Hello tonelovers,

At last here are my tweaks on the OTS layout.
Those mods work for MY TASTE and not necessarily for other players taste and style.

WORNING !!! PLEASE DO NOT MESS WITH TUBE AMPS  if you don’t know how to. You can damage it or worse - IT CAN KILL YOU !!! Better take it to good amp technician !!!

I tried to make OTS bigger, fatter, bit more compressed, even on cleans. Actually get closer to “Bluesmaster” mod. Some of this tweaks can apply to HRM model too, especially removing a negative feedback NFB from V1 (just removing 0.05mF cap) which adds fat to the amp. Actually it would be better if one drills a hall near V1 and installs mini toggle switch for switching 0.05uF cap ON (for humbucker guitar) or OF(for strat and tele).
I hope everything is clear on the diagram.
Note that JAZZ/ROCK switch is three position switch and changes DRIVE CHANNEL gain only – Hi/Dumb/Plexi. Amp itself is always on ROCK setting.
BRIGHT switch is also 3 position for more flexibility.
As you noticed I removed FET board and there is boost gain pot in the FET input hall.
PAB is disconnected and gain boost happens with simply increasing a CLEAN VOLUME via PAB footswitch. With this you can have regulated (via boost pot) volume (gain) boost on both channels without changing the TONE. It allows to get nice crunch on clean channel and awesome drive boost.
Three way switch near V2 adjusts drive’s high cut, so you can go as smooth as you want without affecting clean channel.
Added International power switch (in the ground lift hall) for the travelling musician.

Best wishes to all

Sorry! Shame on me. I’ll correct it soon. It was there originally BTW, we have to tell Nick.

Hi Erwin,

I love sweet mud and dirt , well it does a little bit but 27K (one can put 12K as well) resistor opens up the tone and together it is magic (FOR MY TASTE)!.
Because of the bright 47pF cap on the volume is always ON - I’ve milded drive with 770pF - really Robben’s drive tone.
With experiments I've noticed that better to  keep V2A snabber low and increase V2B’s value – better chirp definition and waterier tone.

Just a couple of questions about the Rock/Jazz replacement switch. Seems like a good idea to me
as I never use the Jazz setting.

You mention that the switching is Hi/Dumble/Plexi.
Am I correct in assuming that in the Dumble position, ie OFF, the trimmer controls the level of drive?

The two caps connected to the switch via the purple wire seem to be connected to wire X shielding.
Should they be connected to the signal wire of wire X? and what is their purpose since they don't appear to be connected
to anything at the switch?

Many thanks

Hywel Harris

Thanks for the clarification. I think I'm going to do the mods one at a time to get a feel for
what effect they have. First will be Rock/Jazz since that will be of greatest use for me.
The Boost control will also be very useful. PAB has always been a little too much
of a volume step with my TMB settings plus I have never had a use for the FET input.

I've added a 500k trimmer with a 1 nF cap across the overdrive master to reduce the lead highs, which works fine. I use 270p snubbers on V2a + V2b so I need a little extra to trim off some highs.

Hello,

This is central scrutiniser again!
Some folks complained that removing the 0.05mF cap from V1’s NFB makes amp TOO FAT!  :
So here is more flexible solution – three way switch with 470pF/OFF/0.05mF.
Drill little hall for the switch near V1  and chose the desired setting.
I’ve added this to the layout.
Cheers.

Hi Pick Master, while the ots is not on my immediate to build list as i am building a couple of other smaller amps at the moment , I may attemp to tackle it in the future. I have quickly glanced over the layouts of both the 100 and 50 watt versions, and forgive me if I am totally wrong as i didn't spend too much time comparing , but they appear similar except for the extra power tubes etc , now your layout shows a 50 watt version . Can your mods also be applied to a 100 watt version , Thanks.