Monkeymatic 18TMB

[Smokebreak]

Another flavor for consideration. This one has some elements of your original intentions. You've got a whole extra ax7 to add a parallel stage, or cascaded stage, etc. Nice cleans and angry cranked. Lose the reverb of course, or use the extra 9-pin for that!

[xtian]

Thanks, guys. That was a lot to digest! Feeling sleepy...

[xtian]

I'd like to keep the Hammond power section. 5U4 rectifier, choke. Three 12ax7 and two EL84.

You could add a switch to jumper the channels similar to the 1974 circuit. Or another switch to go from shared cathode to split cathode like a 1987. And another to switch from parallel/split to cascaded (one-wire mod).

I like this, Colossal. Would you differentiate the coupling caps/tone caps in the two 2061 channels?

I don't mind the idea of another Marshall-sounding, lower wattage box, as I just sold my 18-watt express.

[Colossal]

I like this, Colossal. Would you differentiate the coupling caps/tone caps in the two 2061 channels?

I don't mind the idea of another Marshall-sounding, lower wattage box, as I just sold my 18-watt express.

Well, I guess that depends, because Matt H dropped a lot of interesting ideas. I especially like his power supply thoughts. I'm a fan of chokes so I perked up on the choke input and CLC idea, for something different than the usual stuff.

If you stick with the sort-of Marshall sounding option, leaning towards the 2061x and wanted to have a plexiish parallel/cascade setup, that usually calls for one stage voiced warm with a slightly fatter coupling and the other voiced cooler and crunchier with a smaller coupling cap to control the flab. I tend to lean towards wam/fat but I do NOT like flab/bloat and can't stand the skidding sound of blocking distortion. So warm enough and fat enough but staying tight and punchy. I like articulation and note to note separation in complex chord voicings so keep coupling caps pretty small to control that low end. I hate amps that just make a big >>clunk<< and don't sustain and/or feel dead under the fingers. I like a smoother sound with some compression. I had a 6V6 Plexi, original Huss design, and that thing sounded huge for 22W. It had great compression, maybe too much LOL. It had a 5k 5W resistor in series with a choke between plates and screens. Guess I really like that Marshall Magick

[xtian]

I'm liking the looks of this, but with only two power tubes. Has a unique topology.

[img1691]http://mhuss.com/18watt/schematics/36wTMB5.gif[/img]

[Smokebreak]

Some neat stuff in there and highly tweakable if you get the parallel thing happening . So the NFB switch goes between a sort of fixed presence, or it sends that network to ground via the 8ohm tap? I wonder how the latter works vs. nothing coming off the 8tap.

[xtian]

I'm curious about the Presence, too, and should I just put a pot in there. I know Richie is a member, perhaps he will respond.

[donzoid]

I used exactly the same set of iron on my 1/2 power Rocket but used a zener to drop the volts. a 56v zener was OK, with the 5u4GB but I think that one sounds really a lot better using a 5y3...fwiw. Even more "saggy".

I also like chokes, so I used the reverb choke and the schemo's say its 14H which IIRC was about right when I measured it. It seems to be holding up...and I've been gigging that amp pretty steady for 4 months or more.

[xtian]

Layout drafted, and board populated. Had to abandon the standup 33uF caps at the end of the chain (leads wouldn't reach the board), ended up laying them down.

[xtian]

Progress. Geez, my signature on the board looks like a drunk fifth grader. Fair enough.

[George61]

I'm liking the looks of this, but with only two power tubes. Has a unique topology.

[img1691]http://mhuss.com/18watt/schematics/36wTMB5.gif[/img]

I built this amp with the exact component values on the schematic. Note that the PI is a slight variation from the standard 18W. The normal channel is fed to the second stage of the TMB channel, so it goes through the cathode follower and the tone stack but the tone stack can be bypassed. You can use the TMB channel and bypass the tone stack for no tone control. This amp works really, really good. It's the best amp I have ever owned and is a better amp than the Trainwreck Rocket clone that I built. I used the transformers from GDS. Note that the layout is a Richie Hall design.

Solder on,
George

[xtian]

Finished and sounding great! 380 on the plates--had to bump the cathode resistor to 240R to get bias at 100% dissipation (was closer to 120% with the 150R!). Using all vintage Hammond glass (not shown in photo)--though the bias reads the same with JJ EL84s. Very low hum at idle.

Getting used to the PRE-PPMV. I get a lot more distortion from the PI as I turn up the MV, obviously. Different than my normal POST-PIMV builds.

Let's discuss the power tubes' grid reference to ground. In the old schematic, they were a 330K/330K pair. In this v5 schematic, they are 470K/470K. How might this affect performance?

[Colossal]

Let's discuss the power tubes' grid reference to ground. In the old schematic, they were a 330K/330K pair. In this v5 schematic, they are 470K/470K. How might this affect performance?

The 470k pair is typical of the 1974(x) 18W circuit which featured a clean preamp but drove the output tubes HARD. Lowering the grid leaks to 330k or even 220k as in the Vox and Trainwreck designs will give slightly more clean headroom before the EL84s are engulfed in distortion but recall it only takes something like 11V to drive them anyway. Lowering the grid leaks is essentially like turning down a PPIMV and fixing it at a given value.

Nice build dude. Did you build your PI as shown on Richie's schematic?

[xtian]

Nice build dude. Did you build your PI as shown on Richie's schematic?

Thanks! Yes, PI is to Richie's v5 schem, except I have 330K grid leaks.

[Colossal]

Nice build dude. Did you build your PI as shown on Richie's schematic?

Thanks! Yes, PI is to Richie's v5 schem, except I have 330K grid leaks.

Cool. How do you find the distortion on your build then? Did you do the switchable NFB/presence circuit as well?

Also, to clarify, the PI has 330k grid leaks on the long tailed pair. So you are saying you lowered your OUTPUT TUBE grid leaks from 470k/470k as shown on the v5 schematic to 330k/330k. Just want to make sure I'm not referring to the wrong parts.