Latest acquisition - a Murphy A188C

[Nanozeugma]

This behemoth whispered in my ear that it desired a new home, mine
It is functional, but will need a recap and the cabinet sorting out.
A peculiarity I noted was the alien loudspeaker, expecting a Celestion or Lectrona, I was greeted with an Adastra Hi-Ten 8 ohms 10 watt.
No idea how long ago it was retrofitted - or why - the impedance and the wires wrapped (not soldered) around the voice coil tags shrieked not original.
Can't find out much about Adastra, except there's one on eBay with a 15 ohm voice coil...
Photo's taken as received with 65 years of best quality dust and cobwebs

[Boater Sam]

Another giant Murphy saved!
I have one too, but it will have to go soon, takes up too much space.
I recapped mine and repaired the veneer damage on one corner, fabulous sound but I have the original speaker.
Beware of the UU6 rectifier, they have a propensity for going short circuit.
6P25s getting expensive now.

[Nanozeugma]

Stranger still, on taking the driver out to clean it, THIS became visible...

[mole42uk]

I have two. Both take up too much space but one has a wormed cabinet and the other doesn’t work.
I may have an original speaker if you want to replace yours.

[Nanozeugma]

Originally Posted by mole42uk

I have two. Both take up too much space but one has a wormed cabinet and the other doesn’t work.
I may have an original speaker if you want to replace yours.

That's a kindly gesture, thank you.
How would we proceed with this?
Kind Regards, Colin.

[Synchrodyne]

At least from an on-paper analysis of their circuitry, the Murphy A188C and the A186 covered in this thread: https://www.vintage-radio.net/forum/...d.php?t=147921 were, for their time, well above the average from the major setmakers when it came to receivers for MF programme content listening. So they could be considered as standout models in post-WWII British domestic receiver history.

The RF sections were similar. Both had three-gang front ends, with the third gang used to provide a bandpass input (to the mixer) on LF and MF, rather than to support an RF amplifier. Murphy was on record as favouring the bandpass input for MF, and its TA160 export receiver (which did have a RF amplifier) was so configured on the MF band, with an aperiodic coupling between the RF amplifier and mixer. They also had variable selectivity, and I’d guess that in the wide position the audio bandwidth was at or approaching 10 kHz. Back in those days 10 kHz appeared to have been at least the de facto target for LF and MF broadcasting (and may have been enshrined in CCIR documentation). The BBC managed 15 kHz from Brookmans Park, but the regional transmitters were usually limited to 8 kHz or less by the GPO landlines. Few if any of the other major setmakers were offering variable selectivity AM receivers in 1951.

The bandpass input could have been an aid to achieving an appropriately wide bandwidth over the whole MF range. With conventional single tuned circuits, narrowing of the bandwidth at the lower end of the band was a potential problem. Lowering the Q of the tuned circuits in the wideband mode was one solution, and another, when there was an RF amplifier, was slightly stagger tuning the RF and mixer circuits at the low end of the MF band. But apparently the bandpass input could be arranged to provide adequate bandwidth across the whole band.

Both had 9 kHz adjacent channel notch filters permanently in circuit. In the A188C, it was in the main feedback loop, and in the A186, it was across the output transformer primary. The conventional wisdom of the time appeared to be that for satisfactory wideband reception, the adjacent channel(s) needed to be 70 dB down without the notch filter, but 40 dB down was acceptable with the notch filter.

The A188C had a push-pull output with NFB, whereas the A186 had a single-ended output, with – perhaps surprisingly – no NFB as far as I can see, not even degeneration.

The schematics suggest that they were fitted with three-core power leads, making them true Class I appliances to use the later terminology. It would seem that some other setmakers used two-core power leads on AC receivers of the period, with protective earthing to be done separately, in what would later be classified as Class oI, probably illegal in many jurisdictions now (and I think that form might have been illegal here in NZ even back in the 1950s). So Murphy evidently had also given some thought to safety.

I have the sense that this pair, and the export TA160, also of 1951,were about the last Murphy radio receivers where the design engineers held sway, before the bean counters (those who knew the cost of everything but the value of nothing, and were usually clueless in engineering matters) sunk their teeth into the operation.

(Pye seemed to have staved off that inevitable transition for a bit longer, hence the PE80 (circa 1953, I think) and the FenMan II of 1955.)


Cheers,

[Nanozeugma]

Synchrodyne, I enjoyed your reflections on the engineering concepts behind the A186 and the A188C.
All I would add, in relation to your last (parenthesised) sentence, is that I covet both those Pye receivers.
I suffer from RAS (receiver acquisition syndrome) for which I have yet to find a cure.

[Synchrodyne]

My understanding is that except where contra-indicated by personal health or public good/public safety considerations, syndromic conditions are not best addressed by abstinence, but rather by prostinence (or whatever is the antonym for abstinence – indulgence doesn’t seem quite right…) Aversion therapy is not irreversible, witness that movie line “I was cured…”


Cheers,

[mark_in_manc]

Originally Posted by Synchrodyne

...syndromic conditions are not best addressed by abstinence, but rather by prostinence...

I need to be clear here, doctor - I need to fill my house with sets until I can't cook, go to bed or indeed move and the family have left me, after which I eventually see the light and reduce things to a sustainable level?

[dseymo1]

Adastra were a maker of small PA systems, guitar amps and the like. There's still a company selling similar products under the brand name, but what connection it has I don't know. The Hi-Ten was indeed a Celestion unit rebadged by Adastra for guitar use, and like many such speakers has some financial value - not a lot, but probably enough to cover the costs of your restoration.
Edit: The original company appears to have been dissolved some years ago; however, the current owners of the brand are using the strapline 'Founded in 1949'.

[Synchrodyne]

Originally Posted by mark_in_manc

I need to be clear here, doctor - I need to fill my house with sets until I can't cook, go to bed or indeed move and the family have left me, after which I eventually see the light and reduce things to a sustainable level?

No, no. Most likely personal health and public good considerations would supervene before you got to that stage, and they are legitimate - and often compelling - reasons for abstinence when they crop up. It's abstinence in abstract that is unlikely to succeed.

Cheers,

[Nanozeugma]

Originally Posted by dseymo1

Adastra were a maker of small PA systems, guitar amps and the like. There's still a company selling similar products under the brand name, but what connection it has I don't know. The Hi-Ten was indeed a Celestion unit rebadged by Adastra for guitar use, and like many such speakers has some financial value - not a lot, but probably enough to cover the costs of your restoration.
Edit: The original company appears to have been dissolved some years ago; however, the current owners of the brand are using the strapline 'Founded in 1949'.

Thank you for that, most interesting, I myself was founded in 1949

[Nanozeugma]

Both dial bulbs open circuit - replaced. One small step for me... well, you have to start somewhere

[Edward Huggins]

Adastra also made small Hi Fi amps, there was certainly a 3 valve, 3 watt model. I'd date that speaker (ceramic magnet?) as at late 1960s.