JTM Micro/JTM145

[Bitsleftover]

Hi,
I keep going round in circles about doing a scratch build or a kit and whether it should be a tweed deluxe micro or a JTM45 micro type of thing.
My 5f2a clone is hitting the spot for me tweed wise at the moment, and although I have a 50watt Marshall, it really needs to breathe to sound good. Problem being...it breathes fire, and I play in the house! It's also voiced more 70's to 80's and I'm craving some bluesbreaker-ness. So I'm leaning towards a low watt JTM style build.
I've been checking out the Bassman/JTM Micro by Brother Rob and the Marshall JTM1 as well as the Andertons Marshall JTM145.
Thing is, I really want the luxury of the 4 input/2 channels to experiment with. I don't care about it being micro in physical size. I plan to build it into a 1x12 18 watt style combo cab. I only want the 'Micro' volume.
I would like to build and exact copy of the JTM45 preamp and graft it to a very low watt (5w or less) power section.
Thing is, both Rob's micro and the Marshall offerings all use similar cathodyne phase inverters.
Given that I will be using both halves of 2 12ax7's in the preamp, I wont have a spare half tube for PI duties and will have to add an extra tube regardless.
My very long winded question is... Given the option of using only half a tube as a cathodyne PI, or a full tube for a long tail pair (since I'd be adding a tube anyway), which would you recommend?
Any thoughts?
Thanks

 

[Plumber]

JTM1 is beautiful

 

[Fiat_cc]

I'm pretty sure I read in Robs write up for the Micro Bassman/JTM 45 that a long tail pair phase inverter would supply too much gain and over power the baby output tube in an amp that small.
Having built one, it has no trouble driving into serious dirt territory as it is drawn in Robs design.

 

[Fiat_cc]

Double post

 

[Bitsleftover]

Well that begs the question.....What am I going to use that extra gain stage for???Did you include the "poor man's effect loop" in yours Fiat?
How does reverb sound in there once you get into dirty territory?
I'm loving the one tube reverb you added to your 18 watter. If I get time I'm going to copy yours exactly into my princeton clone. If I get round to this JTM project I might be tempted to go the same. Does your 18 watt tremolo work off half a tube?
Cheers

 

[robrob]

It would be easy to tack on the extra 5F6A channel to the Bassman Micro. Just use the real 5F6A layout as a guide.

 

[Bitsleftover]

Right! That's it then. I'm going to order the parts up for Fiat_cc's reverb and an EC Chap's tremolo for my prince, then once I've got them working I'm going to hit the 2 channel JTM micro. If I like the results of the trem and vibe I might even weave them into my JTM project. Go full bluesbreaker!
Thanks guys.

 

[Fiat_cc]

Well that begs the question.....What am I going to use that extra gain stage for???Did you include the "poor man's effect loop" in yours Fiat?
How does reverb sound in there once you get into dirty territory?
I'm loving the one tube reverb you added to your 18 watter. If I get time I'm going to copy yours exactly into my princeton clone. If I get round to this JTM project I might be tempted to go the same. Does your 18 watt tremolo work off half a tube?
Cheers

Yes, I included the FX loop, although I'm yet to use it. I've just been going guitar, cable, amp. Maybe an overdrive if I need dirt at lower volume (it's a pretty cranking 5 watts when it's wound up).
I didn't put reverb in the Micro, but I'm really pleased with it in the 18 watter. It surpassed my expectations. I like the reverb sound both clean and cranked, but that's my taste.

I am discovering though that the reverb and trem are both sensitive to lead dress, and I have some issues with trem that I think is related to the proximity of the footswitch jack to the reverb part of the circuit. I should have time next week to explore and troubleshoot that a bit more.

Yes, the trem works off half a tube.