Phantom 500 questions

[MakinContacts]

Hello all 1st post, and thanks for allowing me to come aboard! I have a few questions.
So long story short, I found someone looking for D&A parts online, and thought maybe trying mine out, and selling it, but....I don't know what it's worth, and I might possibly have soft tubes?

The other day I brought it up on a variac, and proceeded frome there. I set the grid tune, put all controls to the midpoint area, pur her on high, and started to tune er up. With a Johson radio that hasn't been used in years, I was able to get 300 average out with 3w DK in. The meter I was using did not have a peak selection, and the Johnso also has a back swing ugh! I then turned on the 250W section and lost wattage, but low does about 90 on low, high, 300. All the while testing, my keyups were around 5 seconds, and at no time did I get any cherries (tubes).
I haven't used this thing in years, and frankly, now with old man syndrome, I don't really remember how to use it, however, I kinda remember something about the possibility of the tuning being 180° out, so I stopped.

I'm suspect of the drive section. I think it maybe soft? Is it worth fixing, or is the tuning possibly out of phase to cause the 250W stage to drop.
I don't even mess with CB amps anymore, so I am going to sell it either way.

What say you, any ideas what it's worth? To add further, all tubes light, SSB delay works, all caps are original, fairly good shape for the age. Thanks.

 

[Shadetree Mechanic]

Welcome! That is a big one for sure. As for what it is worth, some would say that the tubes are worth more than the amplifier. I am not that familiar with this one, but I am sure someone more familiar will chime in.

 

[groundwire]

$1,000

 

[MakinContacts]

$1,000

I'll gladly take a 1000

 

[MakinContacts]

I had some time today, so I had a look. After discovering that a majority of the wires were the same color (yay), I decided to look through the manual I had for it, and sho nuff , I had a schematic in there.
If I am on the right path, after looking this over, I think it might be dropping the 900V somewhere? My original thought was soft drivers.
I did clean the relay that carries the 450V/900V several times, but no go.
I will have to get in there with a meter and investigate further.
Oh, one more point to make for future readers, my memory came back to me on how to tune this this once I got the cover off. The top T/L controls are for the finals, and the bottom 2 are for the drive section. Geez, funny how a person forgets some of this stuff after a few decades......

 

[nomadradio]

What I usually tell someone who wants to unload one of these is "Take the tubes out. They will sell for more money alone than the amplifier with the tubes in it."

There seem to be ten guys wanting tubes for every one guy looking for an amplifier.

Age and mileage are both factors. We all know it's from before 1979, and someone has removed the breakdown-prone band switch. That will improve reliability all by itself.

If it was a 1979 car you would be pleased if it still starts and runs, but belts, hoses, gaskets, seals, bushings and such would limit how far you could drive before the first breakdown.

Could be someone has caught up the last 40-plus years of maintenance and it will be a reliable daily driver.

And if it's still full of factory-original stuff that should have been replaced, the question is how many times can you key it before the first "poof!"?

It's not just the years, it's the miles, too.

73

 

[MakinContacts]

What I usually tell someone who wants to unload one of these is "Take the tubes out. They will sell for more money alone than the amplifier with the tubes in it."

There seem to be ten guys wanting tubes for every one guy looking for an amplifier.

Age and mileage are both factors. We all know it's from before 1979, and someone has removed the breakdown-prone band switch. That will improve reliability all by itself.

If it was a 1979 car you would be pleased if it still starts and runs, but belts, hoses, gaskets, seals, bushings and such would limit how far you could drive before the first breakdown.

Could be someone has caught up the last 40-plus years of maintenance and it will be a reliable daily driver.

And if it's still full of factory-original stuff that should have been replaced, the question is how many times can you key it before the first "poof!"?

It's not just the years, it's the miles, too.

73

Hello, and thank you for the reply!!

I totally agree with everything you have posted, no argument from me

I will take your advice, strip out the tubes, and send em their separate ways.

God bless

 

[Jimbo165]

I have 2 D&A triple Stage Phantoms and 1 Dual Stage they are nice amps and I use mine everyday. I find trying to tune a tube amp using a average watt meter a waste of time. Get a meter that reads PEP and it will be a lot easier. Just audio into amp and tune all to highest readings then back load off a little bit and you will be fine. There is a tune up procedure for them on CB tricks also. The amps work real good on 10 meter side band . They are worth at least a minimum of 400 dollars each working and will go up in price depending on condition. I have no problem getting tubes the place I go sells good used for 15 dollar each so 150 dollars you have tube it and it will probably last another 10 yrs.

