Build #124 Problem Solve

[mugen]

Hello guys!

I'm having a problem on my #124 build.
There's no sound coming out on clean channel even in full volume.
When I switch on the overdrive Strange sound is coming out on full volume. Its not a clear overdrive sound.

V1a = 188
V1b = 193

V2a = 197
V2b = 190

V3a = 97
V3b = 373

485 on the power tubes & bias @ 35ma

I followed the latest layout of Talbany.

Need your help guys..

pics of my build:
[IMG:800:491]http://i86.photobucket.com/albums/k86/m ... CN1581.jpg[/img]
[IMG:800:598]http://i86.photobucket.com/albums/k86/m ... CN1578.jpg[/img]
[IMG:800:598]http://i86.photobucket.com/albums/k86/m ... CN1579.jpg[/img]

[mlp-mx6]

The voltages on your PI are screwed up. (I'm supposing that was obvious...)

The clear board is very cool. Odd to look at, but very cool. Where did you get it? What is it?

[mugen]

The voltages on your PI are screwed up. (I'm supposing that was obvious...)

The clear board is very cool. Odd to look at, but very cool. Where did you get it? What is it?

Thanks mlp-mx!

Its a 4mm plexi glass bought it from glass and aluminum shop. Riveted a diy turret with a washer at the bottom with a asbestos insulation.

On the first fire up the voltage on the PI was almost equal and I dont know now what happen next.

[mlp-mx6]

If you remove V3 what does the voltage show for both plates there? With V3 in what do the cathode voltages show?

[mugen]

If you remove V3 what does the voltage show for both plates there? With V3 in what do the cathode voltages show?

with out the tube

V3a = 436
V3b = 421

I tried other tubes on it .. same problem.

V3 with tubes
pin-1 = 373
2 = 41
3 = 93
6 = 47
7 = 97
8 = 93

[mlp-mx6]

Are you sure that the V3 plate resistors are the correct values?

[mugen]

Are you sure that the V3 plate resistors are the correct values?

Yup, I double check the value it is correct.

[moj067]

Check that V3 socket for continuity to all pins, swap it out just to clear any doubt.
Clear boards do make looking at things under boards easier

[mugen]

Check that V3 socket for continuity to all pins, swap it out just to clear any doubt.
Clear boards do make looking at things under boards easier

Socket is good & tried to swap it also, no luck..

[talbany]

PI voltages look screwey.. you should have around 230-260 on the plates
common Cathode looks close @ around 100v.. Check Presence circuit phase inverter tail, and bias supply..





Tony VVT

[mugen]

PI voltages look screwey.. you should have around 230-260 on the plates
common Cathode looks close @ around 100v.. Check Presence circuit phase inverter tail, and bias supply..





Tony VVT

Changed the PI, Tail and presence resistors & coupling caps no luck...

guys, more suggestions please ..

[Fischerman]

with out the tube

V3a = 436
V3b = 421

I tried other tubes on it .. same problem.

V3 with tubes
pin-1 = 373
2 = 41
3 = 93
6 = 47
7 = 97
8 = 93

Mugen,
First off...with no tube you should get the exact same voltage on V3a and V3b plates (pins 1 and 6) and that voltage should be the exact same voltage as the supply.

V=I*R can go a long way! When ever you see a voltage drop across a resistor (like those plate resistors)...that means current is flowing through that resistor. With no tube you should have no current flowing so the plates should be right at the supply voltage (i.e. no voltage drop across those plate resistors).

When you posted the voltages with the tube in you said the plates were at 97vdc and 373vdc. So use your friend V=I*R to see exactly how much current is flowing through those plate resistors. Subtract the plate voltage from the supply voltage...that's your voltage drop. Then divide by the resistance value (the plate resistor) to get your current. When running properly it should be in the .001A (or 1mA) ballpark per plate (that's just a ballpark). It's obvious just from looking at the numbers that provided the plate resistors are the correct value you have WAY more current flowing through one plate than the other. You need to find out why. And I think you need to find out why you have some current flowing with no tube inserted.

Also, whenever you post the voltages it really helps if you always post the supply voltage as well as the cathode voltage for each stage. So everyone else can use our friend V=I*R and see what's really going on. If your plate voltage is 373vdc then it makes all the difference in the world if your supply was 473vdc vs. 373vdc. So just the plate voltage doesn't tell us enough.

To be honest...it looks to me like it's V3b that's screwy but that might not be. The reason I say that is because with the tube in you have way too much current flowing through the B side and with no tube in it looks like you have current flowing through the B side but not the A side. With the tube in the A side looks reasonable.

Hope that helped...good luck. Be patient and stick with it...you'll get there.

[Fischerman]

Doh! I just saw it...you have an 820k plate on V3b. I'm almost sure that's it. You want Grey-Red-Orange not Grey-Red-Yellow.

EDIT: Mugen...can you see why I bolded that part "provided the plate resistors are the correct value"? It makes all the difference in our V=I*R.

2nd EDIT: I sometimes forget that Dumbles use 110k/120k or 100k/110k so you don't want Grey-Red-Orange as that is 82k. 120k is Brown-Red-Yellow so I can see how these two could get confused. That plate resistor on your B-side sure looks Grey-Red-Yellow to me.

[mlp-mx6]

Yep - that was one of my earlier questions also. 820K, eh? How did you see that? Were you able to zoom in and read the resistor value on the pic?

[Fischerman]

mlp...glad you're here I need another set of eyes. Look at that last pic...far right side. The leftmost plate resistor sure looks Grey-Red-Yellow but if it's Brown-Red-Yellow it's OK.