1949 motorola table top

[timmy]

ok so i recapped the power lytics would it now be a good idea to change the hv caps, the 6kv caps, and see what i get from there. the rest of the caps are aside from micas the same values as the color sets, 200v or 600v. the 6kv caps are stated to be oil caps does this make any difference oil or otherwise ?

[Zenith26kc20]

JustRadios has the 6KV capacitors. They are bad if they are the black oily ones or the wax type. These were the major failure in these sets.

[timmy]

i went to just radios site and cannot find how to order these hv caps. is there a special way to navagate the site? the caps in there are oil so can just a film or metalized cap be used in place of oil ? i know mica caps in the hv area are sometimes used for oscillator timing, are these known to go bad even as old is 1949, some say they dont go bad but i dont know.

[Zenith26kc20]

The justradios site has a capacitor shopping cart. Just click it and it will take you to all their capacitors. The original ones were wax, then oil from what I have seen. The ones from just radios are small tubulars. I have used them in all of my Motorola sets and in the high voltage of my Silvertone with total success. Without changing these the sets can act up in so many ways it'll drive you crazy. Also, the 12SN7 tubes can be somewhat critical in vertical and horizontal. Try several if stability or size issues crop up. Also, ohm out the horizontal centering pot. I had one that was 1/2 value and prevented the horizontal centering from working. I had to add resistors on both sides to bring the value to the one listed in the schematic. After that it worked fine.

[timmy]

i found it on just radios and is it ok to use .0047 6kv in place of .005 6 kv ? since i see this as an option but i really dont know.

[Gregb]

I used those in both my Admiral and my Philco and they work just fine.

Gregb

[Electronic M]

Mica capacitors in the deflection stages can cause issues. As far as mica capacitors in any TV go always replace the ones in the deflection stage, but don't change the ones in the IF/tuner unless you have a darn good reason to believe they are bad.

[bandersen]

Careful. The mica caps in the horizontal circuit (200pF, 680pF, 900pF) are rated for 2,000 volts. Hard to find mew mica caps rated for more than 1,000o volts and 900pF is an oddball valuee.

[Zenith26kc20]

Some of the caps in the sweep circuits are tubular types. I've got four Motorola electrostatics running and they all have the tubulars still in them. The ones that look like brown dominos can give problems. In the sweep circuits I try to use 1600 volt replacements. They seem more stable than the 600 volt types (less fiddling with the horizontal and vertical hold).

[bandersen]

Yes, there are some tubular ceramic caps. They are very reliable and I'd avoid messing with them.

[timmy]

does anyone know what the hv should be for the crt and is it a fixed voltage when done. also what is the B+ voltage and the B++ voltage , i have no info in the schematics as to what the voltages are.

[bandersen]

Approximately

CRT = 5,500 at the highest potential right on the 1B3 rectifier. Not sure what you mean by fixed ?
B+ = 125
B++ = 250

[timmy]

fixed meaning how it was built originally, not having an adjustment. thanks for that info. one thing i noticed is voltages are jumping up and down as if its trying to get somewhere but then hits a block so its probably those .001 and .005 6 kv caps waiting for them from just radios.

[timmy]

to change the selenium rectifiers and put in 1n4007 diodes, if this is the ones to use do you know how the arrangement works with the resistor that goes along with and where it goes with the diode to lower voltage. and the value of the resistor used with silicon diodes for a set like this.

[bandersen]

Yes, you can use 1N4007 which are rated for 1 amp. Even better use 1N5408 rated for 3 amps if you have some.

I don't bother using resistors, but if you want use around 47 ohm @ 5 watt in series which each diode. Either end - doesn't matter.