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Uh, this makes no sense to me. The base of Q870 should be pulled toward +15V unreg through R864(? hard to read on the schematic), and the two op amps shunt it towards ground when they detect too high

I had actually done that last nite, but didn't have the parts layout handy to see which probe was on which pin (I had them on the diodes>. Here they are with voltage measurements:

Michael Dunn started TekScopes 20 years ago on August 31, 2000. There was just one post that day from Walter Shawlee who joined that same day and he has been an active member ever since. To Walter:

Here is a shot of both sides of R873 on the 2430A. At power off, both I guess next up is to capture U870 pins 1 & 7, see what's up there when your rail collapses. On one hand, you could be hitting the

Hi Colin, If the contact is not one of the ones dedicated to providing power or connecting to the pass transistors then it may never get used and you can put a note on the top of the TM504 saying that

Hi Albert - Are you doing single-sweep Acquisitions with the 7B87? Single-sweep uses the 7B87's internal sample clock, and I just checked on mine and confirmed that at .5mS, the acquisition works

I have a TM504 which has one of the springy brass-coloured contacts on the back-plane mangled. I have tried removing one of these contacts from a spare back-plane connector with no success - they just

Where are you located?

Both the voltmeter and the 2430A. There's not much garbage on it but I did hang another cap on it and it made no difference. Here is a shot of both sides of R873 on the 2430A. At power off, both

David, Hopefully there is an active HP group where you can get more informed assistance on your 1740A. I will say this: Many years ago,? I purchased a used HP all vacuum tube oscilloscope, which was

Lots of vintage stuff pricing is quite high these days. I also collect 8 bit computer junk and for example a digital doorstop like a Commodore 16 is priced in the 400-500$ US range these days. On the

How are you measuring the collector voltage? The switching frequency is ~25kHz, and it's going to be ugly as heck if the capacitor is out, so the instrument you're using to measure this and its

Assuming a VBE drop across the sensing resistor, then you're drawing roughly half an amp. Harvey

Ok, Q879 collector is solid. When things go sour, it stays. The base voltage is moving, as is the emitter. So it's being told to compensate for the change. However, under normal conditions, the

My mistake: HP1740A. I get the impression vintage TEK scopes are ten times the price they were ten years ago, and now rare. My HP1740A was from a recycling centre for next to nothing, just needed

Hi Nick, It doesn't help you any further, but in a rather tricky way I managed to create a horizontal gap in AVG waveform acquisition. And indeed a (dotted) linear interpolation line between the dots

Raymond: I only need 1 Lemo 4-pin plug. How much would it cost me to have you send me one? How would I pay for it? Here is my address: Gary Bosworth 139 E. Shrode Street Monrovia, CA 91016 Cellphone:

https://www.youtube.com/watch?v=6XDUy-KfMy4

I was given an old 547 that was set for scrapping. It that had some high voltage issue. The tubes were partially pulled but it seems intact otherwise. I'm located in Austin Tx if anyone wants to come

I did a search and somehow this one slipped through the net: https://www.electronicdesign.com/technologies/test-measurement/article/21137778/the-tektronix-function-generator-teardown FG502 Teardown