Tubes up #102 build

[martin manning]

The faulty cap measured as a resistor on my “all in one” component checker. Can’t remember the value right now, but think it was about 300 ohms (will ahve to dig it out my bin if you guys would really like to know).

The cap failed (nearly) shorted due to the high voltage. The PT should be the same as this one: https://www.thetubestore.com/lib/thetub ... ematic.pdf (125P34AX = 022764)

Voltages v1 around 205, v2 around 215, PI 330v and plates 498. Still high!! Maybe replace first 2k7 with a 3k3?

You have some options, and that's one. You could also switch to the 240V primary.

[andresound]

Success!!!! Thank you to all and most importantly Martin who as usual is SO helpful and generous of his time!! Much appreciated .
The amp is sounding glorious and is VERY quiet. Next to make up a foot switch for OD etc. I will post once done.

I have still to check the primary tap. But just enjoying playing her right now

[martin manning]

Credit Steve for studying the rectifier and figuring that out. I was confused by the diode strings that appeared to be in the typical FW configuration ;^)

So what was the issue with V2b?

[sluckey]

Export transformer primary color codes are on the schematic...

https://el34world.com/charts/Schematics ... _schem.pdf

[sluckey]

I just noticed you used the BLK/WHT 210V primary lead. Use the BLK/RED 240V lead instead and your B+ voltages will decrease.

[andresound]

Credit Steve for studying the rectifier and figuring that out. I was confused by the diode strings that appeared to be in the typical FW configuration ;^)

So what was the issue with V2b?

Thank you Steve!! .

V2b sorted itself out after replacing the damaged snubber cap.

[andresound]

I just noticed you used the BLK/WHT 210V primary lead. Use the BLK/RED 240V lead instead and your B+ voltages will decrease.

Thank you Steve. Well spotted. Regarding the high voltages, as stated I suspected that the primary could have been the problem. That will also be a quick fix.

Just before I left the bench, I shorted out the foot switch socket to quickly test the relays. The PAB works as advertised, but there was no OD when engaging that relay. I will revisit that soon. Just happy all is well. And once again TAG ROCKS!!

[andresound]

Had to go back to the bench to try the red/black primary... SPOT ON!!. Wow! 440v on the plates.Thanks Steve! Sounds even BETTER!

[martin manning]

Tried to point you in that direction of using the 240V primary tap a few posts earlier, with the same schematic (different source) showing the PT primary color codes. :^) Still not sure what you had going on with V2b... The shorted snubber would explain the low plate voltage, but not the low resistance measurement on the 150k.

[andresound]

Way beyond my pay grade!!! . But once again thanks for the advice Martin

[sluckey]

The shorted snubber would explain the low plate voltage, but not the low resistance measurement on the 150k.

With the bad cap in circuit the plate was only 300Ω away from ground. That basically places the 150K plate resistor in parallel with that node filter cap. So his meter was just seeing the charging of that filter cap and finally settled on whatever the cap's leakage resistance (in parallel with the 150K) was.

[martin manning]

Ah, yes! Maybe I should look at a schematic before posting ;^)

[sluckey]

I can't find a schematic. If you know where one is would you post a link?

[pompeiisneaks]

Do you mean this one: https://tubeamparchive.com/download/fil ... &mode=view

? The #102 schematic here seems to be the right one, but not sure if that's the one that andresound used.

~Phil

[sluckey]

I've seen that one but dismissed it because the bias circuit cannot possibly work as drawn. It's probably just a drawing error. I suspect the bias tap is actually a totally separate winding and the other winding lead is connected to chassis.