JTM 45 output transformer RS clone

Alex335

Could anyone point me in the right direction finding a Radio Spares Deluxe output transformer clone for a JTM 45 build?.

I’ve tried contacting both Marstran and Merren but haven’t heard anything back from Merren and Marstran stopped replying to emails mid order? 

Many thanks 

ecc83

ICBM will have the full SP but did Marshall use that RS transformer? Seems an expensive, "hi fi" component for a guitar amp. Also, I believe the Deluxe traff had ultra limear taps? The JTM45 schemetics I have found do not use them.

I would have thought any good quality EL34 transformer would have been suitable? Hammond get a good rep.

e.g. https://www.tubeampdoctor.com/en/output-transformer-for-marshall-50w-2x-el34-4-8-16-ohm

Dave.

springhead

Yes they did use the RS Deluxe early on. I think they bought everything from RS to begin with. I was lucky enough to be given an original RS Deluxe by a friend a few years back, providing I build an amp with it.  So duty bound I built a KT 66 based JTM 45. 

I don’t remember it having ultra linear taps, might be wrong. However the windings are presented on solder turrets not captive leads so maybe there’s a couple of turrets for those taps, been a while so can’t remember! 

ecc83

springhead said:

Yes they did use the RS Deluxe early on. I think they bought everything from RS to begin with. I was lucky enough to be given an original RS Deluxe by a friend a few years back, providing I build an amp with it.  So duty bound I built a KT 66 based JTM 45. 

I don’t remember it having ultra linear taps, might be wrong. However the windings are presented on solder turrets not captive leads so maybe there’s a couple of turrets for those taps, been a while so can’t remember! 

Hmm,been a looooong time but I am pretty sure Radspad stocked  an EL34/KT66 traff that was a lot cheaper? Standard Output Transformer" of some such.

Sure, fit a DL for bass but otherwise cannot see the point?

Dave.

springhead

Well it’s definitely what Marshall used so if you want to build a repro early JTM 45 clone then that’s what you go for.  

RiftAmps

The closest that I've found from a tonal standpoint is this - https://www.trans-amp.co.uk/productinformation.html?item=TT5062

However, if you're building a proper early JTM (mk1 with 5881s) then you need a 6k6 pri-Z such as this - https://www.tube-town.net/ttstore/tube-town-outputtransformer-dual-primary-for-marshall-jtm45.html

Alex335

Thanks for all the comments, yes it’s the 6.6k primary I’m trying to source and after a few weeks of radio silence Marstran has finally got back to me. 

From what I’ve found out ( all be it online and trawling through the forums ) these are supposed to be very close to the original spec so I’m going to give it a go! 

Modulus_Amps

I have a few of these left, wound for us by Dagnall TRX, once they are gone we will be making our own.

https://modulusamplification.com/JTM45-Output-Transformer-Based-on-RS-Deluxe-P5295837.aspx

Don't run EL34's with a proper RS clone, the primary winding wire is thin compared to the 50w units that came later and would likely fail with constant overloading

Modulus_Amps

ecc83 said:

ICBM will have the full SP but did Marshall use that RS transformer? Seems an expensive, "hi fi" component for a guitar amp. Also, I believe the Deluxe traff had ultra limear taps? The JTM45 schemetics I have found do not use them.

I would have thought any good quality EL34 transformer would have been suitable? Hammond get a good rep.

e.g. https://www.tubeampdoctor.com/en/output-transformer-for-marshall-50w-2x-el34-4-8-16-ohm

Dave.

I think in truth they used whatever they could get at the start, but yes they did, there are a number of old examples and people that have pulled them apart for rewinds etc

The TAD 50w OT is not a great substitute for someone looking for an RS clone, wrong Prim Impedance, std grade laminations rather than m6, wrong winding pattern , different frequency response etc They do sound different.

pluckbuddy

Modulus_Amps said:

I have a few of these left, wound for us by Dagnall TRX, once they are gone we will be making our own.

https://modulusamplification.com/JTM45-Output-Transformer-Based-on-RS-Deluxe-P5295837.aspx

Don't run EL34's with a proper RS clone, the primary winding wire is thin compared to the 50w units that came later and would likely fail with constant overloading

Sorry to go off topic but are you going to be winding your own transformers? That's interesting...

