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 Music Master Schematic
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 Return to top of page · Post #: 1 · Written at 7:27:06 PM on 23 August 2019.
Alarum's Gravatar
 Location: Toowoomba, QLD
 Member since 6 July 2019
 Member #: 2359
 Postcount: 12

Good evening all,

Finally worked out that the radio I am working on appears to be a Music Master A6 radio.

I'm trying to make sense of the schematic. Everything lines up exactly, including resistors and capacitors. The only thing I can't work out are the two potentiometers that I have marked in colour. The blue pot lines up exactly as in the radio, however I have no idea about the red pot.

My question is, what does the red pot do exactly? The blue pot is the volume control knob, but the red pot is nowhere to be found on the radio.

Will it matter if the red pot is not included and wired up in the radio?

Image removed - see e-mail


 
 Return to top of page · Post #: 2 · Written at 7:58:39 AM on 24 August 2019.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 5498

Photo uploaded.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 3 · Written at 8:37:00 AM on 24 August 2019.
Arty41's Gravatar
 Location: Brisbane, QLD
 Member since 18 September 2010
 Member #: 118
 Postcount: 289

I'd say it's the tone control.


 
 Return to top of page · Post #: 4 · Written at 9:17:52 AM on 24 August 2019.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1073

Yes, it is the tone control using some negative feedback to improve the sound quality.


 
 Return to top of page · Post #: 5 · Written at 10:53:32 AM on 24 August 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3698

Love the Typo I think that might be 6J8 especially if its got Shortwave


 
 Return to top of page · Post #: 6 · Written at 3:45:25 PM on 24 August 2019.
Alarum's Gravatar
 Location: Toowoomba, QLD
 Member since 6 July 2019
 Member #: 2359
 Postcount: 12

Yep, worked out pretty quick that it was a 6JB!

The weird thing is that there is no tone control knob. The on/off switch is exactly that: either off, on with no dial lamp and on with dial lamp.

Would not having the tone control in the circuit affect the radio at all? Will it still work and be able to recieve?


 
 Return to top of page · Post #: 7 · Written at 8:21:35 PM on 24 August 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

So, you are saying that your particular set has no tone control circuitry at all (neither of those caps, nor the resistor and the pot) and no place to mount a tone control pot? If so, then it appears that you may have a variant of the A6.

A receiver doesn't need a tone control in order to operate. The tone control merely allows the user to adjust the tone to personal preference.


 
 Return to top of page · Post #: 8 · Written at 9:14:35 PM on 24 August 2019.
Alarum's Gravatar
 Location: Toowoomba, QLD
 Member since 6 July 2019
 Member #: 2359
 Postcount: 12

Yes, this is a vibrator powered version of the A6 as far as I can determine, and there is definitely no tone control pot/resistors/caps on the chassis.

Once it has been recapped and ready to go, I'll see how it sounds.


 
 Return to top of page · Post #: 9 · Written at 9:16:30 PM on 24 August 2019.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1073

There may still be a fixed network of parts to perform the negative feedback function. Take a look at the 6V6 anode connection and see if there's a capacitor connected there, then see where it leads to.


 
 Return to top of page · Post #: 10 · Written at 9:27:20 PM on 24 August 2019.
Alarum's Gravatar
 Location: Toowoomba, QLD
 Member since 6 July 2019
 Member #: 2359
 Postcount: 12

There is a capacitor (0.01mF, 600V) attached to the anode, however it connects to the output transformer on the screen grid side. According to the schematic, this is incorrect. The capacitor should branch off the anode back to the tone control. No other components of the tone control exist.

There have been a few connections which don't follow the schematic around the 6SQ7 and 6V6 tubes. I'm changing them back to what the schamtics say.


 
 Return to top of page · Post #: 11 · Written at 10:23:38 PM on 24 August 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3698

That still sounds odd 0.01 mfd I would expect across the OP transformer screen to grid. Plate to ground 0.005 mfd.

The DC switch on a battery set would in most cases loose the dial lights, once its put on the station, as they consume battery.

The answer to the tone control lies in it being provided for as a potentiometer, or switched as part of the on off switch?

One would half expect also terminals with the rest of the parts if there was a tone.

If this is a hack anything can happen: Some mods I have seen were absolutely bizarre.


 
 Return to top of page · Post #: 12 · Written at 12:54:16 AM on 25 August 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

The answer to the tone control lies in it being provided for as a potentiometer, or switched as part of the on off switch?

Alarum says in post #1 that there is no sign of a tone pot. Presumably this set has only two knobs: tuning and volume.

.Alarum, please post some photos of your radio.


 
 Return to top of page · Post #: 13 · Written at 1:05:25 AM on 25 August 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

this is a vibrator powered version of the A6 as far as I can determine

The only Music Master vibrator sets that I can find in the AORSM have the typical line-up of 2 volt valves. How are you powering your set?


 
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