5E3 Eating power tubes

[randomhitz]

I have a 5E3 that's costing me a fortune in 6V6s. I didn't build it, a friend did and it was working fine for quite a while. Here's the behavior: It started making snapping, popping noises after being on for 20 minutes or so. I started tube swapping, hoping it was just a bad tube but after one swap the cathode bypass cap for the power tubes exploded. I had it replaced with a 50V cap and things seemed fine for a while so I sprung for a set of Gold Lions. They were working fine and then suddenly the snapping, popping returned. I found that if I replaced V3 with another 6V6 it would seem to be ok.

I put the Gold Lion from V3 in a champ style amp and the popping followed it. that tube was toast, I did some more swapping and the same thing happened again. I wasn't sure that there was something about V3 at that point and in swapping around put the other Gold Lion in V3 so it was toasted too. I then put in a couple of JJs and the amp seemed to be doing fine. However yesterday I tended it on an there was only 60 cycle hum and no signal. I turned it off and put it up on the bench with the back off so I could see the tubes. when. I turned it on the hum came up and then there was a loud pop and a flash from inside the tube in V3.

So in terms of trouble shooting the obvious thing is to start with checking the voltages. Here's my question: does it matter whether or not the power tubes are installed to check voltages? I don't have any to sacrifice. I've examined the solder joints on the tube sockets and filter caps and the amp in general. Here's a clue I just remembered. At one point I found if I banged on the chassis it would set off the snapping/popping behavior. I looked for anything that appeared loose and sprayed the tube sockets with Deoxit. I never did swap out the 5Y3.

Any troubleshooting suggestions will be greatly appreciated.
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[Milspec]

Do you have or can you gain access to a variac or even a voltage limiter?

The fact that it operated fine for a long time before the issue began tells me that the circuit was wired correctly and that something sudden has changed. You said that you could re-create the problem by banging on the chassis which tells me that something is loose or else cracked. Then you also noted that with each tube swap, it worked okay for awhile, so I would suspect something failing after it gets heated up....cracked solder joint perhaps?

I would reduce voltage to the amp with a variac or limiter (easy enough to build one) and inspect for cracked components, burned spots, etc. Such things can appear normal when cold, but once heat is applied, they expand and open up until bad things happen.

 

[randomhitz]

Good idea I do have a variac so ill give that a shot

 

[printer2]

Reflow all the solder joints after the preamp stage. Does not matter what they look at, you have pops when you hit the amp. Just do it.

 

[nathan5782]

RobRob's page has a startup procedure that begins without tubes installed:

Amp Startup

Tube Amplifier Startup

robrobinette.com

 

[D'tar]

Pictures may help, if not, everyone like pictures any way.

What transformers are you using and what speaker load?

With photos we can check component values and ask questions.

 

[Lowerleftcoast]

does it matter whether or not the power tubes are installed to check voltages?

It is likely it will matter. No harm in trying the start up voltage chart without tubes. Pehaps an anomaly will show up.

Reflow the solder joints @printer2 suggested.

It is also possible the first failure may have left a carbon trace (or a crack) on the power tube socket. This would act with snapping, popping noises just like a dodgy solder joint.

Sometimes you can see where the problem is by viewing the tubes, sockets, and wiring in the dark. The snaps and pops may show as electrical arcing at the trouble spot.

Post some clear pictures. There are some sharp eyes at TDPRI.

 

[D'tar]

@randomhitz

You have several threads concerning your 5E3, let us help you get this thing right. Pictures, pictures and more pictures. Didi I mention to take pictures. Have your meter on stand by! No need to run the amp without a little troubleshooting the circuit first, like measuring the 6v6 grid to ground resistance. Cathode to ground... Etc.

 

[VintageSG]

Check the bias.
If a cathode bypass resistor has blown, it's either a) very bad luck with an iffy cap b) installed incorrectly c) there's something not right in there
Replacing with a higher voltage rated cap is not a good idea ( I don't know what the original should be rated for )
Voltage chart the heck out of it, then check the bias.
To kill a 6V6 takes some planning.