# Learned something Today - Dead tube on Deluxe Reverb



## Lincoln (Jun 2, 2008)

I had one of the amps I built a few years ago come back today, Suddenly no sound was the symptom.

It was easy to spot that one power tube wasn't lighting up, but when I checked heater power, it had power.
The problem turned out to be a 6V6 power tube with an open in the heater circuit. It was a Electro-Harmonix rebranded GT/Fender.

I did not know tube heaters failed.
I did not know that one dead 6v6 in a push/pull 6V6 system would be a show stopper. (AB763 DR clone)

Noted here as a public service. The learning never ends.


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## Frenchy (Mar 23, 2011)

Bad tube = Bad amp


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## jb welder (Sep 14, 2010)

Lincoln said:


> I did not know that one dead 6v6 in a push/pull 6V6 system would be a show stopper. (AB763 DR clone)


Loss of one power tube in push-pull will not kill all sound. The other power tube must not be working.
Try a single known good 6V6 in one socket at a time. I think you will find one socket is functional, the other is not. Perhaps an open screen resistor.

Loss of one power tube in push-pull will cause loss of power and early distortion, but you will still have sound (if everything else is functional).

Some amps (certain peavey models for example) will have heaters in series, so loss of one heater will cause other tubes to quit. But you said this is an AB763 circuit, so that should not be the case.


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## Lincoln (Jun 2, 2008)

jb welder said:


> Loss of one power tube in push-pull will not kill all sound. The other power tube must not be working.
> Try a single known good 6V6 in one socket at a time. I think you will find one socket is functional, the other is not. Perhaps an open screen resistor.
> 
> Loss of one power tube in push-pull will cause loss of power and early distortion, but you will still have sound (if everything else is functional).
> ...


good insight, thank you. I did change both power tubes with a matched pair of course, and everything suddenly came to life. I thought it should still push, even without a pull.
I did check voltages, and bias, but it sounds like I better check them again.


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## Lincoln (Jun 2, 2008)

jb welder said:


> Loss of one power tube in push-pull will not kill all sound. The other power tube must not be working.
> Try a single known good 6V6 in one socket at a time. I think you will find one socket is functional, the other is not. Perhaps an open screen resistor.
> 
> Loss of one power tube in push-pull will cause loss of power and early distortion, but you will still have sound (if everything else is functional).
> ...


I went back in again, didn't find anything wrong. I don't have a tube tester, so I can't say for sure, but both tubes must have died. It was biased a little hot when I got it back, 40 mV through a 1 ohm @450 volts. I knocked it back to 23mV.

I took the tube I thought was still good and plugged in into a V-champ. Surprize! virtually zero output and super distorted. So that tube was gone for a while already when the heater went open on the other tube and things got quiet. More learning  Learning is good


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## Yamariv (Jan 15, 2018)

Lincoln said:


> I went back in again, didn't find anything wrong. I don't have a tube tester, so I can't say for sure, but both tubes must have died. It was biased a little hot when I got it back, 40 mV through a 1 ohm @450 volts. I knocked it back to 23mV.
> 
> I took the tube I thought was still good and plugged in into a V-champ. Surprize! virtually zero output and super distorted. So that tube was gone for a while already when the heater went open on the other tube and things got quiet. More learning  Learning is good


If you build amps, get a good old brand of Tube tester, rebuild and calibrate it! They are very affordable to buy if you have the skills to rebuild it. I rebuilt a B&K 707 and love it! Only cost me a few hundred and it's payed for itself more than once


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## Lincoln (Jun 2, 2008)

Yamariv said:


> If you build amps, get a good old brand of Tube tester, rebuild and calibrate it! They are very affordable to buy if you have the skills to rebuild it. I rebuilt a B&K 707 and love it! Only cost me a few hundred and it's payed for itself more than once


I've been looking but I never seem to find one. What do you think of a B&K 606?


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## Yamariv (Jan 15, 2018)

Lincoln said:


> I've been looking but I never seem to find one. What do you think of a B&K 606?


