D&A PDX-400  | | 
08-16-2006, 09:06 AM
| | Senior Member | | Join Date: Jul 2006
Posts: 225
| | 
Quote: |
Originally Posted by nomadradio 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 |
I, uh....., wow. Someone actually taking the time to show someone how to load their amplifier correctly.
My hats off to you, Nomad..
And yes, he's correct... About damn near ANYTHING D & A. Or anything else using the funky receiver cap's that left the stops in them.
Seriously, though, good post. Should make a FAQ..... Correct tuning and loading of your ancient amp 
--Toll_Free  |
08-16-2006, 12:06 PM
| | Guest | | Join Date: Apr 2005
Posts: 1,472
| |
Nomad is the man, that's for sure. He knows his tube amps! You should see his upgrades for the Pride DX-300!
What Nomad sucks at is WEB DESIGN! :P
We have been beating him up for YEARS to put a FAQ on his website. Almost as bad as he has been beating himself up! |
08-19-2006, 09:21 AM
| | Member | | Join Date: Jun 2005 Location: Florida
Posts: 34
| |
Tried out the instructions reguarding two peaks. There are 2 distinct peaks on the knobs as told. Following this lead.....I tuned up using the higher of the 2 peaks on each dial. This gained me an additional 175 watt to 500 on high. |
10-02-2009, 12:31 AM
|  | Member | | Join Date: Sep 2009 Location: Hope, BC
Posts: 67
| | 
Quote:
Originally Posted by nomadradio  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 | Please tell me about the twin peaks.
My amp has 1 peak on TUNE and I don't wanna ruin it.
Should I stretch\compress the coil, or cut it to lenth?
Also what is the objective, does the coil need a certain lenth or number of turns, coil size?
Thanks  |
11-05-2009, 05:23 AM
| | Junior Member | | Join Date: Jun 2009
Posts: 1
| |
I have just acquired a pdx 400.The z-14 is fried.I replaced it and all the tubes.The unit will key but have no power output.Does anyone have a schematic for this beast.It has a 6kv6 driving 3 driving 6.There is a choke off the 6kv6 but it dosent tie to anything but a terminal strip with no other wires connected to it. | | |
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