts)? I assume that is an RMS input?
 
I knew that was coming. IM not to sure on your 4 x 1446 box Steve , but I'd guess around a 2 watt DK in to it / pep could be anywhere between 8 watts or over 20 pep depending on the box and how the radio is tuned ? There's many variables as well as ways to explain it. 28 watts RMS would more then likely fry that baby up ! IM guessing here but 28 watts RMS would be pushing around 40 to 50 watts pep ! it depends on the box , Some boxes are high drive and others are not , when talking high drive , were not talking about radio dead key ,were talking about pep and or RMS modulated swing. I think Freecell could explain it better for you , but he gave you the spec's and not so much the understanding , I think that takes a bit more lip service for some or knowledge by others to understand it.
 
No worries...I don't have the box to fry! I'm just trying to understand this whole thing...the 4x1446 was just an example...

Just trying to understand how a transistor can have a 7 watt rated input, but yet they tend to get driven with much more in actual use. For example, a 1x4 box has a 1446 driving four more 1446s...am I crazy or does that mean the four pills are getting driven by 70/4=17.5 watts each, which is 2.5 times the rated input?

And then you get into the 1x2 and 2x4 boxes that seem like they would be driven extremely hard...

Again, just trying to understand...
 
There is an difference in keeping the transistor just below the 1 dB compresion point, and with decent bias, linear.
11Meter PA's get driven (too) hard, because on the box only the output counts, not spectral purity.

That is why for amateur use we use 2 100 watt rated transistors to get 100 watt clean out.
In an 11 meter p.a they would be driven far over the rated power to 200 or 250 watts.

As said above, look at the datasheets of the manufacturer of the device and if you have an decent spectrum analiser you can see what happens if you start to overdrive the P.A.

Take in acount that the 11 meter P.A's have litle or nothing as bandpass filtering, and you know what happens...

Cor
 
No worries...I don't have the box to fry! I'm just trying to understand this whole thing...the 4x1446 was just an example...

Just trying to understand how a transistor can have a 7 watt rated input, but yet they tend to get driven with much more in actual use. For example, a 1x4 box has a 1446 driving four more 1446s...am I crazy or does that mean the four pills are getting driven by 70/4=17.5 watts each, which is 2.5 times the rated input?

And then you get into the 1x2 and 2x4 boxes that seem like they would be driven extremely hard...

Again, just trying to understand...

you are understanding perfectly . most CB amps (particularly class C biased amps) are over driven to get their power ratings so the transistors are far exceeding their design parameters .

p.s. a 1446 is a 90 watt device @ 30-27 MHz.
 
"A 4-pill box with 1446 transistors should be driven at 28 watts (4 units at 7 input watts)? I assume that is an RMS input?"

read it again. those specifications are for 50Mhz.. there's no such thing as RMS power.


Keep in mind, you're dealing with someone who has limited electronics experience...

I have no idea what I should be looking at when you say 50Mhz...does the input change in relation to the frequency its used???

Sorry, AVG...RMS is a hold over from my stereo days...
 
And then you get into the 1x2 and 2x4 boxes that seem like they would be driven extremely hard...

Again, just trying to understand...

your more right then wrong in your way of thinking there Steve :glare: they are what they are , especially the 2 driving 4 :thumbdown: Do they work ? Yes , are they clean ? No , are they over kill ? Yes , again , with what you already learned , what might be the DK and pep from any given radio into a 2 x 4 ? I've seen many an X-force type amp in for repair with those configurations :thumbdown: 2 x 2290s driving 4 x 2879s , How in the hell could you safely drive something like that cleanly or safely enough to not over drive it ? I read somewhere , that anything under a 3/4 watt DK from radio in AM and then the audio from the radio would then suffer , (not saying it wouldn't work) just that the audio would suffer. The old amp section of this Forum (that they decided to leave out) used to have some pretty good threads on this issue and explained it fairly well.
 
That is why for amateur use we use 2 100 watt rated transistors to get 100 watt clean out.


That was going to be my next question, if you under drive the amp (at or below the rated input of the transistors)...other than a loss of "achievable" power, would a class C amp still splatter (given a clean input)?
 
your more right then wrong in your way of thinking there Steve :glare: they are what they are , especially the 2 driving 4 :thumbdown: Do they work ? Yes , are they clean ? No , are they over kill ? Yes , again , with what you already learned , what might be the DK and pep from any given radio into a 2 x 4 ? I've seen many an X-force type amp in for repair with those configurations :thumbdown: 2 x 2290s driving 4 x 2879s , How in the hell could you safely drive something like that cleanly or safely enough to not over drive it ? I read somewhere , that anything under a 3/4 watt DK from radio in AM and then the audio from the radio would then suffer , (not saying it wouldn't work) just that the audio would suffer. The old amp section of this Forum (that they decided to leave out) used to have some pretty good threads on this issue and explained it fairly well.


See, that's what I'm looking for...clean.

I think I have gotten what I need to know...now to start looking around at options.
 
It depend on the stage. You need to know what you have. If you have a single stage amp with 4X "XXXX" transistors then it is what we call a high drive. 5 watts per transistor. So, for intance you could push it on max power with a Ranger 2950.
However, if it has 2 stages, like a single 2sc2290 driving 4X2sc2879s, then 5 watts in =30 watts out to last 4 transistors.
Its all about gain, you will never really get the full output of the transistor, multiple transistors connected together causes a percentage loss, And driver stages cause distortion. Why they make these Class C i dont know, perhaps for the FM users overseas. Stay AB2 and it will work SSB/AM

If you can find class A, that will be cleanest.

Maybe this will help.
http://www.qsl.net/k3pd/chap12.pdf
This is basic concept or are you trying to do the math?
 
I'm trying to get away from the 2-stage amplifier (I currently have a 1x2) and I'm not sure I like it...it is too sensitive, not very controllable (as SK noted, you need to run an extremely low dead key from the radio to get it set at 1:4).

Freecell noted that the extra power over a straight 2-pill was feel-good watts that only show on a meter...and to verify that conclusion, there was no difference at the receiving end between this 500 watt 1x2 (2290x2@2879) and a 300ish watt 2-pill (2@2879) when driven by the same radio...I was experimenting this past weekend.

I'm hoping I can drive a 4-pill effectively with a tuned and un-clipped PC76 (will dead key up to 5 watts and swing upwards of 25 watts, it does have a variable dead key). I am not going for bragging-rights power, but a good clean signal...so if I end up with pushing 1/2 of what an amp is rated for, but get clean signal that stays on channel, I'll be happy.

As a side note, I found last night that I can key the 1x2 next to a another radio with no distortion (antennas were probably 10 feet apart)...but who knows how many other channels I'm bleeding over. I have not gotten a single bad report from the 1x2...but...
 
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