Interesting, do you have a line on one? I've never played with a 606 but from the pics I found online it looks like it must be very limited in tube types compared to the bigger 700,707 and 747 B&K's. I'd highly recommend any of these three as there is lots of literature and videos online on how to calibrate them.

I found mine on Ebay from a seller here in Canada. I converted mine to solid state rectification for better stability and also did a socket mod to specifically test 12AX7's. For some reason, when the stock 707 test's a 12AX7, it was only an approximate reading for that tube. I guess since these tester's were mostly for TV repair, they must have thought the 12AX7 wasn't an important tube to test accurately. It's an easy mod to do this.


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## Yamariv (Jan 15, 2018)

On a side note, the reason why I love this tester so much is that I've found more than one shady seller on Ebay stating claims of great vintage tubes when they were not


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## keithb7 (Dec 28, 2006)

I worked on a Peavey Valve King one time. No tubes were lighting up. The heater wires were wired in series. When 1 tube heater shorted, the entire heater system failed for all tubes. I found the issue by testing the tubes with my Heath Kit thermionic tube tester. 1 tube had a heater problem. Replaced the one tube and viola! They all lit up again.

It would appear that traditional pilot light heater wire systems, are wired in parallel? Green twisted heater wires on old Fenders comes to mind.


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## Lincoln (Jun 2, 2008)

keithb7 said:


> I worked on a Peavey Valve King one time. No tubes were lighting up. The heater wires were wired in series. When 1 tube heater shorted, the entire heater system failed for all tubes. I found the issue by testing the tubes with my Heath Kit thermionic tube tester. 1 tube had a heater problem. Replaced the one tube and viola! They all lit up again.
> 
> It would appear that traditional pilot light heater wire systems, are wired in parallel? Green twisted heater wires on old Fenders comes to mind.


interesting thought. Heaters wired in series. It would be way easier, there must be a reason most manufacturers don't do it.


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## Lincoln (Jun 2, 2008)

So......I got this cute little Deluxe Reverb back again today. He said it started smelling bad and lost its "punch".
I played it, yup he was right, sounds like sheet. Opened it up and followed my nose right to the bias resistor.








This is the amp I replaced two bad power tubes on in February. I set the bias then, and checked this resistor. Time to dig deeper.
Hope it didn't hurt the transformer.

Diode is dead too btw. open both ways.


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## Latole (Aug 11, 2020)

There would be a short after this bias circuit.
Strange because it feed a 220 K and 1500 K resistors before 6V6 tubes's grid....

Or Nichicon cap is short ?


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## Lincoln (Jun 2, 2008)

Latole said:


> There would be a short after this bias circuit.
> Strange because it feed a 220 K and 1500 K resistors before 6V6 tubes's grid....
> 
> Or Nichicon cap is short ?


Yes, the cap is short something. That 47/100v cap won't even test. 
Everything else checks out, no shorts at all. I even lifted the main board and Looked under it, just to make sure.
The diode is ok after all. I just wasn't getting a good connection while testing. I built a whole new bias board for it with all new components.
Very cautious, I'm still looking and thinking.


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## Latole (Aug 11, 2020)

Lincoln said:


> I built a whole new bias board for it with all new components.


New components right .
Do you need to build a new bias board ? 
Amp will lost some value if not original board. 

I'll only use mostley F&T or Mallory caps on these old vintages amps.


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## Doug Gifford (Jun 8, 2019)

Lincoln said:


> I've been looking but I never seem to find one. What do you think of a B&K 606?


I have this. It was my father's. Comes with a couple of adapters. I'd sell it if I knew what it was worth.


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## Paul Running (Apr 12, 2020)

Doug Gifford said:


> I have this. It was my father's. Comes with a couple of adapters. I'd sell it if I knew what it was worth.
> 
> View attachment 414859


The Stark-911 tube tester was a basic unit. They advertised it as a dynamic tester however, I believe that it is a go-no-go unit. A Canadian made unit built back in the 110V, 25Hz days. The red trim option is rare. The prices will vary from $40 to $100+. Here's the manual:


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