Hi,
Wondering what your opinions are for the OT's in the JTM 45 kit. I guess I'm wondering if the upgrade to a MM OT is worth the cash, or more importantly, worth the sound. That's what I'm really after is the sound.
What do you guys prefer? I know everybody's opinion is different, but I need to start somewhere. I don't mind getting the MM OT if it's going to retain the vintage sound.
Thanks all!
-Rich
Heyboer vs. Merc Mag OT for the JTM 45?
Moderator: VelvetGeorge
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fzfwyv
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Flames1950
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I haven't gotten to compare them. I guess that means I may just have to build another JTM45 with the Mercs. 
But I have no complaints about the sound of the Heyboer trannies. They're chock full of classic 60's tone -- bright with a cutting edge, but not grating on the ear; kind of like when you find a really good Telecaster compared to an average one, a great one has a brightness that's FAT at the same time......you can actually use your treble and presence controls, and yet you can roll back the treble and get plenty of darker tones if you wish too.
I don't think you can go wrong with either choice in the end.
But I have no complaints about the sound of the Heyboer trannies. They're chock full of classic 60's tone -- bright with a cutting edge, but not grating on the ear; kind of like when you find a really good Telecaster compared to an average one, a great one has a brightness that's FAT at the same time......you can actually use your treble and presence controls, and yet you can roll back the treble and get plenty of darker tones if you wish too.
I don't think you can go wrong with either choice in the end.
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thetasigma
I built my JTM 45 with the mercury magnetics OT, but unfortunately I've no experience with the Heyboers, so I can't give a good opinion either. However, I can say that the tone is super sweet. I've been trying different tubes in my 45 (KT66, KT88, and EL-34) and even though different tubes give me different overtones, the overall sound is still very marshally. So, I guess Flames and I need to both build another amp to truly test out the different OT's 
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Flames1950
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YEAH, baby!! Now, can I borrow $950, I swear I'm good for it.......So, I guess Flames and I need to both build another amp to truly test out the different OT's
How are the EL34's in the JTM45? I'd like to base a JTM50 build on the JTM45 kit, but that would still be a different PT, OT and tubes to be historically accurate.....did you end up taking your bias resistor to the opposite extreme to get those biased? 47K maybe?
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thetasigma
Yeah, I did have to use a 47k resistor, and I changed the 470ohm resistors on the output tube sockets to 1k, since that's recommended for EL-34s.How are the EL34's in the JTM45? I'd like to base a JTM50 build on the JTM45 kit, but that would still be a different PT, OT and tubes to be historically accurate.....did you end up taking your bias resistor to the opposite extreme to get those biased? 47K maybe?
The tone is pretty sweet, definitely gives a more crunchy rock tone. I've tried two different set of 34's, JJ and svetlana, and so far the JJ's are sounding a little sweeter to my ear.
I really liked the KT88's too, but they are shriller compared to the KT66's. So for the long run I may have to switch back to the KT66's, but the el's sounded pretty good to me as well.
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Yngve
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OT Transformers
This might help it was posted on www.18watt.com
've built several JTM45 and plexi type amps and have used mostly MM or OEI output transformers, and Heyboers for the PT and chokes. The OEI and MM OTs are very good. I've done side by side comparisons in identical amps and the differences between the MM and OEI OTs are subtle. To me, the MM is slightly more detailed with a hair more chime while the OEI has a slightly smoother and creamer OD (my personal JTM45 has an OEI OT). I've heard good things about the Heyboer OTs from other JTM45 builders and wouldn't hesitate to use one. I've also heard some good things about the prototype Weber JTM45 OT, if price is an issue. As far as "what is best suited for this project?" I think all of these would give you good results. I assume you want to run KT66s, so the only real recommendation I'd make would be to make sure the OT has a primary impedance of 8.0k - 6.6k (for the original Beano tone) and then take a look at the other features (taps, wiring, footprint, cost, etc.) to see if that OT fits your goal.
http://www.18watt.com/modules.php?name= ... 6271#55596
kind regards
Yngve
've built several JTM45 and plexi type amps and have used mostly MM or OEI output transformers, and Heyboers for the PT and chokes. The OEI and MM OTs are very good. I've done side by side comparisons in identical amps and the differences between the MM and OEI OTs are subtle. To me, the MM is slightly more detailed with a hair more chime while the OEI has a slightly smoother and creamer OD (my personal JTM45 has an OEI OT). I've heard good things about the Heyboer OTs from other JTM45 builders and wouldn't hesitate to use one. I've also heard some good things about the prototype Weber JTM45 OT, if price is an issue. As far as "what is best suited for this project?" I think all of these would give you good results. I assume you want to run KT66s, so the only real recommendation I'd make would be to make sure the OT has a primary impedance of 8.0k - 6.6k (for the original Beano tone) and then take a look at the other features (taps, wiring, footprint, cost, etc.) to see if that OT fits your goal.
http://www.18watt.com/modules.php?name= ... 6271#55596
kind regards
Yngve