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HNY to everybody! In my SC-502 scope transistor Q855 died. It is a GE X44HR242 in TO220 case, but I was unable to get its specifications in order to find a suitable substitute. Thanks for your help

ADT name to the list as well, please.

Hi all, I'll add my name to the list as well. You have to grab these things as they go by! Cheers Phil / W1PJE

Jared, Your manual lists S3 as 4P6T. Entering that part number in Digikey shows it as 2P6T. Is there a typo somewhere?

Tom, Thanks for setting me straight. Yes, when I draw the simple schematic it's pretty obvious what's happening, and why the measured resistance of the pot has a humped profile (when you reach the

Hi Jeff, I misunderstood -- I thought that all of your pot measurements were done with at least 2 terminals isolated. If you did not isolate the terminals, your measurements don't really point to

Please add me to the list! it is an interesting project! Thanks Mike

Tom, I measure 2.6 K ohms between the two non-wiper terminals, but the pot is still in circuit, so this is really measuring everything that bridges the +50 V and ground planes in parallel, so is this

The ballpark sounds great, count me in! Dave S.

If it is indeed the trimpot, that is an unusual failure mode. I can recall seeing something similar only once, and it was due to a small sliver of solder that managed to bridge the pads connected to

I lifted one end of C1374 and tested it with my DMM916. It acted much more like a capacitor than like a resistor: while measuring resistance I could see it charge up (the resistance increased over

Yes, the PCB shops really don't like putting black solder mask on boards.? Not yellow or clear, either.? ?Best to go with standard green.? The other colors mess up their production flow.? ?Jim

This is correct. I have an FG504 and such a TM504 that I had to correct the phasing on. The FG504 in trying to reach a +-050VDC rail stacks a 32VDC and a 25VAC on top of each other for both positive

One small addendum to this, the PCB's will likely not be black as that is a premium option that adds significant cost. They will most likely come in the usual green (more period accurate! :) ) to save

I have heard anecdotal evidence that it was something that was occasionally found in early mainframes. When so many mainframes were produced, I'm sure a few slipped through on a tired Friday afternoon

That is the part. Thanks Glenn -- ----------------------------------------------------------------------- Glenn Little ARRL Technical Specialist QCWA LM 28417 Amateur Callsign: WB4UIV wb4uiv@...

Interesting commentary on a test test fixture for TM500 mainframes. it seems there is interest in stuff like this. I'm working on an interface board to enable powering and getting the signal out of a

Jared, Is there a way to easily bring the EBC of each pass transistor to the front panel? These transistors are items that often fail and need to be tested, especially on these old frames. Not trying

Does it look like the pic on the Newark Canada website? https://canada.newark.com/vishay/wsl12064l000fea18/metal-strip-resistor-0-004ohm/dp/18X4713 Specs are listed and data sheet can be downloaded.

Does it look like the device on the Newark Canada website? Don Bitters