JTM45 and JMP50

[sixstringesq]

I have a couple of Marshall clones. The JTM45 is pretty true to the 65-66 era spec with metrospec heyboer trannies. Running it was Blackburn I63s made in 65, and JJ KT66s and JJ rectifier.

The JMP is based off a 73 50watt. It has ClassicTone trannies. Running it with the same I63s and I have some NOS RFT Semiens EL34s.

Both have the ken fisher PPIMV.

I'm finding that the JTM is not only louder but has more gain.

Am I going crazy here? I thought it should be the exact opposite.

I was able to crank both the gain and MV on the JMP and it didn't really compare to the JTM with the gain on 8 and the MV on 6.5.

[Haze13]

Voltages are the same? JTM with KT66 has lower b+ if I'm not mistaken. It's like EVH with his PLEXI and lower B+, you open up your pre, that leads to more gain and more saturation, but less wattage on the output + your bias (negative voltage) is lower, this means that you have more power amp distortion...

[neikeel]

Depends how precise you are on specs

But yes expect the other way round, tubes in spec? What are your voltages? What other components did you use?

Many possible reasons.

[coldengray]

JTM45s, especially when biased hot, can really saturate and get gainy when cranked. Their sweet spot is 6 in my opinion.

Also in my experience using a master volume - LarMar/Fisher - adds some gain.

With that said, the JMP should have more refined rock sound.