[R-390] Arcing in 25Z5Ws

[Bob Camp]

Hi

The only thing I would change below is the rating on the silicon diodes.

The AC power line is not a solid state friendly power source. Spikes  
come along that are well over the 3X line voltage level. Some of them  
make it through the transformer inductance, some don't.

Diodes are cheap, regardless of the power rating. I would recommend  
putting two 1KV diodes in series in place of each tube. It's overkill,  
but the $0.35 you waste is money well spent. The extra volt of drop  
isn't going to hurt anything at all.

Bob


On Feb 17, 2008, at 1:04 PM, Flowertime01 at wmconnect.com wrote:

> Dennis,
>
> Now is the time for that trusty old tube checker.
>
> First off you blew a fuse after the B+ 26Z5 rectifiers tubes.
> This is not good. Most likely a tube shorted.
> Second most likely a cap has shorted.
>
> Then you see you have a dead 26Z5 with no light inside.
>
> So you are only operating with 1/2 wave rectification.
> Lots of hum from this state of operation.
>
> As a 26Z5 did not light up in a known good socket (the other tube  
> light up in
> that socket) you have at least one bad tube and need a replacement.
>
> Run all the 26Z5s through a tube checker for shorts and minimum  
> conducting
> current. A tube checker will do that for you.
>
> It would be good to just push all the tubes in the receiver through  
> a tube
> checker for shorts at this time. Using the receiver as a test device  
> for shorted
> tubes is not considered good use of equipment or good service  
> practice.
>
> Once you find a set of tubes that pass the tube tester (I did not  
> say a set
> of good tubes) and get them back into the receiver, you can apply  
> power again.
> DO NOT over size the fuses. Watch for smoke and flashes. You could  
> still have
> a bad cap. Likely a filter cap. Back when this was not a likely  
> problem. For
> 50 year old caps it is now a common problem.
>
> Fuses also just blow. No problem found. Likely once you get a couple  
> good
> 26Z5 back in the receiver it will work fine.
>
> Have you considered just a couple good 400 Volt 2 Amp or better  
> diodes as
> substitutes for the 26Z5 until you get the other problems sorted out?
>
> You do not have to leave them in the receiver forever. Just  
> something to help
> you get on with trouble shooting and problem solving until the post  
> man
> arrives with parts.
>
> Roger AI4NI   </HTML>
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