Fidelity transistorised Playmaster - reverse engineering? - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Chris55000 · 25th Dec 2021, 1:59 am

Hi!

I've just realised the "Playmatic" TR8/TR9 may be three–speeed machines using the TD10 deck, but the amplifier will be an extension of your "Playmaster 2–TR" with speed change (1⅞, 3¾ and 7½ i.p.s.) equalisation networks added!

If you buy one of the "Playmatic" diagrams, print it out and then scribble out or tipp–ex out everything for 1⅞ & 7½ i.p.s., and short-circuit the 3¾ i.p.s. contacts, I think you're going to get as close to the original board as you can without me being on hand there to actually draw it for you directly from yours!

Chris Williams

david freeman · 25th Dec 2021, 9:03 am

Looking at the circuit description for the transistorised Playmaster, there seems to be nothing that would suggest this recorder should have the abysmal performance measured by Alec Tutchings in his review.

Nuvistor · 25th Dec 2021, 9:04 am

Hi Chris,
I can find the TR8 and TR9 Playmatic in the service data, I have the DVD, this uses an ECH83 and EM87 valves as well as transistors. Was this the one you are referring to?
Perhaps this circuit is different to the one in the thread.

Nuvistor · 25th Dec 2021, 9:18 am

The specifications of the recorder do suggest a much better performance than the review. It could have been a faulty machine but you would have thought Fidelity would have tried to get the review updated with a tested machine.
On the other hand the specifications could be what was intended but in practice never reached them.

I only ever saw the early valve ones, for what they were they did a decent job. Few faults and those were simple, they brought an affordable tape recorder to many if not a top flight piece of equipment. Pity this one didn’t hit the mark.

Borderer · 25th Dec 2021, 9:43 am

Quote:

Originally Posted by Chris55000

Hi!

I've just realised the "Playmatic" TR8/TR9 may be three–speeed machines using the TD10 deck, but the amplifier will be an extension of your "Playmaster 2–TR" with speed change (1⅞, 3¾ and 7½ i.p.s.) equalisation networks added!

If you buy one of the "Playmatic" diagrams, print it out and then scribble out or tipp–ex out everything for 1⅞ & 7½ i.p.s., and short-circuit the 3¾ i.p.s. contacts, I think you're going to get as close to the original board as you can without me being on hand there to actually draw it for you directly from yours!

Chris Williams

Hi Chris,

Plenty to think about there, thank you. The circuit seems very much as you describe in your first post though it has a conventional bias oscillator coil. The Playmatic is a good shout so I will look at that. This is turning into a good project for Boxing Day!

Tony.

Borderer · 27th Dec 2021, 2:58 pm

Looking at the input stage, what is happening here?

Mic socket on the left connected to wafer switch at the top via mustard cap. and grey lead. Brown lead from wafer switch to base of the input transistor via green cap. Red cap, not original, between mic signal and earth. Gram/aux socket not connected.

However the small blue electrolytic to the right of the input transistor has its positive end (lower end in picture) to earth and its negative linked via the pcb to the emitter of the transistor. Shouldn't it be the other way round?

Thanks in advance.

Tony.

TonyDuell · 27th Dec 2021, 3:19 pm

That mic socket looks to be the type with a switch contact in that opens when you put the plug in. You might need to check just what connnects where.

What sort of transistor is it? If it's PNP then expect a -ve collector supply rail. The emitter would be connected to ground via a resistor and thus the emitter is -ve with respect to earth too. That capacitor might be the right way round.

Borderer · 27th Dec 2021, 3:51 pm

Quote:

Originally Posted by TonyDuell

That mic socket looks to be the type with a switch contact in that opens when you put the plug in. You might need to check just what connnects where.

What sort of transistor is it? If it's PNP then expect a -ve collector supply rail. The emitter would be connected to ground via a resistor and thus the emitter is -ve with respect to earth too. That capacitor might be the right way round.

It is a BC109, originally would have been BC107, so NPN.

Chris55000 · 27th Dec 2021, 4:02 pm

Hi!

An upside–down NPN transistor used on a positive–earth supply would have the emitter returned to the L.T. negative supply point, but for signal analysis purposes, power supplies are a short–circuit, so it is immaterial that the emitter bypass electrolytic is returned to the positive L.T. line and PCB earth line – it works just as well as if it was across the emitter resistor directly ! The polarity of the capacitor, therefore, is correct – don't reverse it!

Chris Williams

PS!

