D&A PDX-400

[Zman]

Love seeing an old thread resurrected.

There is a tremendous amount of hate out there for these old sweep tubers. So much so that whenever one pops up on ebay it is often quickly removed. Hams hate them because they are poorly designed, non filtered overdriven splatter boxes designed for low drive radios. In other words, pretty much everything one could want in a CB amplifier.

If one were to obtain an old sweep tuber I would highly recommend having it professionally rebuilt to use a more available and subsequently less expensive tube, as well as a full recap and replacement of old components.

Properly set up, tuned and driven they can and do sound great. The trick is not to run them balls out all the time.[/QUOT

Hams just hate CB altogether so i say piss on em!!
I own a 12 tuber D&A Warrior 2 that has been converted to cheap 31LQ6 tubes that ONLY cost $12.00 each!! Makes for fun times without the worries!!!

 

[Zman]

I'm reviewing the days of my youth when I ran a D&A Maverick into a D&A Phantom feeding an Avanti PDL on a 80' rotor/tower all at 10 meters. The power was interesting while it lasted. Scatter quickly brought it all to an end. The FCC dropped a letter and it was all removed over a weekend. I always wanted to build a real station but it never happened. Now that I'm retired I'm thinking again.

Thanks for allowing me to read your interesting discussions.

HOLY CRAP!!! Ill bet the tubes didnt last!!! What do you mean by "scatter"?

 

[Lawnmowerman427]

I just got a very nice D&A PDX-400 today. Wondering what this amp is worth in today's market? And what kinda wattage can I expect this amp to do? It's already got the SSB mod also.

 

[TonyV225]

Depending on how good the tubes are you should "Safely" see about 800-850 from it some claim 100 watts but then again I dont know how hard they are pushing (Driving) the amplifier which that 200 watts you would be missing by not misstreating the amplifier nobody would ever see or notice on the receiving end

 

[Lawnmowerman427]

Just tested it this evening and AM it's doing 400-500 watts with weak tubes but my radio is only doing 3 watts dead key and swing is about 7-8 watts. So I don't really think that's bad for what I'm driving it with and weak tubes! It's got 1 6JG6A driving 3 6LQ6 driving 6 6LQ6. 10 tubes total. I'm gona see if I can come up with some better tubes and see what I will do then.

 

[Lawnmowerman427]

I have read that you can convert this amp to take either the 24LQ6 or 31LQ6 tubes. Does anyone know what is required to do this conversion?

 

[fixer]

It's got 1 6JG6A driving 3 6LQ6 driving 6 6LQ6. 10 tubes total.

The 6JG6 is not used when it was converted over to an amplifier. It was the oscillator tube when it originally was a transmitter. It still has to be in the socket so one of the 6LQ6's will light up since the filaments are in a series-parallel arrangement. Being basically a 9 tube Phantom the output is usually in the 850 W of audio range.

Alan

 

[Lawnmowerman427]

The enourmous bulky coils they installed for 21 MHz (and on some of them 14 MHz) would get "jumped" down to the the few turns needed to tune 27 MHz. Performance can often be improved by simply cutting these coils down to size, removing the exess turns. Again, copying what was alread built into the older (pre-bandswitch) Phantom would tend to work pretty well.


I have a PDX-400 that was originally set up for 20 meters. My question is how many full turns in the coil does it need for 27mhz ?

 

[Lawnmowerman427]

Think I've got it figured out. Workin good now and does around 800-900 watts! Very pleased

 

[Lawnmowerman427]

I have a D&A PDX-400 and the SWR trimmer (small tuner knob) in the back had went bad and I replaced it with a new trimmer but it still didn't fix the problem. The SWR between the radio and the linear is sky high. Before the stock one went bad it was always good. Any ideas of what's going on with it or how to fix or bypass this completly and get a good SWR between the radio and linear?? It worked Excelent befor the trimmer went bad. Output was 800-850 watts. Any help would be very much appreciated.

 

[Sonar]

Um, much more than any wattmeter's reading, I would be concered that it passes the "Twin Peaks" test.

