Bias problems---

[g1]

V6/7--the meter slowwwwwly creeps up to around 120- 125k ? this is over 10 or 15 minutes until the meter times out and shuts off

V8/9 instantly measure 150k.

Does R73 measure 150K ? Does one end measure zero ohms to ground?

[Valvehead]

Start looking for conductivity or foreign material on the board in that area. Also look for a tip of a component lead nearby touching that trace. If so, trim it back. Follow the trace from pin 2 to anywhere it goes, looking for anything along the sides of that trace somehow touching it.

All looks good.

[Valvehead]

Lift one end of r76 and r78. Is the voltage still there?
(Assuming you already pull those tubes)

no---no volts at pin 2

[Valvehead]

Does R73 measure 150K ? Does one end measure zero ohms to ground?

yes and yes

[g1]

So with C45 removed, you still had 230V at the grids of V6 & 7 ?
But with R78 & R79 lifted it disappeared?

[Valvehead]

So with C45 removed, you still had 230V at the grids of V6 & 7 ?
But with R78 & R79 lifted it disappeared?

Yes sir

[g1]

Sounds like maybe board leakage, not sure from where.
You still have the EL84's out?
Earlier you said 280V at the grids, now it is 230V?
Point C is 290V? How about pin1 and 6 of PI tube?

[SoulFetish]

After you report back with the voltages g1 was asking about, I want you to try something..
Pull the Phase Inverter tube, solder r76 and r78 back in circuit, and power back on. What's the voltage at the grids now?

[Valvehead]

Sounds like maybe board leakage, not sure from where.
You still have the EL84's out?
Earlier you said 280V at the grids, now it is 230V?
Point C is 290V? How about pin1 and 6 of PI tube?

ok--i was measuring wrong--sorry--


el84s out , PI in , all resistors / caps in
v6 220v
v7 220v
v8 0v
v9 ov

point C 355vdc

PI tube pin 1 353v
pin 6 354v

[Valvehead]

After you report back with the voltages g1 was asking about, I want you to try something..
Pull the Phase Inverter tube, solder r76 and r78 back in circuit, and power back on. What's the voltage at the grids now?

PI pulled , el84s pulled

v6 258v
v7 258v
v8 0v
v9 0v

[SoulFetish]

Okay. Just in case you measured something wrong, replace the coupling cap feeding those two grids. Its cheap and thats the logical source of the problem. Report back

[Valvehead]

I replaced the .1 caps before

[SoulFetish]

Okay.
When you power up are those voltages present on the grids immediately or do they climb to those voltages after some time?

[Valvehead]

Okay.
When you power up are those voltages present on the grids immediately or do they climb to those voltages after some time?

Ok... i just got back from vacation last night. Ready for the madness ? I powered it up to test just now .... and now I have 15 vdc at the grids of V6-7 and 0vdc at v8-9................yep !

[The Dude]

Are there any signs that something might have been spilled in the amp? I wonder if there was moisture somewhere that has dried out- maybe under a socket or something? I might hit the board with some compressed air and/or hair dryer. That, and a thorough inspection.