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Old 3rd Jun 2020, 12:16 am   #1
Courtney Louise
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Default EZ81 Rectifier Valve Wanted - Preferably Used.

Due to an amplifier I have in to restore melting (literally) the EZ81, I need a used one that still works to pop in it to see what happens before I shell out stupid money on a new one...

Anyone got one please?
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Old 3rd Jun 2020, 12:42 am   #2
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Another member asked for one of these a couple or three months back. He didn't get any offers other than directions to on-line suppliers.

It should be easy enough to do proper fault finding to see what caused that overload so as not to destroy another one.

Why not do what I did when I ran out of EZ80s, and that was to bypass it with a couple of diodes and a series wire wound resistor - easy enough and won't melt any more glass, and the resistor will act as a sacrificial fuse if things get out of hand. I eventually fitted the proper valve once I'd got more stock in.
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Old 3rd Jun 2020, 1:04 am   #3
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

I have one you can have. You will have to wait till it comes from Australia however.
PM me if you are interested.

Joe
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Old 3rd Jun 2020, 7:06 am   #4
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Should have one Courtney, PM me your address again and I'll bung one in the post if you stump for the postage. Off to town later, see if you can catch us before 10 ish.

Andy.
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Old 3rd Jun 2020, 8:56 am   #5
kalee20
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Why don't you broaden your scope, consider a used EZ80? They are pin compatible!

It could be operating beyond its ratings (90mA max current), but it's unlikely to die instantly because of that. Ten minutes ought be enough to assess whether the amplifier is OK or not.
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Old 3rd Jun 2020, 9:22 am   #6
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

A dead short across the HT would probably be one reason and that would be easily measured. Another might have been the valve itself developing a heater/cathode short especially if one side of the heater winding is earthed. I have seen the odd EZ80/81 self-destruct....one was nearly white-hot!

It's pretty obvious that whatever it was used in, it was left unattended for some time when the fault developed. If the transformer and other critical parts have survived I would think it prudent to fit an HT fuse in the cathode rated at the HT current plus about 30%
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Old 3rd Jun 2020, 11:50 am   #7
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

The whole amp looks like it's been in a fire. The transformer has umped all of it's wax and although it seems to work It's certainly not healthy
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Old 3rd Jun 2020, 11:54 am   #8
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

I have messaged Ed to see if he can rewind it or at least test it's health. It's not an easy one to replace as it has a 30v winding, 2 x 6.3 and 350-0-350
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Old 3rd Jun 2020, 11:57 am   #9
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

I remember TV line output valves sucking their glass in like that. The last time I had a standard rectifier valve that had got so hot that the glass had melted and sucked itself in, the transformer was toast - literally!

I would test the transformer before wasting time and money on valves etc.
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Old 3rd Jun 2020, 12:17 pm   #10
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Just disconnect all the outputs from it and run it unloaded for a while and you'll soon know if it's got shorted turns or not.
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Old 3rd Jun 2020, 12:55 pm   #11
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Quote:
Originally Posted by Techman View Post
Just disconnect all the outputs from it and run it unloaded for a while and you'll soon know if it's got shorted turns or not.
That's my next plan. To remove it and meter it
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Old 3rd Jun 2020, 1:53 pm   #12
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Just tested the transformer on the bench and all outputs are reading as they should. I am leaving it on now to see if it gets hot.
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Old 3rd Jun 2020, 4:03 pm   #13
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Ok so the transformer has been on for two hours and is still cold to the touch and giving correct readings.

Mods can we split this to the amps section please?
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Old 3rd Jun 2020, 4:27 pm   #14
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Hi Courtney, you've done the standard test for shorted windings on a transformer and it appears OK; but there will be no indication of it's interior state. It may be worth the risk of getting it warm (say 50C) and then trying to fill it with spray varnish to improve the internals.

That done it would then make it a pig to strip down.

Ed
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Old 3rd Jun 2020, 5:14 pm   #15
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Quote:
Originally Posted by Courtney Louise View Post
Mods can we split this to the amps section please?
Can you supply a bit more detail, an unidentified amplifier with a dead rectifier and overheated transformer is a bit vague. Probably easier to start again.
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Old 3rd Jun 2020, 5:16 pm   #16
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Sorry it’s a Bal-Ami S100 jukebox Amplifier made by Beam-Echo.
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Old 3rd Jun 2020, 5:19 pm   #17
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

OK I'll sort it out.
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Old 3rd Jun 2020, 5:23 pm   #18
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

A possibility is that the rectifier vacuum went soft to the point where an anode-to-anode discharge lit up.

Suck-ins like that were common with TV line output valves repurposed for amateur radio linear amplifiers and pushed beyond their capabilities.

Must have been quite dramatic!

David
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Old 3rd Jun 2020, 5:38 pm   #19
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Default Re: EZ81 Rectifier Valve Wanted - Preferably Used.

Thread split.

The first place I worked used to burn some rubbish "round the back". That's what happened to valves!
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