No sound from 18 watt TMB

[lpresnall]

Ok, here are some pics. I apologize for the number of them but I don't want to under-do it this time:

[lpresnall]

The next batch. The board only allows 5 per post.

[Firestorm]

Did you use the 1N4007 diodes between the red PT wires and the rectifier plates (inside heat shrink)? That would explain odd AC readings at the plates. Measure AC voltage between the red wires at the terminal strip. If you're up for the task, it might be good to get a fresh set of voltage readings at each tube pin and the B+ nodes at the anode of each filter cap, to go with the pix.

[lpresnall]

Firestorm, you mean each pin of each tube relative to ground and each filter cap relative to ground? I'll get up there and do it and post here if that'll get this thing on the road to sorted.

[Firestorm]

DC relative to ground, except for filaments which will be AC.

[lpresnall]

Mark, Phil, and Firestorm,

Here are the latest readings after checking and re-checking all the wiring as best I can:

(In response to each post, in order):

283.7/283.1 at red wires at tag strip (before diodes)
32.5 VAC Pin 1 rec
32.5 VAC Pin 7 rec
57 VAC across 1/7 rec

VDC at B+:

271/216 (Can cap), 30.8 (100uF), 171 (16uF), 162.5 (16uF)

Yes, I have 1N4007 diodes under the shrink wrap between the tag strip and rec.

Pin readings from 1-9, in order of V1-V5 then rec are:

V1: 92.6, .118, .58, 0 (at 4/5), 81.1, .54, 0
V2: 42.7, 29.1, 31.2, 0, 117, 19.7, 31.2, 0
V3: 97.1, .53, .43, 0, 162, 97, 97, 0
V4: .95, 31.9, 30.6, 0, 0, 1.2, 226.4, 1.64, 211.3
V5: .01, 30.6, 30.6, 0, 0, .018, 233.5, .008, 266.3
Rec: 263.8, .046, 268.4, 253.6, 253.4, .13, 266.3, .069, .051
Just in case, pin 1 at rec is 34.3VAC and pin 7 is 32.3VAC

[mark enger]

that cant be right, if you had 30vac at pin 1 and 7, are the diodes backwards maybe? remove them, and just wire direct, im not sure what those diodes and cap do, a safety net i guess i never use them myself mark

[Firestorm]

that cant be right, if you had 30vac at pin 1 and 7, are the diodes backwards maybe? remove them, and just wire direct, im not sure what those diodes and cap do, a safety net i guess i never use them myself mark

That probably is right. The SS diodes back up the tube so the AC reading at the plates is ripple. But the B+ is low and the other readings seem off even for the B+.

The cap across the tube rectifier plates is shown as 0.01/3kV. I would have assumed ceramic. What is it you have there? It's only included to kill the hash from the SS diodes, which aren't completely necessary.

[lpresnall]

Mark, I removed the diodes and things improved in all areas. The voltages are closer, but now in line with the chart that Phil posted. In some spots I'm 40 VDC low. Also, in checking the grounds I found that I'd left out the dashed line at the top of the 470K's just as Phil mentioned. Thing is, with it in I get no sound at all. With it out, I get an amp (mostly). This is leading me to suspect my other grounds, although I may certainly be wrong. The voltage at the rec now is 287 and 575 across 1 and 7.

[lpresnall]

I also should say that when the ground at the 470K's was in the voltages at pin 1 on the preamp tubes increased, but I lost the sound.

[mark enger]

Cool, I dont get what those diodes are about, you get no sound, have you tried a pop test? just turn on the amp and probe all the plates pins 1 and 6 in the preamp the 12ax7 start with the 12ax7 closest to the powertubes, it called the CF you should hear a pop-like sound when your probing with your meter

[lpresnall]

Ok Mark, I'll do it. I was just in checking the lines to and fro again and saw a missing ground from the output jacks to star. I added it, nothing better, nothing worse. I still get no continuity at the 100K resistor on the east end of the board by the 1 uF caps. The resistor is between pin 6 of V1 and underboard wiring connects like so (I think):

Pin 6 V1, 100K, 100K beside 22 uF cap 2K2, pair of 100K's beside 16 uF, positive end of 16 uF cap, 8K2, then finally to the can cap. It also looks as though it affects V2 as well.

[mark enger]

just run a wire on top to the 100k which i think you call B+4

[mark enger]

Did you forget the blue dotted line next to the 22uf-450 cap?

[lpresnall]

Ok, so go on top of the board with that wiring in case the underboard one isn't connected somewhere?