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Old 19th Jan 2021, 11:09 am   #1
LA9CHA Thorvald
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Default HP8640B signal generator.

Hi, anyone who can tell me a replacement part for hp 8640b, part 1825-0303. Is this a special kind of op.amp? (Perhaps David knows!)
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Old 19th Jan 2021, 6:09 pm   #2
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Default Re: HP8640B signal generator.

1825 prefix isn't one I know.

1820- digital ICs (but a few early linear ones before they split them off)
1826- analogue ICs
1853- Silicon bipolar PNP
1854- Silicon bipolar NPN
1855- FET (either polarity, jfet, mosfet all luped together)
1858- transistor arrays
1901- plain diode
0122- varactor diode
1902- zener diode
1906 diode array

off the top of my head.

David
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Old 19th Jan 2021, 6:31 pm   #3
factory
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Default Re: HP8640B signal generator.

Can you confirm the part is 1825 and not 1826? As 1826-0303 would be a CA741G op-amp.

David

Edit: The fact only 10 results are given for a web search makes me think HP 1825-0303 is an error.
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Old 19th Jan 2021, 6:39 pm   #4
kevinaston1
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Default Re: HP8640B signal generator.

The HP parts reference sheet give 1826-0303, closest I could find. They give this as a CA741G
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Old 19th Jan 2021, 7:29 pm   #5
LA9CHA Thorvald
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Default Re: HP8640B signal generator.

Hello David and again many thanks for answer. The given part number is read direct from the op.amp, and if a 741, no problem as I have several units! I will check its function!
Assume the selection of hi/lo band is made by the range selector, and that this will ground the input line to the op.amp. Please confirm if you can take it by the head! Tks and rgsd!
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Old 19th Jan 2021, 7:59 pm   #6
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Default Re: HP8640B signal generator.

There is a rather nice wirewound precision pot geared off of the main tuning shaft. This feeds a comparator with a little hysteresis, and this controls high/low filter switching within a frequency range.

David
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Old 20th Jan 2021, 5:52 am   #7
LA9CHA Thorvald
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Default Re: HP8640B signal generator.

Very fine David. After checking the op.amp text with a microscope, i found that it should read 1826, so you are dead on! Sorry for the mistake. As my present problem is no RF output , and signal in to the filet but no signal out from the filter on any band, could this have to do with the potmeter and comparator? Is the "filter ricer" the same as "filter"? Hope you will help as I notice you have had several questions on the generator from many peopel.
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Old 20th Jan 2021, 8:15 am   #8
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Default Re: HP8640B signal generator.

If the filter selector was stuck for some reason, then you would get a signal in either the upper half or the lower half of each band.

There are doubts over the reliability of the switching relays.

Do you have RF into the filters, and no RF out of the filters on all bands?

I think this is one of those faults you just have to trace out the slow way.

David
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Old 20th Jan 2021, 1:01 pm   #9
LA9CHA Thorvald
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Default Re: HP8640B signal generator.

well, the rf is missing over all bands, but ot looks as the range selector is of another version as for my unit (s.no: 1703U01332). I am struggeling finding the connections between the range selector (slip -rings and the divider) Any who can help if David cannot take from his head!?
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