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EAR 834P fault-finding

Tony L

Tony L

Administrator
Just landed a nice clean EAR 834P valve phono stage that hadn’t been used for a good while and it seems dead. With the consent of the seller I’m starting this thread for a little technical advice.

The problem as far as I can quickly diagnose is no heater voltage. The valves aren’t glowing at all and I can’t find any 6.3V AC on the ECC83 valve base pins 4&5. Other DC voltages do seem present on other pins (i.e. the thing is not totally dead). The fuse and switch are fine. These things are tightly packed into the box so hard to probe much without fully disembowelling it.

Am I right in suspecting a faulty transformer? It was a little loose and wobbly, but I can’t see any damage, wires off or anything.
 
The heaters are DC Tony.

Could be a faulty rectifier for the heaters. Can you test the AC output of the transformer secondary?

If the transformer and rectifier are OK measure before and after R16 (33R) between C13 and C14.
 
Thanks.

I can see 36.4V AC between P3 and P4 from the transformer (red, white). I can’t get probes in to do the other two.

R16 seems to measure the same at both ends: 1.4V DC or so, black probe in the 834’s earth terminal. This seems to be a moving target, it is slowly climbing, 2V now. This is with V3 removed (I was measuring the pins). With it replaced this reading drops to 0.005V, i.e. nothing.

I’m getting 4.6V DC on pin 5 of an ECC83 base, nothing at all on pin 4. Though again this seems very variable. This with V1 & V2 in place, V3 removed.
 
Many thanks. I’ve had a very close look at the underside of the board (PITA to get to, obvs) and I can see absolutely no evidence of dry joints, cracks or anything and the valve bases seem clean, fine and well soldered to the board (I wobbled a valve whilst looking). It is a beautiful clean example and I can’t see any visual evidence of an issue. Given that it isn’t mine, and that I am certainly not an electronics engineer, that is as far as I plan to go.

PS The supplied valves all test ‘worn’, but I tried a known good set as well and again no heaters. A shame, but I think this is my jumping off point.
 
I’m sure I could fix it given time and effort, but it isn’t mine and I just don’t feel comfortable renegotiating price etc. Had it been blindingly obvious e.g. a lead hanging off, a obvious dry joint on a valve base etc I’d have just fired up the soldering iron and fixed it, but I don’t really want to buy it in non-working condition.

To be honest I don’t even need it! I arranged to buy it as it was priced well and might possibly have a use if I ever wanted to stick a turntable into the passive pre/Leak TL12 Plus system. I was just going to stash it in its box and pretty much forget about it for a few years. I’ve owned two of these things before so viewed it as a safe buy.
 
Read thread is a little more detail and if there is only 1.4V on each end of R16 it basically has to be the rectifier or the transformer or wiring between the two or wiring/PCB track from rectifier to the first 2200uF cap. It is quite unusual, but not unknown, for a rectifier to fail open. They usually blow a fuse
 
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