Trainwreck express (A1a) Rectifier circuit question

[jammybstard]

I'm just starting my second combo build (AF1 for the bedroom) and I'm already starting to think about the third and the Trainwreck express has really caught my eye.
The first thing I'm looking at is the power supply am I right in thinking that the three diodes in series are to increase the reverse breakdown voltage? so for example 3x 1n4004 would be 1200v (3x400v)?
[IMG:507:253]http://i51.photobucket.com/albums/f368/JammyBStard/TrainwreckA1aPowercircuit_zps7bed8a32.png[/img]

[martin manning]

Yes, but typically 1N4007 (1kV) diodes will be used. Technically one is enough, but with three there is triple-redundancy.

[jammybstard]

Technically one is enough, but with three there is triple-redundancy.

Cheers Martin.
that was my next question

[jammybstard]

So, If I'm doing mu sums right to get a B+ 0f 410vdc I would need a PT with a secondary voltage of 450-0-450 would that be right?
[IMG:507:253]http://i51.photobucket.com/albums/f368/JammyBStard/TrainwreckA1aPowercircuit_zps7bed8a32.png[/img][/quote]

[martin manning]

My Express has a Pacific PT from rj guitars, 280-0-280 (VAC or rms voltage). A rough calculation for idle DC voltage would be: 280x1.414 to get peak voltage of 396, and the DC will be just a few percent less than that if the input voltage is 120VAC per the transformer spec. If you want to hit 410, you'd need around 410/1.414 = 290VAC.

[cbass]

So, If I'm doing mu sums right to get a B+ 0f 410vdc I would need a PT with a secondary voltage of 450-0-450 would that be right?
[IMG:507:253]http://i51.photobucket.com/albums/f368/JammyBStard/TrainwreckA1aPowercircuit_zps7bed8a32.png[/img]

[/quote]

Most people are using around a 300-0-300 a 450-0450 would give you around 600 volts

[jammybstard]

I'm obviously doing my sums wrong. I'll have to look into that.

Been in the UK, and transformers been heavy choice seems a bit limited.
Barry from Ampmaker.com has some custom made in the UK which seem fairly cost effective.
There's a 275-0-275V 36W that looks about suitable and there's also an output tran that looks ideal:
http://www.ampmaker.com/store/275-0-275 ... ormer.html
http://www.ampmaker.com/store/18W-push- ... ormer.html

I think I'll start putting the shopping list together.

Thanks for your help.

[overtone]

JammyB, you listed an 18W OT for an express project, did you mean the 36W?

BTW I have and still use both the 18W and 36W OTs, but not on the express. Good value if you do not want to import.