Pye AM/FM Piper P117.

[FERNSEH]

Recently bought this rather sad looking Pye P117. It's a model like the HMV 1920 I've been on on the lookout as long as I have been in the trade. Never accepted one for repair so this is my first chance to take a look at one of these interesting sets. Of course it had to be a rather bashed up example.
Valve line up is ECC85, EBF89, ECL82 and EZ80.
On AM the ECC85 functions as the frequency changer and on FM the first triode section is the RF amplifier and reflex IF amplifier. The second section is the mixer-oscillator. Clever stuff.
The set was easy enough to get going but the sound quality on FM was awful.
It was evident the IFs had been twiddled but putting that right didn't help matters much. Check around the ratio detector. Even on strong signals no voltage could be measured across C40. Changing the capacitor didn't improve matters. Diode V4 was found to be open circuit so the IF transformer was taken out to gain access to the faulty component, not an easy job. In fact later on I found there is no necessity to remove the transformer from the chassis, simply remove two 4BA nuts and the screening can can be removed to gain easy access to the diodes.
Diodes replaced and careful tweeking of the transformer cores and now the set produces surprisingly good FM sound quality.
The truth is I was expecting the set to be a poor performer but in fact it's rather good.
No clue to the origins of this unique circuit design, possibly designed by Pye but a similar set was made in Italy.

DFWB.

[ms660]

Grundig did something similar, the 80u and the100U?:

https://www.rsp-italy.it/Electronics...ig%2080U-J.pdf

https://dspace.mit.edu/bitstream/han...=2&isAllowed=y

Lawrence.

[Leon Crampin]

I have one of these sets. The FM performance is rather average, but my set has a highish residual hum level caused, I think by poor screening within the ECL82. It's an interesting design, but making it and aligning it on production must have been a nightmare. Compared with a traditional design, there's far too much hot switching in the signal path. The build standard is flaky as is usual from Pye, with component joints loose in thin air. Tagstrips are not that expensive....

A nice curiosity to have though.

Leon.

[bobhowe]

Hi David the cabinet shape looks like Philips as well kind regards Bob

[FERNSEH]

Hi Bob,
Pye housed the awful AM only P115 Piper in a similar cabinet.
Pye must have liked the design of this receiver because radiogram versions were made, the P117RG and the P117RM, the record maker model.
BTW, I've bought another P117, at least this one has control knobs.

DFWB.

[bobhowe]

H David why did the P117 have a EZ80 ? they could have reduced the valve count and used a selenium rectifier instead kind regards Bob

[FERNSEH]

Hi Bob, probably just the preference of the Pye design team. The Grundig sets which employ a similar circuit use a selenium rectifier.

Leon Crampin wrote: "but my set has a highish residual hum level caused, I think by poor screening within the ECL82."

Hi Leon, it's the same with my set, hum is worst at mid settings of the volume control.

DFWB.

[Synchrodyne]

The use of a double triode for the AM as well as the FM frequency changer appears to stem from American practice in the early post-WWII era. I think that there may have been viewpoint held by some makers that valve sharing should be a maximized in AM/FM receivers. That RCA presented its post-WWII miniature pentagrid converter, the 6BE6, as being suitable for FM as well as AM reinforced this. In fact the 6BE6 was not so good at FM frequencies, so RCA released the 6SB7Y (octal) with improved FM performance. Meanwhile, there had been some use of the Sylvania 7F8 (Loctal) double-triode as a mixer-oscillator for both AM and FM, an example being the Hallicrafters SX-42 communications receiver. That application suggests that the double-triode AM frequency changer, shared with FM, was not seen as simply an economy device, but was also suitable for higher performance receivers.

In 1947 GE released the 12AT7 double triode, primarily intended for use as a mixer-oscillator for FM receivers and also for TV receivers using the then-standard ’20 MHz” IF. But the 12AT7 was also specified for AM mixer-oscillator use. Zenith was an early adopter of the 12AT7 as a common frequency changer in AM/FM receivers, and used it thus until the late 1950s at least, and perhaps into the 1960s. Somewhat oddly, GE itself did a bit differently. In AM/FM receivers, the 12AT7 was used as a mixer-oscillator for FM, but for AM, just one half was used as an oscillator. The first pentode in the IF chain served as the AM mixer, as well as the FM 1st IF amplifier.

