Power tranny change Bluesbreaker

electricrootrecords

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I just got this build finished.
It's my baby Jtm45 bluesbreaker.
It's biases at about 39Ma and breaks up very early on the volume control. Have tried different preamp tubes so I think It might be the Ot being smaller than spec.. 16466917527252545804589637576787.jpg

It currently has a Classictone Output transformer at 6k6



Ive been searching and just found a Radiospares 275-0-275 120mA power transformer buy the voltage rating is too low.
I'd like to swap into the bluesbreaker and use a solid-state rectifier tube to get maximum voltage on the Kt66 plates.

The power transformer might not handle be able to supply the current though. Would this work since the Kt66 need 62.5 mA X 2 plus 3 12Ax7
 
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Chris-in-LA

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@neikeel is our resident JTM45 expert and can answer most questions.

Amp Parts Direct has the OT you need for a regular JTM45 but they are sold out of the PT. I personally prefer the Heyboer iron to the Classictone stuff for an OT.

 

Pete Farrington

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Kt66 need 62.5 mA
Why do you think that?
At high power output levels, the output valves in a JTM45 type amp are likely to draw somewhat more than that.

275-0-275 120mA power transformer
baby Jtm45 bluesbreaker.
breaks up very early on the volume control
I think It might be the Ot being smaller than spec

What’s your goal with this, eg a lower power output than a regular JTM45?
What actual power output do you measure?
What is the spec of the classictone OT?
 
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electricrootrecords

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I'm using a power transformer which is rated for a tweed deluxe which has 350-0-350 150ma
with Kt66 tubes the Amp has good transients but Its not very clean, even on lowest volumes it'll start to break up with a humbucker.

im looking for more low mids like the bluesbreaker is known for.

39mA biased at 70% dissipation on the Gold lion Kt66 tubes so I think it about 20 watts which is where I got the idea that I'd use the deluxe Output trans.
 

Pete Farrington

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a power transformer which is rated for a tweed deluxe which has 350-0-350 150ma
Please provide links for the power transformer, output transformer and choke that you’ve used.
Consider that if you want to build a Bluesbreaker, it would be a good idea to use parts that are intended for that purpose.
Its not very clean
Please provide a voltage chart, taken whilst the amp is idling, as per https://el34world.com/charts/Schematics/files/Marshall/Marshall_jtm45tr.gif
39mA biased at 70% dissipation on the Gold lion Kt66 tubes so I think it about 20 watts which is where I got the idea that I'd use the deluxe Output trans
I can’t follow your logic. I suspect you’re under a misapprehension or 2, pease explain your rationale behind the above.
 
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