i wonder what percentage of OTS series owners are using their amps with modifications or without.
Already posted about this, but maybe it needs a poll. 
The OTS by itself seems to me to be highly versatile and gorgeous sounding as it is.  I've got no reason to mess with mods. Maybe it's because I'm not trying to sound like someone else.


  I'm bored at work today.

My Mods are:
Replaced the OT Trannie and choke with Magnetic Components
Lower value slope resistor
Removed NFB on V1

Other mods I have tried and then put back to standard:
Played around with the V2 snubber values
Rewired the OD level to the same as a OTS then put it back to how a HRM is wired

So far the biggest increase in tone came from the OT and Choke.

Which particular OTS do you have, Ulf?

My Bluesmaster came pre-modded from Nik with the Mods I wanted, a switchable Sag resistor to simulate having a tube rectifier, and switchable resistors on the PAB. I also run a C-Lator with the tube switched to a low noise 7025. I don't use the Sag that much, and I tend to use the larger resistor value on the PAB (22M) as it gives more of a boost, and, much to my surprise, more of a clean boost (less middy than the standard value).

I have flirted with the idea of changing the slope resistor and bass pot to take some of the muddiness out, but as the amp and speakers have gotten some age and time on them, i have found that this is less of an issue for me. I thought about adding the London Power Scaling Kit to get more Power Tube /PI distortion out of the amp from time to time when i want it, but I have found that I can get it pretty readily by switching power tubes from my usual TAD 6L6WGC's to JAN Phillips 6L6WGB's and turning on the Sag resistor in order to drop the plate voltage down and be able to Bias em to a proper range (they are 23 watt tubes and running them in the OTS under full Plate Voltage is pushing them). Once i do that, i can turn the Preamp and master volumes up a bit and use the C-Lator to control the actual output and get some Output section saturation type sounds.

I have thought about adding a tube rectifier and making it switchable, but I think it would be more trouble than it's worth based on my latest rounds of A/B switching between having the Sag resistor engaged and disengaged.

I thought about adding some switchable bright caps, and a way to switch the HRM post OD tonestack in and out, but after the amp aged a bit i decided against that too

I have found that just by switching Preamp and Power amp tubes around and doing some knob twiddling, i can dial up pretty much any sound i want. The Bluesmaster is quite versatile, just as Nik said it would be.

That being said, i am considering a switchable LFB loop with some different values as the HRM's has no LFB loop and maybe trying some snubber caps on V2, as again the HRM's have none, just to see what the effect would be.

I have a HRM 50 that is darn nice. I thought about messing with snubbers on V2, but definitely not before its broken in and probably never. I think by this point in time, Nik as done most the experiementing for us. The different versions he is offering are darn near spot on and give a wide range of options. IMO...of course!

+1000

Hey Ulf

The NFB Loop is found on V1. It comes out of Pin 6, through a 22M resistor, through a 0.05uF capacitor, and up to the terminal marked B-12, just in front of V1

i attached a pic for ya!

Also, as far as mods go, I added another one today by bypassing the HRM tonestack, thanks to user rogb, who confirmed my suspicion that bypassing the HRM tonestack is very simple. I like it better already. I need to put a switch on it, though so i can switch it in and out. I may even out a three way switch so i can have it bypassed, HRM Bluesmaster style through the 100R resistor, HRM Style straight to ground, to see if there are any sonic differences.
Gregg

Interesting on the NFB loop...I had to look it up on the layouts since my HRM BM doesn't have it.  FYI, apparently neither does the HRM MK2 or OTS 183, but the other models have it there.  The FM50 and regular HRM have a switch for it.  I bought my kit specifically to be experimental with it and learn from the tweaking process.

Long time lurker and thought it was time to chime in! I received my #183 from Nik about 2 months ago. I thought it was good but not great. About a month ago, I dropped it off at a local store to consign it. Yesterday, I decided to pick it up because there was no action on it. I also wanted to try a couple of simple mods to see if I could improve it along the lines of what I wanted to hear from it (basically, the stock OD was a bit bloated in the bass that couldn't be dialed out adequately without messing with the clean tone; it started getting fizzy on the top with the OD settings much above 5 and the OD trimmer above about 5 as well).
As I stated, I didn't want to spend a lot of time tweaking it and picked tow basic areas where I thought I might have success.
I changed the slope resistor from 150K to 82K; I removed the 22pF snubber from V2a and I increased the snubber on V2b to 700pF.
When I fired it up I was stunned. It transformed the amp in my opinion. The OD is now fat but not flubby through the bass and lower mids...there is more usable range to the OD as well...all the fizzy stuff on top is gone and it just sings. That elusive "chirp" and "bloom" that everyone speaks of is now there in all it's glorious incarnations. Tons of harmonics are jumping out of it and it sustains for days (at lower Larry Carlton OD levels as well as higher gain). With humbuckers, the amp is a joy and completely controllable from the guitar's volume pot. I tried the amp with several speakers and all sounded great (Marshall 4X12 with Greenbacks) a 2X12 open back with Weber F150a, a 1X12 with a Celestion Blue (yeah, I know...). I think I will ultimately pair this amp with a 1X12 open back cab with a Celestion Gold or a WGS ET65. I just have to decide on what cab to settle on.
I am running a JJ Gold Pin ECC83 in V1, Tungsol RI ECC83 in V2, a JJ ECC803 in V3 and a pair of Winged C EL34s.
I am so glad I did these mods! The amp is now a keeper! If anyone has a #183 and wants a creamier, lush tone out of the OD with no harshness on the top, try these mods!
Oh, one final observation: when the amp was stock, the OD--regardless of settings--always sounded best with the PAB engaged. With the mods, I don't even turn the PAB on! It really is amazing!