Tube PSU question

[Greyskale]

Hello,

I've been trying to figure out this PSU schematic, but can't seem to work it out. I haven't worked with allot of tube PSUs yet, so the multiple secondary windings are strange to me. Can anyone advise on what kind of transformer to look for?



Unfortunately I can't read German so I can't really make sense out of the site: Zwerg amp

[SY]

This will be either a custom unit or one you can make up out of two or three separate transformers. There are some real advantages to using separate transformers, notably the lack of coupling of HV diode switching noise back through the filaments.

[Greyskale]

I do believe he is using 2 transformers, but doesn't specify type on either.

[jnb]

You can use three transformers for ease of finding them. The voltage and current is noted on the diagram. Multiply the voltage and current to get the needed VA(Watt) rating.

[wine&dine]

Originally posted by Greyskale
Unfortunately I can't read German so I can't really make sense out of the site:

Aw, c'mon - Google is your friend:

http://translate.google.com/translat...hl=en&ie=UTF-8

It does struggle with the awkward combined nouns, for your convenience this should help:

Subminaturröhren = subminiature tubes
Wegwerfgerät = throw-away unit
Basteleien = DIY projects
Sendepentoden = pentode for RF transmitter
Triodenschaltung = triode-connected
allumschließende = all-enclosing
Schmierzettel = notepad ;-)
"The strengthening of 1 runterbringen?" (yikes!) = getting amplification down to 1
Endröhren = output stage tubes
Vorröhren = input stage tubes
AÜ (Ausgangsübertrager) = output transformer
Lötstützpunkte = soldering pads
Lötleiste = pad strip
gegenphasig = phase-reversed
kanalgetrennt = separate channels
übereinandergestellt = sitting on top of each other
Brumm = hum

As it has been pointed out, you can use separate transformers. You could even use a small 230V primary PCB-mount type "in reverse" for the anode voltage (e.g. 230/12V fed 9V to the secondary will give ~180V on the primary).

Buuut ... the beauty of the little "Zwerg" ("gnome", "midget") is the construction with the transformers as part of the case, and for that you'd need the custom ones with just the right windings.

Luckily the designer, Gerd Reinhöfer, runs his own business selling parts and kits for tube freaks at www.roehrentechnik.de. I couldn't find this particular model, but the guy produces them to customer specs anyway.

[Greyskale]

Originally posted by wine&dine
Luckily the designer, Gerd Reinhöfer, runs his own business selling parts and kits for tube freaks at www.roehrentechnik.de. I couldn't find this particular model, but the guy produces them to customer specs anyway.

Ah... see now this changes things... I had run the google translator on it, but had been struggling through some of the more awkward sections. I hadn't realized these were custom iron, rather I was under the assumption they were off the shelf parts. I certainly don't mind using 3 different transformers as I'm not trying to clone the aesthetics of the amp... but I am interested in the circuit . I had just thought if there was readily available iron out there I would pick it up to build this PSU. Thanks for all your help guys.

[Greyskale]

bumping this thread because I just found this:

Zwerg build

This guy seems to have pulled it off with one transformer... I can't tell the branding on the power trafo, but he's using Hammond output iron so it's a good chance it's "off the shelf"... of course the site is in Thai (not a google translator for that). I know nothing of PSU design. Can this be done with one off the shelf transformer?!?

[wine&dine]

Originally posted by Greyskale
Can this be done with one off the shelf transformer?!?

There's nothing magic to mains transformers. Find one with voltages matching what you need and amps matching or exceeding that, and Bob's your uncle. Custom transformers are not too special either - but you need the core and the wire, and having a winding machine helps a lot. Serious tube enthusiasts used to (and still do) re-wind similar transformers to match their needs. Unfortunately, most modern iron has welded cores however.

Over here, we still have a number of transformer and motor repair shops that will make exactly what you need, and then there are mail order specialists.

Since you don't seem to be committed to the building style that requires one transformer, you can just as well use a combination that will match.

My educated guess is you'd be better off with a custom order. Google for "custom transformer us" and have fun.

[jnb]

Not to get too repetitive but I'd like to second what SY said earlier and express my opinion that separate transformers are slightly superior in the areas of noise isolation, load regulation and stage interaction.