Pye Black Box - the versions thread.

[suebutcher]

Thanks for the scans. I assume that the stereo Black Box announced in September 1959 was the G63.

[Edward Huggins]

Nostalgic to see these clips. The WW 1954 shows avery early example fitted with the BSR UA4, BSR's first autochanger. They we already established with the Margolins (Dansette) and then came a knocking at our door. The reference to the G63 will be for a very early batch made for the 1959 Radio Show.

[Synchrodyne]

What kind of audio output circuitry was used in the G63 stereo Black Box? I’d guess that it used a conventional U-L circuit, but did it also include the mixed positive and negative feedback that was used in the earlier PCL83-based model?

The original Black Box had triode-strapped push-pull EL42 output pentodes, which was in keeping with its time. That was just before the Blumlein ultra-linear (UL) connection had made inroads into the UK hi-fi amplifier scene, and triode-strapped pentodes (and tetrodes) were the norm. One could infer that Pye wanted to align the Black Box with established hi-fi practice rather than with radio receiver practice, where push-pull pentodes were deemed to be acceptable (as in the PE80 and FenMan II). But the use of a power amplifier feedback loop for tone control was more in line with radio than hi-fi practice, probably unavoidable absent a more complex control section.

The subsequent change in the Mark II model from triode-strapped to UL-connected EL42 pentodes was logical and followed the general migration of hi-fi amplifiers to this form.

The addition of mixed feedback to the PCL83 version was evidently a manifestation of Pye’s love affair with this idea. As best I can determine, Pye first used it on its PF91 hi-fi amplifier, which had triode-strapped KT66s. It was then carried over to the HF25 (U-L KT66s), the HF5/8 (pentode-connected EL90s) and the Mozart HF10 (SEUL EL34). In all cases the feedback ratio was variable to allow best damping of the connected speakers. But in the case of the PCL83 Black Box, where the speaker was predetermined and not a variable, the ratio was fixed. The continued use of a tone control feedback loop around the main amplifier made the overall layout quite complex-looking.

I don’t know which came first, the Mozart HF10 or the Super Black Box, but it seems likely that the SEUL EL34 output stage of the latter was essentially the same as that for the HF10, using partial cathode loading. I’ve seen it said that the Pye designer of the Mozart circuit had previously worked at Quad, so would have been familiar with PJW’s 1945 partial cathode loading circuit. But whereas the HF10 had the variable mixed feedback circuit, it appeared to have been abandoned for the later stereo version, the HFS20. Possibly Pye had followed the same pathway with the G63 Black Box.


Cheers,

[ukcol]

Originally Posted by Synchrodyne

What kind of audio output circuitry was used in the G63 stereo Black Box? I’d guess that it used a conventional U-L circuit, but did it also include the mixed positive and negative feedback that was used in the earlier PCL83-based model?

The G63 used ECL82s in UL push-pull in each channel. There was a single (negative) feedback path from the secondary of the output transformer to the cathode circuit of one of the ECL82 triodes.

See snippet below.

[suebutcher]

The bass and treble tone controls of the G63 were passive variable RC networks between the ECC83 input triodes and the ECC82 driver triodes. They work reasonably well, but it's hard to get a bass and treble boost at the same time. The interaction between them takes getting used to.

[Synchrodyne]

Thanks Colin and Sue. So Pye went for simplicity with the G63, no positive feedback and no tone control feedback loop. I wonder if whoever in Pye who was behind the positive feedback idea had moved on or retired by the late 1950s.

Passive tone controls probably saved a valve stage. A Baxandall tone control needed its own valve stage, and preferably another valve stage ahead of it to drive it at a fixed and appropriate impedance. So typically, a Baxandall required a double triode, whereas a passive could get by with a single triode. The passive form did have some adherents at the time. For example, Armstrong used the Voigt 1940 circuit well into the 1960s. I suppose that there might have been some renewed interest at about the time that passive RIAA equalization came into vogue. In that connection one sees mention of “passive Baxandall” networks, which is odd, because as best I can determine, Baxandall never published or mentioned such, although he did mention the Voigt network.


Cheers,

[wd40addict]

I suspect someone at Pye kept a careful eye on what was happening in the USA: The Black Box cabinet concept is a direct copy of the Columbia 360 and variable damping was de rigueur on US Hi-Fi power amps. the latter never really caught on in Britain.

[Edward Huggins]

Originally Posted by Synchrodyne

I don’t know which came first, the Mozart HF10 or the Super Black Box, but it seems likely that the SEUL EL34 output stage of the latter was essentially the same as that for the HF10, using partial cathode loading. I’ve seen it said that the Pye designer of the Mozart circuit had previously worked at Quad, so would have been familiar with PJW’s 1945 partial cathode loading circuit. But whereas the HF10 had the variable mixed feedback circuit, it appeared to have been abandoned for the later stereo version, the HFS20. Possibly Pye had followed the same pathway with the G63 Black Box.

The Mozart HF10 and the Super Black Box were basically developed in tandem during 1956. Be aware, they were aimed at 2 different types of user of course. The Super BB had a short production run, it was quite expensive at the time for a "single boxed record player" when the standard Black Box was available as a far cheaper option. By the time of the G63 development, the design team had, er, simplified and the 2 x PCL83 Black Box was the last in a fairly long line of quite exotic circuits. By comparison, the G63 circuit was very conventional, other than in it's use of UL loading.

[Synchrodyne]

Thanks Edward. Well, at least Pye retained UL loading for the G63, so the simplification did go too far. (Maybe the “bean counters” didn’t know enough to ask as to what cost savings deletion of UL would produce, and the engineers did not volunteer that option.) Design crossover between separate market segments, as with the Mozart and Super BB, had also occurred previously, in that the HFT111 hi-fi tuner used the FenMan II RF section virtually unchanged.

