I was Searching on Ebay Recently & came across this Rare Set which uses a Baretter Valve as a Power Regulator, Instead of a Power Isolating Transformer, I Cannot find Any Info on this set, Which normally uses Miniature Valves, Heres the Ebay Link


http://www.ebay.com.au/itm/AWA-RADIOLA-Bakelite-Valve-Radio-Model-539MA-Baretter-/110731739252?pt=LH_DefaultDomain_15&hash=item19c8204074.

Don't see a circuit at a glance in AORSM's

However that is almost bound to be an AC/ DC set if it has a Baretter.

Dangerous little animal if it is?

Chassis will be live and he without knowledge that plugs it in & touches it .... dead.

Marc

The 539MA is in AORSM of 1952 and it definitely has a transformer. There is a picture of that model in Best Years of Australian Radio and it looks to be the same case and dial as pictured in the eBay ad.

On that basis, seems to me the baretter is a hack, possibly to allow use on DC.

If so, I agree that danger possibly lurks within and the seller ought to test for a live chassis, live screws, earth terminal, etc.

Thinking about this further, if it's been hacked for AC/DC usage then the heaters (and dial lamps) will presumably be wired in series, so I would have thought the line-up would not be the usual 6.3 volt valves.

Scary:

If its a Baretter like C1 that hold the current constant at 300mA from memory (have to find out as I have a Stromberg Carlson in the line and it definately is one of them) Isolation transformer job.

IF all the 6.3V tubes drew the same current, then they could be "daisey chained" from 40V (valve number dependant) ....derived how?

The big question to ponder / speculate on is:--- What is that Baretter doing. Sometimes they were used in the PSU as a voltage stabiliser & the SC (on valve heaters).

Was this to stabilise oscillator drift.........?

The only PSU that I have seen with one (in the flesh) was in a "Poly-Metron" pH meter; As a stabiliser.

Some Philips Battery eliminators used them also.

We do need more info:

Marc

Looks like the 6AQ5 and the 6X4 were replaced by a 25L6 and 25Z6. Those, with the 6AV6, 6BA6 and 6BE6 would be a 300ma heater string. And the 25L6 and 25Z6 can accept the 230VAC and resulting 250VDC B+. The baretter (we used "ballast" tubes to drop voltage to run heaters) would have to drop about 170V at 300ma, and that would be 51 watts of heat.

And a chassis that had a power transformer probably would have exposed metal parts that would become "hot".

I would have obtained another power transformer... It should be a fairly standardised item, though it may be a chore to fit it physically.

These AC/DC sets do present problems, don't they. Check out the screws underneath the cabinet - they are uninsulated and are of the same type that are fitted to sets with an isolation transformer. Even if due diligence was used by AWA (and I am sure it was) when applying the correct polarity to internal wiring and the receiver's flexible cord, if you plugged that set into a powerpoint with the active and neutral transposed or with an open-circuit neutral then you are going to get a whack off those screws when lifting the set up.

In many ways I am glad this receiver is being sold by someone who knows the dangers of AC/DC receivers and has taken the time to issue the appropriate warning to buyers. Unfortunately this is not always the case.

Update: Another Ebay member has commented in that sale that the set may have been re-engineered by a previous owner. This may be true, given that the chassis layout diagram on the back of the cabinet indicates that a transformer had been fitted though the chassis shows no apparent sign of a tranformer being fitted - where are the four mounting holes?

Either way, the set is AC/DC at the moment and needs to be treated as one.

The difference between a Baretter & Ballast tube is political.

The Barreter is a filament regulating tube normally an Iron Filament in a Hydrogen Atmosphere and a Ballast tube is........... normally an Iron Filament in a Hydrogen atmosphere.

Good that more info was posted.

That Baretter is in a transformer hole, the diagram shows two bolts and the the holes (slots) are there.

Not that difficult to convert back with the right transformer.

Marc

And I thought a Baretter was the guy that serves the coffee and lattes at Starbucks Coffee.

Anyway, I'd replace the 25L6 with a 6V6 (that's the octal equivalent of the 6AQ5) as it'd be a pain to find a 7 pin socket that fills an octal socket hole (they were made for the purpose, but they are rare). And a number of rectifiers in octal tubes, depending if the new power transformer has a separate 5V winding.

I've seen bakelite adaptors that convert four pin sockets to eight pin so a 5Y3G will service a radio designed for an 80. Not sure if these adaptors were also available for other pin combinations though.

Far easier to change the socket , they are easy to come by, new.

I would check the circuit before throwing in a 6V6, it may have been hacked. 6V6 needs more grid bias than 25L6 which is not a heater altered 6L6.

25L6 may have a screen divider. At 250V plate 6V6 will have 250V screen 25L6 should have around 125V screen.

The one with the coffee is a Barista

Marc