220/110 step down in reverse ... and more

[rvrazvan]

I was looking for parts for my first project and stumbled upon an 220/110 step down transformer. I bought it as it was cheap and it had a metal cover and it was BIG.
Now the question.

Can i use it in reverse, as a step up transformer to get around 400v from it? The thing has 200VA.

This is the manufacturers page (Louth Transformer Company l)...but i'm not sure that it is an autotransformer(case in wich i guess it's compulsory to rebuild it).

Also here is the schematic for my first build. It's popular here. The guy says that a 220/9v trafo can be used as OT. Can i do that as a temporary solution?
http://www.lumeatuburilor.go.ro/ARIT...206W/index.htm
Thx and sorry for the noobish questions

[Wavebourn]

Originally Posted by rvrazvan

I was looking for parts for my first project and stumbled upon an 220/110 step down transformer. I bought it as it was cheap and it had a metal cover and it was BIG.
Now the question.

Can i use it in reverse, as a step up transformer to get around 400v from it? The thing has 200VA.

No. It's core will saturate. If fuses surviwe you'll get awful smell and probably flame.

Also here is the schematic for my first build. It's popular here. The guy says that a 220/9v trafo can be used as OT. Can i do that as a temporary solution?
http://www.lumeatuburilor.go.ro/ARIT...206W/index.htm

You can, but quality of sound will be low: LF response because of low inductance, HF response because of high leakage inductance, and distortions because of DC current bias.

[rvrazvan]

They will be temporary so quality won't be an issue(the ot's). The guy suggests to make an airgap between Es and Is. That i think will help with the HF.
Can you please tell me what should i look for? (VA rating, core area) I plan on rebuilding them at some point for use as an universal SE transformer for testing future projects.
Thank you

[Wavebourn]

I would suggest you to go to edcorusa.com and buy decent transformers. They are nice for price/performance, I use them myself for professional amplifiers. Otherwise you'll save on transformers once, but will have cheap sounding amp forever!

[rvrazvan]

To much hassle for that now. i live in europe(romania). And for the moment i'm just learning the basics.
However those edocors look sweet. Hope i'm gonna use them in a bigger project someday.

[Wavebourn]

You can probably find some transformers from Telefunken, Philips, Grundig, and similar European tube radios. They are nice. Just look at e-bay auctions, it is what I would suggest. Edcors would cost you twice of their price shipped. But don't hesitate to make your first tube amp very nice sounding!

[nigelwright7557]

A common technique is to use two transformers.
One to step down to 6v or 12v for heaters then another to step up to the HT.
You will need soft recovery diodes on the HT supply tho or you will get switching spikes.

[mastodon]

Originally Posted by Wavebourn

You can probably find some transformers from Telefunken, Philips, Grundig, and similar European tube radios. They are nice. Just look at e-bay auctions, it is what I would suggest. Edcors would cost you twice of their price shipped. But don't hesitate to make your first tube amp very nice sounding!

It's next to impossible to find a low-priced set of OPT's in Europe. It's no significant problem if you want to spend upwards from $ 250 (Hammond transformers are usually obtainable here, although at higher prices than in the US/Canada), but if you're looking for something entry-level such as Edcor's cheapish models, then you're out of luck: it doesn't exist in Europe. At least, I haven't found it yet in the past 10 years. All you can get here is high-end stuff, which costs your liver and one-and-a-half kidneys, or the scrap stuff from old equipment you're referring to, but expect to pay insanely high prices for that as well. And usually you can only get one xformer, not a pair.

So using power transformers is about the only option you have if you want to start building tube amps at a low budget. But yeah, the limitations are significant. The best I managed was a stereo PP 6AQ5 amp, which has decent LF frequency response, doesn't suffer significantly from core saturation due to the low power level and PP design, but it still drops off beyond 8kHz. Some negative feedback could improve it, but I'd have to spend some time on optimizing it.

So for a learning experience, power transformers are usable, but they're not going to give you hifi, it's as simple as that. Nevertheless, they may very well give you the satisfaction of creating a tube amp that sort of works. I would strongly recommend sticking to a PP design though, so you can use unmodified transformer's. Something with a 2x115V primary and something in the range of 6 to 20V secondary is easy to come by and can be usable for low-powered PP designs using e.g. EL84's, EL90's/6AQ5's or any of the PCL triode/pentode types that are abundant.

[Andy5112405]

Have a look at http://www.vvtransformers.co.uk their prices are very reasonable.

[rvrazvan]

Well the best thing i can do is to order the transformers from a guy here. The price is around 25euros. But i will try to make some of my own. I will eventually try to rebuild them interlacing the primary and the secondary.

About the PP design. That will be my next step. I hope to have a by-amped system in the near future. SE for mids and high, and PP for LF.
I hate europe in a way. everythings is expensive here. I'm a photographer sometimes ) ...an boy ...i wish i could have acces to the low prices in the US. Same thing about cars.

Back to audio. Has anyone here made an open baffle ...with a spherical baffle? Half sphere that is*.
http://lh6.ggpht.com/_wUDOCViv9D0/Sx...anda-matt2.jpg