On Tue, 07 Sep 2010 09:27:00 +0200, Richard Rasker
wrote:

Since the fuse (F602) has literally exploded, there's no way to
determine its original current rating.

Place an amps guesser in place of the fuse and measure the operating
current. Ummm... replace the blown transistors first. Then select a
value about 2-3 times the measured current. If you're charging a big
filter capacitor, consider a slow blow fuse.

I'm legally responsible for whatever goes wrong (further damage or injury)
if I put in the wrong parts, most notably fuses.

If that's true, then walk away. You were given an impossible
assignment, where there is insufficient information to return the unit
to its original operating condition without you having to make a
decision. Should a liability situation arise, one item the court
might need to determine is whether you are competent to repair the
equipment. Be sure to document your decisions, supply references,
sources, and justifications for your actions. Attorneys just love
impressive documentation and paper trails.

I haven't seen any mention of dried out electrolytic capacitors, which
are the most common source of failures in 20+ year old equipment. An
ESR tester will be required to make the determination. If it still
has the original electrolytics in the power supply section, I would be
seriously worried. I just repaired an HP 8620A sweep generator
mainframe. The major problem was dried out electrolytics.

http://members.shaw.ca/swstuff/esrmeter.html
I buy a lot of older HP test gear off ebay as well as older
radios. Most of this gear is 25-60 years old and needless
to say, the condition of the electrolytic capacitors is
somewhat suspect...

Furthermore, this thing is
used in a university laboratory by quite a number of people, so I really
need to get it right.

No problem. Get one of these university people involved in the repair
so that you have someone available to blame should things go awry.
Students are expendible anyway. Be sure to let them make a few
decisions. If litigation and liability are you primary concerns, it's
always best to have a scapegoat handy.

So in this particular case, guesswork is out of the
question (but if I had to guess, I'd say that the fuse should be something
between 1 and 4 amps, and the tubes look quite similar to PL519's).

Life is nothing but a succession of calculated risks, which are call
guesswork when they fail.

Spend $150 on a carcass. Look inside for the missing values. Steal
what parts are needed:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=350353282625

Richard Rasker

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