Recovered PT with B+, 2 x 6.3v and 1 x 4v windings - Why 4v ? wich was the use ?

[kagliostro]

At the Ham Fest in Friedrichshafen I recovered a pair of OLD Power Transformers

what is strange to me (and I find this thing in other old transformers) is that there are B+ windings and 6.3v windings

but also 4v winding (note, not 5v but 4v)

in one transformer I recovered yesterday there is a 4v winding labeled for 2.2A, so not a poor current, in the other a 0-4v-6.3v winding plus a 0-6.3v winding ............???

I've find this 4v windings also in other old PT, someone knows the reason for this 4v winding ?

Thanks

Franco

[mat janssen]

AZ4 or AZ1 are rectifying tubes with 4 volts on the fillament.

[kagliostro]

I see

Many Thanks for the info Mat Janssen

AZ4


AZ1


Franco

[PRR]

4V was standard for many English tubes.

It probably aimed for two lead-acid battery cells, but lasted long into the AC heat era.

A lot of early US AC-heat tubes ran 2.5V.

The "6.3V" standard really came about with the rise of Car Radio. US cars were mostly 3-cell 6.3V systems. (UK cars were mostly 12V.) New tubes were introduced for car radio. These tubes also worked good in AC sets, once 6V taps were put on PTs.

AFAIK, UK stuck with mostly 4V until WWII. Some time in there it became wise to use a lot of US tubes (large factories not at risk of bombs) so 6V became standard.

[kagliostro]

As always your explanation go deep on the matter

Many thanks PRR

to read yourtechnical story lessons is allways a pleasure

this remembered me I've to open a new thread on "Other Topics" about a discussion we (I and my Radio Amateur friends) had just yesterday

at the Friedrichshafen Ham Fest (the bigger Ham Fest of Europe)

Grazie Ancora

Franco