RCA’s response was twofold. One branch was the release of a noval version of the 6SB7Y pentagrid, namely the 6BA7. The other was to issue an application note showing that its established 6J6 double triode could be used as a common AM/FM frequency changer (although it was probably more microphonic than desirable for the FM case). That was probably something of a stopgap measure, though. The definitive response came in 1951 with the 6X8 triode-pentode. This was primarily specified for use as a TV receiver frequency changer suitable for the then-new “40 MHz” IF, where a pentode mixer was indicated to avoid regeneration at the lower low-band channels, due to their closeness to the IF. But the 6X8 was also specified for use as an AM frequency changer. Clearly, it was also suitable for use as an FM frequency changer, but as an additional facility, in the FM case, RCA specified the mixer section for use triode-strapped as well as in its natural pentode state. So it had pretty much covered all the bases. RCA did use the 6X8 as a common frequency changer in some of its AM/FM receivers, sometimes preceded by the 6CB6 as a common RF amplifier.

The use of a double-triode as a combined FM RF amplifier and self-oscillating mixer appears to have been essentially a European development. I am not sure, but I think that Telefunken was the originator of the ECC85. Philips may have got itself a little sidetracked in that it saw the ECH81 as having something of a common role, in the FM case with the triode as a self-oscillating FM mixer and the heptode as FM 1st IF amplifier. The ECC85 single-valve FM RF amplifier and frequency changer concept did cross the Atlantic later in the 1950s, and was further developed there along more than one vector.

After that digression, in regressing to the Piper, it could be said that Pye evidently combined the American concept of the double-triode AM frequency changer with the European concept of the double-triode FM RF amplifier and self-oscillating mixer, and then went a stage further by reflexing the RF section as an FM IF amplifier. One wonders if Pye also considered reflexing the mixer section as an AF amplifier….

Re-digressing, as it were, working through that makes me wonder if Pye missed an opportunity to improve the AM side of the FenMan II receiver, which was certainly generously endowed on the FM side, with a 3-gang front end and a 3-stage IF strip. Considering that RCA used the 6CB6, 6X8 pair as a combined AM/FM front end in its better domestic receivers, could not Pye have used the EF80, ECF80 pair from the FenMan II FM front end for AM as well, thus allowing a 3-gang AM front end with RF amplifier, without increasing the valve count? Perhaps an EF85 in place of the EF80 RF amplifier would have been better for AM AGC purposes, although maybe fractionally noisier on FM. That said, RCA did not seem to have had a problem with using a sharp cutoff pentode as AM RF amplifier. With this change, the ECH81 could have bene replaced by an EF80 or EF85, and it would also have allowed the opportunity for a second AM IF stage, although for LW/MW purposes, that may have been overkill. With an ECF80 in place of the ECH81, the triode could have been used for FM AFC. Whether that was desirable or not I don’t know, but the fact that the following HFT108 Mozart FM tuner had AFC suggests that it might have been.


Cheers,

[Edward Huggins]

It's interesting regarding the speculation here as to the Designer's motives for these sets? From my time all I know was that the brief was to make these as cheaply as possible mainly for second set use or a cheapo replacement for failing pre-war Woodies. The AM version came out first and I was quite surprised that an FM/AM version soon followed. I never liked them and many Dealers at the time thought that they lessened Pye's Radio reputation....

[Boulevardier]

Originally Posted by Synchrodyne

working through that makes me wonder if Pye missed an opportunity to improve the AM side of the FenMan II receiver, which was certainly generously endowed on the FM side... the ECH81 could have been replaced by an EF80 or EF85, and it would also have allowed the opportunity for a second AM IF stage, although for LW/MW purposes, that may have been overkill. With an ECF80 in place of the ECH81, the triode could have been used for FM AFC. Whether that was desirable or not I don’t know, but the fact that the following HFT108 Mozart FM tuner had AFC suggests that it might have been.

I wonder about that too.

I’ve been doing work on a FenMan II, and working through to an understanding of it’s complex circuit (complex for a domestic receiver, that is). As you say, the Fenman II is well-endowed of the FM side - 11 valves, all used, RF amp stage, and 2 IF stages. Three of those valves are just sitting unused in AM mode (EF80, ECF80, EF85), and I’d have thought that any or all of them could have been used to improve AM performance, which (on mine at least) isn’t exactly sparkling.

Not sure what Pye were thinking of here - all that fussy attention to FM, and seemingly treating AM as not deserving the same. Perhaps they’d already decided that AM was obsolete technology...

Mike

[paulsherwin]

The postwar consensus among UK manufacturers seems to have been that an amplified RF stage was unnecessary for British domestic reception of the MW and LW bands. They were very rare even in very upmarket sets, and Pye even used short superhets in many of their mid range models. The vast majority of 40s and 50s listening was to the 3 BBC services, which provided strong signals almost everywhere. Many listeners also had huge longwire aerials draped around their gardens, inherited from the days of crystal sets and flea powered transmitters.

