Valvehead 3/28/2018 8:01 PM
Bias problems---
working on an orange TH-30 . It has 2 of the el84s red plating , the other 2 do not. Its not the tubes .

Looking at the scem , ive checked all resistors from V5 all the way to pin 2 of the el84s , ground is good , no bad solder joints , and while i had the pcb up i replaced the .1 caps , c45 / 46 coming out of V5 .

with no el84s installed im getting 280vdc at pin 2 of V 6 /7

at V8 / 9 , i get about 0 to 4mv..the meter just kind of jumps around--it wont settle down on a number .

Any thoughts ??

TP13 is 290vdc at "C" so that looks ok according to the scem.
 
The Dude 3/28/2018 8:17 PM
What resistance do you measure across C45 and C46?
 
Randall 3/28/2018 8:24 PM
Which two are red plating and which two are not? V6 and V8 share a cathode resistor and bypass cap, as do V7 and V9. That 4 output/2 output switch and it's pal 3w 100K R84 are worth a look also, since it is how two of the tubes get their cathode grounds.
 
Valvehead 3/28/2018 9:34 PM
v6 / v7 sockets are tubes going red.

i just found something..R84 tests shorted in circuit..but out of circuit tests 100k . both ends of r84 are going to ground no matter where the half pwr is set . R 84 has to be shorted ?? or am i missing something ...

the half pwr switch tests ok

R83 / R85 OK
 
The Dude 3/28/2018 10:22 PM
If the resistor checks good out of circuit it's good. The half power switch switches out 2 tubes by adding the 100k into the cathode path of those tubes. The switch shorts across the resistor for 4 tube operation. If your problem was there, V6 & V8 would be red plating instead of V6 & V7. I believe the problem is that 280vdc at pin 2 of V6 & V7. You need to find out where that's coming from. That's why I asked the resistance across C45 & C46. Even if it's not the caps themselves (since you changed them), there may be another current path there- a solder bridge, debris, socket issue, etc.
 
Valvehead 3/28/2018 10:26 PM
ok--sorry i missed that post-i will measure those here in about 30 minutes----in circuit right?
 
The Dude 3/28/2018 10:30 PM
Yes, in circuit. Basically, we want to know if the plate voltage from V5A is somehow leaking over to the grids of V6 & V7, whether through the cap or some other means. Mostly interested in the resistance reading across C45, but comparing to C46 gives us more data.
 
Valvehead 3/28/2018 10:58 PM
220k and 240k
 
Enzo 3/28/2018 11:07 PM
TP10, TP11 are the 120 ohm cathode resistors for the power tubes. Either of them shorted to ground?

Your caps from the PI to grids may not measure shorted, but can still leak DC when facing hundreds of volts.

Lift C45 from the circuit and see if the voltage goes away.
 
Valvehead 3/28/2018 11:38 PM
Quote Originally Posted by Enzo View Post
TP10, TP11 are the 120 ohm cathode resistors for the power tubes. Either of them shorted to ground?

Your caps from the PI to grids may not measure shorted, but can still leak DC when facing hundreds of volts.

Lift C45 from the circuit and see if the voltage goes away.
tp10/11 are not going to ground.

ill have to pull the board again to pull c45
 
g1 3/29/2018 1:52 PM
Have you checked resistance from pin2 of V6 or V7 to ground? Should be approx. 150K.
 
Valvehead 3/29/2018 3:59 PM
Quote Originally Posted by g1 View Post
Have you checked resistance from pin2 of V6 or V7 to ground? Should be approx. 150K.
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.
 
Valvehead 3/29/2018 6:13 PM
Quote Originally Posted by Enzo View Post
TP10, TP11 are the 120 ohm cathode resistors for the power tubes. Either of them shorted to ground?

Your caps from the PI to grids may not measure shorted, but can still leak DC when facing hundreds of volts.

Lift C45 from the circuit and see if the voltage goes away.
c45 removed--still have 230 vdc there at pin2

so its maybe something to do with the v5 area... ??
 
Enzo 3/29/2018 6:49 PM
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.
 
