changed pre amp valves in my JTM 45 -nice change :)

[norburybrook]

just wanted to share that I changed the Chinese pre amp valves I'd used when I made the amp this year out for something different.

ECC83/ECC83S/JJ-TESLA BALANCED -phase invertor
ECC83-STR/HARMA - Valve 1
ECC83-HARMA RETRO -valve 2


all from Watford valves in the UK


Nice changes, the amp seems louder with these, the chime is lovely on the high treble channel and the rattling/distorted low end has now gone on the normal channel when cranked, it's now just big and full when turned up into my marshall 4x10, you do need to still have the bass turned down though


really is a very very nice sounding amp now, not that it wasn't before but these valves have made a nice improvement.

Marcus

[pdf64]

you do need to still have the bass turned down though

Bear in mind that the JTM45 was copied from the 5F6A Bassman, and so the tonal range / balance may not ideal for guitar.
As a first step, I find it very beneficial to arrange the mid control as a variable resistor rather than a potentiometer, ie link the wiper and hot track end, as per the Fender BF mid control.
This expands the range that the bass control covers, allowing much lower settings (ie reduced bass content) to be achieved, whilst still facilitating all settings previously possible.

[norburybrook]

thanks pdf that's very interesting, might give that a try.

I have got used to the way it sounds though at the moment, which just means turning the bass down further than with most amps.

I'd like to try using an ABY switch as the two channels are so different.


Marcus

[billyoung]

a good audio company supposedly designed the circuit. Alot of "Fender Designs" were sooo sooo good RCA made a time machine so the could go
back and put them in their tube book. lol