17th Jan 2022, 7:17 pm | #61 |
Tetrode
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Re: Fidelity transistorised Playmaster - reverse engineering?
I suppose the extraordinary decision not to include any equalisation circuitry (see post #15) would explain a lot of the shortcomings. The other thing that doesn't seem to have been investigated so far on this thread is the record-head bias. Inadequacy there would also explain the symptoms. I wonder if the OP has tried playing a decent tape recorded on another, working machine...
Mike[/QUOTE] For what it's worth my "reference tape" for this has been an EMI World Record Club issue - Beethoven's 3rd to be precise - which I think would be optimised for domestic machines, and it sounds fine on both my Telefunken and Ferrograph. I had thought about the heads but hadn't really got that far - were they the same as on the valve version and was the wrong type used in error, that sort of thing, but it is all speculation. It is a single speed machine unlike some of those mentioned earlier in the thread so you would expect the EQ to be set accordingly. Sadly I do not have the equipment or skills to test this properly. |
17th Jan 2022, 7:32 pm | #62 |
Dekatron
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Re: Fidelity transistorised Playmaster - reverse engineering?
Fair comment, I think - without recording from radio or disc there was no easy supply of subject matter beyond Grandma's burblings, and tape, of course, was quite expensive. A lot of surviving recordings tend to be either Top 20 or toe-curling family gatherings. There are, of course, the minority of collections made in pursuit of an interest - these are almost all from secondary sources but none the less valuable for that. Most of these were made on more up-market machinery, though.
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17th Jan 2022, 7:43 pm | #63 |
Octode
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Re: Fidelity transistorised Playmaster - reverse engineering?
"For what it's worth my "reference tape" for this has been an EMI World Record Club issue - Beethoven's 3rd to be precise - which I think would be optimised for domestic machines, and it sounds fine on both my Telefunken and Ferrograph."
OK, so the record-head bias doesn't come into it (it's an issue only when making a recording, and wouldn't affect pre-recorded tapes)) "It is a single speed machine unlike some of those mentioned earlier in the thread so you would expect the EQ to be set accordingly." I was going by the Alec Tutchings review, which apparently says there's no equalisation at all (even a single-speed deck would need equalisation circuitry). That would certainly affect playback quite badly, but perhaps wouldn't on its own be enough to explain the very bad quality you're getting. Mike |
17th Jan 2022, 8:10 pm | #64 |
Hexode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Alec Tutchings review states that there was little evidence of playback equalisation of any kind, the accompanying test tape playback curve showing around 200-4000hz +/- 6dB ; then shows a combined record/replay curve taken via the radio input of around 200-3000hz +/- 6dB. Last edited by david freeman; 17th Jan 2022 at 8:24 pm. |
21st Jan 2022, 11:48 pm | #65 |
Nonode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Hi!
Could the OP please identify the values I've marked on the two pictures shown on the attached plan please ? The two capacitors are the Mullard "mustard" and the red one marked with arrows on the first picture, the second is the anode resistor between pins 6 and 7 of the EM87 valveholder - it's usually 100k but something different might hsve been fitted in this case! Removing the valve and measuring between 6 & 7 with a DVM is all that's needed - it is NOT necessary to disturb the valveholder! Chris Williams
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22nd Jan 2022, 1:23 am | #66 |
Nonode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Morning Tony!
Circuit Diagram now well under way! Could I also have the value of the large blue Daly electrolytic used as the reservoir capacitor mounted at the right hand side of the panel in your third pic from the first post please? Chris Williams
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22nd Jan 2022, 7:19 am | #67 |
Tetrode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Morning Chris,
Good to hear of the progress - I will PM you. Tony |
22nd Jan 2022, 9:55 am | #68 |
Hexode
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Re: Fidelity transistorised Playmaster - reverse engineering?
I’m really excited to learn the outcome of this! Over the years I’ve even thought of purchasing a decent Transistorised Playmaster in order to see and hear for myself if it was as dreadful as Alec Tutchings review stated.