 

[linearone]

I have 2 D&A triple Stage Phantoms and 1 Dual Stage they are nice amps and I use mine everyday. I find trying to tune a tube amp using a average watt meter a waste of time. Get a meter that reads PEP and it will be a lot easier. Just audio into amp and tune all to highest readings then back load off a little bit and you will be fine. There is a tune up procedure for them on CB tricks also. The amps work real good on 10 meter side band . They are worth at least a minimum of 400 dollars each working and will go up in price depending on condition. I have no problem getting tubes the place I go sells good used for 15 dollar each so 150 dollars you have tube it and it will probably last another 10 yrs.

Why would you "back the load off a little bit"?

 

[nomadradio]

This is a wacky bit of folklore that refuses to go away.

To start, it doesn't tell you which direction to "back off". More capacitance than the peak setting? Less capacitance? Flip a coin?

Makes a difference.

Peaking the load control for max modulated power is my advice, always has been. As a rule, whether you use a peak or average wattmeter, this will maximize the peak power. The Tune control MUST always be set for a resonant peak.

The peak on the Tune control may seem really broad on modulated power. Odds are it will be sharper an easier to discern on carrier alone.

NEVER, NEVER, NEVER set the Plate Tune control too far from the resonant peak. Bad juju.

About that "more" or "less" capacitance direction to back off the Load control?

The one sliver of reality I can get from it has to do with high-gain grounded grid triodes. Tubes like the 8877, 3CX800 and other so-called "radial-beam" triodes have really high-gain grid structures that are susceptible to harm from excess grid current. Hence the grid-current cutout in (real) amplifiers using those tubes. Exceed the safe limit and the amplifier disables the relay until you cycle the standby switch.

Setting the Load control on the 'less'-capacitance side of the peak, or sometimes ON the peak will cause excessive grid current. Never mind why, has to do with the peak negative voltages on the tube's anode. Increasing the capacitance of the Load control will, as they say "tighten" the output circuit, reducing those RF voltage peaks a bit. Any time the tube's plate voltage falls far enough, the grid current will go up. Naturally the voltage on the anode of your tube is rising and falling 27 million times a second more or less. What matters here are the negative peaks. Adding some capacitance to the Load control reduces the "Q" of the output tuned circuit, and reduces the max RF voltage peaks, both the positive and the (more important) negative peaks.

More than one amplifier that uses this kind of triode has tune-up instructions that will advise you to set the Load control to the one side of the peak-wattage setting that REDUCES grid current.

Naturally, if you choose to "back it off" in the other direction the grid current will rise, maybe high enough to make the protection circuit kick out.

So there is the grain of truth behind yet another urban legend that refuses to die.

73

 

[linearone]

This is a wacky bit of folklore that refuses to go away.

To start, it doesn't tell you which direction to "back off". More capacitance than the peak setting? Less capacitance? Flip a coin?

Makes a difference.

Peaking the load control for max modulated power is my advice, always has been. As a rule, whether you use a peak or average wattmeter, this will maximize the peak power. The Tune control MUST always be set for a resonant peak.

The peak on the Tune control may seem really broad on modulated power. Odds are it will be sharper an easier to discern on carrier alone.

NEVER, NEVER, NEVER set the Plate Tune control too far from the resonant peak. Bad juju.

About that "more" or "less" capacitance direction to back off the Load control?

The one sliver of reality I can get from it has to do with high-gain grounded grid triodes. Tubes like the 8877, 3CX800 and other so-called "radial-beam" triodes have really high-gain grid structures that are susceptible to harm from excess grid current. Hence the grid-current cutout in (real) amplifiers using those tubes. Exceed the safe limit and the amplifier disables the relay until you cycle the standby switch.

