My DIY version of Allen Wright's RTP3C has been showing some odd behaviour. From time to time, the right-hand channel of the phono stage becomes very faint. There is no crackling, popping or other noise - just sometimes all I can hear is the left channel.
I have swapped the single 6922 valve over for a spare one, with no improvement. Swapping the signal polarity at the source select doesn't make a difference; I have reformed almost all the soldered connections, and I have checked the continuity of the tonearm cable.
The phono stage is the left-hand portion of the schematic here: RTP3C circuit. It's such a simple circuit that I would have thought it would be easy to find a fault...
I hate intermittent faults! Has anyone else come across this kind of problem?
Thanks,
Alex
I have swapped the single 6922 valve over for a spare one, with no improvement. Swapping the signal polarity at the source select doesn't make a difference; I have reformed almost all the soldered connections, and I have checked the continuity of the tonearm cable.
The phono stage is the left-hand portion of the schematic here: RTP3C circuit. It's such a simple circuit that I would have thought it would be easy to find a fault...
I hate intermittent faults! Has anyone else come across this kind of problem?
Thanks,
Alex
Last edited:
Hi Nelson,
As it happens, I posted an update to a different thread, since I had no responses to this one!
It turned out to be due to a partial failure of the shunt regulator for that channel, which resulted in a droop of the HT down to 260V after an hour or so. The current sink on the emitters of the input transistors means that a constant 240V is dropped across each 25K cathode resistor, so the HT voltage sag is enough to starve the input stage of voltage - hence the signal dropout.
As I mentioned in the other thread, I replaced the HPHV regulator with the much simpler Salas HPHV regulator, which is still working fine.
Alex
As it happens, I posted an update to a different thread, since I had no responses to this one!
It turned out to be due to a partial failure of the shunt regulator for that channel, which resulted in a droop of the HT down to 260V after an hour or so. The current sink on the emitters of the input transistors means that a constant 240V is dropped across each 25K cathode resistor, so the HT voltage sag is enough to starve the input stage of voltage - hence the signal dropout.
As I mentioned in the other thread, I replaced the HPHV regulator with the much simpler Salas HPHV regulator, which is still working fine.
Alex
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