02-09-2015, 11:01 AM
Arran
yep, could very well be the case.
When I unplug the RF part (these things, TRF with 3 RF stages and a tunable detector are like those Duesenbergs, capable of switching off some cylinders and work on a lower power) the oscillation stops, and the volume reg still works since all three have the Ks biased by the same volume pot.
Which, BTW, while I was writing this, gave me an idea to try another capacitor on cathodes...oh wait, did that already....but maybe a bigger one.
They are all connected with a longish wire that goes to that divider and them the cap is connected at one of the three tubes.....methinks, actually at the 1st RF panel.
In this sch it is shown (and is what Kirk put in the chassis; I take it he put in the same values that were there before) as 0.1uF, and another one has it as 0.2uF (should not be critical if increased, it is the lower value that is more important.)
I tried to increase that 250 Ohm resistor that separates Ks from GND when the col is at its max, to 300 Ohm, as in the other version, did not help. The volume pot comes within 12 Ohm from the max when it starts whining.
As I said, I am not gonna bust my tail trying to quell that but will give it a half-hearted try once more, just to see what it will do.
yep, could very well be the case.
When I unplug the RF part (these things, TRF with 3 RF stages and a tunable detector are like those Duesenbergs, capable of switching off some cylinders and work on a lower power) the oscillation stops, and the volume reg still works since all three have the Ks biased by the same volume pot.
Which, BTW, while I was writing this, gave me an idea to try another capacitor on cathodes...oh wait, did that already....but maybe a bigger one.
They are all connected with a longish wire that goes to that divider and them the cap is connected at one of the three tubes.....methinks, actually at the 1st RF panel.
In this sch it is shown (and is what Kirk put in the chassis; I take it he put in the same values that were there before) as 0.1uF, and another one has it as 0.2uF (should not be critical if increased, it is the lower value that is more important.)
I tried to increase that 250 Ohm resistor that separates Ks from GND when the col is at its max, to 300 Ohm, as in the other version, did not help. The volume pot comes within 12 Ohm from the max when it starts whining.
As I said, I am not gonna bust my tail trying to quell that but will give it a half-hearted try once more, just to see what it will do.
