6SN7 Driver in Paramount 1.0 (Original with 12AT7)

[Brillo]

Hi all.  I just completed the swap to 6sn7 drivers on v1.1 Paramounts with the soft-start board.  I get a strange resistance reading on B2 (previously B4) of 279K ohms versus 130K.  On start-up, I get 355v on B5 (previously B6), and the two LEDs on the left side of the board (those further away from the trim pot) are dim. I double checked wiring and everything is correct according to my translations, but I missed a re-solder on U18, which I've corrected. 

I must have fried something on the board.  I didn't get smoke, or smell, but heard a very slight sizzle which, at the time, I thought was some loose hardware or wire clippings sliding as I tilted the plate to flip the power switch.  Anyway, thoughts on troubleshooting?

[Paul Joppa]

Voltages would tell us a lot, especially those on 6SN7 pins 1-2-3-4-5-6. You may have to unscrew the C4S board and tilt it out of the way. If you can, photos or the socket and both sides of the board would also help. Does the 6SN7 heater glow?

[Brillo]

I will take more measurements this weekend Paul. While not all things are equal since the swap, the manual suggested shutting down immediately if voltages on B5 where above 350vdc. So that's what I did after running for about 60 seconds. Then I went back to check resistances. I'll take photos, and hopefully get them posted to this string.

Chris

[Paul Joppa]

355v is close enough to 350v. This is the voltage set by the Zener string, before the regulator circuit kicks in.  There are 5 Zener diodes, 68v each, for 340v. The diodes are said to be +/-5%, so 324 to 357 would indicate they are functioning correctly.

The regulated voltage will be about 300v, so if you still have 355v after 60 seconds, the regulator is probably not working. Tube pin voltages will help figure out why that is the case.

[galyons]

PJ,
Thanks for being so supportive of the 6SN7 driver conversion!!!  I love mine, (7N7) and, to my ears, it is really worth the extra effort!!!

Cheers,
Geary

[Brillo]

It was a steady 355v for that brief period, but I'll watch more closely tonight and report back. I'll echo Geary and say thanks for supporting me with this customization. I know I'm outside the fence a bit.

[Brillo]

Start-up voltage does not decrease, but climbs slowly.  Heaters do not glow.  LEDs don't light.  Voltages are as follows:
B1: 350v
B2: 350v
B3: 0v
B4: 0v
B5:350v
B6: 0v

Not sure if I did this correctly, but I've tried to attach my photos and the pinout translation table.

[Paul Joppa]

The pin numbering appears to be incorrect.

[Brillo]

Pin numbering is incorrect in the translation table, the top-plate, or the wiring?  The top plate was labeled during the original build, prior to the soft-start install, and doesn't describe the current wiring.

It might be a little hard to see in the slightly blurry photo, but the keyhole is shown, splitting the difference between the standoffs, and pin 1 is to the lower right with the 220ohm resistor going to L20.  Sequence goes counter clockwise from there.

If my translation table is incorrect, then there ya go.

[Paul Joppa]

Pins are numbered clockwise as seen from the bottom. The 220 ohm resistor in the picture is soldered to pin 8, not pin 1. I assume the heater does not glow, because it appears the heater wires are soldered to pins 1 and 2, not to 7 and 8.

[Brillo]

Wow.  I'm embarrassed.  Sorry for the bonehead error, and for consuming your time needlessly.  I'll correct and report back.  Hopefully I didn't do permanent damage to the board.

I will say that the PCB that came with the tube socket mislead me.  Not sure why it would be labeled as it is.  Lesson learned.

Chris

[Doc B.]

I just worked on an amp with a nine pin aftermarket socket that was numbered like that as well. It's useless unless it is marked top and bottom.

[Brillo]

It sure is useless. I've used 9 and 4 pin versions of these sockets, with and without the PCB, and haven't had this problem before. It's my bad though. Hopefully this string will keep others from making a similar mistake. 

[Brillo]

Well, permanent damage has been done.  No voltage on B1-B6, and no LEDs light.  Filaments on 300B glow, but that's the only sign of life. 

[galyons]

Well, permanent damage has been done.  No voltage on B1-B6, and no LEDs light.  Filaments on 300B glow, but that's the only sign of life.

No....permanent repairable damage has been done! Hang in there!!!

Cheers,
Geary