Fidelity transistorised Playmaster - reverse engineering?

[Borderer]

This thing was a charity shop find, which I thought would be useful for my BSR deck experiments. When powered up it proved to be not quite dead, so it deserves a bit of attention. This was not a successful model, so it is of some historical interest. Fidelity were a competent maker, so how did they get this wrong?

There is very little information available and I know nothing much about transistor circuits, so where do I start with it? The transistors are said to be BC107, 2x OC75, 2x AC128, and AC176, but that is all I have been able to find.

It plays back but only at low volume, both the volume and tone controls have some effect so I assume a fault in the output stage. Sound quality is acceptable given the low volume, if anything better than I expected. Not tried recording yet.

Photos to follow. Someone has clearly been in before. I have started checking a few components, but what should I be looking at?

[G6Tanuki]

I can't see exactly where the AC128/AC176 output transistors are placed, but if they are fitted to some sort of shared heatsink - which may or may not be earthed - be aware that these TO-1 Germanium transistors also suffer from the 'tin-whisker-growth' problem which can cause a whole bunch of intermittent and perplexing faults.

It seems to have a "magic eye" and comments?

[Borderer]

Originally Posted by G6Tanuki

I can't see exactly where the AC128/AC176 output transistors are placed, but if they are fitted to some sort of shared heatsink - which may or may not be earthed - be aware that these TO-1 Germanium transistors also suffer from the 'tin-whisker-growth' problem which can cause a whole bunch of intermittent and perplexing faults.

That is worth knowing, thank you. Haven't checked everything yet but two transistors are in a shared heat sink attached to the tone control shielding - all of which is made from brass, presumably not ex-factory...

[Borderer]

Originally Posted by merlinmaxwell

It seems to have a "magic eye" and comments?

It does indeed have a magic eye, which seems strange as they were plugging the "Transistorised" angle. The mains transformer has three tappings, for the amp, magic eye heater and HT.

You would think of using a simple low voltage transformer and a VU meter, but I would guess that small cheap VU meters were not available at the time and they probably had large stocks of EM84s. It is an odd machine.

[Borderer]

A couple of photos showing the transistor locations. The large electrolytics are dated 1963 and the machine is 1966 at the earliest, and the one on the left is hanging in mid air so I doubt if they are original. The shielding/heat sink is heavy gauge brass and roughly soldered on, surely home made.

In the second photo, what is the flat rectangular orange/red/black component on top of the circuit board to the right and above the EM84? I assume some kind of resistor as it appears to have got hot.

[joebog1]

Thermistor

Joe

[Refugee]

It looks a bit too far away from the output transistors to be a thermistor.
The board also looks like it may be common to a battery model going by the added large capacitors.

[dazzlevision]

It’s a Mullard/Philips VA1077 thermistor.

[Heatercathodeshort]

Fidelity must have been experimenting with transistors.
The original "Playmaster" listed in Newnes 64/65 is an all valve model. Two versions are listed. A two track and a four track.
later 65/66 book shows the "Playmaster Major" a much more complicated model With EF86, ECC83, EL84, ECL86 and a transistor AC107 used in the audio preamp stage. A small meter is employed as level indicator. The rectifier is a metal EC1.
The model you have there appears to be quite rare. John.

[Welsh Anorak]

Unusual - I've onlly ever seen the valved model.
The blue Philips capcitors are of a type that don't often give trouble, so I'd agree the fault probably is in the output stage, though check the HT first.
Incidentally, I think those replacement electrolytics are much later then 1963, so I suspect that's not a date code.

[Borderer]

Originally Posted by dazzlevision

It’s a Mullard/Philips VA1077 thermistor.

Thank you, that is very useful and googling it has led me to some good information. I may even learn something! As said, it is a long way from the output transistors, so I wonder whether it does anything useful. But I take the view that manufacturers generally know more about the design than enthusiasts, so will not meddle with it unnecessarily.

[Ted Kendall]

Originally Posted by Heatercathodeshort

The model you have there appears to be quite rare.

This model was reviewed by Alec Tutchings in Tape Recorder around 1968. It appalled him - no attempt at equalisation, rattly plastic cabinet and so on. It was pretty much the last gasp of the Fideity/BSR machines, and soon disappeared.

[Borderer]

Originally Posted by Heatercathodeshort

Fidelity must have been experimenting with transistors.
The original "Playmaster" listed in Newnes 64/65 is an all valve model. Two versions are listed. A two track and a four track.
later 65/66 book shows the "Playmaster Major" a much more complicated model With EF86, ECC83, EL84, ECL86 and a transistor AC107 used in the audio preamp stage. A small meter is employed as level indicator. The rectifier is a metal EC1.
The model you have there appears to be quite rare. John.

John. I am not a Fidelity expert and have no special wish to become one, but these bits of history are always interesting.

As you say the original Playmaster was a valve model and there are several versions of this, and in fact I have an example in a later Braemar, which is cosmetically different and has a different silly name. The transistor version was introduced in 1966 and was more expensive but was withdrawn after a year or so.

It is said that this was due to a bad review in one of the magazines slating the sound quality, but I think this may be taken out of context. I suspect that both Playmasters sounded pretty average through their internal speakers and plastic cabinets, but the transistor model is the one that was tested. To the man in the street, there would be no point in paying extra for a transistor model which looked and sounded the same as the valve model, so it did not sell.

