'65 DRRI Keeps Blowing 5AR4 Rectifier Tubes

[sssmoka]

Greetings and Salutations!

Howdy and hello, all. Longtime lurker. New member.
I've got a Fender '65 Deluxe Reverb Re-Issue amplifier on the bench that is eating 5AR4 rectifier tubes.

The owner brought it in for resolution of a single symptom: an incredibly loud and random crackle when the amp is brought out of Standby.

I replaced a factory-original, spent Groove Tubes 5AR4 with a JJ Electronics 5AR4 and sent it home with its' owner. Unfortunately, he had to bring it back after it developed the same random crackle as before.

I am trying to remedy the issue once and for-all. I see the rectifier tube socket is wired to the power transformer mains. My first thought was a bad transformer throwing inappropriate level voltage and current into the 5AR4. I'm off to test the transformer for proper operating specs. If I find that it is not the problem... I am wandering what else it could be - or if it is even the amp with the p0roblem. Perhaps, the owner needs a power condfitioner?

A thousand thanks in advance, any and all help is greatly appreciated.



Christopher Kennedy
Owner / Operator
Soda City Amp Repair

[sluckey]

I see the rectifier tube socket is wired to the power transformer mains.

That's insane. Are you sure? Pics please.

[xtian]

I see the rectifier tube socket is wired to the power transformer mains.

That's insane. Are you sure? Pics please.

I mean...he MUST mean the PT secondaries... uh...I hope!

[sssmoka]

The tube socket IS NOT wired to the transformer mains. I was iin a bit of a hurry and blurted out an inaccurate (and totally illogical) description of the transformer wiring scheme.


- CCK

[xtian]

loud and random crackle when the amp is brought out of Standby

Standby switches are evil. All rated for 250V, not the 400+ that most see. The contacts get pitted and oxidized, causing all kinds of ugly and mysterious noises. Jump it out of the circuit, and see if that solves customer's complaint. Remember the tube rectifier is allowing a slow DC ramp up for this amp. The switch has no benefit.

[alnight]

I put backup diodes on everything these days. I look at it as cheap insurance. From what you're describing, I think it would be more of a band-aid than a proper fix for your particular issue but it might help, and keep from smoking more tubes while you track down the true culprit.

https://robrobinette.com/5e3_Modificati ... kup_Diodes

[pdf64]

I suggest to try to isolate the issue to a particular amp circuit.
eg remove all 12A_7 valves and see if it still crackles or not.
With a loud crackling, I look to the output valves / connections to them as the most likely suspects.

[martin manning]

I put backup diodes on everything these days. I look at it as cheap insurance.

True enough, and they will keep you going if the vacuum rectifier shorts, but they won't protect against an over-current situation.

I've got a Fender '65 Deluxe Reverb Re-Issue amplifier on the bench that is eating 5AR4 rectifier tubes.
The owner brought it in for resolution of a single symptom: an incredibly loud and random crackle when the amp is brought out of Standby.
I replaced a factory-original, spent Groove Tubes 5AR4 with a JJ Electronics 5AR4 and sent it home with its' owner. Unfortunately, he had to bring it back after it developed the same random crackle as before.

How old are the reservoir and filter caps? I'm wondering if they are leaky or shorted, and the root cause of the rectifier failure.

[didit]

Hello —

Who thinks it’s likely to be inductive flyback? Either off the power secondary or output primary. And therefore potentially a loose intermittent on or around the rectifier or 6V6 sockets.

..

[Stevem]

There has to be an over current draw like a failing filter.

The odd thing is that a current draw great enough to blow out a recto tube should open the mains fuse first.

To that end I would make the mains fuse a fast blow 2 amp from the 2 amp slow blow that it should be and troubleshoot with 2 preamp tubes removed.

[Colossal]

Hello —

Who thinks it’s likely to be inductive flyback? Either off the power secondary or output primary. And therefore potentially a loose intermittent on or around the rectifier or 6V6 sockets.

..

I was thinking that damage may be done to the OT from a previous event and it just keeps taking out the rectifier.

[Stevem]

The OT would have to be shorted from primary to secondary or from primary to core and in all the 50 something OTs I have replaced in my lifetime I have never seen such a short.
Besides the mains fuse should blow under such a condition.

[pdf64]

...
I've got a Fender '65 Deluxe Reverb Re-Issue amplifier on the bench that is eating 5AR4 rectifier tubes.

The owner brought it in for resolution of a single symptom: an incredibly loud and random crackle when the amp is brought out of Standby.

I replaced a factory-original, spent Groove Tubes 5AR4 with a JJ Electronics 5AR4 and sent it home with its' owner. Unfortunately, he had to bring it back after it developed the same random crackle as before.
...

What causes you to think that the amp is eating rectifier valves?
There seems no evidence so far that any rectifier valves have actually failed in this amp.
All there is so far is that the factory original rectifier may have been somewhat worn out (how was this assessed?).

... it just keeps taking out the rectifier.

[sssmoka]

Failed 5AR4 Rectifier tube verified with Fluke 117 Multi-meter diode check between pins 4 and 6 and between pins 6 and 8. 4 and 6 were fine but 6 and 8 were open.

[Helmholtz]

You can't check a vacuum rectifier like a SS diode with a diode tester.
You should have infinite resistance between pins 4,6 and 8 with tube out of circuit.