The final-stage Plate Tune, the right-hand knob of the top pair, has no physical end-of-travel. The Load control on the left will turn only 180 degrees, then CLANG!, it runs into an end-stop. The Tune control on the right has no such mechanicl end stop on it.

Likewise the lower-left Driver Tune knob is this way, too.

BOTH of these knobs should show TWO peaks on the meter in ONE FULL TURN of the knob.

Those two separate peaks may be on opposite sides, 180 apart, or they may be right next to one another.

What matters is that the upper-right Final Plate Tune. AND the lower-left Driver Tune should EACH show TWO peaks in one full turn of the knob.

It's late. I'm gonna skip explaining why this matters. But if you see only ONE peak in that full turn, it isn't really a peak. It's the control reaching the end of its travel, before reaching a peak. Looks like one on the meter, but it isn't, really.

If either knob flunks the Twin Peaks test, you'll next need to know at which extreme the knob that flunked came to rest.

A Tune control with only one peak will be at one of two positions.

1) Plates all the way apart. This is the control's minimum setting.

2) Plates meshed together as close as they will go. This is "Max" capacitance.

Gotta know which it is, to correct the outptut coil on that control.

Any time tubes are changed, there's the risk the Tune control for that set of tubes won't peak like it did with the OLD set of tubes. Running the tubes unintentionally out of tune causes the same stress on the tubes as if you did it on purpose. They last longer if both Plate Tune knobs are "peaked" to a real resonant peak.

73

My triple stage phantom passes the twin peaks test. Both the driver and driver tune peak twice at a full turn of each knob. At two separate points of course.
This is good, yes? Thanks for the information. I've never heard of this before you mentioned it.
Question. The manual says to use the rear tune in order to get max output but I've read many times one should turn it until minimum swr is reached.
If that's true why did d&a suggest tuning for max output? Thanks. 73

 

[Charles hemmings]

I had a PDX 400 Its a great unit!!!
As said before...just a tuned out radio 2-4w dk in 25-35w peak
Even justins 50w pep radios wont hurt that amp if the amp is tuned correctly ...
850-1000 pep watts depending on how good the tubes are..
Its a swing amp not a high deadkey amp...
Let us know when u get it all set up ?

AM POWER

 

[Charles hemmings]

Capt 205,
A PDX-400 is very similar to a old D&A Phantom 500.
Tuning for the first time (assuming the knobs have been moved) is a some what tricky operation.

1. Keep your key up time very short at first, < 10 sec.

2. Tune the final PLATE and LOAD for max dead key, then release the key.

3. Tune the driver PLATE and LOAD for max dead key, then release the key.

4. Repeat step #2.

5. Repeat step #3.

6. Key up your radio (these amps like a low drive) and adjust the grid input tune on the rear of the amp for max output on your watt meter. This matches the radios input (SWR) into the driver tubes of the amp.

7. Now, using a AAAHHHH tone or a long FIIIIVE, adjust the final LOAD knob for max output on your watt meter.

8. Repeat step #7 for the driver LOAD knob.

9. Repeat step #7 for the grid input tune on the rear.

10. Repeat step #7 again for the final LOAD.

The amplifier should now have good dead key with clean, loud audio and good foward swing. Failure to follow the above steps may result in a distorted signal and excessive over heating.

BE CAREFUL!!! The voltage inside this unit WILL kill you. Do not attempt with the case off.

Retune as necessary using ONLY a good quality watt meter, do not rely on the ones on the front of the PDX-400.

They like low drive about 2 watts dead key with lots of audio. Keep the swing down to about a max of 25 watts. Key 2 watts, swing to about 15 watts or so works the best.

As for output, depending on the meter, it should swing to about 850+ if the tubes are good.


Good luck!

Can anyone help me with mines it won't key I tried everything tubes are good the box will not key and make power please help

 

[Wire Weasel]

That's a lot of output on those good ol' TV Sweep tubes. World famous RF bleeders. Hope you don't have any next door neighbors. You might come in all over their ..... everything including the toaster oven

 

[nomadradio]

the box will not key and make power please help

So, does this mean:

The relay goes "CLICK", and no power from the amplifier?

Or is the relay totally silent, and makes no noise at all when the radio is keyed?

You didn't say.

Makes a big difference.

73