Setting the Load control on the 'less'-capacitance side of the peak, or sometimes ON the peak will cause excessive grid current. Never mind why, has to do with the peak negative voltages on the tube's anode. Increasing the capacitance of the Load control will, as they say "tighten" the output circuit, reducing those RF voltage peaks a bit. Any time the tube's plate voltage falls far enough, the grid current will go up. Naturally the voltage on the anode of your tube is rising and falling 27 million times a second more or less. What matters here are the negative peaks. Adding some capacitance to the Load control reduces the "Q" of the output tuned circuit, and reduces the max RF voltage peaks, both the positive and the (more important) negative peaks.

More than one amplifier that uses this kind of triode has tune-up instructions that will advise you to set the Load control to the one side of the peak-wattage setting that REDUCES grid current.

Naturally, if you choose to "back it off" in the other direction the grid current will rise, maybe high enough to make the protection circuit kick out.

So there is the grain of truth behind yet another urban legend that refuses to die.

73

I agree. I think people view the load adjustment as a power knob or something...

 

[nomadradio]

people view the load adjustment as a power knob

I tell them to think of the Load control as the "efficiency" knob.

73

 

[linearone]

This is a wacky bit of folklore that refuses to go away.

To start, it doesn't tell you which direction to "back off". More capacitance than the peak setting? Less capacitance? Flip a coin?

Makes a difference.

Peaking the load control for max modulated power is my advice, always has been. As a rule, whether you use a peak or average wattmeter, this will maximize the peak power. The Tune control MUST always be set for a resonant peak.

The peak on the Tune control may seem really broad on modulated power. Odds are it will be sharper an easier to discern on carrier alone.

NEVER, NEVER, NEVER set the Plate Tune control too far from the resonant peak. Bad juju.

About that "more" or "less" capacitance direction to back off the Load control?

The one sliver of reality I can get from it has to do with high-gain grounded grid triodes. Tubes like the 8877, 3CX800 and other so-called "radial-beam" triodes have really high-gain grid structures that are susceptible to harm from excess grid current. Hence the grid-current cutout in (real) amplifiers using those tubes. Exceed the safe limit and the amplifier disables the relay until you cycle the standby switch.

Setting the Load control on the 'less'-capacitance side of the peak, or sometimes ON the peak will cause excessive grid current. Never mind why, has to do with the peak negative voltages on the tube's anode. Increasing the capacitance of the Load control will, as they say "tighten" the output circuit, reducing those RF voltage peaks a bit. Any time the tube's plate voltage falls far enough, the grid current will go up. Naturally the voltage on the anode of your tube is rising and falling 27 million times a second more or less. What matters here are the negative peaks. Adding some capacitance to the Load control reduces the "Q" of the output tuned circuit, and reduces the max RF voltage peaks, both the positive and the (more important) negative peaks.

More than one amplifier that uses this kind of triode has tune-up instructions that will advise you to set the Load control to the one side of the peak-wattage setting that REDUCES grid current.

Naturally, if you choose to "back it off" in the other direction the grid current will rise, maybe high enough to make the protection circuit kick out.

So there is the grain of truth behind yet another urban legend that refuses to die.

73

Some interesting things I've noted. Most sweep tube amps, there is little to no difference tuning with modulation for peaks, especially the smaller ones. I dunno why.
I've almost always noted the least grid current occurs at the same place as when its tuned for max peak output.
Not to say that is the place of most linearity. But.. it's CB, we aren't sending signals to the mars rover.

 

[jtrouter]

Not to say its right but on the manual that came with my Palomar Skipper it says the following
After tune and load have been adjusted for maximum and the the rear knob have all been tuned to maximum
The amplifier must be over coupled, this is accomplished by talking the load control and turning clockwise 1/4inch. If this is not done, he transmitted
audio will sound "fuzzy" or distorted.

This is how i have adjusted my unit for so many years, So is this now not correct?

 

[linearone]

Not to say its right but on the manual that came with my Palomar Skipper it says the following
After tune and load have been adjusted for maximum and the the rear knob have all been tuned to maximum
The amplifier must be over coupled, this is accomplished by talking the load control and turning clockwise 1/4inch. If this is not done, he transmitted
audio will sound "fuzzy" or distorted.

This is how i have adjusted my unit for so many years, So is this now not correct?

If you tune amp for carrier only yes it will be fudgy sounding .
I watched a hamster yt channel. It was a 29 minute video of a guy tuning up his amp.
People really over complicate it. Yell Claudio and peak all controls for max pep. Hit the tune, peak the load, touch up the tune again..done