[R-390] R390 B+ Expected Tolerance

[Barry]

Hi Jacques,

I tried another 6BH6 and it didn't make any difference (of course they both might be less than ideal).

What I've found is one of the five 5651s has a slightly higher striking voltage (although I can't tell much difference in the current when it does strike).  Using that tube along with virtually any of the others gets me 181.5V which leads me to believe the 5651s are still most likely the biggest hindrance from seeing much over 176V regulated voltage.

I adjusted HUM BALANCE afterwards as well.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Jacques Fortin" <jacques.f at videotron.ca>
> To: "n4buq" <n4buq at knology.net>
> Cc: "R-390 Mailing List" <r-390 at mailman.qth.net>
> Sent: Friday, November 25, 2022 3:29:50 PM
> Subject: RE: [R-390] R390 B+ Expected Tolerance

> 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