Admiral 17T1: Never Give Up, Never Surrender

[Notimetolooz]

Originally Posted by Winky Dink

Hence I wired the 17T1 to be in compliance with the Telaides schematic. Except for R41.

Winky

You shouldn't put a teaser out like that.
The obvious next question would be "So how is R41 wired?".
After searching the schematics that you posted, and ignoring the ones of questionable heritage, the connection of R41 are all the same except the SAMS 19A1. That SAMS shows it connected to B+, the same source as the horizontal size pot, this indeed seems to be how your R41 is done.
The set uses what is sometimes called a "split supply" like many. The audio output stage (V4) receives B+ for power, the audio output tube is one of the tubes in the set conducts a fairly constant high current. A voltage is developed from the cathode (pin 8) that is also fairly constant, this voltage is used by several other circuits for power. The Wallace Telaides schematic shows this voltage supplies R41 not B+. B+ is much higher than the voltage from the audio output cathode.
Just to eliminate them as a source of a problem why not replace C37 and C39 with micas. Micas are available.
https://www.digikey.com/en/products/...102JO3/1918615
Expensive but maybe worth saving the torment of solving the problem.

[Notimetolooz]

Originally Posted by jr_tech

Weak video might cause poor sync... the very low voltage at the plate of v9 will likely cause weak video. Fixing that might help. Check the resistance of L9, R35, L10 and R36 and replace as necessary.

jr

It could be that the video output (V9) is drawing more current than normal.
The current draw could depend on the contract control.
He has checked all the resistors.

[jr_tech]

Is the voltage low on both sides of R-36?

jr

[Winky Dink]

jr tech: Yes, voltage is low on both sides of R36. I tracked it back through a couple more components and it's consistently low.

Notimetolooz: Early this morning I replaced C37, C39 with plastic film caps, each with two 630V caps in series yielding 950pF. I'll see if they make any difference tonight, but I'll order the mica caps as well.

I'll also mention that for audio output my set has a 6Y6 as in the Telaides schematic. The Telaides voltage chart shows a 6AS5 for audio output, and all of the other schematics (regardless of heritage) show a 6AS5.

Winky.

[jr_tech]

So R-36 is connected wrong.... the supply end should have the same voltage as V-9 pin 6, which you measured at 138 volts. Check the wiring around V-9.

jr

[Winky Dink]

I'm working on it. Will pick it up tomorrow.
Thanks.

[Notimetolooz]

Your voltage table shows 138V on V9 (pin 6) screen and 58V on V9 (pin 5) plate. A difference of 80V, most would be dropped across the 8.2K R36, that gives a plate current of nearly 10 ma. which could be. The listed drop should be 15V, but that can be effected by the contrast control. If L9 or L10 has a higher resistance then some of the voltage drop will across them and the current would be lower.
Don't worry about R35, the lower coil resistance will make that value unimportant in comparison.
Things could also be wired wrong.

[Electronic M]

Winky Dink, in the future avoid 'rewiring a set to match a schematic' if a set varies from schematic and the parts and workmanship look original you should keep it that way.
The only time to force a set to match it's schematic is when it's been hacked up by an idiot, or when you know which stage of the circuit the problem is in and you've exhausted all other possible fixes.

[Winky Dink]

I traced every connection from each V9 pin until I ran into a different tube or other stopper, but I found no errors.

BUT!! As I was pondering cutting the coil in a resistor-through-coil to check the resistor, I also pondered Notimetolooz's mention that the contrast controlled the voltage. When reading the voltages, my contrast was set at the max. Although the instructions were to set the controls at the midpoint, I only set the rear controls. My bad. Voltage at V9 pin 6 varied with contrast from 56V to126V, and V9 pin 5 varies to a much lesser degree. Setting the contrast control at the approximate midpoint, pin 5 was 142V and pin 6 was 118V. Ta dah!

It's no solution, but at least that low voltage can be ruled out as a symptom of the problem.

[jr_tech]

“pin 5 was 142V and pin 6 was 118V”

Are these backwards?

jr

[Winky Dink]

Yes. Backwards. I'm trying to think of an excuse. I'll let you know if I find one.

[jr_tech]

“jr tech: Yes, voltage is low on both sides of R36.”

Is this still true when the contrast control is adjusted properly for voltage table comparison? Should be about 24 volts across the resistor.

jt

[Winky Dink]

I'll check that now. Could be up to 30 minutes after now.

[Winky Dink]

Twenty-seven volts. 143V on the pin 6 (grid) side. 116V on the pin 5 (plate) side.

[jr_tech]

So r-36 is apparently connected correctly, and post 34 was in error, as the measurement across r-36 should have shown the 80 volt difference measured between pins 5 and 6 of v-9, as notimetolooz stated in post 37.

jr