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Richardgr · 3rd May 2021, 11:06 am

Hi Lawrence, thanks for your assistance!

I can see what is wrong with the bias for the 2A3, I think. It is a sort of back-bias arrangement, and I should have a polarised capacitor there. Currently I have a 1uF MKP.

I have a variac controlled DC supply up to 400V, so I think I can test without being dependent on the power transformer. The hard part is having so many uncertainties! It could have been dropped, the tubes could be worn out, the transformer seems to make a random fizzing noise, and the speaker is quiet. Need to eliminate some things.

One thing I noticed when testing the transformer is that the heater voltages will not get up to 2.5V, even when I gave the PT more than 235V (I can go up to 250 on the variac). Plus none of the tubes were more than vaguely warm when I tried with them in place.

3rd May 2021, 11:06 am	#27
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 704	Re: Paillard 768 Hi Lawrence, thanks for your assistance! I can see what is wrong with the bias for the 2A3, I think. It is a sort of back-bias arrangement, and I should have a polarised capacitor there. Currently I have a 1uF MKP. I have a variac controlled DC supply up to 400V, so I think I can test without being dependent on the power transformer. The hard part is having so many uncertainties! It could have been dropped, the tubes could be worn out, the transformer seems to make a random fizzing noise, and the speaker is quiet. Need to eliminate some things. One thing I noticed when testing the transformer is that the heater voltages will not get up to 2.5V, even when I gave the PT more than 235V (I can go up to 250 on the variac). Plus none of the tubes were more than vaguely warm when I tried with them in place.