b+ question

[radio nut]

My Muntz tv is finally up and running correctly! Yea!
Biggest headache I have ever had.
I am going to see about getting a variac or another unit that controls the line voltage to a set level (not sure what it is called), until then I still have one question.
The diagram calls for b+ right at the 5u4 to be 390 at 117 line voltage.
My set is running 435, but the line voltage is 125.
The 8 extra line volts makes that much difference?
Is there possibly another issue hiding in this set? Or is this reasonable?

[old_tv_nut]

This calculates to a 5% discrepancy, so not terribly surprising, having no time machine to go back and get the actual unit that was measured plus check the lab instruments' calibrations at the time.

[N8NM]

I agree with the old tv nut.

[bob91343]

Yes, it's just a ratio. If the line is up 10% you can expect the voltages to be up the same amount. Add in your meter calibration, the deviation of the power source from pure sine, the tolerance in the transformer and tubes and capacitors, and you are right on the money.

Of course, you could do what I did. I bought an HP 3456A voltmeter that reads AC and DC volts to six digits. Plus a variac to set the line where it belongs, and the result should be closer to bogie. And measure the input filter capacitor with my GR 1658 digital RCL meter to see if it's the right value.

Go ahead, drive yourself bonkers. I did it.

[jr_tech]

For sure, the ratio calculation is valid, but I am wondering if there is also another small factor that could add another few % to the B+ output at higher line voltage. Could the voltage drop across the 5U4 rectifier tube decrease somewhat when the tube is run with higher filament voltage?
jr

[Zenith26kc20]

I had a Motorola TS-14 that had high B+. I worked hours until I dropped the B+ to factory ratings. The Sync and a number of other problems went away and it's still going strong. I would say yes, get the voltage right. Voltage drop across the 5U4 is probably more due to load than filament.