It will be interesting to hear what it sounds like in due course.

The Playmaster Major I think was a totally different design.

[david freeman]

I have the review of the Transistorised Playmaster from August 1966.
Alec Tutchings discovered no attempt at equalisation, an appalling acoustic response of 400 to 3000 Hz, and a combined record/replay response of around 200 to 4000Hz.
I have the original valved Playmaster which I’ve tested thoroughly, and discovered the frequency response of this model certainly goes up to 8000Hz, and recordings made on it from HiFi equipment sound as good as those from an Akai X150D at the same speed, when played via the monitor socket into the auxiliary input on the HiFi amplifier.
This suggests that the valve Playmaster was not too bad at all for a cheap recorder, but the Transistorised Playmaster was an exceedingly bad design which should never have been sold by Fidelity.

[Heatercathodeshort]

To be fair to Fidelity they were not the only company that struggled to produce transistor models at that time. This includes Radio, TV and radiograms by leading makers that had bad reliability records with thermal runaway and a performance that was much lower than their valve equivalents. Thankfully with the aid of the Japanese it got a lot better. John.

[AndiiT]

Hi, I have some advertising literature that mentions a four-track variant of the Playmaster Transistor however I have only ever seen two-track models.

I see a few folk have already mentioned the bad reviews that the machine received. I have a Playmaster transistor in my collection and brought it back to life by blanket replacement of all the electrolytics, most of them had dried out anyhow.

A very kind forum member sent me a copy of the user manual for the Playmaster transistor which includes a circuit description however no circuit diagram, which I suspect is non-existent. The closest I have seen to the output stage is the one for the Fidelity Playtime (or Playmatic, I can't recall which).

I have enclosed an attachment of the circuit description which may help with reverse engineering the circuit, if anyone does ever come up with a circuit diagram for the machine I would certainly be interested in seeing it.

Andrew

[Borderer]

Andrew,

Thank you for posting the description - very useful. My machine is a 2 track, although the pcb is drilled for the track switches. Would you by any chance like another one for your collection?

The low level of audio I am getting actually sounds quite reasonable, so I am curious to know what it will be like at volume.

From my limited knowledge and research I think the output stage is a fairly common design for the period, similar to the Dansette attached. I'm not sure I am capable of redrawing the whole thing but hopefully someone can.

From the way the description is written with reference numbers there must have been a schematic at some stage. it may yet turn up.

Playmatic was possibly transistorised, the Playtime had valves.

Tony.

[Refugee]

It can't be that different to a Mullard LP1162 on playback.
Obviously there is switching and the bias that would not be on an LP1162.

[Chris55000]

HK!

The nearest I can find that bears some relation to the "Playmaster 2–TR" and "Playmaster 4–TR", were used in Van Der Molen Transistorised Machines from 1967/1968, you can get a few Van Der Molen circuits from "Studio Sound" page of World Radio History, early 1967 issues!

The bias/erase oscillator is a Colpitts circuit that uses the erase head itself as the oscillator coil, this Mullard idea can be recognised by three capacitors in series across the erase head, one about 10n, another about 22n and one about 47n.

These three capacitors have a capacitive tap at each junction, one tap connects to the base of the "top" (AC128) oscillator transistor whilst the second tap down the capacitors connects to the mid–point of the complementary AC127/AC176 bias/erase osc. output stage, because the transistors are complementary, the circuit will work as an oscillator!

The amplifier circuit is one silicon BC107 used "upside down" with a positive–earth supply to provide a lower–noise first stage, followed by two PNP OC75 amplifier stages, then your playback volume control, followed by an AC128 driver and a complementary AC128/AC176 1W audio output pair.

A germanium diode and a small capacitor, about 0.01μ, rectifies and smooths the audio tap–off to the record head and feeds it to pin 1 of the EM87 as record level indication – the triode anode pin 9 connects directly to the control electrode pin 7, then the pair connect to pin 6, the target electrode, via a 100 k resistor. Pin 6 connects directly to the full secondary, about 170V a.c., of the mains transformer, the EM87 acts as it's own rectifier so the display will have a 50 Hz blur on it!

The low voltage L.T. will be tapped off about 15 V a.c., and bridge–rectified to provide a –20 V supply for the amplifier, and finally a separate 6.3V winding feeds the heater of the indicator valve!

Go to "Frank's Electron Tube Data", click on the "Much More!" Button in the top r.h. corner, go to "Manufacturers", then "Mullard" and search for "Book Of Tranistor Radio and Audio Circuits", download this 200 page pdf, and turn to the chapter on Tape Recorder Circuits, where you'll find circuit examples of what I've described above, but don't forget to mentally delete the Speed Change Equalisation Switching, as Fidelity didn't use any!

If you're still stuck, pm me and I'll send my email you can send me pics to, and I'll try and draw it for you!

Chris Williams

PS!

I've just checked "up top", & I'm thinking you'll find the "Playmaster TR8" or the "Playmaster TR9", both of which you can buy "up top" will meet your needs – I can see from the tiny preview that both of these use a 6.3V magic–eye level indicator directly fed off the mains transformer!