Question about iron used in OT's

[John Fisher]

Hello everyone,
I had a question about OT's.
I know that with Hifi Ot's the lamination used are a bit thinner and possibly a little different then the lamination used for power transformers. I realize that this is to have better frequency response especially in the highs for HIfi amps.

I have built OT's myself with both kinds of iron with success. The amp I am using now which I have been using for years successfully, I made the OT using regular power supply transformer iron and it sounds great to me.

I realize that with guitar amps, the frequency response is less demanding then with HIfi amps.
So my question is....
Do the commercial amps like Fender, Marshall or whatever use the iron with the thinner plates for their guitar amps or do they use just regular power transformer iron?

Thanks for your input!

[Steve Conner]

Hi John

Long time no see. I remember your home-made amps from years ago, and thought it was really cool that you made your own transformers.

As far as I know, guitar amp OTs use regular power transformer laminations. I have one OT from an old Japanese PA amp with very thin laminations, but I've never seen another one like that.

[EFK]

Didn't the old Radiospares OT that MArshall first used on the JTM45 have much thinner laminate plates than the later Drake transformer that was adopted? I know that the RS transformers are usually described as having a more hi-fi character, not as dark as the Drake.

[John Fisher]

it is good to be here again Steve and everyone else. I mess conversing with you.
I have been preoccupied with life and undergoing many new life changing experiences. It's all good!

I am now embarking on doing some new projects with tube amps a lot more now so I am sure I will be around more.

So if it is true the that majority of tube amps use normal power supply iron that would be good news for me as it is almost impossible to find the thinner plates where I am but very easy to find the normal ones. So generally speaking even Fender and Marshall use normal iron?

[pdf64]

I'm sure there was a thread a few months ago where this cropped up, and there were some very detailed contributions regarding lamination material and thickness, considerations and constraints.

[J M Fahey]

Fortunately "regular" laminations work fine.
I use 0.35mm with no problems, can get 0.25 mm ones but found not advantage on using them, maybe on a Hi Fi one but not here.
That said, maybe they are the ticket to clone a Partridge built, Hiwatt type OT.

[Gregg]

There's no problem using "power transformer laminations" which are 0.5mm thick and they don't have to be the M6 type either. Good quality low loss new iron will do the job.

[Diablo]

The lamination thickness will effect the core loss and efficiency, all other things being equal. If you increase the lam thickness the heat will go up. There are also many steel compositions you can use for the OT. You could use semi-processed steel or fully processed steel with and without coatings. You can use non-oriented or grain oriented steel steel. The alloy composition varies greatly between these different steel types and the magnetic properties also vary greatly. I won't speculate which ones sound better, only that they might sound different from each other. M6 (grain oriented) appears to be a common grade for musical instrument OTs.

If you need a small quantity or large quantity of E and I laminations you can purchase them from Tempel Steel in Chicago IL. They are a large stamper of laminations for transformer and motor manufacturers. They stock the standard sizes of E and I lams in various steel grades and gauges.