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Hi,new member here.
I built a 18 watt Lite IIb that I used the past 4 years in a Zeppelin tribute band,but I still needed some FX to get the gain I needed for my leads.The clean sound is amazing.
I want to build another 18 watt but am unsure which version I should use?
I was hoping to use an A/B footswitch to change between the two channels,or perhaps just use my guitars volume to clean the tone up.
I play through an Epi LP with the Jimmy Page wiring and treble bleed mods on my volumes,I coil split the stock Epi humbuckers and did the Page wiring myself.
I play through a 2x12 cab I built myself with Jensen Jets
So any feedback on which version to build would be greatly appreciated.
I mostly play Zep,Hendrix,ZZ top,Beatles and contemporary christian music I hope that helps.
Thanks in advance, Brymus

I would suggest the Plexi - The Plexi is voiced to sound period correct for a Marshall Plexi Lead. Screaming guitar lead tones at a much lower volume. The amp can thump and grind with less compressed tone than the other 18 watt variants. The Second Channel (Normal Channel) provides way more overdrive than most 18 watt normal channels while the Plexi TMB channel is capable of the best clean sound we have ever heard come out of an 18 watter. Crank up the gain and you are in crunch tone heaven. The clean boost just adds another dimension, it nails all those old AC-DC tones dead on and has way more gain on tap if needed. Zeppelin should not be a problem.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thank You for the feedback Coco,that helps a lot

I decided to use the V6 MKII Plexi version.
Just a few quick questions:
A) Is R10 supposed to be 33K instead of 56 or 100K ?(V2 the CF into the tonestack)
B) For R18b and R19b is 220K close enough? otherwise I would have to cobble two 100K resistors together to get 200K...
C) Can the optional cascade switch be on the normal channel volume pot?,should I even add the cascade switch or should I just use a jumper from one input of the normal channel to another on the TMB channel?
D) Could I couple both channels to C6 (the PI pin 2) with 100K resistors so I can add a presence control off of C7 ?
E) I plan on using a 1k5 90ma choke in place of the 1k5 5 watt resistor in the power supply,will that be OK?

And lastly do you sell the Trinity power transformer in a stand up version ? I am building this in an old Crate 2x12 cab and there isnt enough room for the lay down transformer.
Thank You for making all this info available,I really appreciate all of this,Bry

Also I noticed that R42 and R8 aren't in the layout for the V6 plexi MKII ,I added them in anyway.
Not sure if this is an oversight or if they aren't supposed to be mounted on the board.
Likewise C21 isnt in the layout,but can be easily mounted on the PI's tube socket.
Also the layout shows C4 as a .022uf cap instead of .01uf.
I hope this feedback isn't redundant,I am pretty green at building amps.

I posted updated layout and schematics. Let's see if they are OK. Please go back and check them out.

viewtopic.php?f=12&t=3398&p=26717#p26717

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks for updating that Coco.
After looking them over,
The V6 Plexi still has the 100K on the TMB's gain pot.
R10 is 56K in the regular Plexi schematic,and 100K in the V6 Plexi schematic /layout.
So I'm not sure what value to use?
That's all I see right now,but its late and I am tired...

Any chance of making a layout with the optional cascade switch?
And I had a couple of questions if you could give some feedback on that would be amazing.

1) Can the optional cascade switch be on the normal channel volume pot?(I have some extra 500K DPDT for my guitar wiring),should I even add the cascade switch or should I just use a jumper from one input of the normal channel to another on the TMB channel?
2) Could I couple both channels to C6 (the PI pin 2) with (100K?) resistors so I can add a presence control off of C7 ?
3) I plan on using a 1k5 90ma choke in place of the 1k5 5 watt resistor in the power supply,will that be OK?
I apologize if these are dumb questions,but I really don't know

I am close to being done with the basic amp,I will post some pics soon.
I still need a better PT and to add the VRM (PA only) and to figure out the presence control and whether or not to add the cascade option.
This is the most complex DIY project I have undertaken yet,I am so glad I found this forum.

For all 18 watt amps from us, R10 should be 56K EXCEPT for the Plexi Mk II where it is 100K.

Use these http://www.trinityamps.com/phpbb/viewtopic.php?f=12&t=3398

You can put a cascade switch on normal channel if you want.
Amp has no feedback loop so a presence control isn't possible. Use or modify the mid circuit.
A choke will stiffen up the amp, raise the B+ voltages plus reduce sag. Not recommended for this amp.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thank you Coco !
So much for taking the time to clear that up for me,and for going out of your way to update the documents.
I am really grateful to you for answering my questions.
I owe you a beer or three

I had no idea a choke would raise the B+ voltages,or reduce sag,which I understand to be
desirable in the older Marshall style amps.

