Fidelity playmaster 4 (TR6) - UK Vintage Radio Repair and Restoration Discussion Forum

ben · 28th Oct 2019, 2:49 pm

From this thread

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!

ms660 · 28th Oct 2019, 3:06 pm

I'm confused already.

Lawrence.

Restoration73 · 28th Oct 2019, 3:15 pm

Check the pcb in the region of the EL84 hasn't become conductive. No sound often due
to the switched socket not making contact.

G6Tanuki · 28th Oct 2019, 3:23 pm

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?

llama · 28th Oct 2019, 3:25 pm

Is C8 OK?
Graham

Welsh Anorak · 28th Oct 2019, 3:35 pm

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).

ben · 28th Oct 2019, 3:39 pm

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.

G6Tanuki · 28th Oct 2019, 3:54 pm

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?

cathoderay57 · 28th Oct 2019, 4:37 pm

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

BillDWVA · 28th Oct 2019, 4:48 pm

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

Bill

Welsh Anorak · 28th Oct 2019, 5:23 pm

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.

ben · 28th Oct 2019, 10:13 pm

Thanks very much for the suggestions.

ricard · 29th Oct 2019, 11:46 am

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.

28th Oct 2019, 2:49 pm	#1
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Fidelity playmaster 4 (TR6) From this thread 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! Attached Thumbnails __________________ Regards, Ben.

28th Oct 2019, 3:06 pm	#2
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Fidelity playmaster 4 (TR6) I'm confused already. Lawrence.

28th Oct 2019, 3:15 pm	#3
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	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.

28th Oct 2019, 3:23 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	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?

28th Oct 2019, 3:25 pm	#5
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	Re: Fidelity playmaster 4 (TR6) Is C8 OK? Graham __________________ Half my stuff is junk - trouble is, I don't know which half!

28th Oct 2019, 3:35 pm	#6
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	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). __________________ Glyn www.gdelectronics.wales

28th Oct 2019, 3:39 pm	#7
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	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. __________________ Regards, Ben.

28th Oct 2019, 3:54 pm	#8
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	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?

28th Oct 2019, 4:37 pm	#9
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	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

28th Oct 2019, 4:48 pm	#10
BillDWVA Pentode Join Date: Nov 2010 Location: Tenby, Pembrokeshire, Wales, UK. Posts: 139	Re: Fidelity playmaster 4 (TR6) Ben, what is the anode current of V3 (EL84)? Bill

28th Oct 2019, 5:23 pm	#11
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	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. __________________ Glyn www.gdelectronics.wales

28th Oct 2019, 10:13 pm	#12
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Fidelity playmaster 4 (TR6) Thanks very much for the suggestions. __________________ Regards, Ben.

29th Oct 2019, 11:46 am	#13
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	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.