Cannot leave well enough alone...

[drano81]

With some newly acquired free time, I figured it was best used to upgrade my crack. I've taken it from a working perfectly with a speedball to no LEDs, strange voltage readings, and 100% non-functional. The changes I made are:

1) Replaced the two PS resistors with Triad chokes
2) Replaced the terminal diodes with Cree on a PCB
3) Replaced the output caps with Audyn 100uF/400v film
4) Some housekeeping on the wiring along the way

I snapped pictures of everything as I disassembled it, installed the new parts from my findings online, and now I have no LED's at all, the chokes run incredibly hot (transformer not much more than room temp), and incorrect voltages from the small SB board.

OA/OB: ~17 VAC
IA/IB: ~75 VAC
B-A/B: ~75 VAC !!

My voltages from the power input, heater output, and output to the diode board is within spec. Occasionally, when measuring my voltages, I will hear something click (sounds like a relay). I spent the last couple hours tracing back through a typical installation, but I cannot find anything that is wrong. Solder joints look good and all are soldered. Both sides of both tubes glow. Being that this is far from stock, I'm really don't know what I should be checking. Can I diagnose this as I would a stock w/SB amp (resistance checks)?. Any help is greatly appreciated!

[Deke609]

Post some detailed pics of mods 1 through 3.  Maybe someone who has made the same mods will spot a problem.

cheers,

Derek

[Doc B.]

DC volts is what you want look at. This is why we suggest to make one change at a time and verify it before moving to another change. Your best bet is to post pictures and see if anyone can spot a miswire, or back off your mods to a stock circuit and reinstall them one at a time (which I think would be more educational). It sounds like your chokes are not wired right. And/or your diodes are wired wrong.

[drano81]

I went against my better judgement and installed everything at once. I know how much trouble this can cause and I'm not sure why I even did it... Things get a little crowded with this much stuff...I've tried to show how everything is wired. The 270 Ohm resistors didn't fare well on their removal, so I am an order away from returning it to stock. I've reflowed any questionable joints. Mind the soldering job...frustrations has taken over.

[Paul Birkeland]

You mentioned AC voltages, what are the DC voltages?

[drano81]

All points on the small and large board show ~ -85 VDC

[Paul Birkeland]

Hmm, that's different.  I would be looking for a loose ground wire.

[drano81]

One thing that concerns me is the PCB I used for the volume pot. It appeared to be for multiple pots. Unlike the stock pot, there was only one ground out which I ran to the center pin of the 9-pin socket and then jump from there to the T3. If there was a grounding issue that early in the circuit, could it affect the output of the transformer?

[Paul Birkeland]

It should not.

[drano81]

I decided to rebuild the PS circuit and test everything along the way hoping to find a mistake. The diodes (individual and PCB amounted) all tested good (voltage drop only biased one way). The voltages I measured were:

Input: 121.9 VAC
Heater: 6.6 VAC
PS Output: 179.4 VAC
1st PS Cap (after diodes): 248 VDC

Everything looks great so far. For the chokes, should I only be testing their resistance? Both metered at 250 Ohm. I’m guessing that’s an OK tolerance for their 270 Ohm rating... Wiring is as simple as replacing the cement resistors, right? 21 to 15 for one and 15 to 13 for the other. Polarity is not and issue either I suspect.

Everything looks like it should work, but I’m keeping my fingers crossed...

[Paul Birkeland]

You had IA an IB at 75V (we never got clarity on whether this was actually AC or DC), and now your power supply is where it should be at ~250V DC (I'm guessing with no tubes conducting).

[drano81]

Sorry, IB and IA were 75 VDC.

I may have found the issue, but I’m not sure what could be causing it. With both chokes wired, I am getting ~185 VDC across the first PS cap, ~91 VDC across the second, and 0 across the last. I tried replacing the last cap but saw the result.

Do I have a bad choke? For testing purposes, is it okay to wire the PS without the chokes/resistors in place?

[Paul Birkeland]

Sorry, IB and IA were 75 VDC.

I may have found the issue, but I’m not sure what could be causing it. With both chokes wired, I am getting ~185 VDC across the first PS cap, ~91 VDC across the second, and 0 across the last. I tried replacing the last cap but saw the result.

Do I have a bad choke? For testing purposes, is it okay to wire the PS without the chokes/resistors in place?

You appear to be wiring the B+ to ground through the two chokes, or you have a backwards capacitor after the last choke.