D&A PDX400

[1912barry]

I just picked up this amp over the weekend and when it was shown to me working it was peaking around 900 with about 400 dk, I get it home and put it on my Daiwa meter and im only seeing 200 dk and can only get about 600 peak. That's quite a bit of a difference. Are my readings more correct for this amp? I have read both ways when researching this online. Also, I have also read that there is a Grid tune on the back but mine does not have any thing back there to turn.
Any info on this would be nice, Thanks.

[Big blue]

First, how many watts were you driving the amp with prior to purchase then once you got it home? Meters are different as well; A Workman, Astatic, Bird.....you are taking readings with your Daiwa yet all will likely give different readings. What was the SWR reading where you bought the amp vs. yours at home? All can affect your power out.

I am running a very similar amp to the one you are using - made by the same company and has 4 tubes driving 6 plus a keying tube. I drive mine with a little less than 2 watts AM and with an Astatic 600 meter, never see a 400 watt dead key.......I load it so the dead key is low but swings like a mother. They are good amps if treated well! Hope that helps.

[1912barry]

First, how many watts were you driving the amp with prior to purchase then once you got it home? Meters are different as well; A Workman, Astatic, Bird.....you are taking readings with your Daiwa yet all will likely give different readings. What was the SWR reading where you bought the amp vs. yours at home? All can affect your power out.

I am running a very similar amp to the one you are using - made by the same company and has 4 tubes driving 6 plus a keying tube. I drive mine with a little less than 2 watts AM and with an Astatic 600 meter, never see a 400 watt dead key.......I load it so the dead key is low but swings like a mother. They are good amps if treated well! Hope that helps.

The guy was using a Cobra 29 classic on a power supply but I have no idea what the radio was putting out or what voltage his power supply was set at. My swrs are flat on my imax and 1.3 on my beam with amp on. I was testing with a stock Cobra 25 classic that DK 3 and swings 11 to 12 hooked up to a boat battery( my 2995 is in for repair) and last night I hooked up my peaked 29 classic that DKs 5.5 and swings about 21 and it got the amp up 290 to just hitting 300 DK and just hitting 700 peak. This tells me that this guy was probably driving a little hard.

[Sporty Mike]

Those are good amps that like a low DK, never run anymore than 4 Watts DK into 'em and given the inherent differences in meters readings I'd personally never run more than a 2 Watt DK.
But if it's the 4 6lq6 driving 6lq6 like a Phantom, with a set of good matched tubes you can see 1000 Watts out of it . But given the age of most tubes, driving it with the radios mentioned and using a "good " meter, I'd say the numbers you're seeing are accurate.
And if you're currently seeing 700 peak tune the DK back to 175, you'll sound much better with a 1:4 ratio and be sure you're not overmodulating.


Mike

Sent from Sporty Mike's phone.

[1912barry]

Those are good amps that like a low DK, never run anymore than 4 Watts DK into 'em and given the inherent differences in meters readings I'd personally never run more than a 2 Watt DK.
But if it's the 4 6lq6 driving 6lq6 like a Phantom, with a set of good matched tubes you can see 1000 Watts out of it . But given the age of most tubes, driving it with the radios mentioned and using a "good " meter, I'd say the numbers you're seeing are accurate.
And if you're currently seeing 700 peak tune the DK back to 175, you'll sound much better with a 1:4 ratio and be sure you're not overmodulating.


Mike

Sent from Sporty Mike's phone.

What is the proper way to tune this amp? I have never had one of these type amps before. There are four knobs for adjustment on the front,,
Top left is Ant Load, top right Final Tune,, bottom left is Driver Tune and bottom right is Driver Load.

[sonoma]

I just picked up this amp over the weekend and when it was shown to me working it was peaking around 900 with about 400 dk, I get it home and put it on my Daiwa meter and im only seeing 200 dk and can only get about 600 peak. That's quite a bit of a difference. Are my readings more correct for this amp? I have read both ways when researching this online. Also, I have also read that there is a Grid tune on the back but mine does not have any thing back there to turn.
Any info on this would be nice, Thanks.

here is a link to an amp that is the newer version of what you have. I looked at a video where a guy has both and says it was the same inside and as far as tuning is the same. here is a link to a manual so you should be able to tune it the same.also from what I read on this amp 600 to 650 is all it is designed to put out not the 900 the guy that sold it to you was showing.

http://www.cbtricks.com/Amp/d ... age_om.pdf

[1912barry]

I have an update here,,, I just pulled the cover and this amp has been modified and now has 12 tubes instead of 10, and the tubes are now 31LQ6 instead of the 6LQ6 that is supposed to be in it! Any one have info on this? There were about 4 or 5 of them that are marked "weak" in red marker pen.

[Sporty Mike]

They made both a 10 tube and a 12 tube version. And there are a dozen or more tubes ending in "L6 ",basically all the same tubes, output wise.


Mike

Sent from Sporty Mike's phone.

[1912barry]

They made both a 10 tube and a 12 tube version. And there are a dozen or more tubes ending in "L6 ",basically all the same tubes, output wise.


Mike

Sent from Sporty Mike's phone.

The upside to these tubes is the cost, These are about $40 cheaper per tube than the 6lq6.

[Sporty Mike]

That is a good thing. Someone has probably retubed it and used those for availability and cost reasons.


Mike

Sent from Sporty Mike's phone.

[bluemeanie]

Unless somebody changed the transformer. The heater voltage is way off. If the amp is set up for the 6lq6 and somebody just stuck the the 31lq6 in it, there is a problem. Just my 2 cents.\
Mark

[1912barry]

Unless somebody changed the transformer. The heater voltage is way off. If the amp is set up for the 6lq6 and somebody just stuck the the 31lq6 in it, there is a problem. Just my 2 cents.\
Mark

Good point. On the inside there are notes in black sharpie that lists things done back in 2012 and the last one on the list was a rewire.

['Doc]

As old as that amplifier is and from the number of apparent modifications done to it, it'd be a very good idea to trace -all- the circuits to see what was done.
Personally, I don't think you got a bargain.
- 'Doc

[1912barry]

As old as that amplifier is and from the number of apparent modifications done to it, it'd be a very good idea to trace -all- the circuits to see what was done.
Personally, I don't think you got a bargain.
- 'Doc

Yes it is old but it does seem to do a pretty good job with good reports over the air and I didn't pay very much for it to start with. After I figured out how to tune it properly I am still getting close to 700 peak with 200 DK and I turned down my radio to 3 watts swinging about 18 and the amp is running cooler now.