SoulFetish 3/29/2018 7:42 PM
Lift one end of r76 and r78. Is the voltage still there?
(Assuming you already pull those tubes)
 
g1 3/29/2018 8:33 PM
Quote Originally Posted by Valvehead View Post
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 3/29/2018 11:27 PM
Quote Originally Posted by Enzo View Post
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 3/29/2018 11:27 PM
Quote Originally Posted by SoulFetish View Post
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 3/29/2018 11:28 PM
Quote Originally Posted by g1 View Post
Does R73 measure 150K ? Does one end measure zero ohms to ground?
yes and yes
 
g1 3/30/2018 2:32 PM
So with C45 removed, you still had 230V at the grids of V6 & 7 ?
But with R78 & R79 lifted it disappeared?
 
Valvehead 3/30/2018 6:08 PM
Quote Originally Posted by g1 View Post
So with C45 removed, you still had 230V at the grids of V6 & 7 ?
But with R78 & R79 lifted it disappeared?
Yes sir
 
g1 3/30/2018 7:07 PM
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 3/31/2018 1:08 AM
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 4/1/2018 3:25 PM
Quote Originally Posted by g1 View Post
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 4/1/2018 3:26 PM
Quote Originally Posted by SoulFetish View Post
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 4/2/2018 12:40 PM
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 4/2/2018 2:51 PM
I replaced the .1 caps before
 
SoulFetish 4/2/2018 7:36 PM
Okay.
When you power up are those voltages present on the grids immediately or do they climb to those voltages after some time?
 
Valvehead 4/6/2018 7:15 PM
Quote Originally Posted by SoulFetish View Post
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 4/6/2018 7:19 PM
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.
 
SoulFetish 4/6/2018 9:05 PM
Quote Originally Posted by Valvehead View Post
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 !
Well Iíd say thatís progress! Only thing is you came back from vacation a little early. Go away for another two days or so, then come back and those voltages should be right we need them to be.
 
Valvehead 4/13/2018 10:44 PM
Absolutely stumped here....

I did a hail mary and installed some new caps and resistors tonight ..i dont know what else to do at this point ? I cleaned the sockets and pcb with alcohol and contact cleaner..i dont see anything wrong anywhere. No cracked joints or lifted traces...no solder blobs or hairs .

So everything from the out of the plates of V5 is brand new ....also replaced R3 / c3 / c4 . All grounds check good . Ive worked through the circuit checking continuity .


same result = V6/7 super high volts ............v8/9 nothing .
 
glebert 4/14/2018 1:12 AM
Quote Originally Posted by SoulFetish View Post
Well I’d say that’s progress! Only thing is you came back from vacation a little early. Go away for another two days or so, then come back and those voltages should be right we need them to be.
I think Mercury is in retrograde until Sunday. Still needs two more days.
 
Jazz P Bass 4/14/2018 8:06 AM
"Absolutely stumped here...."

It appears that the PCB itself is bad.

Have you tried contacting Orange for a replacement?
 
Valvehead 4/14/2018 10:20 AM
Quote Originally Posted by Jazz P Bass View Post
"Absolutely stumped here...."

It appears that the PCB itself is bad.

Have you tried contacting Orange for a replacement?
no, but i can try that
 
Helmholtz 4/15/2018 8:01 AM
Did anyone notice the strange "inverse operation" of V2-B and V4-B in the schematic? I wouldn't trust this sloppy diagram.
 
Valvehead 4/15/2018 12:34 PM
More testing today = with all tubes removed

from the el84 area and after , to the OT and jacks , all continuity is ok

plates at 360v

2 test points are not right at pin3 - should be 9-12v according to scem but i get=
v6 5mv
v7 0 v
v8 5mv
v9 0 v

grounds check good , all speaker jacks getting to ground

R84 tests around 0 ohms in circuit and no matter where the half pwr/ full pwr / standby switch is set = its going right to ground , both ends . But it tests 100k out of circuit??

if something was wrong with C47 or C48 , could that cause the mayhem ??
 
doombass 4/16/2018 6:07 AM
Quote Originally Posted by Valvehead View Post

R84 tests around 0 ohms in circuit and no matter where the half pwr/ full pwr / standby switch is set = its going right to ground , both ends . But it tests 100k out of circuit??

if something was wrong with C47 or C48 , could that cause the mayhem ??
If you disconnect what I recon is a quick connector SW9. Still 0 Ohms to ground? If yes, disconnect SW8. Still 0 Ohms to ground?
 
