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Pye Camebridge Radio set.

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Alastair
(@alastair)
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Had a bit of luck at work just lately....

A local auction-house has disposed of a pile of stuff including a Pye Camebridge Radio.

Other items are a Pye Camebridge radio/record-player with a 'Collaro' 78RPM only deck, and sunburst style speaker-grille All complete--but Very dirty/dusty/scratched, internally with its rear hardboard missing....

There's this small bow-fronted corner-cabinet G Marconi set standing on 'Queen-Anne' style legs that I also rescued

Anyway, my question is about the first set, the Pye-Camebridge. There appears to be no model-number anywhere on or in the set. I am looking for some service info/diagram.....
At first glance, the set looks like just a speaker with a hexagonal shape grille in cloth, the top opens to reveal the controls with a barrel style tuner, there appears to be a moving-magnet meter positioned in the tuner window too. Its obviously Very old, having British 4-pin 5 pin, and 7-pin valves, with screw-topcaps...
The cabinet is Burr-Walnut, and once done would look pretty nice I reckon.....

(I REALLY need to sort how to post pictures, I can Never get 'em to work....!!)

Ive removed the chassis--which comes up outta the top after removing the top wooden control-panel. The chassis is painted a fetching Duck-Egg Blue colour--not first apparent due to the very heavy dust layer--About 1/2" thick!

Unusually, it has a Copper-Oxide/Selenium rectifier, and a 'tuned RF' stage.

Valve line-up is--

PP3/250 Triode output.

MSP-4 detector/pre-amp.

ASC/S1 IF amp.

(Metallised valve with screw-topcap, No Apparent Number) Oscillator.

AC/SG-VM. RF Amplifier.

Its a long-shot, but does anyone recognise what set this is and any info on schematics....

There are lots of dodgy looking caps--that are all black--stained by the pitch so cannot read the values. There's no dates on the leccy-lytics either....

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Topic starter Posted : 12/12/2013 10:16 pm
Alastair
(@alastair)
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After a bit of a search around the web Ive found what the set is.

Here it is!--

http://www.vintage-radio-resources.com/PyeCRAC.htm

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Topic starter Posted : 12/12/2013 10:30 pm
Anonymous
(@anonymous)
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Also
http://www.radiomuseum.org/r/pye_cambridge_crac.html

Though no photos. Perhaps you could contribute photos?

Either email me or use "Contact" link at the bottom of the page on Radiomuseum.

Very tasty !

Year: 1934
Valves / Tubes 5: AC/SGVM ACS2Pen AC/S1VM AC/HLDD PP3/250
Principle Super-Heterodyne (Super in general); ZF/IF 114 kHz
Tuned circuits
Wave bands Broadcast (MW) and Long Wave.

Power type and voltage Alternating Current supply (AC) / 200-250 Volt
Loudspeaker Electro Magnetic Dynamic LS (moving-coil with field excitation coil)

Often too the stands are lost.

Don't tell the Asian Audiophools what the output triode is! (Basically similar to a PX25)
http://www.radiomuseum.org/tubes/tube_pp3250.html

Your eyes would water and legs go weak if you Radiomuseum member and see the prices a PP3/250 fetches on ebay!
It's best where it is :)

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Posted : 12/12/2013 11:07 pm
Alastair
(@alastair)
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Unfortunately--The stand of this CR/AC is missing too--It may well have turned up at work and was recycled into the wood, before it was known just what it was....

I didnt know it was supposed to have a stand until too late so couldn't look for it....

Never mind, We'll content ourselves potching round and renovating this set! :qq1

Not sure what to do with the Pye Radio/record-player, I have no room for it, so its at work but safe.....

The G-Marconi corner set is still in the car at the mo! :ccb

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Topic starter Posted : 12/12/2013 11:13 pm
Anonymous
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Ah. I confused its leg description!

Those Marconi corner sets (really EMI aka HMV) are lovely. Even my wife would like one.

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Posted : 12/12/2013 11:15 pm
neil1974
(@neil1974)
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Luckily you saved the set's before they met their maker Alastair :) and good luck with them.

Cheers,Neil.

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Posted : 13/12/2013 4:09 pm
Alastair
(@alastair)
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Aye--The prices of old British output valves is daft.

Particularly the PX4, PX25, and various KT series power-valves....

I'm not that into radio sets, although have a couple of nice sets and years ago, I sold a Mullard PX25 (ACO44 or summit) for nearly 500 quid! Seems to be the Chinese that go for 'em big time, sold a few older triodes over the years, and its nearly always the Chinese that 'fight' over them....

Ive built amps with these old DHT, and while sound nice--I wouldnt pay anywhere near That amount for 'em, while the Russian valves work just as well and are only a couple of quid!

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Topic starter Posted : 14/12/2013 8:26 am
Cobaltblue
(@cobaltblue)
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There's this small bow-fronted corner-cabinet G Marconi set standing on 'Queen-Anne' style legs that I also rescued

That sounds like the model C10A

The set itself is not particularly interesting as its the same as the T10A table top model but it is a lovely looking cabinet.

