need help with 1 tube redplating !!!!

[dansamp]

so I am getting about 5 volts on pin #2 of the first pair of power tubes
and 0 volts on pin #2 of the second pair of tubes

so I am getting voltage coming out of the left side of the PI and 0 volts on the right side of the PI
note sure if this makes sense

I wouldnt expect much voltage since that should be the signal feeding the power tubes
again that is with the 5Y3 rectifier tube

[Littlewyan]

Right check the coupling capacitor coming from your PI on that side, shouldn't be getting any voltage at all.

[dansamp]

ok,
this is very strange
I disconnected the wires from the PI feeding the power tubes
I am getting 12 v. on pin two of the second power tube !!

[Littlewyan]

Hmmm, try swapping that valve with another to see if the problem moves with the valve.

[dansamp]

reconnected the grid wires to the power tubes
and something is giving me 5.xx volts on pins #2 of the left side
power tubes
I have never seen this before

[dansamp]

ok,
I think I have a bad tube

I swapped the tubes left to right and now the voltage on pin #2
has moved to the other side

[dansamp]

well here is the proof

[Littlewyan]

Nice valve tester! Gotta get me one of those!

So there you have it, bad valve, the positive voltage on the grids explains it as that would counteract the cathode bias in a way. Let us know if the new valves fix the issue.

EDIT: Btw you may or may not have noticed that I started another topic for my own Trainwreck which also had a red plating issue. Although I'm not sure it was actually an issue in the end.

[dansamp]

so,
have to order new tubes from the Sarge
but for the time being
I wired it up with only two power tubes and all is well,
no more redplating and the bias is as it should be ,

slight issue now is ,
treble pot is not as effective as I would expect
it could be the cabinet I am using
5E3 cabinet with a C12Q type speaker

turning the treble pot does not do much tonal change
hi-cut and bass and volume work fine

to be continued...

[Littlewyan]

With a 50pF Treble Cap this might be normal, my express is the opposite, Treble has a MASSIVE range, bass/mid not much. Is the treble pot definitely connected to the bass pot and that .022uf cap?

[dansamp]

With a 50pF Treble Cap this might be normal, my express is the opposite, Treble has a MASSIVE range, bass/mid not much. Is the treble pot definitely connected to the bass pot and that .022uf cap?

Littlewyan,
thanks for asking all the right questions
as I was cleaning up the routing of some of the wiring
I double checked the wire going to from the treble pot to the bass pot and
it looks as if there might of still been some insulation on that lead
I stripped it back and resoldered it and the treble pot is as it should be
now I get nice treble and instant sustain blooming into nice feedback with my Warren Haynes 335 amp volume at about 3:00 0'clock !!!!

now to order a new set of tubes
and pull my Vox Cambridge 2x12 cabinet loaded with Scumnicos out of storage !!!!!

[Littlewyan]

Glad to hear it. Like I said I'm not sure about the Rocket but the express Treble control is VERY sensitive. Also if you turn it on full the amp picks up EVERYTHING, even if you ever so slightly touch the strings you'll hear it.

[rooster]

Dansamp, were the original tube(s) that failed from Sarge? Were these the Saratov versions he is selling currently for $94 a quad?

[dansamp]

Dansamp, were the original tube(s) that failed from Sarge? Were these the Saratov versions he is selling currently for $94 a quad?

no
one Sovtek EH tube failed

I have now purchased a full set of tubes from Sarge
and the amp sounds great

I was getting some 60 cycle hum that I traced to a weber copper cap WZ68
the hum drops to an acceptable level when I subbed an old stock RCA 5Y3
I am now running a 5U4 in it until I can find my Mullard GZ34