Helmholtz 4/16/2018 7:32 AM
[QUOTE=Valvehead;493064]More testing today = with all tubes removed from the el84 area and after , to the OT and jacks , all continuity is ok plates at 360v 2 test points are not right at pin3 - should be 9-12v according to scem but i get= v6 5mv v7 0 v v8 5mv v9 0 v grounds check good , all speaker jacks getting to ground if something was wrong with C47 or C48 , could that cause the mayhem ??[/QUOTE] With all tubes removed there is no current through R83/85 and TP10/TP11 should have 0 V. I did not read all the posts, but can you exclude a conductive V6 socket? If you disconnect the 2k2 grid stopper resistor directly at the V6 socket, what voltage do you measure at open pin 2 (tubes pulled)?
 
doombass 4/16/2018 8:39 AM
[QUOTE=Helmholtz;493130]With all tubes removed there is no current through R83/85 and TP10/TP11 should have 0 V. I did not read all the posts, but can you exclude a conductive V6 socket? If you disconnect the 2k2 grid stopper resistor directly at the V6 socket, what voltage do you measure at open pin 2 (tubes pulled)?[/QUOTE] Answer in reply #18. 0V when grid stopper resistors are lifted.
 
Valvehead 4/16/2018 11:59 AM
[QUOTE=doombass;493126]If you disconnect what I recon is a quick connector SW9. Still 0 Ohms to ground? If yes, disconnect SW8. Still 0 Ohms to ground?[/QUOTE] the standby / half / full power is on 1 , 3 way toggle switch . 2 wires go to the trans and one wire goes to "tx8" on the pcb. With all 3 wires removed that resistor still goes to ground ... both ends
 
Valvehead 4/16/2018 12:03 PM
[QUOTE=Helmholtz;493130]With all tubes removed there is no current through R83/85 and TP10/TP11 should have 0 V. I did not read all the posts, but can you exclude a conductive V6 socket? If you disconnect the 2k2 grid stopper resistor directly at the V6 socket, what voltage do you measure at open pin 2 (tubes pulled)?[/QUOTE] i just clipped that 2.2k out and i get 0v to about 1.5mv...the meter just kind of goes up and down in that range
 
doombass 4/16/2018 3:27 PM
[QUOTE=Valvehead;493145]the standby / half / full power is on 1 , 3 way toggle switch . 2 wires go to the trans and one wire goes to "tx8" on the pcb. With all 3 wires removed that resistor still goes to ground ... both ends[/QUOTE] Oh, I meant the 4 tubes/2 tubes-switch which bypasses R84 to ground. In the 4 tubes setting the switch is actually supposed to short out R84 to ground.
 
Valvehead 4/16/2018 4:18 PM
[QUOTE=doombass;493169]Oh, I meant the 4 tubes/2 tubes-switch which bypasses R84 to ground. In the 4 tubes setting the switch is actually supposed to short out R84 to ground.[/QUOTE] yes- we are talking about the same switch--r84 is going to ground on both ends , in 2 tube mode , 4 tube and even on standby i pulled the 3 wires off it and it made no difference
 
doombass 4/16/2018 4:30 PM
But if we are talking about SW4_A there would be only two wires, on pin 8 and pin 9 with pin 7 not connected. Correct?
 