I am going to finish the amp then consider/install the mods and options later.
I already drilled it out and installed a double pot for PPIMV so as to VRM the PA only.
I also drilled the back and installed switches for NFB ,switchable rectifiers,switching the power tubes cathodes,clean boost,and also bass boost for the normal channel as I am using a 2.2Uf (M150) on the normal channel's cathode with the switch adding in 22Uf.

My advice, get it working as per design first, then add mods. unimind made a lot of mods (SS rectifier, feedback etc.) on his 18W Plexi build after he got it working. Check it out.
As for VRM for PA only - we tried that and preferred the whole amp control, but you may like it otherwise.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Coco,
I was wondering about the VRM as just doing the PA would require adding diodes and at least one more dropping resistor and another bleeder resistor.
I am not going to have switchable tubes with a switch,I will have to swap them out.
My heater tap wont support that many tubes,unless I use the second one then I cant have a tube rectifier.
So I opted for the tube rectifier and will just hand swap the tubes until I can afford a better PT.
I am going to wait on the mods until the design version is working so I have a base for comparison.
All that's left now is to solder up the board to the pots and tubes,everything else is done.
So hopefully tonight I will have sound.
Thanks again for the advice,I really do appreciate your help with this.

Its working,the voltages check out pretty good with 297 and 297 to rectifier 353 at plates and 333 at screens 11.4 at cathodes,so its dissipating 11.7 watts per tube.
I haven't tried 6V6's yet.
It has a little too much hum for me at full volume probably my lead dress as I don't really know what I am doing yet just following the layout.And there isn't much clearance at the back of the chassis.At idle its really quite.
But the old CR212 Crate sounds and looks way better than it did.
I don't really like the VRM at low volume,no scratchy knobs,but I only like the tone to about half way down and its still fairly loud.
Going to try rectifying the heaters unless someone has some feedback on how to improve my lead dress.
Then install the PPIMV and VRM the PA only,or should I VRM the PI and PA ?
I am going to make the bright cap permanent,as well as the boost cap and eliminate all that wiring and switches then try see how I like it.
I must say a kit would have been WAY easier,but I had these parts laying around for 4 years now and saved the old Crate amp just for this.
I really like using the A/B/Y pedal for changing channels and like jumper-ing the channels too.
This is a really great design ,the voltages are spot on with the EZ81 doing the rectifying (although I was reading 35VAC after rectification?) as well as 357.5 DC.
THANK YOU !! Coco for sharing the info and giving feedback,I know why now you get such excellent reviews online !!
EDIT: I just noticed looking at the pics my boost cap for the normal channel is installed backwards ,no wonder it had no effect Evreything else works right,I did have the VRM pot backwards and had to switch two wires

The cap was right but the switch was bad,that's why it didn't change the sound.
B+ a lot higher with SS rectifier,dissipating 13.7 watts per tube.
Will do some more measurements later tonight.
Great learning experience.

I was all set to scale (VRM) the PA only then spent hours reading about how too figure out the extra dropping resistors Still didn't quite understand.
So I decided to wait until after I tried the PPIMV,well that really did the trick for me.
With the VRM at half using the PPIMV I get great crunch at conversation levels,low enough to play late at night.
Got to listen to the 6V6's today really like those too
The volume pot on the TMB channel was making noise when turned even with nothing plugged into the input and everything else set at zero.
Don't know if the pot was bad (it was new) but I changed it and went with shielded wire as well,that fixed that noise.
Still has too much hum for me though its really bad when the guitar is pointed at the amp.
Not so bad when standing away from it or at low volumes,still going to try and fix that issue.I may even add a small transformer and rectify the heaters to DC at least for the pre amp.
Otherwise I am really loving this amp,especially with the PPIMV installed,scaling the whole amp is fine now.
I think picking one set of output tubes and cleaning up the wiring will help as well with the hum,just can't decide which I like better they both sound great!
I didn't notice any difference between elevated and non elevated heaters. I have that on a switch so I can elevate them to the PA tubes I am using,which is odd because its usually a noticeable difference.

FWIW I didn't have a 6V 1w zener and used a 6V .5 watt one instead (for VRM),no issues yet,the HV is fused right after the rectifier for safety as is both heater windings and the AC in.
4 fuses in all.

