Most folk here seem interested in altering the sonics of this wonderful amp in one way or another.
For those that don`t feel inclined or experienced to get involved with a soldering iron, there`s still plenty of scope to play with shaping the OTS tone character.
This does include removing the chassis from the cab, but that`s no big deal.
Just keep in mind being safe around internal components & electricity...!!!

Locate the small cap on the back of the master volume pot.
There`s diagrams elsewhere on this forum that shows the layout of this amp.
Snip one side of the wire from the cap very close to where it is soldered to the master vol pot. This easy mod will even out the highs at lower vol levels & works very nicely..!
The mod can be easily reversed with a hot iron, but chances are you`ll probably stick with it clipped as the results are pleasing.

The 12AX7 pre tubes that come stock in the OTS can easily be substituted
with compatible tubes of lesser gain factor & warmer character.
I personally do like a 12AX7 in the first position (V1) but find the stock JJs produce a very focused  but narrower band of tone in (V1).
I like a Blackface clean tone and a 12AX7LPS (Long plate spirial) in (V1) does the job nicely for producing a broader & warmer sound for the clean channel.

With the O/D channel, a 12AX7 (V2) drives the amp with a hard edged tone that alot of people on this forum seem to be trying to tame one way or another.

Substituting the 12AX7 for 12AY7(60%) of the 12AX7 gain factor, or even a
12AU7 (20%) really warm up the O/D channel nicely, but these lower gain tubes also allow for more scope when fine tuning and dialing in your prefered O/D tone.

This is where the internal gain trim pot needs to be adjusted to suit.
Most folk on this forum seem to agree the best O/D tones come from the trim pot being set somewhere between  9 o`clock & 11 o`clock positions.
(Keep in mind this is with a 12AX7 in V2)

When using  lower gain pre tubes like the 12AY7 & 12AU7, the trim pot will require adjusting up to compensate for the subsituted tubes lesser gain character.
This is where the fun starts and a 12AY7 will probably require a small lift in gain on the trim pot, but you have more scope to find your sweet spot/s.
The 12AU7 will require even more gain adjustment to compensate, but once again
you`ll have a broader range of gain to play with and both these two tubes are much warmer sounding to me.

I`ve just tried a 12AU7 with the trim pot set way up in the 3 o`clock position & that was VERY GOOD. The level & ratio knobs worked together with a broader range for fine tuning your overdrive tone & with more flexability to the user.
If anything, I think the tones are more D-mble like & less of a narrow band gain tone from the use of a 12AX7.
12AX7s are good in the right application, but the down side is the high gain factor
drives harder and can often sound grainy.

I can recommend trying these easy mods, especially if your looking for more
D-mble than Marshall, as i would assume most of us here, are..!

I have tried a 5751 in (V2) but feel it sounds less warm than the 12AY7 or 12AU7.
It was a bit sterile to me.

I hope this might be of help to those looking to experiment and achieve different tones.
Cheers.

A 12AX7LPS (long plate spirial) in V1 produces a warm clean tone that`s very Fender like.

Has anybody considered using, or tried a pair of KT66 power tubes in the OTS..?
My understanding is the KT66 is often compatible as a substitue for the 6L6, but apparently not in all 6L6 amps.
It would seem the tonal characteristics of the KT66 could very well be something worth considering.
Has anyone got experience on the subject of KT66 tone and bias requirements etc..?

Hi there,  
Preamp tubes choice in the OTS makes a BIG difference to the character of this stunning amp.
Although you can coax great tones easily from the OTS, it`s important to experiment with tonestack combinations to get to where you want to be.
A Tele sounds awesome through the OTS, but only if the tonestack is adjusted properly to suit, and when you get it right,.. the tone`s right on the nail.
A tweakers amp for sure.!
a 335 sounds just as good, but with the obvious adjustments to suit the pickups & guitar etc.

Preamp tube info.
12AX7 has a 100/100 gain factor & will drive the amp harder than other preamp tube variations.
The 12AX7 LPS (long plate spiral) is a 12AX7 worth a try in (V1).
Quite smooth, warm and vintage sounding.

5751 is not a 12AX7 type but a compatible substitute.
70/100 gain factor. Slightly less gain ie: 70%.
5751 has a smoother linear quality to its tone character & clips smoothly.
Stevie Ray Vaughan favoured this tube in the(V2) of his blackface amps for a little more clean headroom and a smoother tone.

12AY7 60/100 gain factor (60%) of what the 12AX7 delivers.  Also very compatible substitute for the12AX7 & produces a nice warm round tone.

12AT7. 45/100 gain factor. usually good for reverb and PI positions.
You could try one in the PI (phase invertor) position, but the 5751 or 12AY7 is probably a better choice for experimenting in this positiojn for the OTS.

12AU7. 20/100 with a low gain factor of only 20%
This is a low gain tube with a warm vintage tone, but not much push.

A 12AU7 in (V1) of a Fender Tweed blues deville running the main vol pot on a setting of 8 or 9 & the amp was sounding very open, warm with just a hint of very natural overdrive and the overall volume was about perfect for a gig.
With a 12AX7 in (V1)with the Devilles,. you couldn`t get the vol pot above 3 without splitting ear drums..!!

Pre amp tubes are a relatively effective & cheap way to experient and get some good tone & gain variations.

Ive tried two different cabs to date. 1x12 open back & 2x12 closed back.
My personal preference was for the open back as it gave a noticably bigger sound. The closed back has a very directional sound and lost some of the ambience and subtle tone characters of this wonderful amp.
Ive played Fender combo amps for years and I`m used to the sound of an open back cab, which i feel also suits this amp.
You should consider trying both for yourself.

That`s a great looking amp mate..!
Was it inspired by Robben Ford`s combo, as it looks very similar to his one that`s green & tan..?  Could you supply the weight..? Cheers.