Eico power supply trouble (hlp plz)

[wicked1]

I got an EICO 1030 regulated bench supply to help me w/ some projects. Guy sells it on ebay as tested good, lists voltages and all that. I get it, and the high voltage doesn't work. The bias supply works fine, and of course the heater supply works fine.
So, TX is good, and rectifiers are good. Beyond that, this is my first time ever looking at a tube regulated supply, and I have no idea what is going on w/ the circuit. The plates of the 6L6's glow bright orange. Does that give anyone a clue as to where the problem could be?

Here's a link to a schematic if anyone has a minute to look and point me in the right direction. (W/ the 6l6's glowing they way they are and giving off SOO much heat, I'm afraid to leave it powered up and poke around w/ my meter w/out an idea of where to look first)
http://jlandrigan.com/files/EICO%201030%20schematic.pdf

Thanks a lot

[llwhtt]

If the plates are glowing check for the -52 VDC on pin 5 of each. Are both of your regulator tubes (OB2 & OA2) glowing, usually purple I think? Anyway pull the 6L6s and check for all supporting voltages on the other tubes.

Craig

[Tom Bavis]

First thing I'd look for is a short on the output - that 20 @ 500V cap is one prime suspect...

[Mickeystan]

Hello Wicked1

The advice Tom Bavis gave about the 20uf cap being a prime suspect is very good. If I were you I would recap everything in this old vacuum tube type bench supply. I would focus on anything electrolytic and in the form of paper capacitors. Disc ceramics or micas are less prime targets in my opinion.

Regards Doug S. (aka Mickeystan)

[wicked1]

Originally Posted by Tom Bavis

First thing I'd look for is a short on the output - that 20 @ 500V cap is one prime suspect...

Genius, Tom...
that cap is indeed a dead short. My problem was that I was trusting what the seller said and I assumed it really did work when it left his possession.

(but now that you mention it Craig, the diode tubes are not glowing purple, either.. again, trusted the seller as he said those were just replaced)

[llwhtt]

Check your voltages without 6L6s, the reg. tubes WON'T glow unless there is a voltage present!

Craig

[kevinkr]

Definitely a full recap required before you proceed much further.

Also while the eBay seller might be a liar, he might have also been telling the truth - I have had more than one instance where something worked fine one day and just a couple of days later had a catastrophic failure at power on.

Get the schematic online if you can and observe what the correct voltages are supposed to be with a properly functioning unit - change out all of the capacitors before proceeding any further though.. Vishay amongst others still makes really good quality high voltage axials - you should be able to find them at Digikey IIRC..

Be careful as the raw supply voltages in a 400V supply can be substantially higher than 500V or 600V..

[wicked1]

I did recap, now the plates don't glow, but r1 gets super hot at power up, and the unit still doesn't regulate. The diode on that leg (just before r1) tests alright. My next guess would be to replace tubes. But, all this is getting expensive (considering the unit was sold as working). The ebay person is being helpful and I think last night he said he could ship me another entire power supply. I'm just waiting for a final email from him.

(if anyone wants to take a stab as to what would cause r1 to get hot, but none of the resistors past it (r2, r3, r6, etc are fine), I'm still up for tinkering. My guess is something went wrong w/ the 6l6 tubes, because that's all r1 is feeding (c1-a c1-b have been replaced)
http://jlandrigan.com/files/EICO%201030%20schematic.pdf

And just in case anyone does want to take a guess, I should clarify "not regulating". It's putting out way more voltage than it should. regardless of the setting of the voltage pot, it puts out about 600v (not steady.. my meter bounces all over the place)

[kevinkr]

The most likely cause I can think of is if the screen grid of one of your 6L6s is now shorted internally to the cathode or some other electrode. Try removing them and seeing whether or not R1 still over heats. I would test them if you have a tube tester available. You can probably find replacement tubes for a reasonable cost if you can find a local hamfest or two to visit in the immediate future.

FWIW I would also replace that ancient silicon rectifier with a new one. Once you get the whole thing working I would recommend replacing that rectifier with a FW bridge and changing the value of R1 to compensate for the higher voltage. (The reduced ripple on this supply might result in slightly better performance, but you would probably have to "improve" negative supply as well. Choke?)

[tubelab.com]

Try the power supply with no 6L6's. If the resistor doesn't get hot try just one 6L6 then the other. The power supply will work with only one 6L6 installed. Just don't try to draw more than 50 mA through one tube.

My Knight supply uses 4 6L6's and is rated for 200 mA. The schematic is very similar to yours.