I think the PT is bad IDK... the PT is humming really loud and there is way more hum in the amp turning up any volume or the PPIMV makes the humming really loud even with nothing plugged into the input.I compared it to my 18watt Lite and the Hammond PT on it vibrates/hums a little too. But doesnt come through when you turn up the volume and PPIMV unless you have a guitar plugged in and cranked up.With nothing plugged in and the knobs dialed its quite like it should be.
I started a thread about this issue at 18watt.com

I got it sorted,I will post new pics later.
But it is working good now ,nice and quiet too.

OK ,it's finished for now as I can't wait to play it for a few days.
Mods I did are:
VRM the PA only.
I love this!(35V on EL84 plates min - max 360V with EZ81 )and (380/385V with SS rectifier,would be good for 6V6's)
Switchable tube/SS rectifier
At low V the EL84s break up SO nice at bedroom levels!
The PPIMV (post PI master volume) a must have if you ask me...
Allows me to overdrive the PI as well if I want for more crunch.
I bootstrapped the CF with the previous stage(2 x 68K = 136K + .068uf) this sets the gain of the previous stage to the max of the tube used,and with that previous stage's cathode bypassed on a switch with a .68uf ,Thank You Merlin for this info!!!!!(from his website)
http://www.valvewizard.co.uk/dccf.html
1st stage of the TMB channel is 2K7/.68uf Rk,120K plate R into the stage bootstrapped with the CF along with the 2 x 68K plate Rs it uses a 470K (680P bright cap) gridstopper 1M gridleak, 820 Rk ,the CF uses a 47K Rk.
This gives me TONS of gain available,enough to do Metallica without adding a boost pedal.
The biggest reduction in white noise came from lowering the 1st stage's grid stoppers to 3K with the 1M grid leaks and a 68P G-K,the normal channel has been lowered to 22K grid stoppers,1K5 Rk,bypassed with 2.2Uf and 25Uf paralleled.
I added the 220K/2W screen leaks on the EL84s and am feeding the 100R screen resistor through a 1K 3W resistor.
Removed the octal sockets for now,more room, less to trouble shoot,will probably change back to octals later on.

The hum was from poor lead when I "straightened up" the inside,this caused bad routing.
Along with the heater wires being mixed (possibly)
I ended up using 2 x 1K balance resistors and elevated the heaters to my PA cathodes.I even tried a hum balance pot and it didn't offer any improvement over the resistors.
I also used shielded biwire to the PA and up to the PI for the heaters.
Anyway its all fixed very little hum or white noise.
I did A LOT ! of reading to get the white noise level down as far as possible,and to get as much gain as possible without adding another tube or cascading the normal channel.
I love this amp !!! Thank You Coco for making the schematics and layouts available!!

I will try and get some sound clips recorded so you can hear how much gain the bootstrapped CF adds,and how good the VRM on the PA only sounds at low volumes.

Future mods in planning are adding another tube so I can have a paralleled normal channel (chime and shimmer) and a paralled 1st stage on the TMB channel (lower noise),mixing resistors,an NFB loop and a presence control.
This will mean losing the tube rectifier though,but that will allow me to re rout the HV better from the PT to the rectifier.
Still not sure on these I want to play it awhile as is first.

Well this is intriguing. I've looked at the boot stratping several times but never got around to it.

Your white noise suppression I'm guessing it has a lot to do with the cap from G-K making a low pass filter

One question is on the tmb what value coupling cap did you use between stage 1 and 2?

Very interesting, especially the bootstrapping. I'm not always into a lot of gain, but it might be worth trying that in some cases as it's a simple 3 part mod.
For the PPIMV, what configuration did you use?
On the VRM, we change the lower resistor to 220K to limit the bottom end low voltage.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

At Sasafraz I thought the white noise was more relative to the input grid stopper resistor value,
And the GK cap was for RF (or just HF)suppresion but I am not really sure,I am more a hack than a tech. I will check tonight on the first coupling cap IIRC it was a .022,I've been fixing up an Egnater Rebel lately,cheap junk electros in them,and 1/6 watt CF resistors...
But I labeled all the components on the elusive schematic that I found for it,after lots of searching and none have values on them.
But they do use regulated pre amp filaments and a similiar RC network at the input and have almost no white noise,so I am going to compare and tweak my Plexi some more.

At Stephen I used a dual ganged 1MA pot,but added a 1M MF resistor between pins 1 and 3 on each gang (to make a dual ganged 500K),and used 330k for R18 and R19 on the Plexi version6 schematic.Changing R18/19 to 470K would probably work better as would getting a dual ganged 500K pot,or just change R18/19 to 1M and remove the resistors off the pot making it dual 1M again,but I was afraid that would be noisier.
The pot/s break in between C8/9 and R18/19 bleeding the signal after the PI to ground or not.