[Test-Equipment] Hickok 539B with shorts light problem

[W8ZV]

Hey Pat!!

     You're welcome.  I've been fighting with my own tube tester issues 
as well.  There is always Roger Kennedy out on the west coast.  He's the 
only one left working on tube testers that I'm aware of.  You can call 
Hickok (they are still in business) and see who they are referring 
people to.  It seems that Hickok was somewhat like other manufacturers 
that I know of, in that they would make changes in equipment designs 
with little or no outside documentation.  That always makes it fun to fix.

      As far as fixing switches in these things, most of them were 
standard non-shorting type Centralab switches and can be found at ham 
fests or the like.  Those switches weren't anything special or exotic 
like you find in a radio chassis.  Some of that stuff is still being 
made by Centralab and Switchcraft and can still be bought off the 
shelf.  You gotta look, but it's out there.
> Kim:
>
> Thank you!
>
> I did find Schoo's information and the schematic from Bama. The cal
> procedure he outlines is where I discovered the shorts light wasn't
> working.  The only cause of the light not working that he mentions is
> dirty or broken switching.  I am, of course, hoping to find an open
> resistor. (Something I can fix) Finding the two undocumented 47 ohm
> resistors leaves me wondering what else is hidden somewhere.
>
> I don't think it's a switch just because the general appearance of what
> I can see still looks good. That's not to say there isn't something just
> out of view.
>
> Pat
>
>
> On 9/27/2011 7:05 AM, Kim Herron wrote:
>> HI Pat!
>>
>>       Don't know if this will help, but I'll pass it along anyway.  If you
>> put Daniel Schoo into google, you'll get to his website and in there
>> you'll find about 5 pages of repair and calibration info on the 539.
>> It's still out there.  I was looking at it a few days ago.  I'm
>> guessing that you have an unresolved power supply issue and his info
>> does address some of those things.  Hope this helps.
>>
>>> All:
>>>
>>> I have a Hickok 539B with a non-functioning shorts light.  I have a
>>> known "bad" tube that a BK600 and a TC162 flag as leaky that will not
>>> fire the bulb. Even using a simulated short using a 100K resistor at a
>>> socket will not fire the bulb. Fooling with the switches will not
>>> aggravate the lamp into firing. The switches and interior are still
>>> relatively clean.
>>>
>>> Here's what I've done so far:
>>>
>>> 1. tested the lamp by using a fixed series resistor and a variac, no
>>> problem, bulb is okay firing at about 60 volts
>>> 2. checked the three fixed resistors shown near the lamp in the
>>> schematic and tested the 250k sensitivity pot and toggle switch, all okay
>>> 3. checked plate supply, okay
>>> 4. checked screen supply, okay
>>> 5. general visual inspection for any cold solder joints, none found
>>> 6. replaced paper caps with mylar, none of the originals found leaky
>>> 7. none of the postage stamp caps were replaced
>>> 8. There were two 47 ohm 1/2 watt resistors embedded in the shorts
>>> switch assembly that don't show on my schematic, one was discolored,
>>> both were replaced
>>>
>>> The tester works but reads high due to the bias meter reading too low.
>>> Using a DVM to set bias gives a plausible reading.  I can measure a
>>> resistor across a tube socket on the gm meter but it is off about 100k.
>>>
>>> Is there anything that commonly goes bad after 50 years in this shorts
>>> test circuit that I have over looked? I've probably got about 20 hours
>>> of spare time into this thing already. I've not really been able to
>>> follow the schematic back to the voltage source. Perhaps someone already
>>> knows how to check that source.
>>>
>>> Pat
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-- 
Kim Herron W8ZV
1-616-677-3706