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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 28th Oct 2019, 2:49 pm   #1
ben
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Default Fidelity playmaster 4 (TR6)

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Fitted spare o/p transformer (tested OK prior to installation) but still no sound. Series resistor with rectifier gets very hot. Tried disconnecting R18 4k7 which looked the worse for wear and series resistor still overheats. Something is clearly drawing current in the o/p stage.

Apart from the EL84 I suppose c13 if leaky might cause this. Will look again after work later on, I need to see how much current is being drawn amongst other things. Any thoughts in the meantime appreciated!
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Old 28th Oct 2019, 3:06 pm   #2
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Default Re: Fidelity playmaster 4 (TR6)

I'm confused already.

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Old 28th Oct 2019, 3:15 pm   #3
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Default Re: Fidelity playmaster 4 (TR6)

Check the pcb in the region of the EL84 hasn't become conductive. No sound often due
to the switched socket not making contact.
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Old 28th Oct 2019, 3:23 pm   #4
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Default Re: Fidelity playmaster 4 (TR6)

I'm confused - surely R18 *is* the "series resistor for the rectifier" and if it's got one end lifted it can't be seeing any power so won't get hot?
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Old 28th Oct 2019, 3:25 pm   #5
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Default Re: Fidelity playmaster 4 (TR6)

Is C8 OK?
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Old 28th Oct 2019, 3:35 pm   #6
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Default Re: Fidelity playmaster 4 (TR6)

Hi Ben
Do you mean there's another series resistor before the rectifier that's not on the diagram? If that still overheats with R18 taken out then there's not much left. What happens if you remove the valve? That might narrow things down.
Of course it might not be too much current, just unsmoothed HT due to C18 bein O/C or leaky. That would annoy the resistor(s).
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Old 28th Oct 2019, 3:39 pm   #7
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Default Re: Fidelity playmaster 4 (TR6)

Sorry, I should have explained myself. I had previously replaced the leaky silicon rectifier with a BY255 + 220R 5watt series resistor.

This is not to be confused with R18 which allows 190v to reach other stages of the cct.
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Old 28th Oct 2019, 3:54 pm   #8
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Default Re: Fidelity playmaster 4 (TR6)

Ah, I see.

I'd be checking C18 for massive leakage - and also looking at the circuit, if the 200pF tone-control/NFB capacitor C20 is S/C and the wiper of VR2 is turned o the right track-end, you'll get a short from the anode of the EL84 to ground.

What happens if the EL84 is pulled out?
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Old 28th Oct 2019, 4:37 pm   #9
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Default Re: Fidelity playmaster 4 (TR6)

Hi Ben, isolating the connections to the HT reservoir cap C18 one by one should reveal where the high current drain is coming from. C18 itself sounds like the culprit. Then measure the voltages (with playback selected) at EL84 anode, grid1, grid2 & cathode. Cheers, Jerry
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Old 28th Oct 2019, 4:48 pm   #10
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Default Re: Fidelity playmaster 4 (TR6)

Ben, what is the anode current of V3 (EL84)?

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Old 28th Oct 2019, 5:23 pm   #11
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Default Re: Fidelity playmaster 4 (TR6)

As a matter of interest, was the original output transformer faulty? If so there must be a heavy current flowing. If not, I'd be looking at C18 very suspiciously, which would explain why R18 looks unhappy with the high ripple.
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Old 28th Oct 2019, 10:13 pm   #12
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Default Re: Fidelity playmaster 4 (TR6)

Thanks very much for the suggestions.
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Old 29th Oct 2019, 11:46 am   #13
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Default Re: Fidelity playmaster 4 (TR6)

I suppose you don't have a voltmeter at hand, I'd be interested to know the anode and gate voltages on the output valve for a start.
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