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Old 16th Mar 2018, 8:21 pm   #1
rontech
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Default Pye Mozart mono FM tuner.

I own a Pye Mozart mono FM tuner. I purchased myself new in 1959 and eventually sold it to a friend in about 1964. I was chatting with him recently (Oct 2017) and he said he found it in his loft and would I like it back.

I have cleaned out all the dust and have now replaced the two power supply HT electrolytics. On powering it up; all the valve filaments and pilot bulbs lit up and the correct DC voltages are present at the transformer and output point of the electrolytics.

I have no suitable aerial to hand and am loath to connect the audio o/p to a solidstate preamp in case of high voltage transients. There is a circuit diagram and service leaflet available on line. Can give you the link if it helps.
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Old 16th Mar 2018, 8:25 pm   #2
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Default Re: Pye Mozart mono FM tuner.

What exactly is your query?
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Old 16th Mar 2018, 9:07 pm   #3
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Default Re: Pye Mozart mono FM tuner.

Here possibly: http://www.valve-radio.co.uk/literat...ervice-manual/
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Old 16th Mar 2018, 9:24 pm   #4
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Default Re: Pye Mozart mono FM tuner.

Interesting circuit, presume it is one of the earlier FM tuners.
Pentode RF amp EF80
Pentode mixer/osc with the triode for AFC. ECF80
IF amp EF89
IF amp and limiter EF80
Limiter EF80
Foster Seely discriminator.

Presume the two limiter stages are due to using the Foster Seely discriminator.
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Old 16th Mar 2018, 10:48 pm   #5
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Default Re: Pye Mozart mono FM tuner.

Quote:
Originally Posted by Station X View Post
What exactly is your query?
Perhaps an educated opinion on the advisability or otherwise of connecting it to a solid state amplifier?

Provided C25 (0.5uF) isn't leaky there should be no problem for the amplifier.
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Old 16th Mar 2018, 11:13 pm   #6
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Default Re: Pye Mozart mono FM tuner.

The aerial shouldn’t be a problem, a piece of coax split to form a dipole should be enough to get BBC Radio 2 on 88.6 from a Winter Hill only few miles from Southport, the much more powerful signal from Holne Moss on 89.3 should also be received. Radio Merseyside is not far from you on 95.8.
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Old 16th Mar 2018, 11:19 pm   #7
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Default Re: Pye Mozart mono FM tuner.

Quote:
Originally Posted by Nuvistor View Post
Interesting circuit, presume it is one of the earlier FM tuners.
Pentode RF amp EF80
Pentode mixer/osc with the triode for AFC. ECF80
IF amp EF89
IF amp and limiter EF80
Limiter EF80
Foster Seely discriminator.
Well, it certainly is, how can you not know this....?
It borrows much from the Pye Fenman II. Probably better in some ways than the well regarded Tripletone Mono tuner of the same period - all EF80s and an ECC83 cathode follower output.
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Old 17th Mar 2018, 7:51 am   #8
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Default Re: Pye Mozart mono FM tuner.

The blocking capacitor looks like .05uF to me on the diagram.

As Chris says, unless that has gone leaky there shouldn't be any damaging voltages coming out of that Foster-Seeley discriminator.

David
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Old 17th Mar 2018, 9:57 am   #9
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Default Re: Pye Mozart mono FM tuner.

Positive voltage feed to the grid of the last IF, not seen that before....

Lawrence.
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Old 17th Mar 2018, 10:05 am   #10
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Default Re: Pye Mozart mono FM tuner.

Presume it is to make sure it hard limits the FM envelope, the Foster Seely does not limit like a ratio detector.
Apology Lawrence if you already know this.
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Old 17th Mar 2018, 10:49 am   #11
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Default Re: Pye Mozart mono FM tuner.

Thanks for all the information!
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Old 17th Mar 2018, 11:37 pm   #12
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Default Re: Pye Mozart mono FM tuner.

The use and benefit of positive grid bias for FM limiters was discussed by Tibbs and Johnstone:

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Interestingly, Pye used it in the Mozart HFT108, but had not used it in the preceding HFT111/FenMan II. Neither did it use it in the later HFT113 FM/AM tuner. Both of those models had FM limiter stages quite separate from any of the AM circuitry, so it could have bene done without prejudice to the AM side. Unusually the HFT113 used an EF184 as the limiter valve.

Positive bias on the limiter grid was used by Jason on its FMT3 and FMT4 FM tuners. In the FMT4 case, the AGC bias for the 1st FM amplifier came from the limiter grid (via a divider), so the positive standing bias would seem to have provided some delay. Jason also used positive limiter grid bias on its JTV2, but had not used it on the preceding JTV. In both cases the limiter grid (or rather the diode formed by the limiter grid and cathode) was also the AM demodulator and the source of AGC bias.