Was the PCL83 BB (mono) retained for any time after the G63 was released, or was the G63 a direct replacement?

Variable damping was definitely a US fad, for example mentioned on several occasions in “Audio” magazine in the first half of the 1950s. Crowhurst wrote was essentially a “debunking” article in Radio-Electronics for 1955 November. It was mentioned here and there in the British literature. Hi-Fi Yearbook 1956 had a brief note, pointing to that Crowhurst article. Molloy (in “High Fidelity Sound Reproduction” of 1958) noted that in the UK, it was used by Pye, Pamphonic and RCA. And Pannett (in “High Fidelity Pocket Book” of 1962) provided some circuit details. Another American idea, in this case from the early stereo era and used for cost reduction was the orthogonal amplifier, taken up in the UK by Murphy (and I think others). Evidently, despite its interest in things American, Pye was not tempted into this digression.


Cheers,

[Edward Huggins]

Was the PCL83 BB (mono) retained for any time after the G63 was released, or was the G63 a direct replacement?

The PCL83 BB ran up to about 1961 - I think some of the last of the production used the Garrard "Autoslim" autochanger after the more expensive Garrard 209 unit. The G63 remained in production and then in mid 1963 the Pye 1004 was introduced using in-house Newmarket transistors and the then new BSR UA15 autochanger.

[dazzlevision]

I have just acquired another Pye Black Box service sheet and it has the Mark 2 ultalinear EL42 output circuit, but the cartridges fitted are different to the Mark 2 sheet that I have already listed earlier in this thread:

Black Box (The), sheet, 708004 undated

Covers “all models” (for operation on 100-110V or 200-250V, 50c/s)
ECC83, EL42 x2, EZ41
Two ganged tracks (no taps) on volume control
Single Tone control
Primary taps on the output transformer to feed EL42 screen grids
Two identical 6.5” full range speakers fitted
Four speed auto or single play record deck fitted, with Cosmocord HGP37/IC crystal cartridge or Sonotone ceramic 99/80/SC cartridge (for tropical use only).
Black or brown cabinets available.

[Station X]

One post moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=141728

[suebutcher]

What was the difference exactly between the Stereophonic BB G63 and the Stereophonic BB G63E? I know the front name plate was different on the G63E, and the G63E only used the AT6 turntables, but how about the amplifier? I haven't been able to find a G63E circuit diagram to compare it to the G63.

[Synchrodyne]

Somehow, I’d expect the G63E to be an export version of the G63. But as far as I know the G63 had tappings on its power transformer covering 110 through 250 volts, so a special export version would not appear to have been necessary (except in respect of the turntable, for 60 Hz areas.) So that torpedoes the export idea.

The G63/T was the G63 with the HFT113 FM-AM tuner fitted. That tuner was in a “Mozart” box, like the HFT108 FM-only tuner, but I am not sure that the Mozart moniker was ever applied to it. The HFT113 circuitry looked to be something of a hybrid, with an ECC85 single valve front end (like the FenMan I, although different in detail, and with diode-operated AFC) and an AM front end/FM-AM IF strip somewhat like an updated version of that in the FenMan II/HFT111, albeit with a ratio detector rather than a Foster-Seeley discriminator.

With the G63 tone controls, it looks as if Pye opted for both simplicity and avoiding having tone controls in the main amplifier feedback loop. The latter was generally avoided in true hi-fi practice, where the “design budget” allowed for a separate control section ahead of the power amplifier and its associated feedback loop, but was probably hard to avoid in lower-level equipment where valve count, space and heat buildup were all potential limiting factors. Perhaps Pye’s experience in the earlier BB units with tone controls in the main feedback loop indicated that a change away from this practice was preferable?

The tone controls look to be simpler than the Voigt type, which one might take as a de facto reference point for passive circuits. Maybe Pye was aiming for a lower loss than the nominal 14 dB for the Voigt circuit, in order to avoid the need for additional AF voltage gain. (An additional ECC83, say, might have “broken the budget”.) This could have limited the amount of bass and treble lift available.




Cheers,

[suebutcher]

That's probably right. My ears tell me that the G63 tone controls just roll off bass or treble, there's no obvious boost.

Anyway, if someone has a lead on the circuit diagram for the G63E, let me know. I want to tell Radiomuseum that they've mixed up the G63 and the G63E on their G63 model page, but I need to be sure of my facts.

[dalgwcobl]

To complete the model list, the last models labelled 'Pye Black Box' were not of Philips origin, but designed and built for Pye by Dynatron at King's Lynn. They were three-box music centre designs, starting with, from memory, model 1600, through 1601, 1605 and 1606. The differences were mainly to the cassette tape deck fitted (the 1605 and 1606 had Dolby B noise reduction) and the record deck - all were, I think, BSR single players. The 1600, 1601 and 1605 had similar main mouldings to which everything was assembled. The 1606 had a quite different main moulding with a less fussy design; this moulding was also used for numerous versions produced for Philips as the AH939-15, including some export brands, and Boots the Chemist.
The three-waveband AM-FM tuner and amplifier were in-house designs by Dynatron, with 10 watts RMS per channel output. The speakers were 6.5" drivers in fairly flimsy boxes. Dynatron used the later moulding, with an additional pre-amp PCB for magnetic cartridge input, in a 'budget' SRX32 range in period style cabinets. Much to Pye's disgust, the same speaker drive units sounded vastly better in decent period cabinets. I have model numbers and service data somewhere if anyone is interested.

[dalgwcobl]

Incidentally, we were much amused by a Which? test report on music centres, which included the Pye 1606, Philips and Boots models - all identical except for cosmetic changes.
According the Which?, they were of different sizes, had different features - and the Boots was the best buy!
I never trusted Which? after that.