Its a bit more difficult to work on than the the T10 and the way the speaker faces downwards looks to be a bit of an afterthought.

Got one in Rountuit pile it was working last time I tried it after just doing the minimum repairs, Unfortunately SWMBO doesn't like it so not much point restoring it at present.

Cheers

Mike T

I don't care if it was a bargain whats it doing on my kitchen table.
www.cossor.co.uk

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Posted : 14/12/2013 9:42 am
Alastair
(@alastair)
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Yes--You are quite right, Its a G-Marconi C10A set. Reasonable condition for year, case needs stripping/renovation as its worn/scratched, chassis appears to be complete, all valves present--and has its 'Queen-Anne' legs attached

If anyone would like this set--as I realistically don't have a place for it, message me....

I'm slowly gathering the various parts together to rebuild the Pye, but it will be a functional rebuild rather than re-casing the new caps etc in the old part cases--although I will be using those Russian K40Y PIO type caps that are at least similar size and oldish appearance.....

Heresy I hear you cry! :qq1

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Topic starter Posted : 15/12/2013 12:12 pm
Terry
(@terrykc)
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Heresy I hear you cry! :qq1

There are two schools of thought here: those who want restore a piece of equipment so that it not only works but looks, both internally and externally, exactly as it it did when it was originally sold and those whose interest is simply in getting something working as well as possible.

Whilst I admire the efforts and ingenuity of the restore to 'as new' brigade, in general I favour the latter approach.

Perhaps this stems from my servicing background - nobody sought out waxed paper capacitors when TCC replaced the wax with plastic - their 'Plastiseal' range were otherwise indistinguishable from the originals anyway.

Nobody was interested in tracking down the identical TCC, Hunts or Dubilier to the original. If you needed a 0.1µF capacitor, you fitted whatever you had available. A grey plastic RS branded Dubilier, for example or, later on, a Mullard C296 (mustard).

You would have been no more interested in re-stuffing a capacitor than sticking both hands across the mains!

Anybody conscientious about their job would endeavour to make a set more reliable than the manufacturer - if a ½W resistor was in the habit of changing value because the bean counters at Thorn or wherever determined that, as it was 'only' dissipating 490mW, ½W was the correct rating for the job - it was automatic to fit a 1W replacement.

Don't get me wrong - I'm not knocking those members who slave over their period restorations for months - years even - and, no doubt, derive great pleasure from being able to demonstrate a receiver that it is impossible to determine what is original and what is not. They are craftsmen of a very rare breed indeed.

But that doesn't mean that it is wrong for someone else to devote the same time and energy using conventional techniques, resulting in several vintage receivers in full working order in the time it takes the craftsman to produce one.

When all else fails, read the instructions

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Posted : 15/12/2013 1:18 pm
Anonymous
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There are two schools of thought here: those who want restore a piece of equipment so that it not only works but looks, both internally and externally, exactly as it it did when it was originally sold and those whose interest is simply in getting something working as well as possible.

The third school of thought is to keep the design original, with equivalent new parts (or replacement NOS or decent used valves) rather than replace droppers with capacitors, change valve bases, fit transistors instead of valves etc. I'd regard as reasonable to fit a silicon diode instead of Metal Rectifier, but leaving the Metal rectifier on chassis. In the years when I repaired rather than restored I would have automatically replace valve rectifiers with Silicon, now I refit similar to original valves.

I might restuff an Electrolytic for appearance or leave in place and disconnect + wires as new part may easily fit under chassis, but often wouldn't restuff paper caps. I might leave a few on chassis. But for 1920s to early 1930s I'd leave all original parts in place, but on really old you can fit a new resistor or capacitor inside the original Bakelite or fuse style part without removing the original, only disconnecting at one end.

It depends on the age to an extent. Really old rare stuff it might be better to have it for display than "butcher" it. It needs to be a case by case and part by part decision.

But I'd never fit replacement paper dielectric capacitors. I might fit higher voltage caps, or sometimes higher value decouplers or higher wattage resistors, but I'd not usually change the design*. If I want a "better" radio, best to design or buy one.

(*I'd have said never a few weeks ago, but I got a 1956 Philips Colette and a small change was irresistible. I should probably put it back to "original" idiocy see "Did Philips make a mistake?" http://www.radiomuseum.org/forum/philip ... ion.html#4 ).

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Posted : 15/12/2013 1:43 pm
Anonymous
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G-Marconi C10A set. :

If anyone would like this set--as I realistically don't have a place for it, message me....
--although I will be using those Russian K40Y PIO type caps that are at least similar size and oldish appearance.....

Heresy I hear you cry!

I would like the C10A, but unless anyone is visiting Belfast, Dublin or Limerick it's impossible.

Er, I'd not bother with the PIO, stick small met-poly caps, any caps going to chassis, leave in place, just snip off the "signal"/"voltage" end. Leaving a couple of originals at least in it but not connected would satisfy curiosity of a future industrial Archaeologist, the Russian PIO confusing, may fail, more expensive. No-one is going to see the caps probably ever.

