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Thread: Pye Mozart HF10 stereo pair

  1. #1
    Join Date: Mar 2015

    Location: Finland

    Posts: 153
    I'm Kai.

    Default Pye Mozart HF10 stereo pair

    I already made a thread about this when I first got it back in March or so, though at the time of purchase I mistook it for HFS20. It came in a small cabinet also housing a Garrard HF4 record player. What we have here is a pair of Pye Mozart HF10. The twist is the left one has stereo pots and switches with wires going to the 2nd unit, which obviously doesn't have any controls of it's own then. It seems this was a factory job, since the amp with the faceplate has "Stereophonic" engraved on it in place of the "High Fidelity" regular of regular HF10 faceplace. Also the 2nd unit has the chassis made smaller so there's no empty space where the pots would normally be. I've yet to build a proper case for it, they've been just strapped to this piece of wooden board. On the second photo the other unit is missing one of it's preamp valves since I was taking some measurements from the socket. A couple (bad) photos:






    At the top right on each unit you see an empty valve socket - that's for an EF88 for the phonostage, this is not normal and I'm not sure if it was a Pye Factory job, or made by whoever sold this console or a later modification by someone. The date code on the valves reads D0J which I assume would mean they were made by Valvo in Hamburg in October 1960. All the original capacitors and stock Mullard valves were dated 1958, so I'm assuming this was made then and the EF88 is a later addition by someone or the company who made the cabin and bundled it all together.

    Never seen anything like this trying to dig up information on these old Pye Mozart series amps, I suppose if Pye made more like this it didn't made a whole lot, seems like it could maybe be a 'transitional' stereo setup before HFS20 was introduced. Anyone seen anything like this before? I guess I should try some forum specializing on old British valve stuff

    I've recapped them, changed all paper caps and electrolytics, replacing the smaller ones with film caps and Nichicons for the big cans. Hum was reduced and the sound cleared up, with the 60 year old stock caps the treble was a bit rolled off. Surprisingly all the changed caps still measured within spec at the small test voltage at least, but don't know how they'd behave with the high voltages they see in actual use.

    Sound is awesome to my ears, very full without getting overly warm and fuzzy and both frequency extremes are surprisingly good as well. Would like to try out some a bit more efficient speakers, I've been driving a pair of Kef 104aB and JBL 120Ti, both of which are rather ineffecient. Sounds great but don't get very loud. The Kefs are not that great at high volumes anyway, though I never realized that before I got the JBLs. Stereo imaging
    with the PYE is not the greatest, I mean not that it's horribad or anything, it's very stable but it's more a "broad brush" version as opposed to pinpoint etching. Still it has become my go to amp for most listening. Competition has been some better 80s japanese amps.

  2. #2
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 3,501
    I'm Alan.

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    Wow. Thanks for posting the details and photos.

  3. #3
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,242
    I'm Jez.

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    A strange find there.... I've renovated a few of the stereo version (pre amp and stereo power amp) but never seen that set up you have. I was pleasantly surprised by the power amp. I was expecting it to be awful but indeed it sounds pretty good and surprisingly modern. A very unusual and intriguing design, it uses an EL34 pentode single ended with cathode windings as well as anode and loads of feedback.

    If you are not already doing so I would use it as a power amp only to get the best results from it.
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  4. #4
    Join Date: Jan 2009

    Location: Essex

    Posts: 15,480
    I'm openingabottleofwine.

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    Quote Originally Posted by Arkless Electronics View Post
    A strange find there.... I've renovated a few of the stereo version (pre amp and stereo power amp) but never seen that set up you have. I was pleasantly surprised by the power amp. I was expecting it to be awful but indeed it sounds pretty good and surprisingly modern. A very unusual and intriguing design, it uses an EL34 pentode single ended with cathode windings as well as anode and loads of feedback.

    If you are not already doing so I would use it as a power amp only to get the best results from it.
    http://www.valve-radio.co.uk/literat...ervice-manual/

    Have you listened to this month's choice in the Album Club?

    Barry

  5. #5
    Join Date: Mar 2015

    Location: Finland

    Posts: 153
    I'm Kai.

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    I've been currently using the Pye from the tape-outs of an 80s Yamaha A-700 (with an upgraded phonostage), so the signal goes through the preamp. Power-amp inputs are in the plans, kind of waiting for putting together the enclosure which will be a good opportunity to do other work as well. With some tweaking of the bass & treble knobs the preamp gives a reasonably even response, but I can certainly imagine it being a weak link. The tone control section has the paper caps replaced, but the ceramics are still originals. I'll be changing those as well at some point.

    I'm wondering if I should just do a complete rebuild, I measured some of the resistors and they were nothing close to modern tolerances, some of the values were pretty far from spec, but on the other hand they were same for both units so I guess there was at least some effort to match the channels. Modern resistors would surely sound different though. Also the rectifiers are still the original selenium ones, I've read those to be pretty unreliable. I've got modern bridges waiting but I like listening to my kit more than working on it, so haven't got around to it.

  6. #6
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,242
    I'm Jez.

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    Quote Originally Posted by helma View Post
    I've been currently using the Pye from the tape-outs of an 80s Yamaha A-700 (with an upgraded phonostage), so the signal goes through the preamp. Power-amp inputs are in the plans, kind of waiting for putting together the enclosure which will be a good opportunity to do other work as well. With some tweaking of the bass & treble knobs the preamp gives a reasonably even response, but I can certainly imagine it being a weak link. The tone control section has the paper caps replaced, but the ceramics are still originals. I'll be changing those as well at some point.

    I'm wondering if I should just do a complete rebuild, I measured some of the resistors and they were nothing close to modern tolerances, some of the values were pretty far from spec, but on the other hand they were same for both units so I guess there was at least some effort to match the channels. Modern resistors would surely sound different though. Also the rectifiers are still the original selenium ones, I've read those to be pretty unreliable. I've got modern bridges waiting but I like listening to my kit more than working on it, so haven't got around to it.
    The resistors will have drifted by roughly the same amount rather than been chosen to match!! Almost always high. I don't really buy into resistors sounding different to any great extent personally. I replaced the selenium rectifiers in ones I've renovated but be careful to add extra series resistance as silicon rectifiers will result in considerably higher output voltage.
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

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