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Old 2nd August 2006, 06:13 AM   #1
CLS is offline CLS  Taiwan
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Unhappy 82 Popped

Hi there,

I got 2 NOS RCA 82 on hand, wanted to use one of them in my 6C45 single stage amp....

Last night I hooked up the heater to warm it up, as I've read somewhere that old mercury tubes probably need it.

2.5V AC for the heater is not readily available. So I took a 220V primary / 5V secondary and plugged it in 110V main. Unloaded, I got 2.7V on the secondary, seemed OK.

Plugged the tube into the socket, switched on, the filament was lighted up dimly (like my 5R4 & 5Y3). Measured the voltage on filament, only 2.2V, then drop to 2.1, not very stable.

Suddenly, 2 or 3 flashes popped out, seemed from inside the plate, blueish flashes. Then the filament faded out quickly.

Switched off, & on again, nothing.

1A slo-blo main fuse blew. I changed it to 3A fast-blo. Switched on, lighted up, few seconds later, popped & flashed again. (yes, the pops were audible from inside the glass)

Fuse blew again. This time I had yet to get the chance to monitor the heater voltage. Probably no good.

In the process, I saw some white to light grey vaper growing inside the tube & attached on the inner wall. Just like the mist on the bathroom's mirror.

I didn't try anymore. Pulled the tube out, I measured the 2 pins of heater, they were short.

Is the tube still alive? Or it's gone?

Was it because the voltage dropped? So the heater was not heated enough?


PS. From the very beginning to the end, no high voltage was applied to the plates. Only heater was powered.
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Old 2nd August 2006, 07:28 AM   #2
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An 82 should draw about 3 amps in normal conditions. It sounds like there is some condensed mercury around the filament / plate which is causing the pops and flashes (probably due to the tube being stored for a while). The grey vapour is normal - you should see this on every mercury rectifier as it warms up.
The tube needs to be in its normal vertical operating position when you heat it. I would try again and hopefully the flashing should stop after a few minutes.
If there really is a short across the heater pins (should be a very low resistance even when working fine) its probably down to a splash of mercury in the wrong place. Before writing the tube off as faulty I would keep it somewhere warm for a few days (in vertical position) to allow the mercury to settle to the base of the tube envelope.
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Old 2nd August 2006, 07:33 AM   #3
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useful info here

You will need to use a choke input power supply as mercury rectifiers don't like big capacitors
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Old 2nd August 2006, 07:34 AM   #4
rpapps is offline rpapps  Antarctica
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Would inverting the tube help clear the heater short?
Just a thought.
Cheers
Rob
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Old 2nd August 2006, 07:44 AM   #5
CLS is offline CLS  Taiwan
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Thanks a lot for reply, and good to hear there're still chances.

I've read somewhere that such mercury tubes should be stored & shipped in vertical postition, all the way, to prevent the condense in "wrong" place. I thought, gee, how is that possible? It's already dacades!! It has been probably somersaulting forward/backward/sideways big time.

If warmth helps, I think I'll put it on top of other amps to speed up the inner vaporization

Will get back when I have further progress.
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Old 7th August 2006, 06:42 AM   #6
CLS is offline CLS  Taiwan
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Unhappy Still no good

It just kept flashing & popping & blowing the main fuse

I gave up I think it's gone. And I almost lost the courage to try another one...

Just curious, anyone try NOS mercury tube?

The reading about " keeping the tube vertical all the time from storage to delivery to handle to use... " is from RCA handbook. I really doubt how many of these old stuff can hold that position throughout the years.
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Old 7th August 2006, 07:23 AM   #7
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I got an 866 rectifier from the local surplus place,to play with..
I've no idea it's age,I suspect it was a "pull",and it was stored in a box,in who-knows-what-position, with some other tubes.

I brought it right home and put it in my tube tester to look at the glow,hardly waited for the filament to warm up before I hit the "test" button to see the pretty colors..
It seemed fine,no sparks or anything.
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Old 7th August 2006, 07:33 AM   #8
CLS is offline CLS  Taiwan
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Hmmm, obviously you have better luck!

866, I just looked up the datasheet. Big ST bottle with anode cap, like 811 or the likes. Beautiful !!

2.5V, 5A filament !! You got a strong transformer!!

How do you use it? Half wave? Or 2 of them in full wave?
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Old 7th August 2006, 09:45 AM   #9
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It's still sitting in my drawer,unused.
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Old 7th August 2006, 02:57 PM   #10
amperex is offline amperex  United States
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Mercury vapor rectifier tubes need about one minute warm-up time before B+ is applied. So, I suspect you did perform the one minute warm-up time. I would limit first cap on a capacitor input PS design to 5uF. Or, as stated choke input is best. Small MV tubes do not care for any input capacitance & the 82 is tiny by MV tube rectifier standards. Try an 83 MV tube, more robust.

Anyways, perhaps the MV tube filament broke & is touching the plate or the tube was received broken inside due to rough handling from the carrier. Don't you own a tube tester?

IMHO, I do not like Mercury Vapor rectifiers beyond the cool color when operating. MV tubes are known to produce a lot of RF noise when operating & perhaps some lower frequency noise will mix with your audio downstream creating additional IMD products. That is why a vacuum type tube rectifier usually makes for a better audio amp.
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