[Boatanchors] HP-606 tube failure

[Ron VE8RT]

Hi Ian,

   another source of information on vintage HP gear is the hparchive which is a group on yahoogroups

     Ron VE8RT

On Thu, 27 Sep 2018 07:07:30 -0700
Ian Wilson <ianmwilson73 at gmail.com> wrote:

> No apologies for including a signal generator in this list since it
> weighs more than most of the radios I work on using my trusty HP-606 :)
> 
> Anyway. I have a repeating failure. One side of the 12AT7 that is used
> as a cathode follower in the level-stabilizing output loop dies. This
> effectively
> turns off the output (the unregulated low-level output is unaffected).
> 
> The fix is easy - replace the tube - but doing this requires removing the
> internal RF cage. This is a straightforward but tedious process.
> 
> Looking at the cathode follower part of the circuit, I wonder whether
> the heater-cathode voltage rating is being stressed when the power is
> applied. If so, perhaps this could be protected by a <whisper> zener
> diode or something?
> 
> I also wonder whether, if this was a common problem, whether there
> was a known HP service patch for it...
> 
> Thanks for any suggestions.
> 
> 73, ian K3IMW
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-- 
Ron VE8RT <ve8rt at yknwt.ca>