Dual-rail PSU ála hiwatt possible with separate iron of different sizes??

[kilowhat]

Hi guys, i have some leftover PTs. Please see attached hiwatt PSU for what im thinking. I dont think it possible (been a while, so am rusty on EE), but can i run a similar topology, albeit with two separate transformers of different rating?

The screen+preamp PT is 38va (incl filament heat for preamp, output heating from separate iron), so 240v 120mA which would give about 100mA 290v rectified B+;
Then the "stacked" PT (i.e CT referenced to B+ of above mentioned PT) for output duty, which is a 100va isolation toroid with 115-0-115v @430mA outputs. Would give ~700mA at 140v for output supply after FW(non-bridge) rect;
== total B+430v ontop the smaller PTs B+ feed of 290v.

Doesnt feel feasable (no free lunch), but if anyone know otherwise, i would really appreciate prompt replies cause i have an offer (expires within 24hrs) on OTs that would fit the bill.

Best regards /kw

[kagliostro]

The problem isn't to use two separated PT or the fact that they are rated for different current

The problem is that both transformers MUST be able to feed the current necessary for plates + G2


Which are the voltage and current you need for your project ?

With your transformers stacked you can feed a max current of 100mA DC (as per your math, to me they will be more around 70mA DC)

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100VA @ 115V - 0 - 115V will be around 860mA AC then 520mA DC so 520mA / 2 = 260mA DC for a FW rectified

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May be (or not) we can arrive to it with a doubler

Franco

[kilowhat]

The problem isn't to use two separated PT or the fact that they are rated for different current

The problem is that both transformers MUST be able to feed the current necessary for plates + G2

With your transformers stacked you can feed a max current of 100mA DC (as per your math, to me they will be more around 70mA DC)

Franco

THAT is what i suspected (just couldnt/still cant see it in my head when reviewing the schematic). Thank you Franco, much appreciated!
By the way, the OT offers i mentioned were from a winder in Italy (piemme electra). Maybe you already know of them? Have had successful purchases from them before, and havent found any better prices in EU on iron - so just a tip as thank you.
P.S please let me know if you know of even cheaper winders inside EU! Have tried inmadout, also from Italy. Satisfied there too, but a little more steep pricing, atleast at the time (not sure if still true currently).

/kw

[kilowhat]

Also Franco, sorry for miscalc (still rusty on EE) - you are right on the current! I just divided with 1,2 as per inverse of voltage increase of rect, but forgot the RMS current is supposed to be ~1.8 times the load current. Thanks again! Best regards /kw

[kilowhat]

Sorry missed a question. Dont really have a project in mind. Just had these leftovers (i actually have two identical sets, for a stereo-project that never got build) and started thinking if maybe there could be an output section for guitar use, i could use them for instead. But maybe ill just sell them, or let them rest on the shelf if i ever get around building the initial stereo set. /kw

[PRR]

> 100mA 290v rectified B+; .... 115-0-115v @430mA outputs. Would give ~700mA at 140v for output

You want to pipe beer from here to there. You expect to splice. If you need 700 liters/minute, a 100 liters/minute pipe is not part of a solution.

[kagliostro]

A friend of mine is a loyal customer of Piemme Elektra and the products are very well built, also is possible to have custom transformers, about InMadOut I think he suspended the activity but I'm not sure 100% about

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You say you have an isolation 115v - 0 - 115v transformer rated for 430mA AC

(Note that if the transformer is instead 0 - 115v  /  0 - 115v things are different)

if you don't connect the CT  and use both extremities you can obtain a 230V winding

from 230V AC with a FWB you can have around 320V DC and the 430mA AC will result in something like 260mA DC

add to it a transformer for the heaters (or a 6V or 12V transformer) and you can feed an amp with el84 tubes (or other tubes that are happy with that B+ and current)

Franco