Voltage discrepancies at V1 in an Express

[Noel Grassy]

While checking my Express voltages I was very pleased with the numbers
I was getting until I measured the pins on V1. It's 100 volts more than the
expected voltage on the 2 plates!!

V1a= 296 @ pin1 V1b= 227 @ pin 6 Heaters= 6.38VDC
1.91 @ pin 3 1.9 @ pin 8

V2a= 275.7 @ pin 1
2.95 @ pin 3

V3a= 204.7 @ pin 1 V3b= 205.2 @ pin 6
25.6 @ pin 2 24.6 @ pin 7
38.6 @ pin 3 38.6 @ pin 8

V4= 391 @ pin 3 381 @ pin 4 - 38.6 @ pin 5 383 @ pin 4

V5= 381.5 @ pin 3 381.2 @ pin 4 -33.8 @ pin5 384 @ pin 4

wall voltage= 119VAC Secondaries= 588~590VAC

end of Diode string = 401VDC
B1=395VDC
B2 =382
B3= 316
B4= 306
B5= 299
Across the 1Ohm, .01% resisters from pin 8,1
The measurement of 0.024 volts is my reading.
That's pretty cold considering my bias supply
voltage is the prescribed -33.75 volts measured at the power tube's pin #5. These are brand new GT EL-34 [rated #4]
All the 12AX7/7025 are Phillips with low hours on 'em.
Do those over voltages at V1 indicate an expired or soon to be expired
12AX7? I never seen this specific problem in an amp.
Thanks for looking at my dilemma and any helpful suggestions you can
share with this solder jockey,

Noel Grassy.

[gahult]

Nice catch.

Have you tried a different tube in V1.

I had a voltage reading that seemed way out of line similar to yours, V3 IIRC on one of my builds. I switched the tube out and it came down to a reasonable reading.

It make take more than one.

To bad V1 is so fussy to find the right tube in the first place. Even if it doesn't sound good it will give you a indication if that tube is the culprit.

Just a thought.

Gary

[jjman]

You're only dropping 3 volts from B5 to the plate but the cathode voltage is good. It kinda sounds like the plate and cathode resistors for v1a are flipped with each other.

[Allynmey]

Here's one from a few months ago. Common to most expresses within a couple of volts