Ordering guitar amp OT

[hayun]

Hi guys. It’s my first post on this forum.

I've been lurking around for a long time, I am always grateful for evey useful information.

English is not my tongue, please pardon me if there are strange words..

I have a question;

If I were asking for a 'guitar amp OT’ to Hi-Fi transformer maker - who doesn't know much about guitar amps,

how should I explain it?

I’v read something;
The guitar amp OTs in the past were made haphazardly to reduce costs, that is, they were no different from PT that simply has the turns ratio without any compensation technics.

( https://www.diyaudio.com/community/thre ... st-5260982 )

Someone said that even PT with center tap would be work.

According to this, maybe I ask them to make an OT like a PT? (no interleavings, etc)

Maybe I should show the datasheet of 1750N to him for example? Say.. pointing out the narrow frequency response, primary inductance, leakage..

The reason I ask this is.. there are quite a few experienced iron makers here, Korea, but they are hi-fi guys. I said ‘experienced’, not ‘intelligent’.

However, when it comes to guitar amps.. this is a wasteland. Even I can be the expert. So.. it is very difficult to find ‘guitar amp OT’.

The easiest way is ordering Hammond 1750N on Mouser.
It’ll cost me almost like ordering MM iron in US.. I’ll do it if I have to, but I have alternative way for now. Or, it might be a worthless try in the first place.

Anyway

I’ve built some amps with these local irons.

I built 50w SLO clone 10+ years ago, with the OT, and the amp was absolutely killer!
I know the original DeYoung OT has hi-fi spec.

And Dumble ODS, Fender Vibroverb.. all of them worked great.

I recently built plexi with the ‘verified’ SLO OT.
(It has multi primary 4.4K-3.2K, I run EL34 on 3.2K now. what happened to the SLO? long story..)

However, when it comes to old Marshall circuit, I felt that.. somewhat a suspicion remained on OT itself. It’s subtle thing..hard to explain anyway I think the amp is not on the optimal state.

I’ve checked and tinkered the entire circuit, voltage adjusted, tubes rolled, but you know.. there wasn’t much to look at, since Plexi is simple.
Moreover, this amp is alike ‘all access’ model of Ceriatone, with more efficient structures than that.. so I can convert it to almost every amps that called ‘Plexi’.

The last task is on OT.

Suddenly a thought crossed to mind; if I use the ‘guitar amp OT’, would it be more “vintage-correct” sound?

Of cource it sounds stupid, but..

I’m just wondering, how the lo-fi ingredient of guitar amp OT affect the sound.
Maybe all of this is mislead fantasy, but sometimes it has a thing when it comes to guitar gears.. It’s not an audio system, it’s a musical instrument, right..?

I expect some low cut / smoothed top end, more musical distortion on midrange.. ..in my dream?!

[Stevem]

You’re sweating this a bit too much I think in some ways.

Just have one made like a 1750N which is non Hi Fi like because it’s not interleaved.

Also if you don’t need the 4,8 and 16 ohm taps then that makes it easier to produce a good end result.

Also I would epoxy in the wires where they exit the winding core because I have seen some low quality off shore transformers where a wire it two just pulled out of the core way way too easy.

[hayun]

Thank you for your reply, Steve!

Yes I’m ‘too’ sweating on this, I know.. I wish they were cooperative about the stuff like this.

I just want to prepare some information to explain what I need to them. They make very high quality transformers, just not for guitar..

[martin manning]

Just have one made like a 1750N which is non Hi Fi like because it’s not interleaved.

I don't see anything on the data sheet wrt interleaving. How do you know this?
Heyboer's replacement is interleaved like the original according to this listing: https://shop.amppartsdirect.com/product ... pd-8025a-h
Hammond says they have matched the original construction, so I would take that to mean it is interleaved.

[Helmholtz]

From my notes, the Drake 784-139 is interleaved having 3 primary sections and 2 secondary sections between.

[hayun]

Hmm maybe “interleaved ‘like original’” is depends on era..?

Based on the frquency response data, Hammond 1750N seems to not (or less) interleaved I presume

[martin manning]

The frequency response is highly dependent on the primary inductance, less so on the winding pattern.

[Helmholtz]

Primary inductance determines bass response.
HF response depends on leakage inductance and primary capacitance, which are determined by the winding pattern.
The purpose of interleaving is to improve coupling and thus lower leakage inductance.
A high leakage inductance supports instability with global NFB.

[martin manning]

From https://www.aikenamps.com/index.php/out ... -explained
"The leakage inductance is proportional to the square of the number of turns, so you must decrease the number of turns to reduce the leakage inductance, but this is at odds with the need to increase the number of turns for good low frequency response. In addition, the flux density may be exceeded if you reduce the number of turns. Different winding techniques, such as interleaving, can help reduce the amount of leakage inductance, and improve the high frequency response."

[hayun]

Now I think the Drake OT is interleaved to some extent.

‘less inteleaving’ is making things even more complicated
It seems to need some calculations / do something they don’t usualy do. and maybe good results are not guaranteed with single shot.

I’ve read R.G. said that ‘specific design’ of OT is not that simple and hard to get the actual data without reverse engineering.

I’ll ask them tomorrow anyway, honestly I don't expect much.
Maybe I’d just order 1750N. hoping this is worth a try..

[Helmholtz]

Now I think the Drake OT is interleaved to some extent.

As said before. I verified myself.

[hayun]

As said before. I verified myself.

Thank you for sharing the information! It was very helpful to make my decision.
So Marshall was more serious than Fender on making amps..

[martin manning]

So Marshall was more serious than Fender on making amps..

I wouldn't say that. Both started out using audio transformers that could be sourced locally.

[Helmholtz]

So Marshall was more serious than Fender on making amps..

How that?

[martin manning]

So Marshall was more serious than Fender on making amps..

I wouldn't say that. Both started out using audio transformers that could be sourced locally.

And, Marshall literally copied the Fender Bassman (as best they could using available components) so they could market an amp at a lower cost than the imported Fenders.