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Old 6th Apr 2024, 10:54 pm   #1
unitelex
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Default HP 3200B oscillator, Attenuator Probe

Regarding the HP 3200B VHF oscillator, I have one of these but it is missing the attenuator tube assembly.

This is a tube of 19mm diameter and about 140mm long. At one end it has a pickup coil (L107) and at the other end it has a BNC connector (J100)
It is used for attenuation adjustment and to achieve more consistent output between frequency band selections and can be moved in or out to adjust coupling for best signal integrity and stability.

I don't have much hope of finding one of these, so I would like to fabricate one, can't be that difficult ?

My main question relates to the pickup coil L107, the number of turns, its inner diameter and orientation.

If anyone has a HP 3200B and would be so kind as to send a photo or two of the coil end it would be much appreciated.

I realise that mechanically it needs to be a similar dimensions to the original with 360 degree grounding at the output end. Also there is a built-in capacitance to account for and a transmission line to the BNC output
The output is designed to be 50Ohm so at least that can be a target.

Any information/photos greatly appreciated.

Chris
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Old 7th Apr 2024, 11:23 am   #2
factory
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Default Re: HP 3200B oscillator, Attenuator Probe

Unfortunately many of these 3200A/B are missing the attenuator, I've no idea why, as it's probably no use for anything else.

Here are a couple of pictures of the attenuator from mine, the coil is potted, also the tube is shaped to stop rotation.

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David
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Old 7th Apr 2024, 11:38 am   #3
factory
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Default Re: HP 3200B oscillator, Attenuator Probe

Some pictures of the the clamp, this consists of a plastic pin, clamping ring & spring, which might also be missing from some too. The inside of the clamping ring is machined to move the pin & clamp the attenuator tube.

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David
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Old 7th Apr 2024, 1:54 pm   #4
Radio Wrangler
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Default Re: HP 3200B oscillator, Attenuator Probe

I have a feeling that started out as a Boonton model, so there may be more info from that route.

With any HP instrument, have a search for a "Hewlett-Packard Journal" article. If there is one, there could be a photo of a raw coil before potting.

David
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Old 7th Apr 2024, 2:04 pm   #5
orbanp1
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Default Re: HP 3200B oscillator, Attenuator Probe

Boonton in their 202 series generators had piston type attenuators.
Probably this is where HP piston attenuators originate, HP bought Boonton in the early '60s, though I could be wrong regarding the origin of this HP attenuator.

The service manuals for HP-202H and -202J show details of the attenuator.
The pick up coil is two turns, with a 50 Ohm source resistor in series, and some compensating capacitor.

The BRC "The Notebook" No. 31, '62 spring issue, describes the improvements of the H and J versions over the original B and C versions of the 202 generator.

PS: I added a solid state ALC circuit to my original BRC-202C generator that lacked that feature, it works like charm.

EDIT: The BRC-255 looks similar (in the oscillator circuit) to the HP-3200B.

Regards, Peter

Last edited by orbanp1; 7th Apr 2024 at 2:31 pm.
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Old 7th Apr 2024, 2:21 pm   #6
factory
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Default Re: HP 3200B oscillator, Attenuator Probe

Quote:
Originally Posted by Radio Wrangler View Post
I have a feeling that started out as a Boonton model, so there may be more info from that route.

With any HP instrument, have a search for a "Hewlett-Packard Journal" article. If there is one, there could be a photo of a raw coil before potting.

David
Yes the 3200A started out under the Boonton Radio Corporation brand, but probably after the take over, as they all use the HP system one cabinet/case.

http://hparchive.com/Boonton/BRC-The-Notebook-37.pdf

Some more details from the above BRC notebook.
Quote:
The attenuator piston is completely removable, and the pickup loop, employing a ferrite core for maximum low frequency coupling, is completely encapsulated in a low dielectric constant resin for maximum stability and protection
David
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Old 8th Apr 2024, 3:16 am   #7
unitelex
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Default Re: HP 3200B oscillator, Attenuator Probe

Thanks for the great information chaps, much appreciated.

I will dig into this and attempt to replicate it
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Old 8th Apr 2024, 12:48 pm   #8
orbanp1
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Default Re: HP 3200B oscillator, Attenuator Probe

The BRC-202B, C, and E version generators start at 54MHz, other 202 versions even at higher frequencies.
Probably that is the reason that those generators do not need a ferrite core in the attenuator pick up coil.

Regards, Peter
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