[R-390] R390 B+ Expected Tolerance

[Jacques Fortin]

Hello Barry,

R626 to 1.3K and just 180V on output ??
No good at all: the problem have to be elsewhere...
I am just wondering that your 6BH6 (V607) can be leaky.
If you have another one, please swap it !
R624 at 600K should not make any difference if there is no grid leakage
current from the 6BH6, but it is exactly what I am thinking now...
I already mentioned a possibility of a "higher than normal" 6BH6
transconductance, but internal leakage is also a definitive possibility.

I once encountered a 6DC6 that disturbed the ACG line in my 51S-1
completely.
And this particular tube passed all the test on my AVO VCM163 !
But inserted as the RF amp in the 51S-1, it turns the whole set into a
basket case...
Tubes tester are good, but do not tell you all the truth, obviously.
This does not means that a tube that test bad on the tester will perform
correctly in the receiver, however.

Like testing the 5651 on your Hickock 752A: this is not the real test to do,
because all the testing currents and voltages within are AC.
In the R-390 PS, the 5651s should run at 2.7mA and have 85 volts across each
of them.
The only valid way to test VR tubes is to test those using a DC supply,
monitoring both the current thru and the voltage across.
I took me few years to understand that, but...

OK, let's change that 6BH6 and try again, please.
Don't forget to re-adjust the hum balance with the new 6BH6.
If you don't have any, just tell me: it's another tube type I have enough to
dance on.

73, Jacques, VE2JFE in Montreal