jmp50/jtm45 pre mated with 36 power? Thoughts?

[hedleygrange]

G'day Gentlemen! This is my first post! I have been following the forum for some time but haven't until now decided to make the jump into the world of 18/36 watters. I have been a member over on the PlexiPalace BB for years and currently play a Marshall JMP50 1987x modded with Marstran iron, PTP board, sozo's through Scumbacks etc etc... I have owned many amps and always gravitate back to the JMP50. But...GAS has set in once again and I would like to try my hand at building an amp as the days of blasting a 50watter are gone. So I have narrowed my next build down to a single channel 36 watt, either a lite version or what I have been curious of...the input and tone stack of a JTM/JMP mated to the output of a 36watter. Has anyone tried this? pros?cons? Thanks...

[jaysg]

There are a couple of things to ponder. For instance, an early JTM45 is about a 30W amp. I don't know if you get the same thump from el-84's at the equivalent power level.

The 20W difference between a 30 and 50W amp, may not translate into a noticeable difference. If you still have the original power transformer in your Marshall, you could find a replacement that would give you a B+ at or below 400V for lower overall power.

Beyond that, I'm sure you'd enjoy building a 36W TMB. hth

[hedleygrange]

Yeah I had thought of the JTM45 thing but just not a fan of kt66's. I am looking to have an el84 based amp and like the benefit of the slightly bolder bottom of 4 tubes and the grind of the 36 watter. I agree maybe a single channel TMB would be what I am after. I am a non MV kind of player, is there a layout filling this bill kicking around? Thanks again for any suggestions and or build experience...

[Phil_S]

You can build a JTM45 with EL34's or KT66. The JTM45, 36W and your JMP50 are not going to be far apart in volume or power. If your JMP50 is too loud, you are unlikely to find relief in the 30/36W variety.

In terms of perception, a 50W amp is roughly 2x loud as a 5W amp. What is it you are really seeking?

[zaphod_phil]

Yes, you may actually more comfortable with an 18W, rather than a 36W. It really depends on how much clean headroom you want. If you like to hit the distortion more, as I do, then an 18W will probably serve you really well.

In answer to your original question, Richard Johnson (rjgtr) recently published the details of an 18W Plexi he designed, pretty much along the lines of what you suggested. It has a 1987 front end, mated to an 18W power section, which if necessary could easily be beefed up to 36W with a couple more EL84s.

http://www.18watt.com/modules.php?name= ... c&p=201059

[hedleygrange]

So let me ask you guys this, in your opinions how much more useful is it having tmb as opposed to just a single treble bleed type tone control? I have had only a brief experience with a 1974x in a music store. As for the 18 vs. 36 I like having tighter bass response( I like a good kerrang when I hit an open chord ) and it seems that from what I read there isn't much of a volume diff between them. Do you feel that to be the case. I play a Les Paul and use the volume and tone controls alot. I was recently in a store and tried out one of those Egnater rebel 20 heads through a 212 and it seemed plenty loud. Are 18's comparable in volume?

[zaphod_phil]

A Marshall 18W is every bit as loud as an Egnator Rebel 20W. The small difference in their official wattage is more a marketing thing than anything else. Again, an 18W is not much less loud than a 36W - it just has less clean headroom. That's more where you notice the difference.

I'm perfectly happy with the simple 18W treble boost/bleed type of tone control, myself. IMO that lets the guitar produce the all the tone. But I like TMBs too. I'm sure there are a lot of different opinions out there as to which one is best.

[scottva59]

I am looking to have an el84 based amp and like the benefit of the slightly bolder bottom of 4 tubes and the grind of the 36 watter.

I just finished a 36 watt mongrel, (taking ideas from several sources) and that's exactly how I would describe the sound I'm getting. I get vintage preamp tone with the grind of EL84 output drive and the boost in clean headroom that (to my ears) translates to more balls without EL34 volume. I'm a 36 Watt convert!

I would describe it as a 18 Watt Lite 2b with a ss rect. and two more EL84s and a PT and OT to accommodate four EL84s. Those opposed to he who shall not be named , (and I don't mean anything by that) please avert your eyes to the 1st 5 pics in this photo stream:
http://www.flickr.com/photos/23222974@N05/

[zaphod_phil]

So you've basically bridged the outputs of two 18W power amps, to get the 36W?

[scottva59]

So you've basically bridged the outputs of two 18W power amps, to get the 36W?

Now you have me looking at some of the schematics I plagarized... Yeah, it sure looks that way to me. I would love to get your take on this because I try to read every post you write... (thanks for sharing your knowledge BTW).

Shoulda started my own thread, sorry for the hijack Hedley

[rjgtr]

I think building the 18watt plexi as a 36watt Plexi is a great idea! (of course I would... ).

Here's the thing about making a 36 watt that would be appealing to someone gigging - if you put in a half power switch, you get both a 36watt and an 18watt, so you can scale your headroom to the gig. You could even add the Vajra PP/SE control and have an additional 5 watt mode for practice.

As for the tone control, it all depends on the tone you're after. If you want it more big Marshall plexi-like, then I think you need the TMB tone control. It is a good part of the character. If you want the absolute most gain, then single tone control would probably be a better choice. Both work, both are valid choices.

Honestly, I like the 18watt Plexi but I also like the good old straight up 1974 model. Every amp has it's charms. The 18watt family is just a great, simple, in your face amp.

[hedleygrange]

Thanks guys for all of the input! I think I am leaning toward the 36 watt plexi. I still have the intention of playing the odd gig and would like the option of having the added headroom as I can always get the extra dirt from a pedal when need be. I have pretty much developed my playing style around using one overdrive pedal to give myself "two channels" and tweaking my guitar to suit. I have this feeling that I will end up with both the 36 and the 18 anyways!!!
BTW that 36 watt design of yours sure looks sweet!!

[hedleygrange]

So after giving it much thought I have decided to start off with an 18w first, spend some time with it and then decide if I need the 36w...