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Posted : 15/12/2013 1:56 pm
Terry
(@terrykc)
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... The third school of thought is to keep the design original, with equivalent new parts (or replacement NOS or decent used valves) rather than replace droppers with capacitors, change valve bases, fit transistors instead of valves etc. I'd regard as reasonable to fit a silicon diode instead of Metal Rectifier, but leaving the Metal rectifier on chassis ...

That is really what I would call the second school of though with the re-design option - capacitive droppers, etc. as a third.

A silicon rectifier, provided it is fitted with a series resistor equivalent to that of the original selenium device, is a perfectly acceptable repair but I would remove the original and fit a tag strip for the replacement in its place. *

The cowboy trick of fitting the silicon rectifier directly across the selenium unit - usually without the all important series resistor - is not acceptable!

* A modern solution might be to partially dismantle the original unit and replace one of the rectifier discs with a paxolin one ...

... In the years when I repaired rather than restored I would have automatically replace valve rectifiers with Silion ...

Not, to my mind, a good idea as the original electrolytics are unlikely to be rated for the high peak voltage/current at switch on ... :aae

When all else fails, read the instructions

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Posted : 15/12/2013 2:09 pm
Anonymous
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Maybe there are loads of schools of thought!

Well, I know a bit more now about Electronics than I did in 1960s & 1970s. If no valve rectifier is available then perhaps a pair of VDRs + Silicon. When I leave the Metal rectifier in place it's disconnected at both ends. Just in case.

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Posted : 15/12/2013 4:04 pm
Alastair
(@alastair)
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With that copper-oxide rec, -Is it in order to put a diode in series with each 'half' of it --from the testing Ive done, the rec is still functional...

The rec as designed forms a Voltage-Doubler stage in this set with a couple of 4uF caps, smoothed by a 16uF....
Odd idea, seeing the voltage doubler had only been invented a few years eariler from what I can gather!

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Topic starter Posted : 15/12/2013 6:25 pm
Terry
(@terrykc)
Famed V-Ratter Rest in Peace

Alastair, if, as you say, the original rectifier is OK, why do you want to put another one in series with it?

I'm also fascinated as to why it should need a voltage doubler as it must have a mains transformer.

Any chance of a look at the circuit, if you have one?

...I REALLY need to sort how to post pictures, I can Never get 'em to work....!!

Yes, you must!

What problems are you having? The most common is trying to upload files greater than the 100k limit.

This has been discussed at length here and, if size really is the problem, the Pixillion Image Converter http://www.nchsoftware.com/imageconverter/ can be very useful as it converts between file types (if required), resizes pictures (if required) and has a variable compression setting which can be adjusted if you still have problems getting the file size low enough.

You can download the free version here: http://www.nchsoftware.com/imageconverter/pixsetup.exe

I've been using it for years and it is really useful.

When all else fails, read the instructions

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Posted : 15/12/2013 7:26 pm
Cathovisor
(@cathovisor)
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Alastair, if, as you say, the original rectifier is OK, why do you want to put another one in series with it?

I'm also fascinated as to why it should need a voltage doubler as it must have a mains transformer.

There was a terrific vogue for voltage-doubling rectifiers in power supplies in the early 1930s, especially in conjunction with a metal rectifier. Pye were big advocates of it, as were McMichael (the Duplex Four being just one such set). It was a fashion that lasted less than two years. It has its advantages - lower voltages in the mains transformer being one - but like so many other fads, it went as quickly as it came.

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Posted : 15/12/2013 8:29 pm
Alastair
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Well--Thee reason for an additional silicon diode was to reduce/remove the reverse current leakage that I understand (From limited research) is the cause of the excess heat and eventual failure of the metal rectifier...
--Just as a precaution, the addition of the diode....

Ive always had issues with pictures, seems that photo manipulation isnt one of my strong points!
--Realistically though, there's nothing much of interest to take/post pictures of! This dusty grubby radio-chassis looks very much like any other! :)

I found the schematic on the web via a link from the picture above......

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Topic starter Posted : 15/12/2013 9:04 pm
Terry
(@terrykc)
Famed V-Ratter Rest in Peace

... There was a terrific vogue for voltage-doubling rectifiers in power supplies in the early 1930s, especially in conjunction with a metal rectifier ...

You learn something new every day! :)

Such sharing of knowledge is one of the joys of this forum ...

The strange thing is that with mains transformer technology so far advanced compared with the relatively new introduction of electrolytic capacitors, it is the last thing I would have expected to happen!

(I did go back through the few 1930s PYE service sheets in the library before my earlier post but they all show a full wave valve rectifier ...)

When all else fails, read the instructions

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Posted : 15/12/2013 9:13 pm
Anonymous
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The USA of course used dual rectifier tubes NOT intended for full wave on transformer (PIV would be exceeded) as doublers on Direct off AC line sets for HT as they have only 117V Nominal. So very few of their transformer-less sets work on DC.

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Posted : 15/12/2013 9:16 pm
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