first power up problems

[deiseldave]

Well, I finally powered up the Judy Box -> Plexi6v6 project. Voltages look right, all tubes light, there is hiss.. But signal from the guitar is not being amplified. The hiss volume is in proportion to the volume knobs settings. Just nothing from the input getting in there.
I unhooked V1 2 & 7, and just ran a spare jack with series 56K directly to V1 2. Still nothing.
Since this is my first amp build, I lack the troubleshooting experience that most of you have. Could someone point me in the right direction? Thanks.

[Stevem]

Do not attempt to play thru it any more, but report back with the voltages on all pins of the preamp tubes but 4,5 and 9, and then
Also report back with the output tube voltages on pins 3,4 and 5, and also pin 8 if it's not landed right to ground.
Read all voltages in DC.

[billyz]

From what you describe I would test from the input jack to V1a to the volume pot. Sounds like you have signal after that. Do you know how to "pop" test ? place your test probe set to dc one the first plate load resistor, do you hear a pop ? If so move to the grid of V1a test , do you hear a pop ? yes /no ?
You will be testing for voltages at the same time.

[deiseldave]

Thanks SteveM & BillyZ. I read my voltages again, and will do the "pop test" and report findings.
I must have been too tired at 3am this morning. Because now that I look at the re-read of my voltages. I see they are out of whack.

V1-1 = 235v, V1-2 =9v, V1-3 = 0v, V1-6 = 234v, V1-7 = 9v, V1-8 = 0v

V2-1 = 128v, V2-1 = 0v, V2-2 = .84v, V2-6 = 235v, V2-7 =128v, V2-8= 129v

V3.1 = 167v, V3-2 = 19v, V3-3 = 30v, V3-6 = 172v, V3-7 = 19v, V3-8 = 30v

V4-3 = 385v, V4-4 = 383v, V4-5 = -35v, V4-6 = -35v, V4-8 = 28mv

V5-3 = 384v, V5-4 = 382v, V5-5 = -35v, V5-6 = -35v, V5-8 = 29mv

I used pin(s) 6 of the 6V6 tube sockets to tie the 5k6 resistors to pin(s) 5. The things that deviated from Mark Huss' Plexi6v6 values are:
Tube rectifier, Bias fed from 45vac transformer tap (which of course makes the whole bias section different). I used Hoffman's bias circuit shown here http://el34world.com/charts/Biascircuits.htm however, I didn't have a 27K resistor, so I subbed for 15K which looks like I'll need to go up 20 a 22K or 33K (what I have) because the lowest I can get from the bias pot is -35v.
I think that's it. Unless I made a mistake (probable), all other values mirrored the latest values Mark has posted on his site.

[Stevem]

Something is very wrong with V1, those voltages on pin 2 and 7 are way off!
Double check everything about how that tube is wired and the resistor and cap values around it.

[billyz]

V1 pin 2 and 7 should be 0. pin 3 and 8 should be 1-2vdc. problem, as stevem noted.

[deiseldave]

Found it. Bent pin on V1 tube. The tube shield was bent, and I had to struggle to get the tube in, and didn't notice the pin bending. It's loud!
Now I have a little buzz & hum that sounds like a touch of heater hum, and some grounding buzz. When I touch the pots, the buzz decreases significantly. The jacks are isolated. But, the pots are not. Should they be?
I am doing a start ground style setup. All the preamp section grounds, and input grounds go to a 2 lug isolated terminal near the input jacks. That terminal has a single wire going to another 2 lug isolation terminal that has all the power amp, and power supply grounds going to it. From that I have a home run to the master ground which is a bare wire going from earth ground to chassis. All center taps go directly to the master ground.
I have a section of the board that I put a heater elevation circuit on. I am going to move the heater center tap to it, and see if the hum improves.

[deiseldave]

By the way. Big thanks for the help! You guys are awesome!

[labb]

I'm sure more will chime in but the grounding scheme you describe is a little strange. If by master ground connected to earth ground to chassis and the earth ground you are refering to is the ground for your incoming 120 volt ac power the I would not do that. The incoming 120 volt power ground should be on a lug by it's self. Go over to EL 34 World and take a look at that grounding scheme. It works pretty good. Note:I don't try to solder to the back of the pots. Just take the pot grounds to a buss wire.

[deiseldave]

Thanks. I will follow that grounding scheme, and see if it helps.

[deiseldave]

Whoa! I did the Hoffman grounding plan, and this thing is way quieter. By the time you crank it up loud enough to hear any noise, if you hit a note it is an earschplitten loudenboomer!
Wow! I am so satisfied with the sound of this amp. Thank you guys so much for all your help.