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Old 23rd Jun 2022, 2:28 pm   #1
G6Tanuki
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Default Clansman PRC320 ramp generator - transistors.

Does anyone know what the transistors used in module 9f - ramp-generator - of the Clansman PRC320 are?

A slip with a 'scope-probe has destroyed a couple of them; they're handling 110V or so to drive the varicap-tuning line hence I'm not going to try shoving-in a couple of generic BC1xx-types.

The 3rd-line servicing manual, though it lists the actual values/types of resistors and capacitors and [some] ICs, is distinctly unhelpful at identifying the transistor-types.... see below.
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Old 23rd Jun 2022, 2:40 pm   #2
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Default Re: Clansman PRC320 ramp generator - transistors.

I put the Plessey part numbers into the SAP database but it looks like they preceed it and would have been on the old printed "Part locator files" not seen one of them since the early 1990's.

If I get in the office next week I will see if any of the "old" buyers have a stash of the old Plessey part numbers anywhere.

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Old 23rd Jun 2022, 2:46 pm   #3
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Default Re: Clansman PRC320 ramp generator - transistors.

BF257/8/9 maybe? Most of us will have a few HV transistors in the junk box, scavenged from scrap monitors and portable tellies.

https://www.alldatasheet.com/datashe...ICS/BF257.html
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Old 23rd Jun 2022, 2:54 pm   #4
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Default Re: Clansman PRC320 ramp generator - transistors.

Thinking it might give a clue, I looked at the parts-list for the high-voltage part of the power-supply inverter; the transistors are listed as "FRB700" and "U14906/4" which is equally unhelpful, though there is a BSY95A in there too.

Equivalent to the FRB700 _seems_ to be suggested as the BSV29
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Old 23rd Jun 2022, 5:02 pm   #5
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Default Re: Clansman PRC320 ramp generator - transistors.

ZTX857 appears to be a substitute according to here:-

https://g8jnj.webs.com/PRC%20320%20P...e%20faults.pdf
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Old 23rd Jun 2022, 5:54 pm   #6
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Default Re: Clansman PRC320 ramp generator - transistors.

There are some good suggestions being made; thanks all.

This particular PRC320 has been a bit of a 'nuisance radio' - it's one of the first made [S/N 0353] and shows signs of quite a bit of subsequent rework. The power-supply [module 5] went wobbly early-on, so I fixed it, but then the randomly-shifting-by-a-few-hundred Hertz burblies returned; replacing the oozy Tantalums in the ramp-generator fixed things - for a bit. It was while probing the ramp-generator that I shorted a couple of transistors, hence the problem. It's also strange that this particular radio seems horribly susceptible to external magnetic-fields: I've got a CB-style fist-microphone with a magnet in it so you can 'park' it on any suitable ferrous surface, and waving this around within a foot of the PRC320 causes its frequencyu to wander. My later 4500-series-numbered 320 doesn't suffer this!

Perhaps I should just do the DDS VFO mod as shown here:

https://www.youtube.com/watch?v=GcYcLwVGH24
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Old 23rd Jun 2022, 8:26 pm   #7
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Default Re: Clansman PRC320 ramp generator - transistors.

That's an intriguing mod, though it seems a bit drastic - it depends on whether keeping your 320 original or not is a priority I guess. Mine has started to do the odd 'burblie' now and again, switching off and back on usually fixes it. Hopefully just the power supply tants.

Equally intriguing is your comment about the effect of a magnet, I'll try that on mine just to see what happens. I can only imagine that the magnetic field is affecting a ferrite core in the VCO. It might depend on which bandswitch position the set happens to be on.

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Old 25th Jun 2022, 6:57 pm   #8
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Default Re: Clansman PRC320 ramp generator - transistors.

I've got a couple of 'original' 320s here [with good strikeouts on the mod-record plate] so I'm happy to be preserving 'originality' and working it regularly on 3615 AM and on sideband on 5MHz.

This 'problem-320' I will happily rework using modern digital-synthesis tech, some may criticize me for this but I view it as the continuity of the ham-radio tradition that reworked loads of 19-sets, R1155s etc in order to make them better-able to operate on the post-WWII ham-bands.

'Better to wear out than to rust-out'
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Old 25th Jun 2022, 8:38 pm   #9
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Default Re: Clansman PRC320 ramp generator - transistors.

The DDS conversion will be an interesting project.

I just tried the magnet test on my 320 and sure enough it is sensitive - on the top, above the turret just behind the panel in the most sensitive spot. I tried it on various spot frequencies throughout the range - on a CW signal from a sig gen - and it is sensitive on all of them.

Unfortunately, as I was doing this, the frequency started warbling and switching on and off makes no difference i.e. the fault is now permanent. I hadn't run it for a while - a few months in fact. So it looks like the caps will need doing. Oh well...

Cheers
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Old 25th Jun 2022, 9:25 pm   #10
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Default Re: Clansman PRC320 ramp generator - transistors.

This magnet trick is a very bad idea. Some ferrite is permanently affected by strong magnetic fields.
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Old 25th Jun 2022, 10:58 pm   #11
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Default Re: Clansman PRC320 ramp generator - transistors.

Noted Jon, thanks - I think that is good advice.
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