I am wondering if anyone could help. The radio has valves 6AN7, 6AQ5, 6N8, 6BD7, 6N8, and 5Y3. It works quite well except that the rotary on/off switch was blown. At the time I connected it directly without a mains switch but over the years I lost the circuit that I had quickly jotted down. The defunct rotary switch also had connections to a mains filter and probably a hi/low tone control function. I would like to restore the on/off switch, mains filter (chokes etc still there) and tone control (?) if possible. I think I have plenty of options in rotary switches and other electronic components (collected over the last 35 years). Thank you.

Fixed typo.

The mix of valves probably puts manufacture of this set at around 1950, when both baseless and octal valves were used. Knowing the date of manufacture can make it easier to hunt down a circuit diagram, which some members here a lucky to have a fair few of. Would you happen to know the model number? It is usually stamped on the back of the chassis or on a riveted plate in the same location.

Stamped number at the rear wall on right of chassis is: 6981. Stencilled printed black letters (for valve numbers, antenna (A), PU (pickup) & E (earth)) include a black line through the first two numbers (69) and printed letters A6 next to the black line.
The set is a 2 band mantel radio. On the dial lower band is SW - 49m to 16m with some international radio station names shown. The upper MW section is divided into 6 parallel sections (2, 3 , 4, 5, 6, 7) with respective radio station call IDs shown.
Operatic logo is on front top centre just below the glass dial. Near the bottom centre is another oval logo, 'Mignon'.

Does it look like the one in this thread?

Mignon appears on several sets.

The only one I see in AORSM with 5Y3 showing has push pull 6AQ5 or a 6J6 twin triode not two 6N8's (Pentode double diode). the later rectifier showing was 6X4 (Minature)

That was a common line up But every one I see is a 32V DC Vibrator set.that has no rectifier. Vibrator was possibly synchronous?

Some battery ones AG, A12, A72RC. Not unlikely the same basically, but with a transformer & rectifier for mains?

See if there is a number similar.

Marc

Perhaps this model was aimed largely at the man on the land, in a similar way to the Big Brother Empire State Radiolas. I have heard from several sources that 60% of the R51s were battery models.

Yes it looks like the one in the picture but is is not cream. Dark brown Bakelite.
Interestingly I just noticed that the printed letters on the back wall of the chassis said 32V (crossed out by hand and scribbled 240V AC by someone). So someone later (?) must have added the mains isolation transformer and the valve rectifier to replace the 32V DC circuit.

It was more common than many believe that DC-AC conversions were performed. Whilst, when correctly done, this makes the set more useful and inexpensive to run it does devalue the set. However, this isn't a consideration if you just want the set as a conversation piece or something to listen to whilst eating brekky.

This perhaps also explains why the rotary on/off/tone switch blew up. It was meant to switch no more than 32V but had been wired for 240VAC! I will just insert a 250VAC rated push on/push off switch. It would help if I knew the mains filter circuit diagram (all my electronics/ham radio books are in Adelaide..).

This may be the case though in an AC set the current flow on the primary side of the transformer would have been much lower than the combined current flow of the heater, dial lamp and high tension circuits. Whilst the switch's contacts would have been better able to handle the current flow with mains than the battery, the switch's insulation properties may have been too weak, stopping any arcing from extinguishing even though AC is better for this purpose.

An upgrade to 240VAC switches is definitely recommended. To preserve the set's value I would try to obtain rotary switches rather than pushbuttons. The Services Directory on this site contains contact information for people that sell hard to get spares like this.

Update: I just had another brainstorm when pressing the submit button. If your set has a pushbutton on the side, this is likely to be for the dial lamps. It was not common for dial lamps to remain on in the case of a battery set because they significantly reduced the life of the charge in the A Battery. If your existing pushbutton was for the dial lamps I would leave it there to maintain the set's value and just bridge it out do the dial lamps remain on.

G'day,

Stuart Irwin's superb radio list which is on the HRSA website lists two operatic Mignon models with your valve lineup. The most likely one is the Mignon AG which has the shortwave band and the 32V power switched by a rotary which also is the tone control.

The other model is BC only (Mignon A6B), but has a similar circuit with some changes to the vibrator power supply.

If you would like a copy of these schematics, email me at gfr53bigpond.com, and I'll forward them on to you.

Cheers, Graham...

I would think that consensus is that it was a battery set.

The ones that I saw had the heaters in series, these may have been changed to parallel? That means that you could use 6.3 V AC on the globes. As said the original would have switched them. The Airzone 612 I serviced recently also had tone & lights on the same switch.

2v Filament (A): 135V (B). Set circuit was not modified. But a plug in power supply was placed on its battery wires.

Do look carefully at the circuit before you attack, B+ was not very high.


Marc

I have a circuit for an Operatic Mignon 32volt 5 valve if you need it. Contact me at ozenginesyahoo.com.au

Peter

In addition to the Operatic circuit and as mentioned above here, I did not see the comment, you can build a power supply to remove the 32v vibrator. I have a circuit for that as well.