The OP mentioned the aux/gram socket isn't used on his machine – it does seem, that Fidelity only intended it to be used as a speech/dictation machine but never admitted to such in their advertising blurb – if Fidelity had said that the amplifier had been designed only for use with the small crystal mic. supplied, maybe Andrew Tutchins may not have been so critical in his review!

Without drawing it myself I can't offer an opinion as to what items in the circuit limit the frequency response, but looking at the curves in T.R. Magazine, it's obvious that it was, in it's initial form, only intended for speech/mic. use!

Borderer · 27th Dec 2021, 4:16 pm

The input stage is I think similar to this one (Playmatic) although without the mic/gram switching. The audio problem seems to be a bad transistor in the output stage, so I thought I would have a look at the rest of it while waiting for parts. One thing at a time, anyway.

Borderer · 27th Dec 2021, 5:59 pm

Quote:

Originally Posted by Chris55000

Hi!

The OP mentioned the aux/gram socket isn't used on his machine – it does seem, that Fidelity only intended it to be used as a speech/dictation machine but never admitted to such in their advertising blurb – if Fidelity had said that the amplifier had been designed only for use with the small crystal mic. supplied, maybe Andrew Tutchins may not have been so critical in his review!

Without drawing it myself I can't offer an opinion as to what items in the circuit limit the frequency response, but looking at the curves in T.R. Magazine, it's obvious that it was, in it's initial form, only intended for speech/mic. use!

I have just checked again and the aux/gram is in fact connected - sorry if that was misleading. I suspect that Tutchins had a faulty machine and it is odd that Fidelity never responded publicly. As said, from what I can hear this one sounds quite reasonable, so I would like to get it working as well as possible and we may learn something.

david freeman · 27th Dec 2021, 7:37 pm

I couldn’t understand why Alec Tutchings took all the response curves from the 15 ohm speaker socket instead of using the monitor out socket. Most of his reviews took the response curves from the line/ monitor outputs.
Also, Fidelity advertised the transistorised Playmaster as for the “discerning”, and the concurrent valve Playmaster as for the “value conscious”.

Chris55000 · 27th Dec 2021, 8:49 pm

Hi!

Quote:

I have just checked again and the aux/gram is in fact connected - sorry if that was misleading. I suspect that Tutchins had a faulty machine and it is odd that Fidelity never responded publicly. As said, from what I can hear this one sounds quite reasonable, so I would like to get it working as well as possible and we may learn something.

Fair enough, now we know we've not stumbled across an unknown "mic/speech only" variant!

A transformerless output stage, as yours is, shouldn't have an inherently poor audio frequency response, providing there are no dried–up or leaky electrolytic capacitors in it, or resistors seriously altered in value to the point that the frequency characteristics of the circuitry is too fair impaired – I've never heard of any transistors, whether germanium or silicon, causing a fault that would seriously impair frequency response without also causing atrocious non–linearity distortion as well!

Grotty R/P wafer switch contacts underneath the deck (a 6 pole 2 way wafer was sometimes supplied with the TD2 when new) could conceivably cause a poor frequency response, but this would as you probably found, would almost certainly cause lack of gain as well – although a bad contact may not be obvious on a meter test, the very small millivolt–level signal from the R/P head in playback can be seriously impaired by even small amounts of tarnish on the contacts – this has been my experience, I have a Heathkit STR–1 with virtually zero output on the L.H. channel, both R & P, due to grotty switch contacts in all the signal paths, and looking at the internal wiring & soldering of it, me thinks I will have to strip the lot to all the individual bits (deck included – the joystick is jammed solid with ancient old grease!), and begin again from "Start Here!" of the PCB Assembly pages – it'd be less aggro rebuilding it than trying to trace all the faults!

Chris Williams

david freeman · 27th Dec 2021, 11:30 pm

This is one of the advertisements for the Transistorised Playmaster!

Borderer · 28th Dec 2021, 12:03 am

Quote:

Originally Posted by david freeman

This is one of the advertisements for the Transistorised Playmaster!

A great piece of copy writing. What could possibly go wrong?

It does seem to confirm that there was a 4 track version, also that a high impedance mic was used which I had wondered about - like the magic eye, an odd feature on a transistor machine.

Visually it is just like the valve model except for the "Transistorised" badge, which on mine and all those I have seen pictured, is stuck on at a crazy angle and isn't even printed straight, which is a bit sloppy for 25 guineas.

Silicon · 28th Dec 2021, 9:12 am

Does it use a Selenium bridge rectifier in the power supply?

