Duncan's 1960 Magnavox

[Mr.Duncan]

I forgot to mention, I have a set of these coming in the mail so I can finally test voltages with the chassis installed.

tubes by Thomas Duncan, on Flickr

[old_tv_nut]

This question of resistor tolerance reminds me of the question of whether the major brand TVs were actually better quality than second tier. In terms of component tolerance the answer is yes, since the high volume of Zenith or RCA meant that they could get parts cheaper. At Motorola, standard practice was to use 10% resistors in designs unless 5% was absolutely necessary, while Zenith used 5% as the default until analysis showed 10% would not reduce final yield. When I moved from Motorola to Zenith I was surprised to find the lab stocked with 5% resistors instead of mostly 10%.

[old_tv_nut]

I general, don't replace composition resistors with wirewound, because they may affect frequency response of high frequency circuits. Replacing wirewound with wirewound is a good idea.

1% tolerance is a waste in consumer tube sets, because the variation from tube to tube in a circuit will completely swamp that out. The exception is test equipment where multiple low-gain feedback stabilized sections are used to make the gear maintain calibrated state at least for a while.

In transistor circuits, variations due to the transistor itself are usually much smaller than variations due to passive components.

5% film resistors when replacing other than wirewound are usually not a bad idea.

[Mr.Duncan]

Checking ESR on both capacitors on the vertical circuit.

Both these new capacitors are .1uF @ 400volts.

I checked and found ESR ratings of:
C40: 16.6
C39: 16

I de-soldered them, and got the same ESR ratings, with the same .1uF.

I cant seem to find a chart/data on ESR ratings for high voltage, low uF capacitors. Are these ESR ratings bad? The uF test shows the correct uF value.

tube by Thomas Duncan, on Flickr

C40
PXL_20240810_233255415 by Thomas Duncan, on Flickr

C39
PXL_20240810_233312649 by Thomas Duncan, on Flickr

[old_tv_nut]

According to this page
https://www.eevblog.com/forum/beginn...ll-capacitors/
your ESR meter may be reading the capacitive reactance of small capacitors in series with the resistance.

In fact, if you plug in 0.1 uf and the frequency of your tester (100 kHz) on this page
https://www.omnicalculator.com/physi...tive-reactance
You get 15.9 ohms

[old_tv_nut]

square root [16^2 - 15.9^2] = 1.79 ohms ESR

[Electronic M]

I rarely test new film capacitors, but when I do I use my Heathkit C3 which will tell me if they're going open or if they leak at full rated voltage.
I only use my ESR tester on solid state stuff.

[Alex KL-1]

For high voltage low current circuits, the leakage is the most important parameter. For high current low voltage PSU's, the ESR can play a important role.

[kvflyer]

Originally Posted by Alex KL-1

For high voltage low current circuits, the leakage is the most important parameter. For high current low voltage PSU's, the ESR can play a important role.

Originally Posted by Electronic M

I rarely test new film capacitors, but when I do I use my Heathkit C3 which will tell me if they're going open or if they leak at full rated voltage.
I only use my ESR tester on solid state stuff.

Exactly, for what it's worth I agree, it is the way to do it.

[NowhereMan 1966]

I have the same exact rabbit ears, my parents got them when they were married in 1959. I still use them on my 1982 Zenith.

[Electronic M]

I've got a set too. They were too cool to pass up. Have yet to hook them up and see if they paint the corners...

[Mr.Duncan]

Still digging into the vertical issue. Removed the chassis, triple checked all capacitors, re-did all the solder points to be safe.

Swapped out both Vert OSC (6BF6) and Vert Output (6DT5) with some good NOS tubes.

Replaced R50 with a new resistor.

Still got vertical collapse. - I guess I could work backwards from 6DT5?

Set the line voltage to 117v AC.

When checking 6DT5 I got the following voltages:

1. Pin# 1 280.1v (spec is 275)
2. Pin# 7 20.52v (spec is 20v)

PXL_20240818_023303382 by Thomas Duncan, on Flickr

PXL_20240818_023131537 by Thomas Duncan, on Flickr

PXL_20240818_023143176 by Thomas Duncan, on Flickr

tube by Thomas Duncan, on Flickr

PXL_20240818_023948540 by Thomas Duncan, on Flickr

PXL_20240818_024008008 by Thomas Duncan, on Flickr

PXL_20240818_023359388 by Thomas Duncan, on Flickr

[Electronic M]

Originally Posted by Mr.Duncan

Still digging into the vertical issue. Removed the chassis, triple checked all capacitors, re-did all the solder points to be safe.

Swapped out both Vert OSC (6BF6) and Vert Output (6DT5) with some good NOS tubes.

Replaced R50 with a new resistor.

Still got vertical collapse. - I guess I could work backwards from 6DT5?

Set the line voltage to 117v AC.

When checking 6DT5 I got the following voltages:

1. Pin# 1 280.1v (spec is 275)
2. Pin# 7 20.52v (spec is 20v)

Those voltages are completely normal. With line voltage set to the same 117V as Sam's anything within +/-25% is normal (in stages like vertical or CRT gun grid/cathode where the bias is controlled by potentiometers the normal range can be much larger than 25% and it's sometimes wise to adjust the relevant pots to make sure they can get the voltage that sam's says should be there.

If all the vertical voltages measure normal you may want to check the output transformer, and yoke and their connections to each other.

[Mr.Duncan]

Originally Posted by Electronic M

Those voltages are completely normal. With line voltage set to the same 117V as Sam's anything within +/-25% is normal (in stages like vertical or CRT gun grid/cathode where the bias is controlled by potentiometers the normal range can be much larger than 25% and it's sometimes wise to adjust the relevant pots to make sure they can get the voltage that sam's says should be there.

If all the vertical voltages measure normal you may want to check the output transformer, and yoke and their connections to each other.

I'll check those tonight. I did find a low voltage PIN#7 of the 6BF6 tube.
(Vert Mult / AGC clamper)

I believe pin#7 is the output that feeds into 6DT5 Tube?

I was able to vary the voltage of pin#7 between 7.47 to 11v, but no higher than 11. (using the vertical adjustment pot)

Voltage spec: 25v
Reading: 7.47-to-11v

Some good news:
Im getting clear audio out from the TV- was broadcasting signal on channel #7 with my Blonder Tongue.

Checked the Yoke- Ohm reads are within spec.

tube by Thomas Duncan, on Flickr

[Username1]

.

Good Morning - Just a quick note - Things to check - On pin 3-6 of V10 the vert output,
put your finger or a DVM probe on it with nothing attached and see if the line on the
screen moves up or down, or if you can put any 60Hz signal on it like from a Signal
gen, or radio speaker on it there should be deflection. If none - then you should
check for any voltage on the plate of V10, since there is no deflection, it should
be completely safe, looking for about 280V. If nothing, track through the T2
to see if you have it or if T2 has open windings. If you get deflection when
you touch G1 of V10, then you have to go Back into the Osc, Don't forget
to look at the feedback loop through R45, & 46. Also, most important -
Since this tv worked before you replaced parts, keep an open mind to
the possibility that you wired something wrong, My money is on a
mistake in wiring or part placement. Also, see that 25ma current
reading for the cathode of V10, that is often printed where they
tell you not to measure the plate voltage, You can lift one side
of R51 and check the current, to see if the tubie is conducting.
Also be ready to check voltages on V9 as well.... Also -
The Vert Hold has a plug & socket in the schematic - If you
have this on your tv be sure to check that if you had to
undo it to work on the set.... Good Luck!

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