Unfortunately, they are as rare as hens’ teeth. |
25th Jan 2022, 2:21 pm | #69 |
Tetrode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Apart from the technical aspects it would be very interesting to know what was going on with Fidelity's management that allowed the machine into production in the first place. There is probably no-one around now who would know.
It must have been signed off somehow without proper testing, but even then you would have thought that someone in Marketing would have listened to it critically and called it out. It also seems odd that it wasn't styled differently from the valve version, to capitalize on the "new" technology. A different colour for the plastic case would have done. Then again, looking at the advertisement posted earlier, they explain how you can mute the internal speaker with a plug and a resistor, then go on to say how the controls have been simplified for convenience - well, yes, but surely a muting switch would have cost nothing in production and been a much better selling point? It all seems a bit half-hearted, as if they really couldn't be bothered. If, as we suspect, the circuit is a relatively easy fix, then it is surprising that Fidelity didn't revise it and use it in future models. They reverted to valves for the cheaper machines although they did use a different transistor circuit in the more up-market Studio TR18. |
25th Jan 2022, 9:53 pm | #70 |
Hexode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Yes, and the Studio had switched equalisation for each speed!
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29th Jan 2022, 7:53 pm | #71 |
Nonode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Hi!
Circuit Diagram ⅔ completed, and no, I haven't found any obvious playback or record equalisation in the amplifier circuits either! (Two little yukky–looking cylindrical yellow sleeved components which I first thought were small inductors turned out to be a particularly grotty type of electrolytic capacitor, one was 25 μ @ 25 V, the other was 2 μ @ 12 V, which was C9 in series with the signal to the base of emitter–follower TR3!) Diagrams should be ready to post tomorrow or Monday, hopefully! Chris Williams
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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; 29th Jan 2022 at 8:01 pm. |
30th Jan 2022, 3:55 am | #72 |
Nonode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Hi!
By the way, I should mention that the board I received had no transistors fitted apart from the BC107 1st preamplifier TR1 and the heat–sink for the o/p transistors TR5 and TR6 was also missing, but I can still work out what went where! The circuit description posted mentions a preset used to set the quiescent current of the output transistors, but I can find no trace of one on the board I got, also there's no sign of one on the OP Tony's board either – I think there was simply a fixed resistor across the VA1077 bias stabillising thermistor, with possibly a series one as well – I'll double check when I get back to my diagram later today & Monday! Chris Williams
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31st Jan 2022, 12:36 am | #73 | |
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Re: Fidelity transistorised Playmaster - reverse engineering?
Quote:
...Sorry, I'll get my coat.
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31st Jan 2022, 8:30 pm | #74 |
Hexode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Olaf indeed! Only a Fidelity afficionado will appreciate your comment!
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1st Feb 2022, 11:46 am | #75 |
Dekatron
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Re: Fidelity transistorised Playmaster - reverse engineering?
Er... please put us out of our misery!
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1st Feb 2022, 12:04 pm | #76 |
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Re: Fidelity transistorised Playmaster - reverse engineering?
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1st Feb 2022, 1:07 pm | #77 |
Dekatron
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Re: Fidelity transistorised Playmaster - reverse engineering?
Is the 67/68 above, the 1967/1968 year reference in Post 14 of the linked Thread above, that Post says the Fidelity factory was at Olaf Street but still unclear as to what the olaf reference in Post 73 of this Thread actually means ?
David |
1st Feb 2022, 1:21 pm | #78 |
Tetrode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Glad it's not just me, then.
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1st Feb 2022, 1:26 pm | #79 |
Tetrode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Olaf = a laugh, perhaps. It's what they call a pun, innit?
Perhaps we take all this a bit too seriously! |
7th Feb 2022, 11:43 pm | #80 |
Nonode
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Re: Fidelity transistorised Playmaster - reverse engineering?
Hi!
Unfortunately the central heating at our place broke down a week ago and with temperatures in the front room where I do my circuit diagram work down to 3–4°C (37–39°F!) it's simply too cold to sit in there for more than a few minutes at a time, so I've had to pause this project until we can get the heating working at home again ! My apologies everyone ! Chris Williams
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