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PAS voltages

77.101.128.233
Posted on October 1, 2009 at 11:55:53
bhamham
Audiophile

Posts: 10
Location: Birmingham UK
Joined: March 23, 2009
 Hi everyone,

I replace my old shorted power transformer in my PAS-2 with a new Triode one. I also rebuilt both the boards. I get two different readings for the filament voltages (pin 5) - 12.8 & 13.2vDC - shouldn't they be the same? One tube in each board reads 12.8 and the other two - one on each board reads 13.2. All the other voltages from the other pins read like that too, where there's two different sets.

If I wanted to drop the voltage to around 11v do I just put a resistor in series with the filament circuit after those doubler caps? What wattage would you recommend?

Thanks for any help,
Bruce

RE: PAS voltages, posted on October 1, 2009 at 12:53:13
Joe Curcio
Manufacturer

Posts: 1094
Location: Northern CA
Joined: October 10, 2001
Contributor
  Since: July 1, 2002
 The tube filaments are wired in series so, if I understand your question and you are measuring _across_ each tube's filament (pins 4 & 5) then it is very possible to see a variation between each tube (depends on the filament resistance).

Either way, other than having the tube with the higher filament voltage see a minor decrease in life, the variation you cite will have no impact on the preamp performance or specs.

RE: PAS voltages, posted on October 1, 2009 at 13:32:49
bhamham
Audiophile

Posts: 10
Location: Birmingham UK
Joined: March 23, 2009
 Thanks Joe. In the post above, I was taking the voltages from pin 5 to ground but I just did them from pins 4 to 5 and they measured 13.1 - 13.4 - I guess I still don't understand why they would measure differently to ground. I'm still pretty new at this.

RE: PAS voltages, posted on October 1, 2009 at 14:05:38
Joe Curcio
Manufacturer

Posts: 1094
Location: Northern CA
Joined: October 10, 2001
Contributor
  Since: July 1, 2002
 The junction of the filaments are tied to ground (pins 10 and 20 if I recall) so the measurement should be the same.

Frankly - I don't think you have a problem here

RE: PAS voltages, posted on October 1, 2009 at 23:05:21
bhamham
Audiophile

Posts: 10
Location: Birmingham UK
Joined: March 23, 2009
 Thanks Joe, I appreciate the help. I'll hook her up and see how she sounds.

Bruce

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