Vertical Issues on a Philco 50-T702

[jr_tech]

Is the voltage on C 77 around 1200 volts? How about the focus voltage?

jr

[Crist Rigott]

Originally Posted by jr_tech

Is the voltage on C 77 around 1200 volts? How about the focus voltage?

jr

C77= 750V
Focus:
1.5M side=1450V
Center tap=1300V
470K side=825V

[Crist Rigott]

I forgot to mention that C77 voltage starts out at about 1400V then goes down to 750V about the time the tubes warm up.

[Crist Rigott]

I also swapped the CRT but no joy. It was something I had to do even though I really didn't think it was the problem.

[jr_tech]

Looking reasonable... have you tried another 7N7?
Does the voltage drop across r-99 match r-102 and r-100 match r-103?
C-5 ok?

jr

[Crist Rigott]

Originally Posted by jr_tech

Looking reasonable... have you tried another 7N7?
Does the voltage drop across r-99 match r-102 and r-100 match r-103?
C-5 ok?

jr

I just saw this. Let me get back to you.

[Crist Rigott]

Originally Posted by jr_tech

Looking reasonable... have you tried another 7N7?
Does the voltage drop across r-99 match r-102 and r-100 match r-103?
C-5 ok?

jr

Yes, I swapped out V13 and V12 both 7F7 with no joy.

C5 is good. I removed the C5 wire from pin 7 of V13 and gator clipped in a new 10uf 450V cap. No joy. Restored the wire.

Measured the voltage at the junction of R99 and R102 = 400V, the junction of R100 and R103 = 500V. R100 ohmed out to 2M while the others at close to 2.2M.

Voltages at V13 with the tube pulled are pin 3=1120V, pin 6=1020V.

Tried subbing C81 and C80 at the same time, no joy.

Both pin 3 and pin 6 of V13 drop down when the tube starts to conduct.

I ohmed out the vertical transformer and it ohmed out pretty close to specs.

I'm at a loss right now.

I appreciate your help and suggestions.

[jr_tech]

For grins.... what voltage do you measure on v-13 pin 7?
Do you have another 7F7? unlikely both are bad, but possible.
Do you have a scope? I could measure a few waveforms for comparison. I need to bring the Philco back to the bench to replace the seleniums, that I forgot about, anyway.

a real headscratcher,
jr

[Crist Rigott]

I also ohmed out the Vertical Amp tube V13. All the resistances were very close to what Sams called out for.

[jr_tech]

Was thinking that these old high meg resistors might behave in a non linear fashion when current is passed through them. Voltage drop comparison during operation under load might reveal some odd behavior.

Pin 3 & 6 measurements with the 7N7 pulled might reveal socket problems if the voltage is still low with the tube pulled.

grasping at straws,
jr