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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 26th Mar 2020, 12:39 am   #21
Chris55000
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Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
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Default Re: Diora Pioneer U3 dropping mains voltage help please

Hi!

Is this diagram I've found any help?

Chris Williams
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Old 26th Mar 2020, 12:59 am   #22
Chris55000
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Posts: 950
Default Re: Diora Pioneer U3 dropping mains voltage help please

Hi!

I'm not sure if the circuit diagram I posted exactly corresponds to the OP's particular set, but it should be noted that the figure of –13V for the UBL21's negative G.B. only applies to Va and Vg2 operated at 180–200V, and with the relatively low H.T./G2 voltage (120V) employed in this set, the G.B. will have to be reduced for the valve to operate correctly, hence the "–8V" shown on the diagram I included in the previous post!

Chris Williams

PS!

To check the coupling capacitor C26 from the triode anode (pin 3) of valve L2 for leakage, monitor the negative G.B. across the 120 ohm bias resistor in the neutral lead, then short pin 3 of L2 (UCH21) to chassis briefly – if the negative G.B. changes when pin 3 of L2 is earthed, C26 is duffy!
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Last edited by Chris55000; 26th Mar 2020 at 1:22 am.
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