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Old 12th Dec 2019, 12:41 am   #121
allan
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Default Re: Moreton Cheyney

I'd like to get the receiver working to the point where it meets the original design claims, as far as they're known, and I'm slowly getting there Steve.

I don't believe this set ever had a cabinet so I suppose I'll just fit it to a baseboard.

I'm using modern components to replace resistors that are too far gone and new capacitors except for a couple of dozen Sprauges, two block condensers and a variety of silver mica etc which seem to be in perfect order. Above the chassis it'll look completely original except where I've used a metal 6K8 and raised its valveholder level with the chassis, but as there isn't another Moreton Cheyney (or a picture of one) it doesn't really matter.

The matching amplifier/PSU is in a very poor state but if the major parts test OK I'll remove everything from the chassis and restore it to the condition it was last used. The consensus is that it may have used PX4s but when it arrived it had one extant KT66 and quite possibly a larger output transformer.
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Old 12th Dec 2019, 9:10 pm   #122
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Default Re: Moreton Cheyney

Hi Allan, plenty of silver micas here if you need any odd values and want to keep it looking authentic.
I would have thought the OPT for a PX4 would be about as big as that for a KT66. For initial tests you could even run it on 2 of the less expensive valves (6L6 etc)


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Old 12th Dec 2019, 11:01 pm   #123
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Default Re: Moreton Cheyney

I've been following this epic thread from the beginning. Coils wound with resistance wire are a new one on me. I've spent a lifetime trying to maximise inductor Q.

A chassis with no cabinet and no info about what one looked like is an interesting puzzle. Moreton Cheyney sounds like one of those quaint little English villages in the Cotswolds with an absolutely phenomenal murder rate. You just know that if you stop there you'll hear the church bell ringing at an odd time, and when you go to look, the very recently deceased vicar will be found hanging from the bell-rope. Guaranteed. This thread seems to be giving an afternoon whodunit a fair fight on episode count as well.

May I suggest that an up-market cathedral style cabinet would be appropriate. Miss Marple or Monsieur Poirot wouldn't have anything less.

For audio output devices as an alternative to PX4s, I'd go for triode connected 6L6 or 807. Prices are sane and there's plenty about. You need triode connection, or you might wind up with excessive gain.

David
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Old 12th Dec 2019, 11:21 pm   #124
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Default Re: Moreton Cheyney

Quote:
Originally Posted by Radio Wrangler View Post

May I suggest that an up-market cathedral style cabinet would be appropriate. Miss Marple or Monsieur Poirot wouldn't have anything less.


David

Surely something Art Deco would suit Poirot at least, rather better?
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Old 13th Dec 2019, 2:28 am   #125
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Default Re: Moreton Cheyney

A quickish response as it's getting a bit late here.
No problem with capacitors thanks Ed....
I purchased the entire stock of the long defunct Greenwelds including loads of NOS NATO packaged condensers. Maybe tens of thousands in all.

I do like the idea of a fancy cabinet.
The receiver chassis is pretty substantial being larger than an AR88 and the matching amplifier although slightly smaller weighs over 40 pounds.

My stock of valves includes a large box full of NOS KT66s so I plan to fit a couple of these and run triode connected?

Coil Q. It's the coupling winding using resistance wire so the tuning bit should be OK. I think it uses Litz wire.

Cabinet design proposals invited on A2 or A1 paper.
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Old 13th Dec 2019, 3:51 am   #126
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Default Re: Moreton Cheyney

At least according to the Wireless World 1946 November item, the Moreton Cheyney receiver was available in either chassis form, or in console form with a 12-inch speaker. The console was said to be available in two alternative cabinet types, although no details were provided. Console price was £78 before tax, as compared with £52 for the chassis.

It is anyone’s guess as to what the console versions looked like. Two versions could mean two different wood finishes, or it could mean two different layouts, for example one with the tuner face at the top of the front panel, perhaps slanted inwards at its upper end, and another with the tuner face mounted on the top panel, maybe with a lid. Perhaps the other more upmarket console receivers of the period would serve as suitable prototypes for the design of a suitable cabinet, for example the Dynatron Merlin.


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Old 13th Dec 2019, 9:21 am   #127
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Default Re: Moreton Cheyney

There's a beautiful (if huge) Dynatron 1940s radiogram cabinet on eBay for £40 at the moment...
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Old 13th Dec 2019, 9:29 am   #128
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Default Re: Moreton Cheyney

I have to agree with Chris about art deco. How about something on the scale of one of Atwater-Kent's most dramatic ouvres with art deco flourishes?

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Old 13th Dec 2019, 9:30 am   #129
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Default Re: Moreton Cheyney

Now there's a thought. Do any of the mentions of the thing say whether or not there was a turntable included?

David
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Old 13th Dec 2019, 10:47 am   #130
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Default Re: Moreton Cheyney

My example has an external amplifier so was probably not fitted into a cabinet with loudspeaker?
Receiver chassis is square approx 400mm x 400mm x 300mm high
Amplifier chassis is rectangular approx 425mm x 330mm x 200mm high

Nice Ether Conqueror cabinet Nick but wrong shape and the XYL would consign it to (one of) the spare room(s) with other exiles...

and it does have a gram socket David...

