[Test-Equipment] Hickok 800 Tube Tester

[Bill Abate]

Thanks to those that offered their thoughts in this matter.  After more
head scratching I've come to another conclusion.  I don't think the
transformer is being overloaded or at least that's not the only
problem.  I think the main cause is the 25 watt pot on the primary used
to adjust line voltage.  I guess a pot was cheaper than a variable
transformer!  Obviously as the load on the transformer increases when
you push the test button the voltage drop through the pot in the primary
increases, lowering the primary voltage and the filament voltage.  With
low power tubes it must not be significant but it is with a 6146.  So if
you add a filament transformer, put it before the pot.  But then you
loose the on\off control.  I guess a good solution would be to put a
variac in place of the 25 watt pot but one that small may be hard to
find.  I have a 3 amp one that is twice the size!  I just wish Hickok
would have used a separate transformer for the filaments.

I'm going to jump out the pot and substitute an external variac for line
adjustment and see how it behaves.  Another thing for the job jar!

Happy New Year,

Bill Abate


> 
> Bill Abate wrote:
> >
> > I've had this tube tester for a few years and it has performed well when
> > I needed it.  I typically use it to separate out the bad tubes I pick up
> > at fests or flea markets.  Recently I bought some 6146 tubes and noticed
> > that the reading stated out fine but then dropped after a few seconds or
> > so of holding the test button in.  It eventually dropped almost 40%
> > after a minute or so.
> >
> > This puzzled me but I thought it was a weak tube so I went to the next
> > one.  Same thing.  After some head scratching and testing I found out
> > that the filament voltage was low but sank even lower during actual
> > testing.  After inserting the 6146 and adjusting line voltage, I found
> > 5.6 volts on the filaments.  About 10% low. I felt this was borderline
> > voltage but I was not happy.  When I pushed the test button, the voltage
> > dropped even lower to 4,8 volts!  Rats!!!!
> >
> > Evidently the test voltages on a 6146 load the transformer even more.
> > Anyone else notice this?  I doubt if the transformer is defective.
> > Bedsides compensating with more line adjustment which would be hit or
> > miss, I figure I can add another transformer.  I would add a 5V, 6.3V
> > and 12.6 volt 4 ampere transformer to the tester.  I figure to
> > disconnect the original transformer taps for those voltages, tie the
> > transformer commons together at the original tapped secondary common and
> > attach the other ends of the supplementing transformers to the switch.
> > Hope I'm saying that clearly.
> >
> > My question is am I going to mess up the original circuitry.  Tube
> > tester schematics always make my eyes glassy.  I figure the directly
> > heated cathodes require same connection to the tester, e.g. 5R4.  So I'm
> > trying to maintain continuity.  BTW, the 5R4 voltage measured 4.4 volts
> > but did not change under test, which I would expect.
> >
> > With testing miniature tubes I never noticed it before because the
> > filament load was minimal.  Any thoughts??
> >
> > Bill Abate