Just picked up a JTM-45. Has a stock PT, a Heyboer 8113 OT, and a MM choke. Would chaning the PT to a Heyboer make a noticable difference in tone?
The way PT's affect tone/feel is from changes in voltage. Lower plate voltages mean lower headroom, but a more "touch responsive" feel to the amp. Higher plate voltages mean more headroom and a tighter/stiffer feel. Bu there is zero reason to juct swap it out. It it specs out right, it is right.
How about replacing both with MM's?
There is no magic to making transformers...if they spec out the same, they will sound the same. The Heyboer 8113 is a popular over-the-counter JTM-45 OT that can be found in plenty of high-end boutique clones.
Worth the cash? Thanks.
No. MM's are
great transformers, but they are certainly no better than Heyboer (who make Allen, Mojo, Metro, Marstran and others), Hammond, Magnetic Components (Classictone and Allen), and probably another half dozen other manufacturers. So, no, it is not worth twice the price for the same quality.
Don't swap parts just to swap parts. At this stage, you should make a mental list of everything you love and don't love about the amp and address those issues directly. Swapping parts with the expectation that they will somehow sound magically better (despite everyone's taste being different) is just wasting money by shooting in the dark.