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Old 27th Mar 2019, 9:46 pm   #1
Colin Boggis
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Default Barker 88 - Another audio arrangement

As I'm sure you're all aware, Barker 88 radios were made around WW2 and used whatever components were readily available at the time of manufacture.
I've just restored one, simply because I had another when I was 16 (an eternity ago!). This version is totally different from those on which I could find data.
The audio stages use a 6H6G as the detector, a 6SL7GT as phase splitter in long tailed pair mode, and a pair of KT61's for the output. All that was really needed to bring it back to life was replacement of the main reservoir & smoothing can and , for good measure, all the Sprague waxed paper capacitors plus the cathode bias resistor on the KT61's. For anyone that's interested, I've attached the audio stages circuit. The main electrolytic was opened up and refilled with 4 x 22ufd 450 V 105C caps. which explains the 44 ufd shown in the schematic, which, incidentally, was prepared using the free software from Digi-Key known as "Scheme-it".
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Old 28th Mar 2019, 10:47 am   #2
ronbryan
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Default Re: Barker 88 - Another audio arrangement

I wonder if the phase splitter anode resistors should be shown referred to the 212V point on the HT rail rather than the 110V point.

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Old 28th Mar 2019, 11:29 am   #3
Sideband
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Default Re: Barker 88 - Another audio arrangement

It's amazing how many variants there are. Mine has a 6Q7 AF amp/detector/AGC valve followed by a 6J5 triode phase splitter with two 6V6's as output. I couldn't find an exact circuit anywhere and had to 'reverse engineer' the diagram.
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Old 28th Mar 2019, 1:54 pm   #4
Bryan M
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Default Re: Barker 88 - Another audio arrangement

Mine hasn't yet had any attention from me but it appears to have the same valve lineup as Colin's. I received it with the attached brochure which may be of interest.
Bryan
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Old 30th Mar 2019, 10:01 pm   #5
Colin Boggis
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Default Re: Barker 88 - Another audio arrangement

Thanks Ronbryan for spotting my error - yes, the phase splitter anodes are fed from the 212V rail! And thanks Bryan M for the leaflet which certainly looks to be my radio.
I just fitted a 6E5 tuning eye with minor rewiring of the base connections - a lot cheaper than another 6Y1 or 6Y3 but it works fine.
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Old 31st Mar 2019, 10:50 am   #6
Colin Boggis
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Default Re: Barker 88 - Another audio arrangement

Here is the corrected circuit with phase splitter anodes fed from the 212 volt line. Also I've reduced the 22K HT feed resistor to 15K to increase RF stage voltages.
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