I am using JJ's as well. I think they sound great. Got em from eurotubes, called them on monday afternoon got them wed afternoon.

Played a gig the other nite,amp was acting up.  Decided to replace the power tubes and phase inverter. Wow!   What a difference, the tubes wore out so slowly I really wasnt noticing it untill they were shot.  Now my power amp input sounds great. Just thought i would put a follow up on here in case anybody wants to know.

After using this input, it doesnt work as well as i had originaly thought. It seems as if im overdriving the amp even with a clean signal at low volumes. Am I overdriving the phase inverter , power tubes or both? and is there a easy fix such as maybe a 12at7 tube for the PI or maybe a resister or something i could add to keep the amp from beaking up ?? thanks ,John

As a follow up  note, I did the install on the ef86 side using a 1/4"switching female socket( not sure of the exact terminology for the part)  works well!!  Thanks to wyatt for the help!   

Wyatt, Thank you for taking the time to explain this situation and for the time it took to look at this. I greatly appreciate it!! It definately helps me to understand whats going on. Thanks again. John

This is all I could find for a schematic. Im trying guys...                      site.tubedepot.com/pdf/british18w_v6b.pdf

Here is the answer i recieved on th 18 watt forum,zaphod_phil
Builder, Moderator



Joined: Mar 19, 2003
Posts: 14025
Location: Rush Country
 Posted: Wed Jan 26, 2011 9:42 am    Post subject:   

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The easiest way is just to feed your preamp into the Normal channel's input and keep the Normal channel's volume control turned down fairly low. Alternatively, if you wanted a better but slightly more complex way, it would be to feed your preamp in right after the Normal channel's volume/tone controls, and before the PI. So you would place a switching jack between the wiper of the Volume pot and the 0.01uF that comes after it.

You would certainly *not* want to "hit both sides of the phase inverter", as that would make the signal cancel itself out.
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I've been trying to get some detailed help on this, Will anyone be able to direct me? This has to be a very simple thing for you guys.  I have a Mono signal from a seperate preamp that I want to feed into the power amp section of my 18 watt TMB/EF86 amp. Nick at ceriatone suggested using the TMB side to gain access. Will anyone tell me where to make the connections? Nick said it has to hit both sides of the phase inverter.  here is the link to the layout  . Please help me.... http://www.ceriatone.com/images/layoutPic/marshallLayout/TMBEFceriatone.jpg   

This was nicks response.if anyone could look at the layout and be more specific it would help. I am a newbie...> John
>
> For sure, man.
>
> What you need is an interrupt style loop.
>
> This is on a lot of my amps, for example the Dumble clones. So it's also
> known as preamp out/ power amp in.
>
> However, the 18W TMB EF86, each channel enters the phase inverter on each
> side of it.
>
> This means, your loop needs to be on each side. So it'd be similar to the
> DZ30 (matchless DC30)'s loop, where stereo jacks are used for the purpose.
>
> To operate, you'd need a Y cable.
>
> To make things simple, perhaps you can just put the loop to 1 of the
> channels only.
>
> This way, you can still access the power section, without too much
> complication.
>
> If that's the case, do it on the TMB channel perhaps.
>
> All you need is 2 cliff jacks + some wire (shielded cable, preferably).
>
> Thanks!
>
> nik

 Wyatt was kind enough to give me a link to an effects layout for my 18 watter, (Nicks) unfortuately I have the EF86/TMB 18 watt model. I dont know if that changes things. Upon looking at the layout ( im only interested in accessing the the power amp for use with a preamp) I see wires C&D linked so I assume I have to use a stereo 1/4" plug? Other wise the tip would end up being shorted out to the ground? Or can I just solder both C&D to the tip end of the jack so i can use a standard plug. Any help in this matter would be greatly appreciated. I hope I was clear enough in my description,Thanks again.   John

Thanks Again,I appreciate it!

Thank you for the help!!!

Does anyone have this info?  Id like to put an input to just drive the power amp so I can use a AMT SS-11 preamp. This preamp was not designed to go in the standard input of a guitar amp. Thank for any info all!

Has anyone figured out how to install a acousonic reverb tank into their ef86/tmb 18 watter ? I would really like to do this but have no clue where to begin,Right now im thinking of putting in the effects loop as shown in Nicks mod layout and just using a reverb pedal but would really like a permanant solution.Thanks to all for any help!!