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Old 31st Oct 2019, 2:14 pm   #31
ms660
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Join Date: Apr 2011
Location: Cornwall, UK.
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Default Re: Vintage Radio and Phonograph cutter schematic

The pin voltages look to be for 6SJ7's, more about that below.

First I would disconnect that Y Class capacitor and connect the chassis to mains earth, that will prevent the chassis from becoming live if there is any leakage, that AC voltage reading might be due to capacitance that exists between the primary and secondary windings of the mains transformer in conjunction with using a high impedance digital multimeter, if you do as above and the supply doesn't trip I would leave it like that for the moment (chassis earthed, Y Class capacitor disconnected)

For the valve voltages etc let's make it easy and number the valves V1, V2, V3, V4, V5, V6 and V7 from left to right (V1 to V6) then down for V7 (the rectifier)

Also note the voltages quoted by the manufacturer were measured using a 1,000 ohms per volt meter, this means that some of those measurements will be low or none existent compared to what you have measured using a DMM.

V1 (6SA7) You recorded no heater voltage for this valve but the -ve voltage on the oscillator grid (pin 5) suggests that the valve is working in that department, ie: the oscillator is working...This valve is used as the receivers mixer/oscillator (aka a Pentagrid Converter) The anode and g2g4 voltages (pins 3&4) seem reasonable and the other measurements seem ok except the heater...so can you check pin 2 and 7 again for 6 volts AC on one of them so as to clarify the situation?

V2 (6SF7) The voltages look reasonable to me....This valve is the receivers IF (Intermediate Frequency) amplifier and signal detector.

V3 and V4 (the two 6SJ7's) the voltages on the anodes (pins 8) and g2 (pins 6) look low if measured with a DMM, what's the voltage at the junction of C10 and R39 etc? (circuit refs are per the dropbox link schematic) So far as I can make out these two valves are voltage amplifiers for high or low level inputs from a microphone or high level inputs from an auxiliary source.

Lawrence.

Last edited by ms660; 31st Oct 2019 at 2:20 pm.
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