Author Topic: WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array  (Read 973 times)

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Offline ikovacs2

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WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array
« on: January 24, 2022, 09:47:37 pm »
Hi,

I'm looking to buy a HP 1858-0015 either new or used.

It consists of differentially connected NPN transistor pairs in DIP-16. It is used in limiter circuit between a local oscillator and a double balanced mixer in HP 3586 Selective Level Meter.

Istvan
 

Offline Wallace Gasiewicz

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« Last Edit: January 25, 2022, 04:52:32 pm by Wallace Gasiewicz »
 

Offline ikovacs2

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Re: WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array
« Reply #2 on: January 27, 2022, 01:49:49 pm »
Thanks.
cycle_collector checked his stock and doesn't have this part. I will try the group.
 

Offline factory

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Re: WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array
« Reply #3 on: January 27, 2022, 08:45:47 pm »
Mislabelled by clueless seller as Agilent, bet it's a pull too. Looks like a custom part.
https://www.ebay.com/itm/274939212830

David
 

Offline cncjerry

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Re: WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array
« Reply #4 on: January 28, 2022, 07:18:52 am »
there is a common npn and pnp transistor array.  It is called a CA3086 as an NPN, good to 120Mhz.  Considering the SLM doesnt go that high at all, I would check that part or there is a PNP equivalent.  HP used them a lot, the last I replaced was in a 3457a volt meter.  I had 0one blow out once and I just wired up some matched NPN transistors.  there isn't any real magic in that part other than the transistors are all temperature compensated considering they are on the same chip.  The audio guys that built oscillators for synthesizers used to epoxy transistors together to accomplish the same thing.  If you are sure one of the transistors is blow out, then you can clip the leads to that one transistor and solder the appropriate one in its place.

The SLM is a great box, I have 3 or 4 of them, one of each model a,b,c and two c's I think.  You can use them for all kinds of things, automate them with gpib and a frequency generator to do selective plots, etc.  I think one model could act like a source and control a generator of the same class and do bode plots.

Jerry
 

Offline ikovacs2

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Re: WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array
« Reply #5 on: January 28, 2022, 10:32:38 am »
Yes, I will use CA3086 if I don't find a direct replacement part.

Attached the circuit diagram. U1 is 1858-0015. The limiter operates in 50MHz to 82.5Mhz range. The IF is 50 MHz.
[attach=1]

1858-0015 has two differential pairs. CA3086 has one differential pair and three separate transistors.
[attach=2]

I'm wondering whether a pair with externally connected emitters has the similar parameters as the pair with internally connected emitters. If the internally connected pair is better then the externally connected one, might it be better to use the differential pairs of two CA3086s?

I replaced the part by four general purpose transistors as a temporary solution and the HP3586 works. Nice meter really.
 

Offline doktor pyta

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« Last Edit: February 04, 2022, 07:57:21 am by doktor pyta »
 

Offline Wallace Gasiewicz

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Re: WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array
« Reply #7 on: February 04, 2022, 01:31:39 pm »
Congratulations on your repair.
I have a HP 3746 Selective level meter and it is a great piece of equipment.
If you have a little patience with it you can use WWV and adjust the oscillator very close. The oscillator is quite stable.
 

Offline ikovacs2

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Re: WTB (EU): HP 1858-0015 High Frequency NPN Transistor Array
« Reply #8 on: February 07, 2022, 04:01:01 pm »
Thank you all for your help.

As there is no direct replacement part I've finally changed my mind and ordered the original part.
 


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