My Majestic Ellswood looks the part
http://www.radiomuseum.co.uk/majestic.html
Not from the Cotswolds but from Chicago via Ebbw Vale.
Moreton Cheyney definitely does not sound like it was born next door to Stafford Gaol.
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Old 14th Dec 2019, 6:56 pm   #131
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Default Re: Moreton Cheyney

I spent a couple of hours looking at the audio section of the MC receiver and discovered that AVC really meant that and not AGC in respect of RF.
Whatever input, both RF, and audio via the gram input, resulted in a constant audio output. When I'd tried peaking various trimmers, RF and IF, nothing seemed to happen at the output other than the odd transient change before settling back to constant output.
The very strange circuitry around a couple of the audio amplifier valves, including the use of a 6B8 is to arrange a steady output amplitude. It allows intantaneous changes to deal with the audio waveform, but over a second or so the output reverts to something like 2.5 volts RMS (for a constant tone input at almost any amplitude).
The output waveform is very distorted, having a second harmonic distortion shape. If the input level is reduced there comes a point when the output is distortion free then it drops following the input.
Whether this distortion is a side effect of the constant level circuit or one of the components not up to scratch or a missing wire I haven't yet discovered.
Maybe the circuit needs looking at and comparing with similar circuits of the same vintage?
http://www.radiomuseum.co.uk/moreton2.html
The volume control appears to work normally.
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Old 14th Dec 2019, 9:54 pm   #132
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Default Re: Moreton Cheyney

Might be worth checking capacitors etc filtering the AVC control like. If it gets pumped at audio frequency, it will introduce even order distortion.

David
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Old 16th Dec 2019, 1:35 pm   #133
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Default Re: Moreton Cheyney

I've been reading stuff on a guitar amp forum and it seems 2nd order distortion is common in cathode followers especially when anode and cathode resistors are selected to actually introduce this type of distortion.
As most of the resistors in this receiver are way too high that might explain what's happening so time for some experimenting. Looking at my V11.. this is a strong candidate but I'm thinking also about the purpose of V10 diodes...

It seems the mellowness of valve amplifiers can be because of 2nd order distortion.. but let's not go down that path. Leave it to the guitar enthusiasts...
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Old 16th Dec 2019, 1:46 pm   #134
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Default Re: Moreton Cheyney

Just to note, I believe Cossor also used resistance wire in some of the oscillator coils in some models of their radio receivers.

Lawrence.
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Old 16th Dec 2019, 7:12 pm   #135
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Default Re: Moreton Cheyney

Alan

I'm just wondering if Moreton Cheyney were attempting a "Volume Expander" circuit, in common with high-end receivers from the USA. If this has been inadvertently modified (got at) it might be operating as a Volume Compressor instead. I cannot imagine Volume Compression, plus added harmonic distortion, was what they originally intended !

Cheers, John (Mr 1936)
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Old 17th Dec 2019, 2:25 am   #136
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Default Re: Moreton Cheyney

Yes, as mentioned upthread, volume expansion was one of the features originally listed for the M-C receiver. (So was AFC but that, apparently, did not make it to the "production" version.)

Cheers,
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Old 17th Dec 2019, 10:55 am   #137
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Default Re: Moreton Cheyney

I'm gradually sorting out the audio section.
The two controls which I labelled as bass and treble do seem to work after a fashion now that I've fitted a new pot to one of them. The other pot that's fitted with an on/off switch is a bit iffy and I'll change that sometime. The switch went to a red/black mains lead and possibly was used with the main amplifier/PSU. The second harmonic distortion is not as visible as before now I've changed some capacitors and resistors.

Currently, I've noticed the AVC line is a bit weird. As you tune across Radio 4 on 198KHz the AVC voltage goes more positive instead of going more negative. This results in an initially nice clean audio distorting then, as you tune further, it cleans up.
I fitted OA91 diodes with their cathodes corresponding to the red ends of the two Westectors but clearly more testing is needed. It's possible the QAVC and AVC IF stages which are separate and not used in audio recovery are inadvertently offset from 465KHz by a few KHz. I plan to use a spectrum analyser to look at the IF strip including the QAVC and AVC stages. Hopefully that will reveal all.

The Westectors (both open circuit) are in circuits using a "delayed" feature. The question is "what's the forward voltage of a Westector.. is it similar to a germanium diode, a silicon diode, or neither?" I can easily change the resistor values to match the delay for the OA91s.
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Old 17th Dec 2019, 3:26 pm   #138
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Default Re: Moreton Cheyney

Hello Allen,

I thought you might be interested in the attached Moreton Cheyney Silver Dragon report.

It is just a photocopy in my archives, sadly I don't know which publication it is from, but it is marked 'Feb 1947' on the reverse.

Phil.
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Old 17th Dec 2019, 6:55 pm   #139
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Default Re: Moreton Cheyney

Hi Phil
Thanks for the piece on the MC Silver Dragon.
It adds a bit more to the saga.
My receiver must be the other ie. the Silver Knight which has QAVC instead of AFC etc.
I'd like to add this to my history bits and pieces if you have a reasonable definition file? I'll look round the Feb 1947 publications and see if I can spot it.

I've just been looking at the IF curves and I'll be adding some pictures later.
There's still an elusive fault between the detector and the first audio amp so recovered speech etc is at a very low level and only audible with AVC and QAVC shorted to ground. I think the IF voltage is healthy at several volts but demodulated audio seems to be only a millivolt or so. AVC is solid reaching minus 6 volts on a decent broadcast. I think the detector diodes are part of a 6B8 (V8 on my circuit) and may be biased off via R82 so may try swapping these for an OA91 to ground. Before that I'll attempt to measure the voltages around c77/r72/c78 (the RF filter) and ground C60 to remove any reverse bias to the 6B8 diodes.
Any thoughts welcomed.
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Old 17th Dec 2019, 11:37 pm   #140
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Default Re: Moreton Cheyney

Is it possible that the AVC uses the negative half cycles of the IF and that the other half cycles are used to recover the audio?
The solid state detector diodes would make this possible.
This would also help to get rid of any distortion that may arise from loading caused by the AVC circuit.
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