18 watt layout questions

[lespaulplayer]

Can someone please explain to me the difference between these two layouts? I see the obvious differences in values and everything. Just noticed The Valvestorm layout is quite different and I was wondering what exactly to expect sound wise from each layout? I'm wanting a vintage warm tone that can breakup and get a nice vintage overdrive, nothing too grainy. I don't want 2203 sounding grainy gain. When I say grainy that doesn't mean I don't want distortion. I do. Just don't want that modern sounding Marshall distortion. I want the old school plexi tone. I'm thinking based on that I want to go with the Triode layout, but would like a further explanation between these two layouts. Thanks for your input!

http://valvestorm.com/sites/default/fil ... Layout.pdf

http://site.triodestore.com/18WTMB120VLight.pdf

[Colossal]

I would not use that Triode layout. That looks suspiciously like Mojotone's 18W TMB layout. The Triode layout places the Phase Inverter in the middle position, adding long plate leads and needlessly crossing wires. The gain on the TMB channel is significantly higher than the Normal Channel. The Normal Channel is just killer (Lite IIb format) and the distortion is probably more in line with what you are looking for. The Valvestorm layout is very much the warm/vintage Plexi and 18W vibe. The Triode layout is a good invitation to hum and oscillation. Get good transformers, that's where the sound is that you want. Heyboer or GDS (Heyboer wound) or Mercury.

[pdf64]

The bass control on the Valvestorm is noted as 1ML as in linear; seems wonky.
With either, putting a master vol right by the input jack, with 2 cascading CC stages between them, seems ‘non ideal’.

[lespaulplayer]

I do see what you're talking about with the wire crossing on the phase inverter in the Triode layout. That's something I overlooked at first glance. Ok that convinces me to go the Valvestorm route. I was thinking about going with Classic Tone transformers. I used them in my JTM 45 build and in my 5F1 build and I like the sound of those amps a lot.

[Colossal]

I think ClassicTones would be great.

PT
http://www.classictone.net/40-18035.pdf

OT
http://www.classictone.net/40-18037.pdf

[ViperDoc]

The bass control on the Valvestorm is noted as 1ML as in linear; seems wonky.
With either, putting a master vol right by the input jack, with 2 cascading CC stages between them, seems ‘non ideal’.

Hi pdf64,

By "CC", do you mean "cold clipper"? How would you improve it/smooth it out? I actually just built the Rev B version of this layout and the gain is a bit too harsh for my taste. I solved a fizz problem just now using a 47 pF fizz cap between the PT plates and a Paul Ruby mod across the grid leaks. Perhaps the OP might benefit as well. Thanks.

[pdf64]

Sorry, common cathode. I wasn’t thinking of it being a tone thing per se, but rather stability. The point being that it seems poor layout practice to me to have parts in close proximity that have a lot of gain and 2 polarity flips between them; the close proximity , those features being a recipe for an oscillator. Add to that a tone stack that shifts the phase response all over, and the thing that surprises me most is how such arrangements don’t oscillate
Lots of modders seem to get away with it, but to me it seems to be asking for trouble.

Regarding the harsh overdrive often reported with 18W, I wonder if at least some of the issue may be due to the use a lowish spec OT, eg non interleaved, high leakage inductance?
As such info is hard to access, it’s difficult try to make a correlation.

[Colossal]

Regarding the harsh overdrive often reported with 18W, I wonder if at least some of the issue may be due to the use a lowish spec OT, eg non interleaved, high leakage inductance?
As such info is hard to access, it’s difficult try to make a correlation.

Pete,

I have often wondered this myself. The original 18W Marshalls had Radiospares "De Luxe" output transformers which were interleaved, made from grain oriented M6, and frequency response of 40Hz to 25kHz, and low leakage inductance. The secondaries were for 3, 7, and 15R loads.

I would posit that some providers of "18W iron" make an 8k primary which is suitable for 2xEL84, yes, but with no interleaving, high leakage inductance, different wire gauge, and other cost-cutting measures.

[ViperDoc]

I used the Heyboer 18-Watt OT through mojo for this build. Initially it sounded like that was a solid go-route. Who would you recommend as an upgrade? The fizz I was hearing is tamable in the lower MV settings, but it’s quite noticeable when you mic the cabinet. Better, but not as smooth as I like.

[martin manning]

18W buzz has been a topic of discussion for years. See here: https://ampgarage.com/forum/viewtopic.php?f=6&t=15332 Page 2, Ruby mod, for one possibility.

[ViperDoc]

18W buzz has been a topic of discussion for years. See here: https://ampgarage.com/forum/viewtopic.php?f=6&t=15332 Page 2, Ruby mod, for one possibility.

Thanks, Martin! I installed the Ruby mod with 16V 1.3W Zeners and UF4007 diodes and it helped tremendously. That said, there’s still a bit of fizz and I don’t know what the different distortions sound like, or whether this circuit is supposed to sound this way.

[Colossal]

I used the Heyboer 18-Watt OT through mojo for this build. Initially it sounded like that was a solid go-route. Who would you recommend as an upgrade? The fizz I was hearing is tamable in the lower MV settings, but it’s quite noticeable when you mic the cabinet. Better, but not as smooth as I like.

Some of the EL84 distortion characteristic may be considered fizzy. However, the amp should be smooth and not harsh, buzzy, or like crushed glass. As far as OTs go, I wasn't suggesting that there is anything wrong or that needs upgrading with your amp. I select for a true Radiospares interleaved type transformer for these amps. I am still wondering why some get the dreaded Crossover Distortion Fizz that needs the Ruby Mod to fix, and some don't. I am leaning towards issues with lead dress and/or an underspec'd OT, as Pete suggested. Anyone can make an 8kΩ output transformer and call it an "18 Watt Marshall" transformer. But the original transformer was quite unique.

[ViperDoc]

Good to know. Thanks, brother!