JTM30

[TIMBO]

Hi guys, TubeGeek has inspired me with his great JTM45 build and guitar playing and after getting the jubilee sounding pretty awesome (but way too loud for what I want) got me thinking of the JTM30 I bought in 1997.
After surfing the net for info,i found that it had its problems, overheating and cutting out and a very ordinary overdrive but still producing that infectious marshall sounds.  MARSHALL JTM 30

Finding a schem, it has a lot of SS stuff happening, so I trimmed it all off to find a neat circuit underneath. I think the circuit is ok but it sounded like the design of the chassis and components let it down.

So, can a circuit that had some very smart people designed, able to be made better???

Well this is what I had in mind :-
A combo build, as I have a Valvestate combo cab with two 10" Celestion,30w gold back 4ohm speakers that I will parallel as I have an OT that is a Hammond 1750K with only one speaker tap of 2ohms.
I have JJ6L6s but would like to sub them for a pair of KT66s so I will put in a adjustable bias and from what I read the bias circuit wasn't great. This output of around 30w will suit me nicely, but i'm sure i'll get some complants.
I will add a mosfet CF before the TS as per the JTM45 and so on, i'm not sure of the resistor values so I will try the 100k source resistor as per the standard CF in the JTM45 and the 820r on V2b cathode, any thoughts.
The clean channel got the nod from most that commented on this amp,so that will stay as is.I like it TOO
I deleted the reverb but I might still add a one tube reverb as I have a long tank waiting to be used but i'm still thinking of building a stand alone unit but as this a combo I have plenty of room for it 
Again I have a Hammond 372JX PT that is a little lite on for volts but i'll adjust the dropping resistor between nodes B and C to bring the preamp volts up
I'll add a tube rectifier socket and try a GZ34 for some SAG but other wise i'll just stick a SS plug in. I also have a 5U4GB to try.
I'll use the relay circuit in the jubilee as it worked well.

The OD was NOT well liked ( I thought it was OK), and using some diode clipping and two gain stages to get the sound, I think that this is the area that might need some TLC, so some tweaking in this area ( diode clipping) might be fun 
A passive FX loop works for me.

The preamp/OD circuit has some merits, so I am hoping that some of you marshall lovers will put your 2c in. Thanks
 

 

[Glennjeff]

Hope it works out well for you.

[Tone Junkie]

Glenjeff he's trimming of all the SS stuff to make it a decent 30 watt marshall. Timbo I like some diode clipping myself but more in the line of a saturation switch 2, 5408 diodes back to back just before the tonestack I will find schematic and send it to you i thinik I got that one from the hairy brown eye if i remember right (LOL) bad name for an amp. Do you have the jose schematics that used the diodes. I can send you those too if you would like so you can mix and match. I like kt 66 in a marshall circuit they sound good.
Bill

[TIMBO]

Hey Glennjeff, Sorry but that ain't me play'n, if it was me, the review would state great amp, Sh*t player  but thanks anyway.

Bill, any info about the diode clipping would be great, I like it as well. Thanks 

[Tone Junkie]

Timbo after playing with it for awile I find I only like a very lite diode clipping and like extra gain stages for clipping more .
But I just found some stuff on diodes i hadnt seen or tried. When I get home i will try and get that up for you .
Bill

[TIMBO]

Hey Bill, found some good stuff here. http://beavisaudio.com/bboard/projects/bbp_DiodeMods.pdf

[Tone Junkie]

Thanks Timbo That was one i havnt seen yet.
Bill