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Old 17th Mar 2018, 11:51 pm   #13
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Default Re: Pye Mozart mono FM tuner.

Quote:
Originally Posted by Radio Wrangler View Post
The blocking capacitor looks like .05uF to me on the diagram.

As Chris says, unless that has gone leaky there shouldn't be any damaging voltages coming out of that Foster-Seeley discriminator.

David
If it's only 0.05uF, bass might be a bit thin if the solid state amp input impedance is much under 100k.
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Old 18th Mar 2018, 12:35 am   #14
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Default Re: Pye Mozart mono FM tuner.

Yes, it was intended for feeding load impedances of not less than 100k:

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The output level, 100 mV at 30% modulation, might be a bit low for more modern amplifiers, which might expect to see something like 300 mV at 30% modulation. But the output level could be adjusted:

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Old 18th Mar 2018, 9:49 am   #15
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Default Re: Pye Mozart mono FM tuner.

Generally speaking, I remember being taught that a good match is/was achieved by 'low into high by a factor of 10'. In the case of the Mozart, this would imply that, ideally it should be connected to an amplifier having an input Z of 250k, which would probably be true of many valve amplifiers, but not of solid state ones.
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Old 18th Mar 2018, 10:25 am   #16
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Default Re: Pye Mozart mono FM tuner.

Yes that was my understanding. At present I do not have a valve pre amp. I think the best thing would be to build a simple EF86 - ECC83 gain stage / cathode follower. The amps I have in my "den" are QUAD 303 and 606. Just using a passive pre amp for the time being.
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Old 18th Mar 2018, 10:32 am   #17
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Default Re: Pye Mozart mono FM tuner.

Quote:
Originally Posted by Herald1360 View Post
If it's only 0.05uF, bass might be a bit thin if the solid state amp input impedance is much under 100k.
There's a speck on the scanned image dead centre, right in front of the zero, and there's a dot between the zero and the five which is all a little out of focus. With the value of the load, half a microfarad seems more sensible.

David
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Old 18th Mar 2018, 10:40 am   #18
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Default Re: Pye Mozart mono FM tuner.

This is quite an early FM tuner and its choice of RF valves were soon upstaged for use at 100MHz, and self-oscillating mixers were dropped. It's also mono.

Don't spend too much effort on it until you've tried it out and decided whether you like it or not. It's vintage, it's valved, and the Mozart amplifiers fetch a lot of money at auction, but that doesn't guarantee it will satisfy you. It may be exactly what you want but it would be irritating to spend effort building a preamp before finding otherwise.

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Old 18th Mar 2018, 11:17 pm   #19
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Default Re: Pye Mozart mono FM tuner.

As an alternative to building a valve preamplifier/buffer, perhaps find a Quad 33 or 34 control unit? The "Radio" inputs on these are 100 mV, 100k, and so pretty much an exact match for the output loading requirements of the Mozart FM tuner (as stated by Pye). In selecting 100 mV at 30% modulation as the Mozart tuner output level, Pye had followed the Quad norm of 1953. (So did others – the Armstrong 600 series tuners had a “low” output of 100 mV at 30% modulation as well as a “high” output of 775 mV at 100% modulation.)

Quote:
Originally Posted by Radio Wrangler View Post
…and self-oscillating mixers were dropped.
I’m not sure if the data would support the notion of a general trend away from self-oscillating mixers in FM tuners during the valve era. But that is getting off-topic. In the Pye case, the trend was the other way. The HFT111 (c.1955) had used an ECF80 with the pentode as mixer and the triode as oscillator. The Mozart HFT108 (c.1958 or 1959) used the pentode as a self-oscillating mixer and the triode as an AFC reactance valve. I suspect that the desire to include AFC without increasing the valve count led to the compromise of using a self-oscillating mixer in order to free up the triode. Then the HFT113 (c.1961-62) had an “industry standard” ECC85 single-valve front end, with one of the triodes as a self-oscillating mixer. (AFC was done by a crystal diode.) The ECC85 single-valve front end had been used in the FenMan I radio receiver of 1955, whereas the higher-positioned FenMan II of the same year had the same RF circuitry as the HFT111.


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Old 19th Mar 2018, 9:46 am   #20
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Default Re: Pye Mozart mono FM tuner.

I built a FET buffer for the multiplex output of an FM tuner. Powered by voltage doubler on the 6.3V supply, it was small and required minimal rewiring.

Somewhere I have one of these tuners picked up from a car boot. I got an output from it after replacing the selenium rectifier and discriminator electrolytic and kept it only for it's bizarre looks. From what I remember they are small and packed pretty tight.
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