What is the actual DC power supply voltage?

Small electrolytics tend to be more unreliable than the larger ones.

Can you inject a good signal into a phono input or at the top of the volume control?

Borderer · 28th Dec 2021, 9:48 am

Quote:

Originally Posted by Silicon

Does it use a Selenium bridge rectifier in the power supply?

What is the actual DC power supply voltage?

Small electrolytics tend to be more unreliable than the larger ones.

Can you inject a good signal into a phono input or at the top of the volume control?

It has a bridge rectifier, see picture. Presume selenium, haven't researched it yet. I measured 15 volts in and 22 volts out.

.

slidertogrid · 29th Dec 2021, 2:58 pm

I have been following this thread with interest. The circuit board seemed familiar but I couldn't remember ever having seen one of these Transistorised models. Over Christmas I had a look in the junk store and I have found a panel which looks as if it has come from a 4 track version.
Various parts are missing but it may help clarify some of the points raised ?
I will attach some photos. I Hope they are helpful!

Rich

Borderer · 29th Dec 2021, 3:27 pm

Rich.

Many thanks for posting those. They will indeed be very helpful for comparison as I have never seen another one. Interestingly the large 1000uf cap is identical to those on mine, and they really do not look original. And a few more things besides...

Tony

ben · 30th Dec 2021, 12:30 am

Just seen this thread. I have the 4 track version of this unit, got it from ebay months ago and is in the round- to- it pile!

I plugged it in to give a quick test, and there is no audio at all, in record mode the magic eye does not light up either. Transformer is probaly o/c. The internal speaker was disconnected with two bared wires poking out, so someone has been in there

25th Dec 2021, 1:59 am	#21
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: Fidelity transistorised Playmaster - reverse engineering? Hi! I've just realised the "Playmatic" TR8/TR9 may be three–speeed machines using the TD10 deck, but the amplifier will be an extension of your "Playmaster 2–TR" with speed change (1⅞, 3¾ and 7½ i.p.s.) equalisation networks added! If you buy one of the "Playmatic" diagrams, print it out and then scribble out or tipp–ex out everything for 1⅞ & 7½ i.p.s., and short-circuit the 3¾ i.p.s. contacts, I think you're going to get as close to the original board as you can without me being on hand there to actually draw it for you directly from yours! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

25th Dec 2021, 9:03 am	#22
david freeman Hexode Join Date: Aug 2005 Location: Lincoln, Lincolnshire, UK. Posts: 262	Re: Fidelity transistorised Playmaster - reverse engineering? Looking at the circuit description for the transistorised Playmaster, there seems to be nothing that would suggest this recorder should have the abysmal performance measured by Alec Tutchings in his review.

25th Dec 2021, 9:04 am	#23
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: Fidelity transistorised Playmaster - reverse engineering? Hi Chris, I can find the TR8 and TR9 Playmatic in the service data, I have the DVD, this uses an ECH83 and EM87 valves as well as transistors. Was this the one you are referring to? Perhaps this circuit is different to the one in the thread. __________________ Frank

25th Dec 2021, 9:18 am	#24
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: Fidelity transistorised Playmaster - reverse engineering? The specifications of the recorder do suggest a much better performance than the review. It could have been a faulty machine but you would have thought Fidelity would have tried to get the review updated with a tested machine. On the other hand the specifications could be what was intended but in practice never reached them. I only ever saw the early valve ones, for what they were they did a decent job. Few faults and those were simple, they brought an affordable tape recorder to many if not a top flight piece of equipment. Pity this one didn’t hit the mark. __________________ Frank

27th Dec 2021, 2:58 pm	#26
Borderer Tetrode Join Date: May 2009 Location: Hereford, Hereford and Worcester, UK. Posts: 93	Re: Fidelity transistorised Playmaster - reverse engineering? Looking at the input stage, what is happening here? Mic socket on the left connected to wafer switch at the top via mustard cap. and grey lead. Brown lead from wafer switch to base of the input transistor via green cap. Red cap, not original, between mic signal and earth. Gram/aux socket not connected. However the small blue electrolytic to the right of the input transistor has its positive end (lower end in picture) to earth and its negative linked via the pcb to the emitter of the transistor. Shouldn't it be the other way round? Thanks in advance. Tony. Attached Thumbnails

27th Dec 2021, 3:19 pm	#27
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Fidelity transistorised Playmaster - reverse engineering? That mic socket looks to be the type with a switch contact in that opens when you put the plug in. You might need to check just what connnects where. What sort of transistor is it? If it's PNP then expect a -ve collector supply rail. The emitter would be connected to ground via a resistor and thus the emitter is -ve with respect to earth too. That capacitor might be the right way round.

