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Old 4th Jan 2012, 1:04 pm   #7
glowinganode
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Join Date: Apr 2009
Location: Aylesbury, Buckinghamshire, UK.
Posts: 1,522
Default Re: VMARS RA17 product detector modification

Nice one, good thinking with the audio amp.
I replaced mine with a 6AQ5 and an output transformer from a scrap domestic set. I fed it from the anode of the 600 ohm line output valve as there wasn't sufficient drive. This also allowed me to replace the 2Mohm AF control with a more common value 470kohm, the brush had worn down to the metal.
I've boxed the RA17 up now, I want to run it for a bit before I attempt alignment as I'm sure there are one or two gremlins still to come out. I've had some quite obscure faults with this set (it got dropped), including intermittant loom cores, jumping capacitors and a semi conducting insulating sleeve that took a long time to track down. This last fault made a really stringe ringing / whistling noise rather similar to a microphonic valve.
Any further improvements in SSB resolution will be carried out in the from of an add on convertor, as I'd like to eventually return the set to standard.
Is there any chance you could post some circuit diagrams of your modifications please, as then all I need to look out for is a spare BFO.
Kindest regards,
Rob.
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