Working on an Admiral 20X12

[old_coot88]

The 6AS5 is used as a B+ dropper in lieu of a big fat resistor. There should be well over a hundred volts at the cathode (pin 1).
The tube voltage chart says 0V. on pin 1, which is flat out wrong. Typical Sams screwup.

What's the voltage on the plate (pin 7) and screen grid (pin 6)? The chart voltages look 'waay too low here, too.

[Kevin Kuehn]

Sams has a note that shows pins 1,2,5,6,7 are all measured from pin 1 of V11. Which is why they show 0 volts on pin 1. Also why the the other voltages seem low. I'm not sure why they don't want to reference ground on those measurements.

FWIW, have you checked the 1/4 amp fuse in the fly cage?

[Kevin Kuehn]

I have a copy of what I think is a factory schematic, and they show the following for the 6AS5:

Pin 1 135v
Pin 2-5 120v
Pin 6 270v
pin 7 260v

Sound more reasonable?

[Kamakiri]

Originally Posted by Kevin Kuehn

Sams has a note that shows pins 1,2,5,6,7 are all measured from pin 1 of V11. Which is why they show 0 volts on pin 1. Also why the the other voltages seem low. I'm not sure why they don't want to reference ground on those measurements.

FWIW, have you checked the 1/4 amp fuse in the fly cage?

First thing I did. I'll scope out the 6AS5 in the morning.

[old_coot88]

Originally Posted by Kevin Kuehn

I have a copy of what I think is a factory schematic, and they show the following for the 6AS5:

Pin 1 135v
Pin 2-5 120v
Pin 6 270v
pin 7 260v

Sound more reasonable?

Hyup. I shoulda reddit closer.

[Kevin Kuehn]

Everyone's starting to talk like Sandy around here.

[Sandy G]

And WHAT'S wrong w/THAT ?!? (grin) Tim, sorry yr having such TROUBLE w/this Bad Boy... I always thought these Admirals were sposed to be "Easy-Peasy" sets. Guess I was Wrong. By the Bye, I'm told that I DON'T have too bad of an accent. I DID "Cheat" a bit, & cranked it up to 11, when I went up to meet LA's family in Cape Cod.. THEY were Damyankees from the very Heart of Damyankeeland. I was rather scared they would chew me up, & spit me out..Surprise-They were LOVELY people, & couldn't have been any nicer. But I DID drop an awful lot of "Yes, Ma'ams/No Ma'ams/Yes, Sirs/No Sirs" just in case. 2 of LA's aunts/cousins said you NEVER hear that up there any more.. I told 'em that I DIDN'T want the ghosts of one or BOTH of my Southern grannies rising from the grave to jerk a Knot in my tail because I'd forgotten how to treat a lady.. They grinned at that... Little did they know I was about half SERIOUS...

[Kamakiri]

Originally Posted by Kevin Kuehn

I have a copy of what I think is a factory schematic, and they show the following for the 6AS5:

Pin 1 135v
Pin 2-5 120v
Pin 6 270v
pin 7 260v

Sound more reasonable?

Assuming Pin 2-5 means 2 and 5, not 2 through 5 , everything is spot on.

[kramden66]

Once you get the Uv running if you get no reception check the rf chokes. Ive had a couple admirals and a choke was open. The fly is ok?

[Kevin Kuehn]

Originally Posted by Kamakiri

Assuming Pin 2-5 means 2 and 5, not 2 through 5 , everything is spot on.

Correct

Lets check your dc voltage across C1, section C(20 MFD) - just to make sure your focus coil isn't open. Whatever that measures, you should have the same voltage on either side of the 1/4 amp fuse in the fly cage.

[Kamakiri]

Yep, we're looking good there. What's next?

[Kevin Kuehn]

So what voltage did you measure on C1, section C? What dc voltages do you measure on pins 2 and 5 of the 6SN7 horizontal oscillator tube?

[Kamakiri]

Measuring 438V on C1 and on pin 5 of the 6SN7. Pin 2, I got nuthin. Ahaaaa.....that gives me some direction.

[Kevin Kuehn]

Did you mean 338v on C1 sec C? 438 seems too high based on your other measurements.

[Kamakiri]

Positive. C1C is at 438V.