Modulus_Amps

@pluckbuddy said:

Modulus_Amps said:

I have a few of these left, wound for us by Dagnall TRX, once they are gone we will be making our own.

https://modulusamplification.com/JTM45-Output-Transformer-Based-on-RS-Deluxe-P5295837.aspx

Don't run EL34's with a proper RS clone, the primary winding wire is thin compared to the 50w units that came later and would likely fail with constant overloading

Sorry to go off topic but are you going to be winding your own transformers? That's interesting...

Yes we are already doing so, started June last year, but it has taken some time to pull all the designs together to get them where we want them, I put an OT shoot out between various different deluxe OT's on my youtube channel last week.

I don't know if it is from this thread or not but we will be winding a 6.6k RS style OT this week for a customer.

pluckbuddy

Ok interesting. I just assumed you had them made.

I saw that shootout and preferred your offerings. I want to build a tweedle see soon and will be grabbing one of your OTs. Probably the smaller vintage spec one

Modulus_Amps

@pluckbuddy said:

Ok interesting. I just assumed you had them made.

I saw that shootout and preferred your offerings. I want to build a tweedle see soon and will be grabbing one of your OTs. Probably the smaller vintage spec one

I have worked with a number of companies to get transformers made, UK and abroad. During the pandemic supply became an issue and even more so now, so I made the decision to start studying and ripping transformers apart left right and centre to learn about them. I would say it has been worthwhile experience, even just to know the products I am offering now are the best I have ever offered.

ecc83

You have my everlasting admiration Mods! I have been tasked with 'reverse engineering' a transformer. Counting the turns and the layers of insulation. It is a boring, ballsaching job!

Dave.

Modulus_Amps

ecc83 said:

You have my everlasting admiration Mods! I have been tasked with 'reverse engineering' a transformer. Counting the turns and the layers of insulation. It is a boring, ballsaching job!

Dave.

The counting is the easy part, removing each 0.35mm lamination on a 2" stack when its all varnished together is the really dull part, I have my tricks now though

hywelg

Try InMadOut in Italy

https://www.inmadout.com/

Very highly thought of in the Dumble building market and will do custom specs 

Keefy

Modulus_Amps said:

@pluckbuddy said:

Modulus_Amps said:

I have a few of these left, wound for us by Dagnall TRX, once they are gone we will be making our own.

https://modulusamplification.com/JTM45-Output-Transformer-Based-on-RS-Deluxe-P5295837.aspx

Don't run EL34's with a proper RS clone, the primary winding wire is thin compared to the 50w units that came later and would likely fail with constant overloading

Sorry to go off topic but are you going to be winding your own transformers? That's interesting...

Yes we are already doing so, started June last year, but it has taken some time to pull all the designs together to get them where we want them, I put an OT shoot out between various different deluxe OT's on my youtube channel last week.

I don't know if it is from this thread or not but we will be winding a 6.6k RS style OT this week for a customer.

That would be me! I’m building a 50W bass head. Michael kindly answered my questions and offered to wind an OT to my requirements - top service!

ICBM

ecc83 said:

Hmm,been a looooong time but I am pretty sure Radspad stocked  an EL34/KT66 traff that was a lot cheaper? Standard Output Transformer" of some such. 

Sure, fit a DL for bass but otherwise cannot see the point?

The JTM45 was originally designed for bass as well as guitar - they were building a 5F6-A Bassman copy. Regardless of cost, it is what they used.

Ironically it’s what made the JTM45 quite different-sounding from the Bassman - as well as the closed 4x12” Celestion cab vs the open 4x10” Jensen - because they didn’t compensate for the very different output impedance and reduce the negative feedback ratio, with the result that the JTM has almost three times the NFB of the Bassman.

RiftAmps

hywelg said:

Try InMadOut in Italy

https://www.inmadout.com/

Very highly thought of in the Dumble building market and will do custom specs 

These are the TXs sold by Tube-Town in DE, they're very, very good