[Johnson] 866A catastrophic failures?

[Ray V.]

The usual failure mode is an arcover which results in a dead short, 
usual result is whatever HV transformer that is in the circuit losses 
all its smoke and we know what happens when the smoke is let out of an 
electrical component.

Seriously, usually the HV transformer is burned open due to the direct 
short / excessive current draw.

The good news is this usually occurs only with tubes that have not been 
warmed up such that the mecury is vaporized. Most likely situation is 
where tubes have been bounced around or laid on their side such that the 
liquid mercury gets between the elements and doesn't get vaporized prior 
to applying HV. Then you usually see a very bright flash and prepare to 
call Peter Dahl to order a new (and very expensive) HV transformer.

While the 866/866A family looks pretty glowing, a 3B28 is a far more 
reliable substitute and doesn't result in the higher voltages encountere 
with a SS replacment.

That said, I still use 866A's in my Valiant, because I like the glow. 
And while my Valiant is used several times a week, it's always warmed up 
for at least an hour before I first apply HV. And it is rarely moved 
from its operating position so there is little risk for the mecury to 
flow between the 866A elements. However in my KWS-1 I swapped the 866A 
out for 3B28's, those KWS-1 transformers are just too expensive although 
the Valiant xfmr is no slouch either. And you can't see the purple glow 
in the KWS-1 power supply.

Good luck, 73, Ray  W2EC

kwylow zinjanthropus wrote:

> Can anyone cite any catastrophic failures that occur with equipment using 866A's (merc vap recs) that's a direct result of the same? Just wanted to know as I'm looking to retrofit a Courier with a pair of these jewels. Let me know and thanks. Cal. N6KYR
> 
> 
> ---------------------------------
> Do you Yahoo!?
> Yahoo! Mail Plus - Powerful. Affordable. Sign up now
> 
> --- StripMime Report -- processed MIME parts ---
> multipart/alternative
>   text/plain (text body -- kept)
>   text/html
> The reason this message is shown is because the post was in HTML
> or had an attachment. Attachments are not allowed.
> Please post in Plain-Text only.---
> _______________________________________________
> Johnson mailing list
> Johnson@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/johnson
> 
>