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Old 15th Sep 2019, 6:55 pm   #1
RF Burn
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Default KW2000 Unobtainium Parts

I'm trying to sort out some spare parts for my KW2000E to pack away with it when we move home, but have come across a few items for which I can find no data and hence no possible replacements. Does anyone have data sheets, know the ratings of, or equivalents to the following:
BY236 Diode
BY238 Diode
BYX36-150 Diode
8SC20 Varicap Diode
3A05 Diode/Rectifier (I suspect 50 PIV 3A, but could be wrong)

Thanks.

Adrian
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Old 15th Sep 2019, 7:18 pm   #2
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Default Re: KW2000 Unobtainium Parts

https://www.radiomuseum.org/tubes/tube_byx36.html

https://www.radiomuseum.org/tubes/tube_by238.html
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Old 16th Sep 2019, 1:02 am   #3
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Default Re: KW2000 Unobtainium Parts

The 8SC20 is actually the 6.8SC20 by International Rectifier Corp.

Data I could find on it is limited, so if anybody has an old IRT databook (1985 ish).

50pF@0.1V to 2.5pF@-200V yes, that is minus 200V

And Motorola lists the MR501 as the equivalent of the 3A05 which as you suspected is 50v 3A
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Old 16th Sep 2019, 6:12 pm   #4
RF Burn
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Default Re: KW2000 Unobtainium Parts

Thanks for the info chaps.

It is somewhat amazing that the 'older' active parts i.e. valves are all readily available with data sheets a plenty to down load, but when it comes to the solid state parts they seem to be almost unobtainable both in parts and data.

Adrian

Last edited by RF Burn; 16th Sep 2019 at 6:17 pm.
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Old 17th Sep 2019, 12:20 pm   #5
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Default Re: KW2000 Unobtainium Parts

I seem to have misplaced my ECA replacement guides, but they almost certainly have the basic data on the three BY.... types mentioned. Also, an ultrafast 1000V 3A rectifier such as the UF5408 is an almost universal replacement for hundreds to thousands of older diode types.
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Old 17th Sep 2019, 1:13 pm   #6
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Default Re: KW2000 Unobtainium Parts

Ther following information might be of help Adrian:

BY238 Datasheet avaiable here:

https://www.web-bcs.com/diode/dc/ba/.../ba/BY238.html

BY238 diodes available from Little Diode’s ebay shop at £3.09 post-free:

https://www.ebay.co.uk/p/BY238-Silic...am/25012056300

BYX36-150 Data here:

https://www.silicon-ark.co.uk/datash...et-mullard.pdf

Diodes available here, but it looks like just a 1A 600V rectifier diode – nothing special. (EG 1N4007 etc):

http://www.weisd.com/test/GenericPar...d1=BYX36%2F150

3A05 is equivalent to Motorola MR501.

See Motorola equivalents catalogue here:

http://bitsavers.trailing-edge.com/c...iodes_Data.pdf

The MR501 is in stock at Little Diode eBay shop at £3.79 post free:

https://www.ebay.co.uk/p/MR501-Silic...kaAj9MEALw_wcB

Good luck in your quest.
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Old 17th Sep 2019, 1:31 pm   #7
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Default Re: KW2000 Unobtainium Parts

THe varactor will be the difficult one.

Remember you can parallel them and add their capacitances if you need to. But varactor types have been vanishing for years. For some capacitance ranges there are now no longer any parts made.

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Old 17th Sep 2019, 1:57 pm   #8
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Default Re: KW2000 Unobtainium Parts

Quote:
Originally Posted by Radio Wrangler View Post
THe varactor will be the difficult one.

Remember you can parallel them and add their capacitances if you need to. But varactor types have been vanishing for years. For some capacitance ranges there are now no longer any parts made.

David
I have been experimenting a bit recently and have seen some of the larger values which appeared to around years ago are now gone.

The trouble with varactors in parallel is that they have the problem that the minimum capacitance is also doubled. For a large value varactor (say 100pF) I have noticed that the minimum capacitance value is highish anyway unless getting very close to maximum reverse voltage.
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Old 17th Sep 2019, 3:01 pm   #9
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Default Re: KW2000 Unobtainium Parts

If that varicap diode is in the RIT circuit it may no require a large change in value.
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Old 17th Sep 2019, 7:58 pm   #10
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Default Re: KW2000 Unobtainium Parts

Sorry Frank. I was being general rather than specific as I found them less amenable than mechanical circuitry so sharing my findings.
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Old 18th Sep 2019, 2:04 am   #11
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Default Re: KW2000 Unobtainium Parts

A little more digging on the varicap shows references to it as far back as 1967, so it goes back a fair way (no extra data at this stage though).

However, if you look at the schematic of the KW2000E, you will find a different varicap on the actual drawing - 1N4803 - even though the 8SC20 is listed in the parts list.

May be another avenue to explore for a substitute.
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Old 18th Sep 2019, 6:46 am   #12
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Default Re: KW2000 Unobtainium Parts

Varactors in parallel to make larger values, if you keep all the same type, at least retain the capacitance ratio. All capacitances scale up by N.

The age of this part puts it before the hyper-abrupt varactor diodes came along with their higher capacitance ratios. The -200v capacitance spec fits as well.

David
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