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 Return to top of page · Post #: 1 · Written at 6:54:58 PM on 6 July 2019.
Alarum's Gravatar
 Location: Toowoomba, QLD
 Member since 6 July 2019
 Member #: 2359
 Postcount: 12

Good evening,

How often do you see radio's that have been extensively modified?

I have found console radio from which I can tell the following:

- The radio dial is in plastic and says it is a Music Masters Radio Co radio. No mention of any names or models.
- The chassis itself I have identified as a STC radio. Valve lineup and label suggests it is a "635" model.
- The wooden console just has "Monarch" formed in the bakelite around the radio dial.

Most of the capacitors look like they are the original Ducon paper type.

Is something like this worth restoring or simply using for parts?


 Return to top of page · Post #: 2 · Written at 7:29:37 PM on 6 July 2019.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1619

Worth practicing on but that's about it.

 Return to top of page · Post #: 3 · Written at 8:38:08 AM on 7 July 2019.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 923

Hi Alarum, depends on what you mean by "worth".

No vintage radio is "worth" more than $50 if you are talking about monetary value.
Any vintage radio is "worth" $5000 in experience if you strip back to metal, restore and refurbish and make it work and look like new.

That is the worth in my eyes, to take a rusty rotten wreck, work out how it should be put together, de bug the electronics, restore the woodwork, the chassis and learn about the theory and practical of wireless transmission and reception.

That STC is listed as around a 1930 model TRF with 35/24/47/80 valves.
You don't say if you have the whole console cabinet or just a chassis, but anything that age is eminently restorable.
I don't give a fig about originality so even if you just have a wreck of a chassis you can still then knock up your own cabinet using Bunnings stuff. I did a similar thing with an unknown TRF chassis, see the special projects section on this site and look for "Yackandra TRF" .
Was that project "worth it", money wise no, its still only worth about $50 if that, was it worth it for the stuff I learnt? You bet!

Cheers, Fred.

 Return to top of page · Post #: 4 · Written at 11:54:13 AM on 7 July 2019.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1007

indicates that there were 635s produced in 1932 and 1939.

The 1932 lineup was
3*35, 24, 47, 80

The 1939 line-up was
6U7 6K8 6U7 6Q7 6AG6G 5Z4 and 6T5 indicator valve.
Can provide a circuit for the 1939 radio if needed.

Yet AORSM (Aust. Official Radio Service Manual) does not have a circuit in the 1939 book, but does have for the 1941 book, with the above lineup, without the 6T5.

Yet there is a further wrinkle. I have a photo of the Code label for a 635 which shows valve lineup
6U7 (substitute 6B8SG stamped on)
6U7 (substitute 6B8SG stamped on)
6AG6G (possible substitute stamped on - obscured)
There is no 6T5 on the label, though the wiring for it appears to be there on a photograph I have of the chassis. Unfortunately the valve itself if it is there is obscured by the radio's cabinet, a console. Will submit these to Brad for posting if of interest.

It looks like there may have been some wartime driven substitution, for the ASRTS&P label is a G, indicating 1940/41.

So might take a bit of head scratching to work out what the real circuit of your radio is Alarum.

 Return to top of page · Post #: 5 · Written at 12:46:46 PM on 7 July 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

Extensively modified normally translates to "hacked". More often than not the reasoning, for doing so is vague and the execution flawed.

I constantly get them, with the really old sets one often finds there is no circuit & in many cases of many manufacturers even if their is a circuit, critical info like element voltages are conspicuous by their absence.

There are sets where WD scarpered off with valves like 6B8 & some IF ones. In the main these were more often replaced with Philips.

In the field, with valve scarcity around war time & after, repairs were often done, with whatever was on hand. So it is never unusual to find 6A8, 6J8, 6K8, or something like ECH-35 subbed. Normally subbing 6U7 to Philips required a circuit change & HMV did that. However, finding a 6K7 in there was not unusual.

Where there is hacking one needs to go back to the original circuit if found (I say that as I had to draw one for an STC chassis 59). I actually bought an AutoCAD in the 90's (still have) just for drawing wiring diagrams. This now has pre-loaded symbols (came with lots) of most types of radio valves. So its only a case initially of making a layout diagram & then, using different colours: Play join the dots.

Most radios of the era followed a similar plot, so its relatively easy to do. Once you have a circuit you can analyse it & see where its all gone awry. The resistances & wiring often point to the original valve.

 Return to top of page · Post #: 6 · Written at 1:45:33 PM on 7 July 2019.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1007


The substitutions on the Code label are stamped on with purple ink, so it looks like a factory mod., though of course you never know until it's turned over.

 Return to top of page · Post #: 7 · Written at 4:06:27 PM on 7 July 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

There is something odd about that set. Music Masters Qld. were being squeezed out in 1936 when the big boys started to deprive them of parts.

The only STC listed with 6B8SG info scarce, is STC 410, 411, 413. 6B8 & 6G8 were subbed but it cannot sub a 6U7 without a socket rewire & likely a change to screen volts and AGC attack if it can actually be applied at all?

All of those STC numbers all use 6A8 (Heptode) and 6K8 is a Triode Hexode and may have an 8μF cap in the oscillator plate circuit as it is inclined to flutter on BC band.

The STC 236 here is stamped in black inc & is consistent with the schematic. This set may actually be Music Masters own, & they were struggling for parts.

One can normally tell if its been got at underneath. However HMV, Astor& others tended to list the mods made. The cabinet is often not a guide Astor 11-4 and others were Heinz 57 varieties of not the same & we had 3 same Astor cabinets containing three different chasses.

It may be a case of reverse engineer.

 Return to top of page · Post #: 8 · Written at 4:39:46 PM on 7 July 2019.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1007

A couple further points

There can be errors and omissions in STC circuits in AORSM.
I have an STC 632 where the serial number is written rather than stamped on the Code label.

No doubt other makers are the same - humans under the pressures of production.

 Return to top of page · Post #: 9 · Written at 8:54:55 AM on 8 July 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

If you want to see a Friday afternoon rush before public holiday; nobody really checked it circuit : Have a look at the circuit for Philips 172 in AORSM's

 Return to top of page · Post #: 10 · Written at 12:18:47 PM on 8 July 2019.
Gandhn's Gravatar
 Location: Cameron Park, NSW
 Member since 5 November 2010
 Member #: 770
 Postcount: 351

I couldn't find it in AORSM, but Radiomuseum has a circuit.

The antenna input seems a bit odd, going into the bottom of the RF coil, but I'm not an expert on permeability tuning, so it may be right. I also noted the first filter cap negative is grounded, when it more commonly is returned to the back bias resistor.

Am I missing something?


 Return to top of page · Post #: 11 · Written at 3:44:45 PM on 8 July 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

Sorry wrong Philips it was Philco 47-40.(still Philips). That is in AORSM, The 172 I got from Kevin Chants site; Always have issues with Radio Museum, & circuit downloads.

The tuning circuit is not earthed & the loudspeaker has no cone.

It was done in a hurry before the UPS ran out of battery & there is a 172 in the newsletter I was working on.

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