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Hello

I have an 18 watt build that is kind of a hybrid. The transformers, power section and TMB channel are all Trinity 18 watt. The normal channel is actually EF86 based.

I don't find myself using the Ef86 all that much and I am debating converting the normal channel to that of a normal Trinity 18watt.

I am trying to decide if I want to use the normal channel layout from the sIII,Plexi,TMB version

This is a youtube video of an 18watt clone and it looks like he is plugged into the normal channel.
http://www.youtube.com/watch?v=BKwIQlrvPMM

Which configuration of normal channel would get me closest to this tone?

Thank You
Seth

That is the classic 18W tone! You will get closest to that IMO with the sIII's Normal channel, but with R29 and C19 removed, so that you get the channel's full gain level. Make sure you're using real good tubes - preferably NOS.

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Great tones come in small glass jars!

Thanks zaphod

That's the one I was leaning towards. The classic 18w normal channel. Removing the 470Kohm to ground and removing C19 to increase gain makes sense. I already get a nice low gain with the sIII TMB channel.

Do you recommend keeping the C15 value at .0047 or would you use the .022 value instead?

What I'm planning on doing is using the extra tube socket I have available from the EF86 for the "normal" 12AX7. Instead of the traditional "high"/"low" input wiring I will have a "single triode"/"parallel triode" setup since I have the extra triode. I did this on the sIII TMB channel and it has a nice "fat" tone in the parallel mode. The extra tube is there so I will use it.

Just so we're clear, the "Normal" channel of the sIII IS the "Tremolo" channel from the original 18 watt. [Pedal Monkey r5 schematic updated to match Ian's amp, built by Jim Marshall]

Might be worth switching that 470K tho.

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Stephen
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0.0047 is the stock value with the big cap on the preamp cathode. That, plus the parallel/single inputs, means you'll basically have an 18W Lite II on your Normal channel. In other words, following on from Stephen's comment, that's a Normal channel with the Trem channel's tone control, which gives a wider sweep than the regular 18W Normal channel's tone control.

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Great tones come in small glass jars!

OK. So The recommendation is to use the "normal" channel from the sIII which is in fact derived from the "tremolo" section from the original 18watt. The use of the 470K ohm resistor is optional. The 0.0047 is the recommended value for C15. The single/parallel option is still a go.

Yes, that's right. Like I said, that effectively gives you an 18W Lite II channel. The tremolo channel tone control will give you more room to tweak the tone the way you want. The two 0.0047uF (or 5nf) caps with the 470k resistor to ground in the 18W Trem channel formed a high-pass filter, which was probably intended to help filter out low-end tremolo thump. It's not needed when you don't actually have tremolo. And the parallel triodes thicken up the tone very nicely.

_________________
Great tones come in small glass jars!

Thanks Zaphod and Coco.

The parts are on order!

-Seth

I have been looking at some 18Watt Lite II schematics and I see what you mean about the extra .0047 and the 470K. I am going to try it with or without these to see which I like.

One difference I see between the sIII "normal" channel and the Lite II is the preamp cathode cap value. 1uF vs 47(50)uF. I will have to play with this. I'm guessing the higher value will give me more gain and possibly a flabbier bass.

No it doesn't give flabbier bass because of the 5nF coupling cap(s), which rolls off a lot of low end. The end result sounds real good. In the sIII IIRC the 1uF cathode cap is complemented by a 0.022uF coupling cap after the stage. So it's two different ways to achieve a similar kind of result...

_________________
Great tones come in small glass jars!

OK. I finished the modification over the weekend. I ended going with the sIII "normal" channel(18watt tremolo voicing). I also ended up using a .01uf tone cap from the tone control to GND ala Lite IIb. I also used the parallel/single input scheme.

The mod took a little longer than I expected because I also added the VRM kit and the input mod for "scratchy pots". This was a bit of a pain due to the physical size of the 0.1uf Sozo's and the fact that I had to wire the caps on 4 triodes because of the "parallel" wiring on both channels.

I haven't had a chance to really play at full volume(vroom) yet to judge the new channel. The VRM is cool. It will never equal the tone of the cranked amp with speaker breakup, but it is a good way to get some nice tube breakup at very low levels.

Thanks again for all of your help.