Pye HFT111

[Radio Tech]

Well folks I eventually got hold of this FM - AM Tuner minus the cabinet but what a state it was in. According to the previous owner he said it had been found in a garage, it just looked like as if a bale of straw had fell on it, still never mind.

The underside all original and not been tampered with but I fear the main smoothy will have to be renewed and the waxies, the knobs I managed to get two off but there is one stuck on the band change switch, tried drilling the grub screws but no such luck so looks like brute force, I may even find some replacement knobs. The top side had a EF80 broken.

The panel behind the dial will have to be re painted and drive cord replaced. Should keep me out of mischief for bit. More on this later with some pics.

Ken

[Radio Tech]

Hi Folks

Here are some photos of the instrument,

Ken

[cathoderay57]

Hi Ken, that's an interesting circuit. It uses a lot more valves than more economical AM/FM circuits (e.g. Bush, Grundig). I reckon Pye must have run out of chassis space for an EL84 so they produced it as a tuner! They seem to like using EF80s in the FM front end (as per the Fenman). I bet you will have some fun if you need to realign it. Maybe it's time to build the wobbulator.... Best of luck, Jerry

[Radio Tech]

Hi Jerry

The fun has started with this tuner, Pye did not make it easy to re-thread the tuning drive cord, have you or anyone else had to re-thread or replace the cord on one of these sets and the fact of getting some cord the correct thickness.

Best wishes

Ken

[cathoderay57]

Sorry Ken, I've never tackled one of these sets. My comment resulted from a cursory look at the service sheet. I'd recommend fishing line - it's readily available on-line and comes in different diameters, solid core as well as stranded. Hope you don't need to open a swear box..... Cheers, Jerry

[Synchrodyne]

Originally Posted by cathoderay57

Hi Ken, that's an interesting circuit. It uses a lot more valves than more economical AM/FM circuits (e.g. Bush, Grundig). I reckon Pye must have run out of chassis space for an EL84 so they produced it as a tuner! They seem to like using EF80s in the FM front end (as per the Fenman).

I suspect that Pye started out with the idea of a common RF-side design for both the FenMan II and a hi-fi tuner, the latter to both complement its HF25 amplifier system and to be sold as an independent unit. The FenMan II was released in 1955 May. The HFT111 was noted in Wireless World 1955 October, so was probably released not long after the FenMan II.

Pye had covered the more parsimonious end of the FM-AM receiver market with the FenMan I, which had standard circuitry (although to its credit Pye did retain delayed AGC for the AM side (using a crystal diode), something that was often dropped in the then-new FM-AM era. (Although arguably, as AM might then be used for the reception of more distant stations, something better than the hitherto standard AM circuitry was desirable.) Thus it was free to endow the FenMan II and the HFT111 with quite elaborate circuitry, including, on the FM side, a three-gang front end, a three-stage IF strip, and a Foster-Seeley discriminator (lower distortion than a ratio detector of similar bandwidth). Pye’s use of variable inductance tuning might have been a purely technical choice, but also it might have come about because three-gang FM tuning capacitors from UK suppliers were probably scarce in 1955.

In the HFT111, there was no need for ECH81 triode to double as an AF amplifier on AM and gram, nor for EABC80 triode to be used as an AF amplifier, so it was instead used as the AM AGC diode, a function of one diode of the EBC41 in the FenMan II, but not required in the HFT111.

From the high point of the FenMan II and HFT111, the general direction appeared to be downhill. The Pye Mozart HFT108 FM-only tuner had a two-gang capacitor-tuned front end. It added AFC, but this took the ECF80 triode, so that an autodyne mixer was used. The three-stage IF strip was retained, as was the Foster-Seeley discriminator, now with crystal diodes. The later Pye HTF113 FM-AM tuner had an ECC85-based FM front end, two-gang but with a return to inductance tuning, maybe a third-party unit. The FM IF strip was still three-stage, but with a ratio detector. An interesting point was that the FM limiter was an EF184. Just possibly, Pye wanted better limiting to allow the use of a wider bandwidth ratio detector, for lower distortion. I haven’t seen the circuit for the FM-only HFT109, but judging by the valve line-up, it was the HFT113 minus the AM side, and with an EF89 in place of the ECH81.

Returning to the HFT111, I think that on FM, it would have compared fairly well with other higher performance tuners that were available in the UK in 1955. On AM, with a single bandwidth, it would have been at a disadvantage to the variable bandwidth tuners then available. It was described as having “wide band I.F. coupling”, but my interpretation of that is that the IF bandwidth was wider than customary for domestic receivers, say around 5 to 6 kHz in AF terms, probably about as far as one could go in a single-selectivity receiver, but not in the true wideband class. True wideband tuners typically allowed 10 kHz or more, but also required a narrow band setting to deal with more difficult reception conditions.


Cheers,