Valvehead 4/16/2018 7:11 PM
[QUOTE=doombass;493179]But if we are talking about SW4_A there would be only two wires, on pin 8 and pin 9 with pin 7 not connected. Correct?[/QUOTE] ok--sorry i was referring to the front panel switch . There are 2 switches . On the back of the amp is the 2 tubes/ 4 tubes toggle ( sw4)...and the front of the amp there is the "half power / full / standby switch..so i was looking at the front one .. SW 2 ill take some more measurements later tonight --the confusion was on my part as usual....
 
doombass 4/17/2018 9:10 AM
Quote Originally Posted by Valvehead View Post
ok--sorry i was referring to the front panel switch . There are 2 switches . On the back of the amp is the 2 tubes/ 4 tubes toggle ( sw4)...and the front of the amp there is the "half power / full / standby switch..so i was looking at the front one .. SW 2

ill take some more measurements later tonight --the confusion was on my part as usual....
Yes, and you will most likely find readings of R84 to come out at the approx 100k it is supposed to be once you have flipped the switch to 2 tubes operation. Then we're back at the strange stray current in the path/junction of C45/R43/R76/R78.
 
Valvehead 4/17/2018 8:15 PM
Quote Originally Posted by doombass View Post
Yes, and you will most likely find readings of R84 to come out at the approx 100k it is supposed to be once you have flipped the switch to 2 tubes operation. Then we're back at the strange stray current in the path/junction of C45/R43/R76/R78.
yes R84 is fine.

I took some readings -measuring at pin2 , V6

sw4 2 tube mode / sw2 half power mode = amp starts around 118v and slowwwly...slowly drops down to around 22v......then all of a sudden it jumps up to 90v...then starts slowly dropping again. Im talkng about 1 volt per minute.

sw4- 2 tube / sw2 Full pwr mode = starts at 200v and creeps up to 214v

sw4 - 4 tube mode / sw2 Full pwr = 214v

sw4 4 tube mode / sw2 half pwr = 214v that drops slowly down to 104v...then slowly up to 107v..then back down to 104v

does this sound like a cap creeping up and down / discharging ??

V8 / V9 never changed voltage during this , still around 0v at pin 2
 
The Dude 4/17/2018 9:09 PM
SW2 lowers B+ by using a different transformer tap.
SW4 adds a high resistance into the cathode of two tubes to basically disable them.

I can see no reason why either of these is causing your problem, which is DC voltage on two of your tube grids. You need to figure out where it's coming from. If it were me, I'd start unsoldering things connected to those tube pins until the voltage went away to try and determine where it's coming from. It may even require unsoldering socket pins and checking the voltage on the trace to see if the socket is somehow "leaking". Look for moisture. Look for solder blobs. Look for debris stuck under the socket, Look for a part lead shorting a trace, etc.
 
doombass 4/18/2018 1:29 AM
Yes, one way to go could be to lift C45, R43, ,R76 and R78 ends towards their common junction point which in a healthy amp sets it free from everything else. If you still have that high voltage you clearly have a leaking pcb or something else shorting the trace on that junction. Then measure for continuity to other parts. I'd say for example "C" feeding the PI plates would be a logical start. If you find anything there you might initially want to isolate for example the B and C supplies from each other at the PSU end instead of unsoldering the sockets to narrow down which one is the culprit.
 
Valvehead 4/18/2018 9:28 PM
I did some testing tonight-- the following readings are with C45 and C46 removed from the amp pcb. I have it propped up so i can pull more parts easily now . No tubes in amp .

So , at V5a plate 340v ---- V5b plate 340v

the joint of C45 + R73 is 196v
the joint of C46 + R74 is 0v

r73/74 are going to ground like they are supposed to on other end.

joint of R71 and V5a plate is 340v
joint of R72 and V5b plate is 340v

point C is 344v

the switches are in full power and 4 tube mode

im not seeing any solder blobs or anything ..
 
doombass 4/19/2018 1:10 AM
Quote Originally Posted by Valvehead View Post
I did some testing tonight-- the following readings are with C45 and C46 removed from the amp pcb. I have it propped up so i can pull more parts easily now . No tubes in amp .

