guys i have handwired JTM45 which i took to my tech a couple of yrs back needing more volume, he switched the valve rectifier tube for a s/state rec, replaced the KT66 with EL34's and i'd got a 50 watter,  the ohm selector does have to be mis-matched to opperate correctly, the 16 ohm setting is now really 8ohm & 8ohm is now 4 ohm etc etc basicly i have to set the amp at 16 ohm to match my 8 ohm cab.....i don't remember anything else being done as i was there.....

oh!! i do remember a resistor being added to the bias pot!!! could that be due to the change of tube?

anyhoo, i'd like to return it back to it's original JTM45 form, and i'd quite like to do the job myself...eversince i got my Ceriatone plexi 50 i've shown more interest in how my gear works.....

oh!!! one last thing, i've searched 'n' searched for any info on this mod 45 to 50 etc etc and can't find a thing, have any of you guys herd of this mod?
                                   thanks for your time....

hey mate........i'm asking for help with regards returning the amp back to it's JTM45 form....

i guess what i need to know is.....

1...do i just pull out the ss rectifier and install a valve rectifier??? and it's back to being a jtm45???

2...does it matter much what output tube i use, el34's or kt66???
 
 Denis Cornell builds a plexi 45/50 with a switch to sellect either the jtm 45 (valve rec) or the 50 watt (ss rec)... but i can't find any other info on the mod, i though it would be quite common given the amount of mods there are these days....

thanks again buddy............ray.

hey myfriend......i'm not interested in being able to switch between the ss and the valve rectifier....i just want to return it to the jtm45 (30 watts) rather than the 50 watts it's running at now....

so am i right in thinking that i just put in a valve rectifier and bias to whatever tube i use?...

will this also correct the ohm's selected??? ie the 16 ohm setting is 16, 8 is 8 etc etc...the miss-matching must have been a huge factor for the mod to work without re-wireing or replaceing the trani right?

if it helps you at all to see pic's of the amp i'll be more than happy to send some if you wish?

thanks for your time/help mate...........ray

That would be doing it the hard way.

99% chance he used a SS plug in the tube recto spot.  That's what must people do, heck for years Fender shipped the Bassman RI with one.  These things ahev been around since tubes became obsolete in the '60's, so most techs are familiar with them.



If so, the mods are easy, remove the plug, put a 5AR4 in there and rebias. 

Chances are the extra resistor because of the extra plate votlage the SS rectifier provided.  It may or may not bias with the resistor in there.  If you can't get the bias in the right range for either the El34's or KT66's, then you'll need to go in and mod the bias circuit.

The mismatched secondary remains the same if you stick with the EL34's.

sorry for any confusion guy's.....i did list eveything that had been done to the amp to the best of my knowlege... a jtm 45 running el34's and putting out 50+ watts (not switchable 45/50) would class as a mod, i'm sorry for this...you must understand that i'm asking questions because i don't know how these things work, right???