Hi Guys,
This one has me stumped! Two 6V6 valves, but only one
audio transformer and speaker output,
but it has two antenna and earth connections.

5Y3, 6V6, 6V6, 6J7, 6SQ7,6U7,6J8.

Any help with a schematic would be appreciated.

It still looks familiar, this being my third Music Masters.

Image Link

Image Link

A limited knowledge of radio is showing. It looks like an A7 which may be on it somewhere? there are two models this is the earlier.

6J8 Triode Heptode: Mixer/ converter

6U7 RF amp: IF amplifier 455kHz

6SQ7 Duo Diode AF Triode: Detector & first audio

6J7 Low Noise Pentode: Phase splitter.

6V6 Beam Pentode: Push Pull amplifier.

There is only one centre tapped (primary) 10K There are two speakers likely woofer & tweeter? and it uses negative feedback from the secondary, to cause oscillation if it's wired wrongly.

Shielded transformer so rewire with three wire flex and use a minimum of 500V filter caps (3).

Circuit is in AORSMs

Marc

Thanks Marcc, I didn't get any speaker assembly, but the audio output former is in the chassis, and there is only two conductors to the speaker socket, same as my other single speaker Music Masters.

Curious there are two 6V6. Surely a driver and tweeter could be run from a single 6V6?

This is the only one with no stamp on the chassis for model number.

Any chance of an email? I'm not a member of the radio society yet.. though I likely will be. would be much appreciated.
bushprogrammergmail.com

I think I get it, there's a 6V6 for either side of the audio sine wave,
so it would have more guts than the single 6V6 with 5K primary transformer?

I've sent you a copy of the A7 from the AORSM Vol. 8. It also appears in volume 9. Unfortunately I am missing volume 9 from my AORSM book collection.

There are also later versions of the A7 that use miniature
valves, but is virtually the same circuit wise.

Another thing about push-pull outputs is the output valves (6V6) have to be of a matched pair. This will usually mean the valves are from the same manufacturer and the same production batch. Matched pairs will have the same plate current and mA/V (mutual conductance) readings.

If the valves are not properly matched you'll get a distorted output as one valve will be working harder than the other.

The good news is that the 6V6 is still in current production, are cheap and can be purchased in matched pairs.

This is a higher end radio, not designed as "run of the mill". I always advocate that in order to fix something,it is a good idea to know how it works, as that gives a clue as to why it won't, when it all goes pear shaped.

This is (as before) a "push pull" amplifier that uses the 6J7 as a "phase inverter" (phase splitter), instead of a coupling transformer. Each 6V6 is amplifying a different "phase" and that is being corrected in the Output transformer.

As per previous post. The two tubes must have the same characteristics, distortion being the penalty, if they are not.

The PP amp may have more than 250V on the 6V6 plates albeit I have seen single ended in PYE with 315V.

The two speakers are aimed at sound quality. The "woofer" handles the lower frequencies and the "tweeter" the higher in treble. That is less of a compromise as the Woofer can go lower in bass and the tweeter higher. The next step in high end, is to have a third speaker in the "mid range" allowing even more and better coverage of the audible range. Most of the run of the mill have Mid range speakers only. Not all speakers are the same, some are sets.

With 250V plate SE 6V6 about 4.5 WattsRMS
With 285V plate PP 6V6's about 14 watts

The 5Y3 should get quite hot running at 100mA

Marc

I'm getting there, I didn't know current could move through space six months ago,
because modern electronics doesn't need to know.

We are talking about this though:
http://www.ebay.com.au/itm/Music-Masters-Radio-Co-Beethoven-Valve-Radio-/231132090088....

And it does warrant, in my eyes, a matched pair of JJ electronic 6V6.
It has phono input, what I was mistaken for a second antenna,
it's switched by the same rotary that is also the band selector.

I would not bother with valves just yet, Jaycar has the Globes for the dial as do others.

There are preliminary steps to take, before plugging it in & blowing it up. It is more than probable that all of the Wax paper caps & Electrolytics will have to go long before you worry about valves. Dud resistors should also be changed as you change caps.

There are set procedures for refurbishment, plugging in an unknown set, to see if it goes, is not one of them.

Modern electronics can be destroyed by ancient technology. Many modern meters cannot handle valve radio voltages and there are a few DVM's that can be flashed over with RF. and DVM's and dirty voltage can lead to significant error.

One big test area, is a re-flexed set where the det audio tube will have DC, RF and audio flying around in it

Marc

Do I have to go find a retired technician's analogue multimeter?

My $39 Jaycar crap has measured 795 Volts AC correctly.

If it's really a requirement, I'll do it though.

Yes I do understand changing the caps and whatnot.
I'm not planning on even giving any original electro/paper caps a chance.

Valves are the only component that I cannot test,
at least with some level of understanding, so they come last,
but I can have them arrive either from EVATCO, or vintage provided tested by a ham.

When it gets down to finer detail it's difficult.
I disagree somewhat with Radio Society ethics about how
we are only the custodians of the pieces we own,
and they are not ours to do what we want with.
Some people don't learn that way.
I wouldn't have learned, for example, how to deal with a field coil speaker,
if I didn't have to do that to fix a radio.

It depends whether or not a technology is more important
than some individual radios.
It would be one thing if Humans lived forever, but they don't.

What is important with the meters is to understand them, how they are applied, and what effect they have on a circuit if used on it.

If the meter is not applied properly, you can destroy it, or damage the circuit that is being measured. Both Analogue & digital can be damaged or give false readings.

Where things can go awry, is from the person drawing the circuit failing to list the Ohms per volt of the meter being used.

The lower the ohms per volt the bigger is the load it places on the circuit. This means that, say a DVM, can read higher, in the same circuit.

On the other side of the coin the DVM has a "sample rate". It reads, averages, and then sends that to the display, whilst reading a new sample. That is where they get into strife with a dirty source and fluctuating volts.

Marc

I disagree somewhat with Radio Society ethics about how we are only the custodians of the pieces we own, and they are not ours to do what we want with.

I also disagree and that is why I am no longer a member of the HRSA - Whilst this certainly doesn't apply to all HRSA members, there are just far too many unelected dictatorial despots there trying to govern everyone's lives and it makes me sick.

I've always held the view that collectors are the ones that invest a lot of money in their collections and that means the items, whether it be radios or parts, belong to those who purchased them, not the hard-line elements in the HRSA or any other organisation. I know there's a few people in the HRSA that would like that society to have absolute control over everything the rest of us do with our collections but I am one who is glad that will never happen.

I wouldn't have learned, for example, how to deal with a field coil speaker, if I didn't have to do that to fix a radio.

Hear Hear. It is sometimes said that the best way to learn is to make a mistake first. There's not many things you can do that will permanently damage a radio, particularly one that isn't rare and spare parts are available for. I've made a few stuff-ups along the way and not on any radio that I didn't end up getting going again.

Whilst this certainly doesn't apply to all HRSA members, there are just far too many unelected dictatorial despots there trying to govern everyone's lives and it makes me sick.

I have yet to meet any of these despots. Perhaps they live outside of Sydney.

I haven't joined yet, I just got an old sample Radio Waves magazine,
and this ethics appeal was made in honour of a former member that had passed.
I will give some of them heart attacks and get kicked out.

It's a bit common sense, naturally you'd have that goal anyway.
A classic car enthusiast would be faced
with the same issues like "when is a car so bad that it's for wrecking",
and "do I want to die waiting for every original part".

If anyone is looking for a Music Masters console there is one at Cammie's Antiques on the Sturt Highway in Paringa, SA. I was there yesterday buying another console so the chance of it still being available is good.