I have a question, I recently bought a 1930's amplifier that looks like it was designed to run on DC mains.

What was the voltage back then? Was it still 240?
Was there more than 1 voltage depending where you were?

Many thanks Josh.

The mains voltage was 240 volts for AC or DC mains going to domestic premises. 240V and other voltages were supplied to commercial and industrial premises.

DC appliances don't have a mains transformer so extra caution is required for restoration work and subsequent use of the appliance. If the power cord or the GPO the appliance is plugged into is incorrectly wired then the appliance is a definite shock hazard. Such appliances are also unlikely to work on AC mains, unless it was specifically designed for use on either system. The clue here is the presence of a rectifier valve.

There is a listing in the 1937 Trade Annual (have a copy) listing who had what at the time. There was no "Grid". Right up into the sixties many Farms were still running 32V.

A lot of the AC/DC sets had Barretters (Ballast tubes).

There is a listing in the 1937 Trade Annual (have a copy) listing who had what at the time.

If you can find the time to scan that I think it would be a good item to have on here in the Articles and Tutorials section.

It's a Berretter Amp (picture coming)
They Bridge all the heaters
Am looking at building a power supply style unit to run it but for the time being
using a rectifier and cap on a variac for testing

Josh

There is a listing in the 1937 Trade Annual (have a copy) listing who had what at the time.

That information can be found here:

https://vintage-radio.com.au/default.asp?f=1&th=954#7136

I believe that was scanned some time ago as, a really handy reference.

Normally all of the valves have the same current draw on the heater/ filament & one of possibly more than one element in the Barretter holds that current constant, in a series train.

What is the purpose of the Variac? If it is to keep volts down fine; But, if it is to provide isolation... no Way! It is an auto transformer, not an isolation transformer.

Below 130VAC an RCD will not trip 30mA on a tester. Did that deliberately, to prove to myself, that relying on the RCD with a Variac was folly.

If the set is 230V, what I acquired for not a lot of money was an isolation transformer (in box). I had to change the socket. It had a fuse inside. Device rated a 3A and I would say continuous.

I did add surge protection & some line caps to get rid of the RF that rides on the 24KV aerials and a bezel on the secondary to show when it was dead (fuses fail) On Off has light.

The major addition was a "Kill" switch on top. Great if you start a radio & things start going awry. You can have your hand on it.


Marc

Brad: perhaps you could put this document in the Article and Tutorials section so that we can easily point to it in future.

No worries Marc the Variac is purely for test purposes and working what value transformer I will need to build a proper power supply.

Roughly calculating 170v Transformer through a rectifier and a cap should give me just over 230v DC

Josh

GTC, all done.

Thanks Brad

(PS: I note that the URL appears to not be on a new line)

Hmm, looks okay in IE but I will check it tonight. Thinking back, you are probably right. On the last line I always leave out the trailing '<br>' and this is the line I copied/pasted before altering the URL.

(Might like to fix the thread title's typo, too)

Both now sorted. Just to make people aware, more care is needed in titles as there is no spell checker for them and it won't be offered as the existing one already slows down the site a bit.

Beautiful, all side contact bases, even the baretter. Never seen anything like it.