Low voltage tap - really low voltage

tonepilgrim · Post by **tonepilgrim** » Fri Sep 07, 2007 11:01 pm

Just checking in with the experts to be sure I don't have a problem.

Finished my 100w build, using the low voltage tap. When measuring the B+ w/o tubes, I have around 390v which I figure is close enough to the advertised 400v. However when I put the power tubes in, I my B+ moves to around 360v. Is that much of a drop normal?

Also, I found that I couldn't get my bias up past 15ma or so. So, after reading the forum here, I saw where the dual voltage switches add a 25k ohm or so resistor in series with the 27k. So I went ahead and replaced the 27k with a 56k, which worked to get my bias range up to a workable level.

Does any of this sound fishy other than the low B+? If not, then I'm cool I guess.

Thanks for your help.

Flames1950 · Post by **Flames1950** » Fri Sep 07, 2007 11:34 pm

I thought a few of these were miswound and voltages were lower than spec. What's the voltage when switched to the high voltage side? If it's uniformly low then I'd e-mail George and see what he thinks.

tonepilgrim · Post by **tonepilgrim** » Fri Sep 07, 2007 11:45 pm

Thanks Flames. I will probably check in with George, but I'm not sure there is much he can do if it's one of the underwound trannies. I'll check the high taps too. I may like those better any way, even if they are slightly low. I was just attracted to the lower voltage as I always run my amps wide open, and thought the lower voltage would be easier on everything (tubes, load box, etc).

Flames1950 · Post by **Flames1950** » Fri Sep 07, 2007 11:48 pm

Well if you like it as is, there's nothing wrong with that!! If it's not right and you don't like it, I'd guess George will make it right with you. Only your ears know which way to turn..........

tonepilgrim · Post by **tonepilgrim** » Sat Sep 08, 2007 12:01 pm

The B+ on the high taps is about 513v w/o tubes, 480v with the tubes in. This seems about right for the hi tap. I guess the real question is - is a 30v drop (in my case with both hi and lo taps) in B+ when I put the power tubes in a reasonable drop? Or is this indicative of something I did wrong?
Again, thanks.

Flames1950 · Post by **Flames1950** » Sat Sep 08, 2007 5:12 pm

I doubt it's anything you did wrong. Maybe a different set of tubes would respond differently. But the 480V on the high side isn't too bad, 350V will definitely feel liquid-y in comparison.