Phono 3S heater voltage problem

[bearded fiddler]

Lately my Phono 3S's heater voltage has been dropping to a very low level and then coming back to normal. The symptoms were a very faintly glowing led and having to turn the volume right up to get any sound. As the sound remained undistorted I presume the cause is not a bad solder join. I checked the umbilical cable and the socket looks alright too. Of course, as is common with intermittent faults, voltages measure ok when I check them
Any ideas?

[bearded fiddler]

More info: a moment ago when the led grew dimmer I measured a heater voltage of 4.9V instead of 6.3V. Then suddenly the led was bright again and volume went up a bit.

Jan

[Richard]

Hi Jan, yes sounds like a bad heater connection. Is Pre3 OK? If it is only happening on Phono3 then you only need look inside that box and the umbilical and connectors feeding it...

[Richard]

Jan, run Phono with the cover off and see if you can catch sight of the valves when the sound goes to see if the heaters on all the valves or perhaps just the cathode follower output valve is the culprit. The valve heaters are paralled so one two or all could work/not work and I'm not sure at what point the led is connected.

[bearded fiddler]

Thanks Richard. I'll report back.

Pre3 seems ok. By the way, better valves in Pre3 make a big difference. At this very moment a pair of Philips JAN 6189W is making very nice noises and I have a couple of Full Music 12AU7 ready for testing.

Jan