Products > Test Equipment
Vintage HP 3721A Correlator : Repair, Restoration and Enhancement
factory:
--- Quote from: dazz1 on September 29, 2024, 09:07:56 am ---Hi
I have part numbers for the broken knobs, but they don't appear to be valid.
I am wondering if the part numbers were for the big chunky knobs usually seen on photos of HP 3721A.
I have attached annotated photos of what I am looking for.
If you know of where I might source these, please let me know.
--- End quote ---
As I said in the TEA thread, the manual quotes part numbers for the knobs fitted to the earlier ones, they are valid for the oldest ones, remember this was designed in the late 60s, the fragile beige & dark grey knobs didn't exist then. The black knobs with aluminium trim discs were chosen, these were commonly found on the 180 series & a few other products introduced in the 1960s, then disappeared for most products (except the 180 scopes), to be updated to with those later beige/grey knobs.
If your change sheets cover the your instruments prefix, then you should have an updated parts list with these, probably won't help much, as used part dealers won't know the part numbers.
Of the half dozen 3721 I've seen on ePay over the years, only one was an early one with the black knobs, the rest were later ones with the newer beige/grey ones, also control legends were engraved on the first and printed on the newer ones.
It may take a while to find a 3722 at a fair price & in good condition, I hate to tell you, but they are known about by the modular synth crowd. You might want a H01 option, this is the one with the set of delay function thumbwheels in you picture, the internal picture is the standard version, H01 has an extra board.
David
dazz1:
--- Quote from: factory on September 29, 2024, 04:12:55 pm ---
As I said in the TEA thread, the manual quotes part numbers for the knobs fitted to the earlier ones, they are valid for the oldest ones, remember this was designed in the late 60s, the fragile beige & dark grey knobs didn't exist then. The black knobs with aluminium trim discs were chosen, these were commonly found on the 180 series & a few other products introduced in the 1960s, then disappeared for most products (except the 180 scopes), to be updated to with those later beige/grey knobs.
If your change sheets cover the your instruments prefix, then you should have an updated parts list with these, probably won't help much, as used part dealers won't know the part numbers.
--- End quote ---
Yes, I looked at the change pages and none of the numbers returned knobs on Google. I did the annotated images to show what I am looking for rather than quote dead end part numbers.
--- Quote from: factory on September 29, 2024, 04:12:55 pm ---It may take a while to find a 3722 at a fair price & in good condition, I hate to tell you, but they are known about by the modular synth crowd.
--- End quote ---
I am patient. I will wait until I find what I am looking for.
Google suggests other noise generators are being recommended ahead of the 3722. Maybe because of lack of supply. I found one 6 year old listing here https://reverb.com/item/13307500-hewlett-packard-hp-3722a-noise-generator-oscillator-1965-grey for $USD35 or so. I'd be happy to pay that for one in good condition. There is an awful 3722 on e-bay at present. No one is buying.
--- Quote from: factory on September 29, 2024, 04:12:55 pm ---You might want a H01 option, this is the one with the set of delay function thumbwheels in you picture, the internal picture is the standard version, H01 has an extra board.
--- End quote ---
What does the delay function do? Is it worth waiting for?
factory:
--- Quote from: dazz1 on September 30, 2024, 07:56:33 am ---
--- Quote from: factory on September 29, 2024, 04:12:55 pm ---You might want a H01 option, this is the one with the set of delay function thumbwheels in your picture, the internal picture is the standard version, H01 has an extra board.
--- End quote ---
What does the delay function do? Is it worth waiting for?
--- End quote ---
I can't really answer this, I don't know how much use the additional "delayed binary output" would be, or if it's relevant for the options installed in your 3721. Information isn't really out there on the web, except for this application note, which only shows it used with a demonstration unit; https://www.hpmemoryproject.org/an/pdf/an_98-2.pdf
David
dazz1:
--- Quote from: factory on September 30, 2024, 08:26:33 pm ---
--- Quote from: dazz1 on September 30, 2024, 07:56:33 am ---What does the delay function do? Is it worth waiting for?
--- End quote ---
I can't really answer this, I don't know how much use the additional "delayed binary output" would be, or if it's relevant for the options installed in your 3721. Information isn't really out there on the web, except for this application note, which only shows it used with a demonstration unit; https://www.hpmemoryproject.org/an/pdf/an_98-2.pdf
David
--- End quote ---
It looks like the selectable delay would be used where there is a fixed delay in the signal path to the DUT as shown in Figure 2. Adding delay would enable synchronization of the OUTPUT signal and the delayed prbs. With modern circuits, it would be relatively easy to add an external delay that was clocked by the process control. That would make the HP 01 option desirable, not essential.
dazz1:
Hi
Just did a bit of playing around with the HP 3721A connected to my very basic Elektor audio signal generator, that includes a frequency sweep (FM) output.
These were not calibration runs. These were confidence checks of functionality.
Pleased to say that I saw what I expected. The attached are summated probability distributions for sine, triangle and square waves. Note that changing the signal frequency made no difference to the displayed output.
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