View Single Post
Old 28th Jun 2017, 1:41 pm   #5
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
Default Re: Cossor Melody Maker 494 A.C. Valve radio

Quote:
Originally Posted by stuboy57 View Post
..... I have downloaded the service data, trader sheet etc,
It's quite a decent set - it has a large speaker, a tone control and three wavebands. It has a rudimentary 'frame aerial' wound on the back panel, which will pull in a few stations on MW/LW but would benefit from an external aerial, especially on short waves. It has a double-wound mains transformer so the chassis is isolated from the mains input, and hence, is safer to work on than sets with a 'live chassis' - the Bush DAC90A for example.

This is one of those cases where the Maker's sheet in some respects gives less detail than do the Trader Sheet and ERT sheet.

The Maker's data gives no component layouts for above and beneath the chassis, nor a dial string diagram. The Trader Sheet and ERT Sheet each give that detail, and it's worth having all three sets of data. However, if you quote any component numbers on the forum, do make it clear which data you are referring to, because they differ. For example, the Maker's sheet calls the audio stage cathode by-pass capacitor 'C29' whereas the Trader Sheet and ERT sheet refer to it as 'C21'. The output stage audio coupling capacitor (a 'must change' item), is called 'C26' on the maker's sheet, C18 on the Trader Sheet, and C19 on the ERT sheet. And so on it goes.

When restoring any valve set, which can take many hours over many weeks, I'd recommend making a simple cradle to hold the chassis upside down to work in as it minimises the chance of damaging something - a valve for example - if you try to balance the chassis on bits of wood or whatever. A cradle makes it easier to work on, and safer to carry out live testing.

I've attached some pics of a Melody Maker 501, similar in appearance to your 494, which I restored some time ago. The first pic shows it mounted on a simple cradle made from 4 pieces of flat steel and a scrap piece of plywood. Second and third pics are before & after underside views of the chassis. Note that the original 2-core mains flex was restrained only by having a knot tied in it, which I replaced with a 3-core flex and cable restraint. If the flex on your set is original, it will be the same, so I'd recommend changing it.Third and fourth show the original unstrained 2-core flex and the replacement 3-core and rear chassis apron cable restraint.

Plenty of room to work, which makes restoration a bit easier.

Hope that helps a bit.

Good luck with your restoration should you go ahead with it.
Attached Thumbnails
Click image for larger version

Name:	Chassis cradle.jpg
Views:	318
Size:	55.8 KB
ID:	145289   Click image for larger version

Name:	Under chassis view.jpg
Views:	463
Size:	93.0 KB
ID:	145290   Click image for larger version

Name:	Underside of chassis after renovation.jpg
Views:	440
Size:	95.8 KB
ID:	145291   Click image for larger version

Name:	Unanchored unearthed mains entry point..jpg
Views:	322
Size:	86.3 KB
ID:	145292   Click image for larger version

Name:	New earthed mains lead and cable restraint.jpg
Views:	325
Size:	79.3 KB
ID:	145293  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is offline