27th Dec 2021, 4:02 pm	#29
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: Fidelity transistorised Playmaster - reverse engineering? Hi! An upside–down NPN transistor used on a positive–earth supply would have the emitter returned to the L.T. negative supply point, but for signal analysis purposes, power supplies are a short–circuit, so it is immaterial that the emitter bypass electrolytic is returned to the positive L.T. line and PCB earth line – it works just as well as if it was across the emitter resistor directly ! The polarity of the capacitor, therefore, is correct – don't reverse it! Chris Williams PS! The OP mentioned the aux/gram socket isn't used on his machine – it does seem, that Fidelity only intended it to be used as a speech/dictation machine but never admitted to such in their advertising blurb – if Fidelity had said that the amplifier had been designed only for use with the small crystal mic. supplied, maybe Andrew Tutchins may not have been so critical in his review! Without drawing it myself I can't offer an opinion as to what items in the circuit limit the frequency response, but looking at the curves in T.R. Magazine, it's obvious that it was, in it's initial form, only intended for speech/mic. use! __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 27th Dec 2021 at 4:16 pm.

27th Dec 2021, 4:16 pm	#30
Borderer Tetrode Join Date: May 2009 Location: Hereford, Hereford and Worcester, UK. Posts: 93	Re: Fidelity transistorised Playmaster - reverse engineering? The input stage is I think similar to this one (Playmatic) although without the mic/gram switching. The audio problem seems to be a bad transistor in the output stage, so I thought I would have a look at the rest of it while waiting for parts. One thing at a time, anyway. Attached Thumbnails

27th Dec 2021, 7:37 pm	#32
david freeman Hexode Join Date: Aug 2005 Location: Lincoln, Lincolnshire, UK. Posts: 262	Re: Fidelity transistorised Playmaster - reverse engineering? I couldn’t understand why Alec Tutchings took all the response curves from the 15 ohm speaker socket instead of using the monitor out socket. Most of his reviews took the response curves from the line/ monitor outputs. Also, Fidelity advertised the transistorised Playmaster as for the “discerning”, and the concurrent valve Playmaster as for the “value conscious”.

27th Dec 2021, 11:30 pm	#34
david freeman Hexode Join Date: Aug 2005 Location: Lincoln, Lincolnshire, UK. Posts: 262	Re: Fidelity transistorised Playmaster - reverse engineering? This is one of the advertisements for the Transistorised Playmaster! Attached Thumbnails

28th Dec 2021, 9:12 am	#36
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,162	Re: Fidelity transistorised Playmaster - reverse engineering? Does it use a Selenium bridge rectifier in the power supply? What is the actual DC power supply voltage? Small electrolytics tend to be more unreliable than the larger ones. Can you inject a good signal into a phono input or at the top of the volume control?

29th Dec 2021, 2:58 pm	#38
slidertogrid Octode Join Date: Apr 2005 Location: Peterborough, Cambridgeshire, UK. Posts: 1,898	Re: Fidelity transistorised Playmaster - reverse engineering? I have been following this thread with interest. The circuit board seemed familiar but I couldn't remember ever having seen one of these Transistorised models. Over Christmas I had a look in the junk store and I have found a panel which looks as if it has come from a 4 track version. Various parts are missing but it may help clarify some of the points raised ? I will attach some photos. I Hope they are helpful! Rich Attached Thumbnails __________________ The rotation of the earth really makes my day...

29th Dec 2021, 3:27 pm	#39
Borderer Tetrode Join Date: May 2009 Location: Hereford, Hereford and Worcester, UK. Posts: 93	Re: Fidelity transistorised Playmaster - reverse engineering? Rich. Many thanks for posting those. They will indeed be very helpful for comparison as I have never seen another one. Interestingly the large 1000uf cap is identical to those on mine, and they really do not look original. And a few more things besides... Tony

30th Dec 2021, 12:30 am	#40
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Fidelity transistorised Playmaster - reverse engineering? Just seen this thread. I have the 4 track version of this unit, got it from ebay months ago and is in the round- to- it pile! I plugged it in to give a quick test, and there is no audio at all, in record mode the magic eye does not light up either. Transformer is probaly o/c. The internal speaker was disconnected with two bared wires poking out, so someone has been in there __________________ Regards, Ben.