Hi All, I've just purchased my first project radio - Mullard World Master Model 61 from 1940. It will need a little work so trust the enthusiastic and knowledgeable people in this forum can help if I'm stuck.

First step is to locate where info I can find about this model.

I have some VTVMs, a Valve Audio generator and some Valve Ham TX radio so not entirely new to electron burning.

Currently looking for a valve tester also.

Chritta (Christopher)

Welcome to V-R.

The schematic can be downloaded from here: http://www.radiomuseum.org/r/mullardaus_61.html

If you need assistance going forward, best to create a new thread in the Tech Talk section under the model name.

Hi Christopher,

You can obtain a circuit diagram from your radio from http://www.radiomuseum.org/r/mullardaus_61.html. On this site and on the HSRA web site the model 61 and 61A are given as 1939 models, the HSRA list does not mention any new mullard models from1939 until 1941 so your date of 1940 seems quite plausible.

Joe

Hi, Welcome

That Model is listed in AORSM's there is a 61 and 61A.

Can send you a scan of it but you will need to unhide your email in your profile.

You need to have a decent Multimeter and a good soldering iron as a minimum.

Make it safe (New power lead, replace internal rubber wire that is perished)
Replace Electros, Coupling Caps, Check Resistors Etc....

Valve tester is a good thing to have but not a must have. I have a few of them and admit not using it all that much.

I do have one that I am thinking of selling but I have offered it to someone else first.

EDIT: Wow people beat me to it..... The time it took me to write this you 2 jumped in!

G'day Chris,

Welcome to the VR forums.

There's a valve tester on Ebay at the moment:-

http://www.ebay.com.au/itm/322557475946

It is showing "as is, untested" so it probably needs a resto but these things are always fixable.

I have one of those thankfully in much better condition.

That one has also been modded in the past to accept the 7 and 9 pin valves. If you do buy that one then the manual is available as well as the valve data charts. I would definitely check it out before using.....

I, too, have this model radio and would be closely following the thread regarding the restoration of the radio.

It seems the model radio I have, has been also been subjected to modifications to, as a brief look in the back shows a missing final valve however the socket is a B4 type. Just right alongside the socket is a rather large resistive coil on a white former that was fitted to the chassis. This barely gives the final valve any room to be fitted.

Must make a back panel to not only make the radio safe, but also to prevent anybody trying to pick up the radio by the top of the Bakelite case.

Really nice cabinet after a clean up, however there are some small paint spots to remove.

Thanks for the responses and welcome. Looking forward to this project to really get my head around receivers, valve radios. I am a Ham operator and have several valve hybrid TXs and a Drake TR4C which is all valve but even these are beyond my skill to repair on my own.

Hi Bushman - we should certainly be comparing notes on findings. My case is in good condition and I have some plastic polish on the way to give it a real clean up. The chassis and components are rather dirty so need a proper scrub.

Looks like an isolation transformer is something I will need for when it's plugged back in to test, align. Where can these be obtained and is it just 240 to 240 volt? What sort of VA rating would suffice?

First task is to remove chassis from case to fully inspect and start cleanup. Will need to source suitable caps - are there some recommended places to purchase these from.?

Hi Chritta

I wouldnt say you need an isolation transformer, Its not a Hot Chassis (ie it has a power transformer). An isolating transformer is only needed when playing around with Live Chassis sets. Dont get fooled into thinking because you have an isolation transformer you are safe!

Caps can be purchased from a few sources. If you are a HRSA member then available there, If not then Carl Tallar (username: Tallar Carl) has taken over supply of them from another person. There is also a person in adelaide area who sells them on ebay (User QCH).

I would suggest getting the 630V ish Yellow axles as they are reliable and not too expensive. as for the electros C47 and C48 the set will have had 525V ones. DO not use anything lower in voltage.

Dan

I would like to see a under chassis shot of this radio . In another thread of cause, possibly in tech talk.

Now that the thread has begun, best to keep it here.

I've encountered a grub screw in the volume control pot which is stuck and now stripped so haven't been able to even start on the radio as it's still in the cabinet. I've spent hours on it over the past two weeks and had many good suggestions - all to no avail.

The grub screw is quite recessed so using a dremel disk to cut a deeper grove in the screw head is not an option.

It's too small to use an easy out screw extractor

Some ridge on the pot shaft is preventing knob for sliding off although it's very loose.

I'm at the point now where using hacksaw to cut shaft of pot appears to be the only remaining option?

How hard or easy would it be to find a suitable replacement pot?

I think the pot is stuffed anyway with all the twisting and pulling it's been subjected to.

Very frustrated that possibly the smallest component in the entire radio has caused this much grief! The other 3 knobs took 30 seconds each to remove.

Hi Chris,..........OFF WITH ITS HEAD!

I have had the same experience and after WD40/drilling/hitting/pushing/pulling/heating came to my senses.
The knob and the cabinet are far more important than the shaft of the pot.

I used a hacksaw blade to slice through the shaft and protecting the knob and the cabinet with strips of metal as guards.
The internal brass collar had 'welded' it self to the shaft.
Once the set is out you will see what type of pot it is.

The only warning is the pot may be a complex type with a switch or tappings that cant be found in the junk box.
If irreplaceable the other thing to do is to sacrifice the knob, cut the bakelite and brass collar away and free the shaft.
I'm not familiar with the set so other members may know if the pot is an 'irreplacable' type that would need re-building from scrap parts.

Yes I am a 'gung ho' type!

Cheers, Fred.

My last resort is trying "freeze spray" to see if the this will provide the tiny extra clearance needed.

The control in question is the volume pot - not a bandswitch or anything complex. I think it is R22 on the diagram I have which is rated .5meg ohm, tapped at 35, 000 ohms.

Ive got easy access to the shaft as the knob is VERY nearly off- just catching on a ridge near the very end of shaft. So hacksaw wont touch cabinet

The knob must be saved and even lopping off the pot still presents grub screw removal exercise.

the knob is VERY nearly off- just catching on a ridge near the very end of shaft.

In that case, if you use a Junior saw you may still have sufficient shaft remaining to refit the knob afterwards?

A tapped pot such as that will be difficult to find these days unless someone has a donor set.

Alternatively, people have been known to turn up new shafts on a lathe to repair rare pots.