VBITNGC building & comment

[VT67]

Anybody here that has a source for a 45V-0-45V / 5-10VA toroid transformer.
The lowest VA rating I can find with those secondaries is 160VA, and that is a bit overkill I figure?

Regards

[Hanzwillem]

Originally posted by GeWa
Anybody here that has a source for a 45V-0-45V / 5-10VA toroid transformer.
The lowest VA rating I can find with those secondaries is 160VA, and that is a bit overkill I figure?

Regards

You need only one winding of ~45 VAC. So you can use a tranny ranging 18-0-18 to 22-0-22.
These should be no problem to find in that VA range.

cheers.

(please correct me if I got confused between my projects )

[VT67]

You need only one winding of ~45 VAC. So you can use a tranny ranging 18-0-18 to 22-0-22.

Now that you mention it. Just had a quick look at the schematic and it's indeed only "1" secondary winding.
What's even worse, I have two 22V-0-22V / 35VA trannies in my goodies cupboard. I really feel stupid now

Thanks for the hint Hanzwillem

Regards

[Franz G]

I have two 22V-0-22V / 35VA trannies in my goodies cupboard. I really feel stupid now

Why stupid? Just use two secondaries in series, resulting in 44 VAC, what is perfect for the anode voltage!

BTW: I use one single torroid, about 165VA. It is including 14.8-0-14.8V (LM3875), 17.6 and 19.8 in series for the anode voltage. Then I added some windings for the 6V part (about 60 windings in my case, just try 20 windings, measure under load and calculate the needed windings, its linear).

It is a good idea, when you use the small case and relatively small heathsinks, not to use too high voltage and to much gain for the LM3875.

Franz

[digi01]

Originally posted by Hanzwillem
There seems to be an error in the silkscreen of the PSU board.
I suspect D1,D2,D3 to be printed the wrong way. I don't see this work as a proper bridge as it is drawn at the moment...

Yes,there are silk layer missed of bridge and delay parts,I am so sorry for all troubles.I will release a 'PATH' for the psu board soon.please keep it for a while.

to wim,sorry for delay.because I couldn't surf net during weekend.


P.S.
the attached photo is the connection of 'T' network.

[digi01]

Originally posted by GeWa
Anybody here that has a source for a 45V-0-45V / 5-10VA toroid transformer.
The lowest VA rating I can find with those secondaries is 160VA, and that is a bit overkill I figure?

yeah I have the same problem to find a proper transformer.I use a 20VA 8VAC wallwart directly powered the tube filaments and delay.A step-up transformer(200VAC to 24VAC,in reverse) converted the 8VAC to about 73VAC.


Zang

[wim]

Mayby i missed something, but what is the need for a 45-0-45 VAC trafo? I assume you will put the windings paralel to get about 62 VDC after rectification?

Why not a trafo between 18-0-18 VAC and 22-0-22 VAC, and put the windings in serie? These trafo's are common with a much lower VA rate.

Or do i mis something?

[VT67]

No Wim, you got the point exactly. I think I'm the nitwit who started this confusion. I was under the impression that a 45-0-45 trafo was needed. Look at post #23.
Sorry for all this

Cheers

[wim]

Okee GeWa, now you can choose a suiteble trafo. i take 18-0-18 VAC. RS Components have them in very small VA ratings (cheep and compact). Succes.

[planet10]

Originally posted by GeWa
I was under the impression that a 45-0-45 trafo was needed

For the tube which needs something between 35-0-35 & 100-0-100 @ 15+ mA or so...

dave