[Test-Equipment] HP-608D parts for sale

[Richard Knoppow]

----- Original Message ----- 
From: "wabate" <wabate at verizon.net>
To: "Test Equipment" <test-equipment at mailman.qth.net>
Sent: Tuesday, December 04, 2007 8:57 AM
Subject: [Test-Equipment] HP-608D parts for sale


> My trusty 608-D finally died yesterday when the output 
> attenuator failed.  In reading the manual it does not seem 
> practical to repair nor do I have the equipment necessary 
> to recalibrate the output.  So I'm offering it out to the 
> list as parts.  This is a nice clean generator and 
> everything works except the output attenuator.  Meters are 
> not cracked, knobs are all there, tubes all appear to be 
> fine, cabinet is pretty nice, nice manual, crystal, etc.
>
> Let me know what you need.  Too heavy to ship.  I'm near 
> Philly.
>
> Bill, K3PGB
>
     Its been more than 40 years since I worked on 608s 
for -hp- but I still remember changing the resistors in the 
probes. The originals were tiny deposited carbon but modern 
metal film resistors should work fine. Instructions are in 
the handbooks available at BAMA. If you make sure to get 
everything back in the same place the output calibration 
should not change much.
     The main cause of probe problems was burning them out 
by connecting the generator to the output of a transmitter 
for some reason. Its also possible for the capacitor to 
short. My memory is that this was not very common.
     A couple of notes from memory:
     V-5, the 6CL6 output regulator, is quite sensitive to 
heater to cathode leakage. We had to select tubes that would 
maintain constant output level with varying line voltage. I 
was never able to find a cure for this although my memory 
still itches that I saw some method of compensating for this 
leakage somewhere.
     Note 2: The oscillator uses conventional L-C tanks. The 
inductors are held in place on the forms by coil dope. This 
often cracked and loosened even in generators which were 
only a few years old causing the frequency to be off. The 
curious thing is that no one at the service center seemed to 
realize that the coils were adjustable and the routine was 
to cut new dials. Not necessary at all. Simply adjust the 
inductors at the low end and the trimmer caps at the high 
end of each band. some juggling is necessary. The lower 
frequency coils have shorted turn adjusters on the coil 
form. They can break loose and move. Also, the coils 
themselves break free of the form. Squeeze them into 
calibration if they are loose and fasten them with coil 
dope. If the coils are tight the error will probably not be 
large and can be corrected by moving the shorted turn a bit. 
Again, once its set lock it with coil dope. The higher 
frequency coils must be adjusted by adjusting the turn 
separation by squeezing or stretching a bit. Again, once in 
place dope them down. The calibration must be checked with 
the side cover on. Its a PITA to have to remove it to make a 
small adjustment and then put it back but, once done, it 
won't need attention again for a long time. After getting 
the thing adjusted close it up and let it run for at least 
48 hours and re-check the calibration. You may have to make 
a small adjustment at the top end of each band. When 
properly calibrated the dial tracking is excellent and 
should be right on the mark everywhere.
    Defective oscillator tubes can cause calibration errors 
so another tube should be tried if the calibration was right 
and is serously off with another tube. I had to do this 
occasionally even though I was using -hp- inspected tubes.
    The rule with all older (vacuum tube) -hp- gear is that 
anything that was not better than half-specs was broken.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk at ix.netcom.com