On Sun, Mar 13, 2022 at 08:33 PM, P F wrote:
Interleaved
I think one of the subsequent modifications that Tek put out, which was the
replacement of Q247, a 2N3739, to a more robust 2N4240 transistor, helped
control some of these 'A Supply' power aberrations caused by advancing the
Amplitude potentiometer.
I¡¯m not sure what was inside my unit. I know C was shorted to ground. I don¡¯t exactly remember why I chose this one, but I replaced it with a 2N3585. By itself it has been running fine until now. I have no facts to support this, but I don¡¯t think it was the cause for the failure of D233.
It certainly seemed to be the cause of many of the
problems in my unit, whose serial Nr is well below the range for the
modification. Before I replaced Q247 with an NTE 175, which was the only
equivalent available for the discontinued 2N4240, the unit not only ran quite
hot but seemed to have destroyed the original 2N3739 and stressed many other
components, although I did not realize it until other components failed.
Hmmm. Interesting. 2N4240 are available from Mouser I think, but they are extremely expensive.
Tek put out a modification kit, which had instructions in the cumulative 106
file on Tekwiki, and this allowed me to correct most of the problems with my
106,
I have yet to go through those. I did see, however, that my unit has a 4.7K R257, which I remember is part of one of the A Supply mods.
although I am now on the hunt for the source of some amazing oscillations
in the power supply that might be the cause of some weird distortion in the
square wave or vice versa.
You¡¯ll find the cause.
(I had held off on writing to congratulate Stephen
on his successful fix
No sweat. That¡¯s ok. I was just lucky, I guess¡
because I thought that were I to mention any of the
problems with my instrument, I should include photos of the wave forms, etc.,
and haven't gotten around to photographing them yet. I had also been overly
optimistic that I would have solved them by now.)
Anyhow, if your 'A Supply' is behaving well, you might not need to change Q247
and some associated components.
As I said, I already had to. So many power supply components had failed, and others kept failing one after the other, that it was quite a difficult repair.
I undertook the modifications in my unit only
because it was still quite unstable after replacing the original Q247 with
another 2N3739
I¡¯m going out on a limb here, but maybe try a 2N3585?
Once again, I am quite happy for Stephen's being able to repair his 106.
Thank you¡. Until next time (hopefully not).
The more you work with this signal generator and read the circuit description, the
more that even the output stage and its seeming 'upside down' electrode
voltages will come to make some sense. Not enough for mere mortals like us to
design it but enough to work with it and maintain it!
±á´Ç±è±ð´Ú³Ü±ô±ô²â¡
By the bye, the file name on the Tekwiki 106 'site is Tek_106_irb_no_ocr
Yes, I have it too. Thanks P F.
