D&A Warrior 1000 / new 10k

[Atlasta]

A bit of clarification: The source radio remains the same: A Barkett restored and tuned Tram D201A. The meters used remain the same: Either a Palomar model 500, a Kicker 500 TS or a Wawasee meter (don't know the number).

When this radio and meters are used with any of my other amplifiers (many of which fall into the 'crappy CB sweep tube' category) I don't get any downward deflection. Only with the D&A. As stated previously, this behavior was documented in the original user's manual:

"Should you use an inline r.f. watt meter, use it only to determine actual power out. As an inline r.f. watt meter is not a modulation meter, it will not tell you whether the linear is correctly loaded as it will deflect downward under almost any conditions of loading."

That's taken directly from the user's guide. My question is why does this happen with the D&As and not my other sweep tube amps?

FWIW, my Phantom triple stage is not the typical 40 year old relic that has passed through the hands of a dozen golden screwdrivers trying to squeeze every last watt out of it. I sent it to Alan a few years ago and he did a superb job of not only converting it to the more common and cheaper 24LQ6 tubes, he also restored it to better than original condition. The way it is now is the way D&A should have built them in the first place. Operated within design parameters it does not splatter nor cause interference on other bands. If it did, my ham friend up the street would be the first to tell me.

 

[wavrider]

Your HAM FRIEND up the street would only be able to hear if you were splattering if he was operating on 10 meters.

Unless of course you have proof that there is such a thing as negative harmonics?

 

[WA8ZYT]

Only an oscillograph-stroboscope can tell the tale.

 

[Shockwave]

This problem is not related to harmonics or the "cheapo sweep tubes". It's a simple matter of overdriving an amplifier that already has two driver stages built in. Lets go out on a limb here and assume this triple stage D&A had a matched set of full emission tubes. It might on a good day produce up to 2000 watts PEP. Any amplifier that has a maximum output of 2000 watts can only operate at 500 watts AM carrier if you expect to modulate it at 100% with minimal distortion. AM requires that you only use 25% of the amplifiers capacity for carrier and the rest is headroom required for the positive peak on AM. Without that headroom, the positive peak cannot develop so the amplifier "swings" downwards when audio is applied.

If D&A actually claimed it was normal for a watt meter to swing backwards with modulation under any condition, it leaves a lot to be desired from their technical department. There is no case whatsoever where it would be considered acceptable to operate AM with downward modulation indicated on any watt meter. Even the most stingy average reading watt meters should be showing a 50% increase in power on the loudest audio peaks while the PEP meter shows a 400% increase!

Some tips to correct this problem would be to make sure you are tuning the amp correctly. Do not tune with a dead carrier otherwise you have matched the output section at 25% of rated full power rather than achieving the match where it's most important. At full power under peak modulation conditions. That's where we need the efficiency to be highest on these sweep tubes to prevent over dissipation. Never attempt to key over 500 watts with one of these amps. Never "detune" the amplifier in an attempt to reduce the carrier or output, that just wastes more power as heat within the tubes. The only appropriate remedy if it keys over 500 is to reduce the carrier power from the radio. You should start to see forward swing with improved audio following these guidelines.

 

[Atlasta]

Have done all of that and there is no change.

This amplifier was only rated for 1375 watts input. Assuming 50% efficiency it should do about 550-600 w resting carrier - which it does. Maximum output is about 700w. I can get more out of it but then the waveform starts looking like a square wave.

The 4 driving 6 setup of this amp was absurd in the first place. D&As were known to be overdriven from day one.

It has to be something in the way it's designed. I've a collection of sweepie amps and it's only the D&As that exhibit this behavior.

FWIW the meters on the amp itself show forward swing. OTA audio reports are excellent and as stated previously, the waveform looks great.

Thanks to all!

 

[Shockwave]

Well the output is lower than I expected. At 1375 input you can safely figure about 60% of that as output. That's 825 watts of maximum PEP output. That means the carrier can only be 206.25 watts. Way under the 550 to 600 watts you may be running now. As I recall the meters on this amp are actually current meters and not RF meters. If current to the amp increases with modulation, that is a good sign and contradicts what you're seeing on the watt meter. If input power increased with audio, output power should be doing the same thing.