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Old 13th May 2021, 8:57 pm   #1
lloydwells
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Default Wartime civilian receiver what to replace Westector with ??

I have a WCR I've replaced the leaky Caps and got it generally going but nothing other than static I'm assuming the Westector has had its chips. What can be used to replace one ??
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Old 13th May 2021, 9:35 pm   #2
wartime sounds
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Default Re: Wartime civilian receiver what to replace Westector with ??

Hi lloydwells,

MR1 (the WX6 Westector) can be replaced with a germanium diode such as an OA81 or OA91 and as the Westector comes easily apart can be hid inside for originality.
Hope this helps

Peter
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Old 13th May 2021, 10:45 pm   #3
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Default Re: Wartime civilian receiver what to replace Westector with ??

Many thanks
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Old 13th May 2021, 11:54 pm   #4
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Default Re: Wartime civilian receiver what to replace Westector with ??

The only thing to consider if a germanium diode is to be used as a replacement for the Westector is that a 4volt forward bias is applied across the device.
The bias will not be required for an OA70 or the like.
How about trying out the EA50 or the VR92 thermionic diode? Again, no forward bias will be required.
https://www.radiomuseum.org/tubes/tube_ea50.html
The valve is about the same size as the Westector. A B3G socket will be required which can be difficult to find.
The attached circuit diagram shows how the bias for the Westector is derived.

DFWB.
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Old 14th May 2021, 3:59 pm   #5
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Default Re: Wartime civilian receiver what to replace Westector with ??

That Westector diode MR1 on the thumbnail seems to be reverse biased.

I assume that is something to do with 'delayed AGC'.
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Old 14th May 2021, 5:19 pm   #6
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Default Re: Wartime civilian receiver what to replace Westector with ??

Not the way I read the circuit. It is a bit convoluted, took me a minute or two to really see what is going on.
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Old 14th May 2021, 5:22 pm   #7
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Default Re: Wartime civilian receiver what to replace Westector with ??

Back to the OP request, a few silicon diodes in series, 4V would be 4/0.7 = 5.7. As diodes only come in integers tweak the number for best performance. I had one of these sets nearly 40 years ago, I replaced the Westector with a power diode, that was all I could find at the time, it worked!
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Old 14th May 2021, 7:50 pm   #8
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Default Re: Wartime civilian receiver what to replace Westector with ??

Hi

Looking at the Westector data sheet, the "knee" in the forward characteristic of a WX1 (single element) is at about 0.2 volts. The WX6 has 6 series elements so the 0.2 volts becomes 1.2 volts. I therefore find it quite surprising that in the WCR design the Westector is treated to 4V forward bias, pushing it well into a conducting state. I guess if it still conducts more in one direction than another then it still counts as a detector, albeit a rather "soggy" one. Maybe the designers found this gave the "best" performance.

If you replace with a single semiconductor diode, I suspect it would be happier with the forward bias reined in a bit or even reduced to zero.
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Old 14th May 2021, 8:55 pm   #9
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Default Re: Wartime civilian receiver what to replace Westector with ??

Apologies for the confusion.
After studying it further I realise the Westector is forward biased.

Although it has +8.6V on the cathode, the Anode is +12.6V.

If I take the 47k and 330k series resistors into account, the forward bias current seems to be about 10 microAmps.

That should be no problem for an OA70.
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Old 16th May 2021, 10:21 pm   #10
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Default Re: Wartime civilian receiver what to replace Westector with ??

Anyone any idea why a Westector was used rather than a thermionic type detector in the original design?
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Old 16th May 2021, 10:42 pm   #11
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Default Re: Wartime civilian receiver what to replace Westector with ??

flyingtech wrote: "Anyone any idea why a Westector was used rather than a thermionic type detector in the original design?"
That's right, I would have thought the Westector was something quite exotic in 1944. Or, perhaps the device was more plentiful than say, an EA50 thermionic diode. To use the EBL31 double-diode-pentode would have limited the choice of maker to only Mullard.

DFWB.
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