[R-390] OT: HP-410B Tubes

[Jon Schlegel]

Barry,

I observed somewhat the same behavior on my 410B although not as 
pronounced.  I had enough 12AU7's to swap around until I got the 
meter to zero with the zero pot pretty much in the center.  Not much 
else I can offer here.

Another thought.  The 410B I have had numerous bad solder joints 
especially on the printed circuit card(s), believe it or not.  It 
took many hours of elbow grease to ferret out all of these 
problems.  They certainly didn't make working inside the unit very easy.


Regards,
Jon - WA3MVM



At 09:51 PM 3/1/2011 -0500, Barry wrote:
>I have an HP-410B that I have cleaned, recapped and trying to get 
>working properly again.  The problem is with the tubes.
>
>It came with 5814's in place of the 12AU7's.  These work great, but 
>they draw extra heater current and I would like to get 12AU7's in 
>there again.  I ordered a set of 12AU7A's but the meter will not 
>work well at all with them.  It won't stabilize, zero, or do 
>anything else correctly (well, the ON lamp does work, but...) with 
>them in place.
>
>The  pair of 12AU7A's check quite strong on my Hickok 752A (they 
>check about the same uMho values as the 5814's).  Is this just a 
>case of finding a pair of well-matched 12AU7's (non-A, whatever...) 
>that work?  I'd rather not continue throwing money into tubes that 
>don't work but at the same time, I don't like the extra stress the 
>heaters in the 5814's put on the old transformer.
>
>Any ideas?
>
>Thanks,
>Barry - N4BUQ
>
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