So , at V5a plate 340v ---- V5b plate 340v

the joint of C45 + R73 is 196v
the joint of C46 + R74 is 0v

r73/74 are going to ground like they are supposed to on other end.

joint of R71 and V5a plate is 340v
joint of R72 and V5b plate is 340v

point C is 344v

the switches are in full power and 4 tube mode

im not seeing any solder blobs or anything ..
This confirms your previous measurements. That high voltage is still present. Now you need to begin checking why you have that voltage (post #49 and #50).
 
Valvehead 4/19/2018 3:01 PM
Made some progress !! Got rid of that high v at the grids. It must have been a trace or the pcb ... I have some parts " flying " off the pcb now = C45 / R73 / 76 / 78 --going directly to the pin at v6.

Now im measuring -2mv to +3 mv at all grids ..and the meter is just jumping up and down constantly

the pcb is grounded where it needs to be and no tubes are in yet

so without tubes im needing around 20mv or so yes?
 
doombass 4/20/2018 1:16 AM
Nice! I may be wrong but without tubes and healthy C45 and C46 I would'nt expect you to see much of any DC voltage at all on the power tube grids. Possibly your meter might detect a small amount of AC ripple from the DC supply depending on the efficiency of the filtering?
 
Valvehead 4/20/2018 4:25 PM
Ok, here is where Im at. Amp up and running--no red plating,,passes signal fine .

All tubes are in , but my grids arent settling down . So its in full pwr and 4 tube mode , at V6- V9 grids my meter is jumping around from 5mv up to 16mv...its all over the place on all tubes , but it settles on 12mv for about 2 seconds then moves up and down , fairly quickly . I re-checked my ground and tried a different meter .
Any ideas ?

When it cools down ill try a diff set of el84s i have

Also that bad trace i bypassed runs directly under C3 (radial cap 33u/450v )...i wonder if that is going bad or leaking...
 
The Dude 4/20/2018 4:37 PM
You aren't running signal through the amp when you check grid voltage are you?
 
Valvehead 4/20/2018 4:55 PM
Quote Originally Posted by The Dude View Post
You aren't running signal through the amp when you check grid voltage are you?
nothing plugged in... controls at 0
 
The Dude 4/20/2018 4:58 PM
IMO, if it's just mV, it's not anything to worry about anyway, unless you hear noise.
 
TimmyP1955 4/20/2018 6:36 PM
When the power tubes are in, make sure the amp is connected to a load - without one it might oscillate.
 
SoulFetish 4/22/2018 7:27 PM
Quote Originally Posted by Valvehead View Post
Ok, here is where Im at. Amp up and running--no red plating,,passes signal fine .

All tubes are in , but my grids arent settling down . So its in full pwr and 4 tube mode , at V6- V9 grids my meter is jumping around from 5mv up to 16mv...its all over the place on all tubes , but it settles on 12mv for about 2 seconds then moves up and down , fairly quickly . I re-checked my ground and tried a different meter .
Any ideas ?

When it cools down ill try a diff set of el84s i have

Also that bad trace i bypassed runs directly under C3 (radial cap 33u/450v )...i wonder if that is going bad or leaking...
leaking electrolyte can absolutely cause instability/conduct voltages and could have been (could be) the cause of HV leaking on the grids. Often this can be tough to diagnose with radial caps. I've seen what looks like a complete breakdown on the underside of the caps with no apparent bulging or visual indication when looking over the top of the PCB. It can be easily obscured by silicone or a densely populated board
 
Valvehead 5/7/2018 2:24 PM
Just reporting the find---it was a radial electrolytic cap..it was leaking "porridge" under it and i couldnt see it until i replaced that cap. it was right on top of that trace going to V6 .

Thanks for all the help boys !
 
SoulFetish 5/14/2018 12:44 AM
Quote Originally Posted by Valvehead View Post
Just reporting the find---it was a radial electrolytic cap..it was leaking "porridge" under it and i couldnt see it until i replaced that cap. it was right on top of that trace going to V6 .

Thanks for all the help boys !
It's a son of a bitch, ain't it? You're not going to forget about this one.
Glad you sorted this out, man. Thanks for staying with it and updating us on your progress. It kinda' sucks when you get into a troubleshooting thread and the OP disappears and you never find out what the problem/solution was.