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lordearl 5th January 2012 09:38 PM

Broskie "Unbalancer" - transformer specifications
I'm currently in the process of soldering Broskie's "Unbalancer" PCB:

On pages 13 and 18 he specifies what sort of secondaries are required for the transformers, however I am a little confused as to how I need to specify the windings to the transformer manufacturer (it is an r-core type).

The input tubes I am using are 5963 tubes, whilst the output tubes are 5965. Hence in both cases the closest recommendation as per the chart on page 13 of the manual is the 12AU7 - with a B+ of 240V. And an AC secondary of 330VAC. However on another page he specifies the following:

The power supplies require an external power transformer(s) with two secondary windings (120Vac to 260Vac and 6.3Vac to 12.6Vac).
Presumably he is assuming that the 330VAC is centre tapped?

The r-core manufacturer has asked for a specification in the following format:


240VAC input

60 - 0 / 60 - 0 each 150ma = 300ma

6.3 - 0 / 6.3 - 0 each 1.5A = 3A

For the Unbalancer using 12.6v filament tubes - would this be the correct voltage specification?

240VAC input


330 - 0, 1 Amp (200mA for each tube)
12.6 - 0, 4 Amps (say, 1 amp per filament)

Zibi 5th January 2012 10:24 PM

Correct, but for 100W guitar amplifier:
Hammond Power Transformer 290HX

lordearl 6th January 2012 12:00 AM

The Hammond looks good but may be overkill.

A custom wound r-core is probably about half the price and hopefully with those specifications will supply enough juice!

Zibi 6th January 2012 10:05 AM

You don't need 400W power transformer!!!!!

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