Vibro Champ XD Voltage Problem: Update: Solved & Working

[plexi50]

How in the **** am i getting 392 VDC on pin #8 of the 6V6 power tube? C4 bad? I don't understand why the 22uf/450uf + is even there on the cathode of the power tube

[sluckey]

R34 is open or reading very high resistance. B+ from the plate is leaking thru the tube to the cathode.

[plexi50]

Will check it now. How you doing?

[plexi50]

I replaced R34 with a 470 r 5 watt. It was open and i changed it an hour ago

[sluckey]

So, all good now?

[plexi50]

No it smoked the 470r. I just replaced another one and again it smoked it. Let me pull the board up and look underneath it.

[Willabe]

Same tube? Change the tube and the 470R.

[sluckey]

Could be a shorted tube or socket. Pull the tube. Does the voltage on pin 8 go away? If not, suspect the socket or something on/under the board.

[plexi50]

Pulled the 6V6. Still 392VDC. The board is charred at the bridge rectifier diodes. Put in new 1n4007 diodes. Traces are so burned i cant see where they would have gone. I have 470r to ground and other end to positive of C4. Need rectifier B+ connection point. I can not find a pic of this amps underside circuit online.The schematic isn't to clear. I see B+ on the output transformer center tap but no other specific bridge feed.

[plexi50]

A butcher has been in here.

[Willabe]

A butcher has been in here.

 

[plexi50]

A butcher has been in here.

 

Someone gave me this amp and a Super Champ XD to me. And they said they were not  worked on. Screws missing etc.

[PRR]

What is the 6V6 *grid* voltage?

Should be zero.

If the coupling cap has shorted or the grid resistor opened, it could go up to a high positive voltage. The cathode will follow.

But a "gift" amp could have much more wrong.

[plexi50]

What is the 6V6 *grid* voltage?

Should be zero.

If the coupling cap has shorted or the grid resistor opened, it could go up to a high positive voltage. The cathode will follow.

But a "gift" amp could have much more wrong.

But a "gift" amp could have much more wrong.

You can say that again. Especially these amp. I have heard that there is a design flaw in the Super Champ XD. Don't remember what the issue was i read. Don't care all that much about these amps. But i like trying to get them going again if it is feasible.

I have checked the Vibro Champ XD coupling cap and grid 1.5k and they are good. The B+ is being fed from the bridge recto to the OT center tap. The 470r R34 keep smoking up right after power on. I replaced the BR 22/450 radial cap C2B. There's no love loss if the amp never works again. It's conquer thing that bothers me. Why is that C4 22/450VDC cap there at all? It looks like it is acting as a cathode bypass cap and rated at 450 volts in case the other 22/450 volt cap C14 fails. But that dose not make sense either.  What is C4's function?
To explode? I'm lost. That's good sometimes. 

[shooter]

with the amp OFF and tube pulled, look at 1.jpg, ohm between 6V6 pin 8(cathode) and the red wire point you labeled B+, what value do you get?  If appears there is enough carbon tracking that it's very low ohms to shorted, which would explain the smoking 470ohm.   The cap will boost gain, keep cathode swings in check, give you a tighter bass response and I forgot what else 

[plexi50]

with the amp OFF and tube pulled, look at 1.jpg, ohm between 6V6 pin 8(cathode) and the red wire point you labeled B+, what value do you get?

Well the 470r cathode resistor is open again so i would have to replace it before getting reading measurement in ohms resistance correct?
If so i will tac another one in place later this evening.

[plexi50]

with the amp OFF and tube pulled, look at 1.jpg, ohm between 6V6 pin 8(cathode) and the red wire point you labeled B+, what value do you get?

00.2 ohms/ Also no continuity between single ended OT red & blue B+  leads

Grid voltage is 390 VDC just before 470r cathode blows. Then reads a steady 0.32 volts thereafter. No tubes in amp.
 

[shooter]

00.2 ohms/ Also no continuity between single ended OT red & blue B+  leads

.2 ohms is a short, which shouldn't be.  the 470 doesn't matter since you should be measuring  from pin 8 to the red wire marked B+ in your pic.

I can't read the *J* number, but you should be able to disconnect it and ohm on the OT side to verify the OT

[plexi50]

Have it fixed and working good. All effects work as well. The 470r was strapped to the bridge recto and pin #8.
Cleaned up bridge recto area. Got all the burned carbon out of the board. Pulled back cathode pin #8 trace and B+ trace to OT to isolated them from the board carbon contaminated area.

Plate - 365 VDC
Screen - 313 VDC
Grid - 64.1
Cathode +30.5 / Cathode on schematic says +23.7. Should i care? Powered on 30 minutes. Power tube does not red plate.

I have 373VDC between r7 & r8 vs 380 on the schematic.  All plate and power node resistor are reading in spec.

[shooter]

glad you're up and runnin!  gotta love the smell of burnt fiberglass in the morning 

[Willabe]

Your very good. 

[plexi50]

Thanks Willabe! Couldn't do it without all of you. I need a push here and there to think anymore. The board is actually nothing like an old tube amp board so it gets a little misleading looking at the schematic and expecting the parts to be in the same general location. Not the case exactly. Sounds great through my Peavey Classic 410E cab.

Burning fiberglass is the worst smell ever. One of them anyway.