OT transformer position

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norburybrook
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OT transformer position

Post by norburybrook »

Hello Trainwreck people.

I'm about to start my first express/Komet amp and have a marshall 50w OT which I bought some end bells for hoping I could mount it standing. Unfortunately only one side will fit meaning I have to do through hole if I use it.

so my question is; can I cut a hole for the OT over the other side of the chassis in an express type build without it having a negative impact on it? I'm not bothered about tradition or correct aesthetics, only sound.


Marcus
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didit
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Re: OT transformer position

Post by didit »

norburybrook wrote: Thu Aug 10, 2017 12:13 pm so my question is; can I cut a hole for the OT over the other side of the chassis in an express type build without it having a negative impact on it? I'm not bothered about tradition or correct aesthetics, only sound.
Is it similar to this? -- Image

If so 3.6K primary is a poor fit. Stancor A-3801 or close 6.6K clone quite significant to the Express formulation.

Best .. Ian
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norburybrook
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Re: OT transformer position

Post by norburybrook »

I'm not getting an image there....

what effect will using a 3.6k primary OT have then on the build?

obviously a 50w plexi uses this transformer and sounds great with two EL34's.

or

I could get a JTM45 one which is 8k.


thoughts..

M
sluckey
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Re: OT transformer position

Post by sluckey »

norburybrook wrote: Thu Aug 10, 2017 3:59 pm I'm not getting an image there....
That's because it's not an image. It's a pdf file. Try this link instead...

http://www.classictone.net/40-18074.pdf
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norburybrook
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Re: OT transformer position

Post by norburybrook »

yep , it's like that but an original Dagnal 50w OT. 3.5k primary.


So am I better getting a JTM45 8k transformer then instead?

that's the only choices we have this side of the pond.


M
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didit
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Re: OT transformer position

Post by didit »

Hello -
sluckey wrote: Thu Aug 10, 2017 4:14 pm That's because it's not an image. It's a pdf file.
Sorry for that. Checked OK using "preview". Too clever at trying saving a step.
norburybrook wrote: Thu Aug 10, 2017 4:17 pm yep , it's like that but an original Dagnal 50w OT. 3.5k primary.


So am I better getting a JTM45 8k transformer then instead?

that's the only choices we have this side of the pond.
Propose JT45 is better choice, but still missing formulation target. Absolutely encourage others wiser than me chime in.

Personal but limited experience with Express suggests one might make the exception paying Atlantic crossing for this key elemental. In my one amp sample, tried six different OPT. A vintage rusty black A-3801 and the Mercury clone from RJ topped ear-testing list, with different but equally pleasing qualities. Should repeat testing more systematically someday, perhaps adding in a few more transformers and make recordings.

Best .. Ian
Groove1
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Re: OT transformer position

Post by Groove1 »

Hi Marcus,
I took this one for my Express build.
https://www.tube-town.net/ttstore/Trans ... anguage=en

So you can get the 6.6 K primary. I think it is important for the Express-Sound. And you get the end bells also. The factory is In Mad Out in Italy. They make the transformers for the Tube Town-Brand. It sounds great.

Best, Klaus
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norburybrook
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Re: OT transformer position

Post by norburybrook »

thanks Klaus,

they've just made me the power transformer (inmadout) shame I didn't order this as well as postage is £20. I was just wanting to use up things I had lying around here . I'm sure using the Dagnal will sound fine, maybe not 100% express but I'm not that bothered really, I've heard a few of my friends express type amps that are built with very random components and layouts etc and they all sound great. HIs current one uses 4x 6L6's and sounds amazing :D


Marcus
Groove1
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Re: OT transformer position

Post by Groove1 »

... so have a try. The Dagnall is a big name in transformers, especially on the Marshall side. And if it is not the right sound part of the amplifier, you can change the iron.

Good luck, I'm curious how it sounds ...

Klaus
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norburybrook
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Re: OT transformer position

Post by norburybrook »

Groove1 wrote: Fri Aug 11, 2017 11:09 am ... so have a try. The Dagnall is a big name in transformers, especially on the Marshall side. And if it is not the right sound part of the amplifier, you can change the iron.

Good luck, I'm curious how it sounds ...

Klaus
Sure :D As I said my friend is a big fan of the express and has made quite a few most of which are made from very random bit's and pieces and don't follow the tradition in any way other than the component values for the pre amp/PI. They all sound great, regardless of transformer/output valves/voltages/wiring layouts.

marcus
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didit
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Re: OT transformer position

Post by didit »

norburybrook wrote: Fri Aug 11, 2017 12:01 pm
Groove1 wrote: Fri Aug 11, 2017 11:09 am ... so have a try. The Dagnall is a big name in transformers, especially on the Marshall side. And if it is not the right sound part of the amplifier, you can change the iron.

Good luck, I'm curious how it sounds ...

Klaus
Sure :D As I said my friend is a big fan of the express and has made quite a few most of which are made from very random bit's and pieces and don't follow the tradition in any way other than the component values for the pre amp/PI. They all sound great, regardless of transformer/output valves/voltages/wiring layouts.

marcus
Have at it. It will work. Note 2x3.5K close to 6.6K, so "mismatching" impedance with speaker load lands in the ballpark.

Back on original Q -- cannot visualize quite the placements your imagining. Perhaps a photo of mock-up? There are fine reasons for placements in Express. Fine working deviations demonstrate flexibility.

Best .. Ian
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didit
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Re: OT transformer position

Post by didit »

Hello --

Some evidence 6K/8K and perhaps laydown PT & OPT is on a good path Re: chassis. Perhaps more extensive posts on Mark's designs lurking.

Best .. Ian
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