Hi

The radio in question is an Operatic "Mignon". Its a 32V vibrator set.

Just has a Marantz SR7001 go up in flames on the bench so the radio isnt at reach. I am sure it uses a 24V OAK vibrator can.....

Modern amps are junk... This Marantz was only about 10 years old, All Main Electros had popped their tops and leaked.

There were some counterfeit caps made in the 90's that did Billions of dollars in damage; They did that. I found a couple of that era in my "No Break" (had the build date on the unit) They failed testing & I had a set with one in it last week: Also a dud.

Marc

Hi everyone,

I have an STC Model 556 Mantel (or rather a Table model as it is quite a large radio) that was given to me many years ago and only recently I did a search online and found it to be a 6 volt powered radio.

This surprised me as the radio has a figure of eight cord with a Cat No 99 Bakelite 3 pin plug on it. I can assure you I have not plugged it in but the question I have is would the radio have been modified or not to work on 240 volt AC or is it not possible?

I can only assume that someone in the past must have thought the radio works on AC power and so fitted a 3 pin plug.

As it was originally designed to work on 6 volt DC, I would like to either construct a 6 volt supply or if someone would be happy to construct one for me to acquire. I think the first thing to do is to check through the radio along with a circuit diagram to check if the radio has not been modified/damaged in any way.

Standard practice I keep reading is to replace suspect capacitors and any resistors that are out of spec.

Can anyone advise that if the radio had been powered from 240 volt AC, what should I look for as part of the process of fault finding and assessing if the radio is worth fixing.

I raise this because I notice the forum was commenting on DC powered radios and I thought there may have been situations where people in the past, ignorantly think the radios work on AC power instead of what the radio was originally designed. These radios must have been made for country areas where there was no AC power available.

Bushman

Someone might have added a power supply, but you'd have to look inside to determine that.

If it's still set for 6 volt operation and it was plugged into 240 volts it would have been terminated with extreme prejudice.

Look to see where the power cord goes, does it go to a separate power supply, as Robbbert indicated, or into the main chassis. If the latter, look for a power transformer and check if the power cable goes to it.
Also have a look to see if a vibrator is present and if it is still connected.
Tracing where the power cord goes will probably give you your best clue, (in my opinion!).
Harold

Some of those sets were modular: The vibrator box could be removed and a mains PSU dropped in. 556 is not one of them.

It is listed in AORSM. So its a 6V battery, or PSU. If you use a PSU you can bypass the vibrator & that will cut the power need substantially. 6V Transformer alone may need around 5A

That would require a separate supply for "A" & "B" and power supplies to do that are made, or are in kits to assemble yourself. Set will still likely require overhaul to get rid of Wax Paper caps & Electrolytic's: MInimum. That part's simple but you need to make a slight mod to accommodate the different supply.

Marc

My 6V STC vibrator set (fully restored to original condition with its synchronous vibrator) pulls about 1.1 amps at 6V. The 2V battery valves contribute to this low current. As well as low heater/filament power, battery valves pull far less B+ current than indirectly-heated types. The royer converter (vibrator power supply) will be about 60% efficient when it's running properly so will not contribute much to the current consumption.

You can run it from a large plug-pack, provided the plug-pack doesn't radiate too much rubbish. That's why I grabbed the old-school iron and copper power supply from the side of the road....

You can even use 4 x D cell alkalines. A 4 pack of D cells will run my 6v farm radios and my AWA WW2 Amenities Radio just fine.

If your radio has in fact been wired directly to 240V, you can be certain that the valves will have O/C filaments and the inside of the vibrator will be carbon and bits of melted metal.

Make sure you read posts about the critical high voltage high current capacitor across the secondary on the vibrator transformer. Usually around 0.01 μF 2kV, you cannot use just any capacitor in this position. If it goes O/C it can cause considerable damage.

For earlier comment: Operatic 30T &31T are further examples of 32V radios.

These were designed to work off 32V rural lighting systems. These were common before reticulated power via state grids.