G'Day Folks.
Chasing a circuit for a Music Masters A524M.
The closest I can find, is for an A5 in the AORSM for 1948, which has the same valve line up.
Some one has been at the radio at some stage as
It has one end of the HT choke connected directly to the wiper of the volume control, which heads off to the SG of the 6SQ7.


Many thanks....

Ew, that sounds bad. Hopefully nobody powered it up since that was done.

Good luck fixing it !


btw, what is the valve line-up?

G'Day Robert.

6J8, 6U7, 6SQ7, 6V6 and 5Y3GT.

Not sure if the A5 circuit is the same as the A524.
Only thing I can find that fits the valve line up.
Nothing appears to have suffered any stress.
all chokes and transformers, test ok.
Might have to wire it as per the A5 circuit.

Looks like a typical valve line-up for the period. It should be a straight-forward job, as long as the 6U7G still has its shield and you replace the usual suspects.

A523 matches that line up too. Schematic here. Double click to download it:

https://www.radiomuseum.org/r/musicmast_mendelssohn_a523m.html

Thanks GTC.
That 523 circuit is the same as the A5 in the AORSM, which is different to the A524.

I was sent a hand drawn 524 circuit, which looks more like what I am seeing in this radio.
I think some one has tried to set it up as per the 523 circuit, but only half did the repair. ??

Thanks again have a great weekend.

I think some one has tried to set it up as per the 523 circuit, but only half did the repair. ??

Stranger things have happened. Hope you can get it back to something approaching the original.

The badge on the front does not necessarily indicate who built it nor does the model number correlate with what the chassis is. STC was a bit like that where there were models more related to the cabinet whilst several models had the same chassis.

The plot of most of those were similar, there are three models in AORSM with that line up. The last one is possibly the same as all the others, or has had the bugs ironed out. I have an Astor made chassis here where it has factory mistakes, is labelled one model, but has the miss wired front end of the previous one. This is not the first time in 50 years where I have seen that.

Wire for the one that looks the closest. Eg the amended one.

I would be tempted to use 600V filter caps in that but not less than 500V It's showing a shielded transformer: Here, that would automatically result in a mains grounded cable.

I wouldn't use 500 volt caps on these as some of the ones I have seen only have a surge capacity of 500 volts. yes that's correct a 500 volt electro with a surge capacity of 500 volts. Sound ridiculous but that is the case. I have 600 volt electros available so email me if you wish. Email is open.

One should take a hint from what was original. The universal Red Ducon cap used nearly everywhere On "B" voltage, had a surge rating of 525Volts. If it didn't it was probably 600V. There were lower surge voltage ones, however, they were normally in sets with lower "B" voltage, but mainly heater rectifier sets.

I have had supposedly new 500V caps let go at below that. That's a great way of loosing a customer.

I have replaced with 600 Volt 8μF caps.
and I will check
Tallar Carl and Steve for components on the forum, when I need more, which isn't too far away, best to support the people on the forum, I normally buy from Evacto, the original company and the owner, was on the same road, we rented a house, while we waited for our house to be built two roads away, but that was around 20 years back, have moved further west twice, since then.
and since they were very large acreages, there, was around 10 houses, at the most on the road. bit of a remote rural area.
The company was sold a few years back, and is now a Brisbane based company, but it's not the same.

And yes there is a 3 core flex fitted, with grommet retainer
I think these are not factory mods ,some one has replaced the paper caps and not sure what they have done or why.

The tone control wiper had HT directly connected and that went to the SG of the 6V6.
There was no back bias to the 6V6 and the signal from the anode of the 6SQ7 never made it to the grid of the 6V6.
I now have a working audio stage.

The oscillator is working down to about 1 MHz, drops out after that.
Have been replacing many resistors, I had two marked as 20K that read 65K and the 300 Ohm resistors on the Cathodes of the 6J8 and 6U7 were both very high around 700 Ohm and 1.5K

Voltages are looking a lot better.
Bit more time and it should be working
many thanks for the assistance.
now the painful part, coming up will be restringing the dial.....

Hi, I haven't read all of the replies to your post but I would suggest that you disconnect the HT from the rest of the circuit and check the available HT voltage, then connect the output valve and after checking voltages put a signal (your finger on a screwdriver) into the input grid this should give you some noise through the speaker. If all is OK up to this then connect the audio driver and check again for noise from your finger coming out of the speaker. Make sure you only touch the grid(s) with one finger and that your other hand doesn't connect to chassis ground.
Let me know how you go to here and if everything appears OK we can then n=move onto the next stage. A bit more complicated to ascertain it's operation.
Cheers,
Mike

Mike, I would suggest reading the replies, always worth the read, so many people with so much experience, always pick up something.
I normally spend some of my lunch hour at work reading the postings on the forums.

Thanks for the advice, and it is a good reference for for everyone.
Audio stage is working very well now, IF stage also working very well.
In this case, checking the Grid on the 6V6 with my finger, prior to making the changes, would not have done very much as
The tone control wiper had HT directly connected and that went to the SG of the 6V6.
There was no back bias to the 6V6 and the signal from the anode of the 6SQ7 never made it to the grid of the 6V6.
I normally connect the Scopemeter to the grids, I use the 10:1 probe to check if there is any leakage through the coupling caps from the previous stages. as a quick check, and it also has the same effect as the screw driver, I try to avoid the finger on the screwdriver, never know who has been there before and if for some strange reason the grid has HT on it

I do have an issue where the oscillator stops around 1 MHz when the tuning gang is meshing.
No shorts to the tuning gang, though, measured the continuity between the plates and nothing when meshed.
still a few more components to change, I dare say and I will try another 6J8.
but almost there.

This is the first Bakelite Music Masters I have worked on.
I have many consoles and a wooden mantle.
I grew up with a couple of 1930's Music Masters Consoles, I had one in the bed room and used to listen to a lot of shortwave broadcasts and HF aircraft frequencies, prior to the switch over to SSB, although two radios would allow me to have a radio to receive and one to use as a very crude BFO for SSB. I used to listen to the navy on 8.122 MHz and Raaf on 8.975 MHz back then.
memories...

I drive past the birth place of the Music Masters company most days to drop Heather at work in Auchenflower on my way to work.

My biggest issue will be the tight access to set up the dial cord, I had it set up and the screw that tightens against the tuning gang shaft and also retains the spring for the tuning cord, came loose, it took me an hour or so to get it set up, was working so well, the drum is cast and has may cracks, I had to epoxy the section that retains the nut, It just broke away, this glue seemed to work, but I must not have tightened it up enough..

Oh well back to work...tomorrow

Thanks for all the help and advice folks.
Cheers
Peter..