[FERNSEH]

Synchrodyne wrote: "The use of a double-triode as a combined FM RF amplifier and self-oscillating mixer appears to have been essentially a European development. I am not sure, but I think that Telefunken was the originator of the ECC85. Philips may have got itself a little sidetracked in that it saw the ECH81 as having something of a common role, in the FM case with the triode as a self-oscillating FM mixer and the heptode as FM 1st IF amplifier. The ECC85 single-valve FM RF amplifier and frequency changer concept did cross the Atlantic later in the 1950s, and was further developed there along more than one vector."
Right up to the end of the fifties Philips favoured the use of two EF80 or UF80 pentodes in FM tuner modules. Likewise GEC employed a pair of RF pentodes in their first FM receivers. Both companies made their own valves so perhaps they were reluctant to use another manufactures valve, the ECC85.

At least the P117 Piper has a mains transformer, albeit just to supply the valve heaters. I notice the Grundig employs an EBF80 and an ECL82. Both valves of the 50s and the 100U has post 1960 types, EAF801 and ECL86.

DFWB.

[Synchrodyne]

The use (or not) of RF amplifiers in domestic AM receivers in general is in and of itself an interesting topic, but I think too much of a digression for broader consideration in this thread.

Nonetheless, the Pye Fenman II AM section does look anomalous when compared with the FM and AF sections. Both of the latter were evidently designed to be a significant step above the level of what might be called the “standard circuit”. The latter of course was exemplified by the Pye FenMan I. But the FenMan II AM circuitry does not look as if it were materially better than that of the FenMan I, even though noticeably better could have been done using the existing FenMan II valve line-up. One could argue that in an era when FM would be used for listening to the BBC domestic services, the primary utility of the AM section would be for listening to distant stations, both UK and European. For that purpose, often involving skywave reception, better, not worse AM performance than had been provided by the typical AM circuitry of the immediate pre-FM era was probably desirable, and even if outruled on cost grounds for “standard” receivers, might have been reasonable to expect on premium models.

On the other hand, the Piper P117 was evidently aimed at a point that was a clear step below the “standard circuit”, with unusual and innovative circuitry used to get there whilst keeping the valve count within bounds. In other words, it was done by more than simple deletion of stages and their associated valves.

Mullard had also proposed a simple, or at least low valve-count circuit for a low-cost AM/FM 2nd receiver, see Mullard Technical Communications #22, 1957 March, p.36ff. This was similar to the Pye P117 in that it used an ECC85 as the input stage on both AM and FM. On FM, it was used normally. On AM, the second triode was used a self-oscillating mixer, and the first as an aperiodic RF amplifier.


Cheers,

[Edward Huggins]

Pye were motivated to produce very good FM receivers after 1955. I think some BBC influence came to bear via C.O Stanley. Indeed, if you look at the model line up in the following 10 years, no great design effort was put into AM sections and they were certainly of "standard" circuitry. Some of the sets in this period were Multiband (at that Pye had a very strong Export business) but again these had little or no "fancy" IF treatment or an RF stage. However, we were pressed to design the tuning scales to look like those to be found on Communication receivers!

[FERNSEH]

Leon Crampin wrote: "I have one of these sets. The FM performance is rather average, but my set has a highish residual hum level caused, I think by poor screening within the ECL82."
The position of the mains input filter choke L23 doesn't help, it's too close to the ECL82 triode section connections.
I'll reposition the coil and report the results.

DFWB.

[FERNSEH]

Moved L13 well away from the ECL82 valveholder. No improvement. Will try something else to reduce the hum level.

DFWB.

[Leon Crampin]

I had a look at this when I restored my P117. I made a marginal improvement by making a copper foil screen around the ECL82 triode grid connection on the valve holder, and by improving the screening of the lead to the volume control.

My conclusion was that the valve itself was picking up hum, probably from the heater. I left it at that, but a re-wire to take an ECL86 might yield a result - and more gain.

I would be interested to see your observations and conclusions.

Leon.

[FERNSEH]

The triode section of the ECL82 is biased by grid current. Changed leaky coupling capacitor C44. Better sound quality now but the hum prevails.

DFWB.

[FERNSEH]

The simple answer to get rid of that hum is replace the grid current biasing with cathode biasing for the triode section of the ECL82.
Find the correct value for the resistor and use a 100microfard capacitor for cathode bypass. The 0.01mfd capacitor C44 and the 10meg grid resistor removed and the triode grid connected directly to the slider of the volume control.

ECL86 was used in the Grundig 100U.

DFWB.

[FERNSEH]

Modified the triode audio amplifier from grid current biasing to cathode bias using a 2.2Kohm resistor and 47uF capacitor.
To honest very little improvement, still have hum at mid volume control settings and the sound quality isn't much either. Have tried another ECL82 and the hum persists.

DFWB.