Just picked up an Emerson 600/639 Electrostatic
 

I just picked up this set for a reasonable price. So, I am going through the sams I found online to figure out what kind of caps I need, and i suddenly realized that this is an electrostatic set which means it needs those goofy 6KV caps.

Any idea where to get those? I looked at allied and they dont have the ones I need plus they are very expensive. Yikes. just a handful of those will cost more than I have in the whole set.

I haven't restored a TV since an RCA console, and that was 13 years ago so I am a little rusty.

Anyways, According to the SAMs, I need 6KV caps of:

1 .0047
2 .005 (probably cant find those, maybe .0047?)
2 .001
1 .0005

No idea why they used .0047, and then .005 for the vertical.

Any ideas?

At Just Radios. You will find the 6KV caps in the lower portion of the right hand column. These are film capacitors and yes, they are 4.99 apiece. You cannot use ceramic caps in this application. You can use .0047 for both vertical plates.

I know you cant use ceramics. The fact that ceramic caps have a property that causes the capacitance to change over a given applied voltage range makes it undesirable at best.

Thanks for the link, I had totally forgotten about justradios. Thats where I used to order my Sams and Cap Kits back when I was in high school.

Might wanta verify that the HV supply is healthy before delving in too deeply.

Funny you mention that. I took the set apart and someone had already completely recapped this thing.

Powers up, I hear sound. No HV. Also noticed the CRT cathode has a good shade of bluing from heat :-(

Just want to chime in that I had the wood version and now the "pig-skin" covered portable and, after the chassis resto, have been one of the best performing 7" electrostatic I've ever had in the collection.

I got 615 ohms between the plate of the 25L6 and the cap of the 1B3 rectifier, so that is a reading between the primary and secondary windings. Specs call for around 630. Eyeballing the transformer with a flashlight I dont see any carbon tracing or damage. I will have to pull out the ol blue anatek ring tester.

I tried measuring the voltage at pin 3 of the 25L6 which is the plate, half the tubes are removed so there should be no current draw, I saw it shoot to 25V or so DC, and it slowly falls. while plugged in.

So I have to do some investigating thats for sure.

I may be needing a replacement 7JP4, I dont know yet. The cathode looks pretty blue/black at the tip.

The ETF had 2 according to the spreadsheet, but he replied saying he doesnt have any so his sheets are not up to date.

Edit: Now that I think about it, I should just pull out my VT-71 chassis which I haven't finished 100% yet, and test the tube that way. I really need to get a CRT tester.

Its quite OK to use ceramic HV caps in these sets. Note that no use
of the very HV ones should have AC across the cap. If you use caps
at say 85% of rated voltage you just need three times the listed capacitance.
At 50% of rated voltage twice the listed capacitance will do.

I've used them in both a Pilot 37 and one of these Emersons and they
work just fine.

I noticed the 7JP4 sheets do not specify the HV current draw. Anyone know what it is?

Tried the CRT in my TS-4D chassis and its still throwing a decent picture. However the ballast tube is shot though. Ill figure that out later.

So I found that C76 was shorted. the screen of the HV Oscillator. it was a maroon drop from god only knows when, someone probably pulled out from their stash and yea. Anyways, it was shorted and it fried the 1500ohm resistor.

I changed those two out, and now I have a raster! However, I noticed after it was on for 30 seconds or so, the resistor in line with the diode started smoking.

Someone took out the original 2.5 Ohm resistor that was in series with the selenium rectifier, and replaced it with a little 10 ohm with a silicon diode.

Its probably apparent that the little 10 ohm 1/2 watt resistor isnt big enough to hold the load of the system, so I wonder originally what its wattage might have been?

Assuming your 10 ohm is not drifting you can probably calculate how much power is running through it by measuring the DC bus off the rectifiers with it as is and with the resistor shorted...That difference should give you the voltage drop across the resistor and P=(V^2)/R. You probably want a resistor rated at twice the power dissipation of the circuit so that it runs cooler...Many power resistors run almost hot enough to desolder themselves at their full rated power.

I figured that much, but I dont know how much that B+ is supposed to draw normally. Without that, I cant tell if there is an overcurrent situation somewhere or if its just a bad value chosen for the resistor.

Well when the set totally warms up I get about two volts across the resistor. So according to the calculations that's about 2 Watts or 200 milliamps. That seems pretty excessive considering according to the Sam's the 2.5 Ohm resistor that used to be there is only rated for a half watt....

Edit: nevermind I can't math right now