filament voltage for 6a3

[Analogluvr]

Hi Guys,
My filament voltage for the suppllied EH 300B is bang on at 5 and 4.9 volts.  I tried a pair of beautiful 6A3 1940's tung sol and they sounded very good with more extanded frequency extremes but maybe not so sweet mids.  After about 3 hours of listening I measured the filament voltage at 3.91 and 4.01 with 49 and 51 ma respectively.  THe data sheet calls for 6.3volts and 1 amp.  My questions are,
1.  Will the sound change if I adjust it to the proper voltage?
2.  What would I need to use for resistors to get 6.3 volts?
3.  Is tube life affected running status quo?
THanks so much!

 

[Chris65]

Your measurements don't look right, should get around 6V on the 6A3 filament with a stock BeePre & they would draw a lot more than 0.05A.

 

[Paul Joppa]

What terminals did you connect the meter leads to?

I ask because the filament terminals are (ideally) at +5.0 and +10.0 volts with respect to ground for a 300B, and at +3.7 and +10.0 for a 6A3. What is properly called "filament voltage" is the voltage DIFFERENCE between the filament terminals, 5.0 volts for a 300B and 6.3 volts for a 6A3.

I don't understand where or how you obtained 49-51mA, so no comment on that yet.

 

[RPMac]

I just measured the Philco 6A3's that have been on for 4 hours.

Filament voltage...Right--6.12V  Left--6.08V
Current....R--0.95A  L--0.95A
Plate voltage...R--110.7V  L--108.6V

This is typical of the measuements I get. Filaments are always slightly starved, but I've read that it helps with microphonics.

 

[Analogluvr]

I got those measurements from terminal 11 and 16 in relation to ground. Got the ma from the same terminals.
Actually that may be right then presuming the terminal that is supposed to be at 10volts is. I will measure that terminal and post back in a few minutes. 

 

[Analogluvr]

Good News!!!!!  My voltages are at 6 and 6.1 volts when I subtract the difference.  I thought it sounded much too good to be that far off.
Thanks a million for the help guys!!!
One other question since I have all your your collective experience on tap.  The capacitors people are changing for the best results are the ones laying across the chassis from terminals 12 to 17 and 2 to 7 correct?  Not the ones that connect to the XLR terminals at the output?  I only use single ended by the way.
And I was going to go with Mundorf Silver in oil, could I get away with the 8.2uf value?  Or even lower?  I do love my bass and do not want to have audible roll off.  I am feeding a 20' interconnect to either my Sophia 845's or my WE 91B clones.  I think that once the new Bottlehead 300B amp comes out I will try 2 of those and run them as monos.
Not sure if all that info is needed but better to be well informed right

 

[Doc B]

That 20 ft cable could be an issue. Or it might not. We ran 30 footers at the California Audio show and had a bit of a problem with HF rolloff. The math says it shouldn't be so, but I am the 'break the theory" guy around here. Just giving you a heads up.

 

[Analogluvr]

So meaning to be safe I should spring for the 10uf's?

 

[Doc B]

aI ment your cables might be too long and cause a high frequency rolloff. Nothing to do with the caps.