Ceriatone Forum

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.  :chairdance: I've got no reason to mess with mods. Maybe it's because I'm not trying to sound like someone else.


 8) I'm bored at work today.

Modded, but nothing crazy. I wanted to tweek the amp to my tastes. I basically fattened it up with a lower value slope resistor, and removing the NFB from V1. For the OD I just adjusted the snubbers, V2a now has no snubber while V2b is about 880pf, I prefered the tone without the first stage, seems smoother and less "fizzy."

I also upgraded the choke and im using KT88's which sound phenomenal with this amp, IMO.

Despite these "fattening" mods I still run the treble at 3, mids at 10, with the mid boost on. And I use overwound pickups. I have a serious midrange addiction. ;D

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.

Can someone please explain where I can find the NFB (resistor, cap?) on my OTS,
and what value it is.
Thanks.
-Ulf

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.

Got an FM50 in stock format. Perfect as is.

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!

Because all dumble amps were different in one form another I think every d~style amp could benefit from specific mods to voice the amp for a particular player

+1000

I have an regular OTS 50W, lightly modded.

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

Ok, got it!

Thanks for the pic Gregg  :)

// Ulf

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.

I must add that the HRM mod was kindly given to me by Henry at Redplate Amps, so he should be acknowledged for passing on his tips.
It's a great thing when a top pro builder takes the time to help you out, even though you've never spent a cent with him and (being poor) are not likely too, even though his amps rock big time!

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!

Hi Beanbag, welcome to the forum and great report on your amp.

I guess we all experienced the same as you have -  a new dumble clone amp sound very harsh and unforgiving.

Nice mods the 82k slope and 750pf on V2a.... I'll bet in two month you won't need the 750pf on v2a, in fact I have just removed the additional 220pf on my #183, leving me with 22pf on both v2a and v2b and no the OD top is much more open. However, like you , when the amp was new it had much to much OD top.

I have 20 years experience with DIY tube amps and repairs and untill 2 years ago I wouldnt have believed in the fact that these amps need burn in time.

I have an '08 OTS 50 and the only mods I've done are: removed the FET input, (didn't use it), and put a "deep" switch
in it's place, put the OD trim pot on the back panel, and put a 15pf bright cap on the master volume pot. I LOVE THIS AMP!!!!!  Built a D-style cab with an EVM-12L and I can get just about any tone I want from Carlton, Ford, SVR and even Bonnie Rait's slide tones. Yeah, these amps are amazing for slide, clean or overdriven! 

I have got an OTS as well Plus a D'lator (made by Erwin)
I experimented with tubes a lot but still found the OTS a bit to  much "in your face" Erwin now changed the amp and made it into a combination between a Bluesmaster (cleans) and an OTS (lead). He also added a 0,47pf cap on the (push pull) master volume.
Great mod.

How did he change the OTS cleans to Bluesmaster spec then?? My OTS's clean channel sucks ass. Apparently the Dumble is supposed to be a modified Fender Twin, my clean channel certainly doesn't sound Fendery at all. Zero headroom and sounds spanky than the chimey cleans Fender are renowned for. I use a strat through my OTS and the OD channel is a bit too fizzy and no bottom end at all, but when the PAB is engaged, it sounds much better, more open and harmonic. Maybe has something to do with the V30 I'm using instead of a EVM12 or G12-65??

There's got to be something wrong with your amp, either construction error, faulty component or improperly adjusted bias. Not something some mods are going to fix. Did you make it yourself?

I would have to agree with axiology on this one. It really sounds like there maybe something wrong. The V30 isn't the best speaker for the OTS, but I played through one for a bit and it wasn't that bad. What tubes and settings do you use? Where is the O/D trim set?

Edit: I just saw that I spelled forum member "axiology" incorrectly and could have been taken the wrong way. Complete accident....sorry.  :-[

I have no idea what he did to my amp. I can't even solder a guitar cable. Perhaps you could pm him (Erwin_ve).

I didn't build the amp myself. I bought it from a well respected amp builder, but maybe he can fuck up sometimes I guess. I haven't adjusted the bias or the internal OD trimmer. To be honest I'm not sure how to tweak an amp like this. As in, how much is too much? Will I damage the amp by this. Is there a setting on the bias/OD trimmer I could set it to sound great without messing with it. I do have an ear for tone, but I'm also prone to breaking amps by fucking about with them too. I was told on here to set the bias to 35-40mv, the same as milliamps because of the 1ohm resistor that's supposedly installed on the circuit.

I just tried biasing the OTS via black to earth point and red probes into the test points either side of the power tubes, flicking the amp on to Operate and switching the digi MM on. The readings kind of baffled me somewhat. The reading on one side was 150.6mv and the other was 170.6mv, surely I must be reading this wrong, but it's a simple thing to do. I also turned the dial to one end to the other and not much of a difference in readings. Maybe 20mv difference. Please help on this cos I seem to be doing something totally wrong.

Did you replace the HT fuse? First, are you getting any sound from the amp. Position the bias pot to it's halfway point and try the amp. If no sound, then there's a greater problem then bias. To answer your question, Yes there's somehting not correct in you bias measurements. When you say "earth point" are you placing the probe in the black test point between the two red ones?

Yes, the amp is fully operational. I replaced the HT fuse which cured the problem of no sound. Now the amp is back like it used to be - loud and proud. I put the black probe into the black test point in between the two power tubes, then the red probe into the red test point of each tube left and right. I switch on the multimeter on to read 'mv' and begin testing.....then the readings baffled me.....don't know what else to do!! I don't want to blow the amp again. If anything, I'd rather run the amp 'cold' to prolong tube life, I just don't know which way to turn the dial, it's either 'blow' the amp again or 'cold'. But I'm not taking a chance in guessing! Please help.

I have an OTS 50w. Can't quite seem to find the tone I'm lookin for. Recently modded to FM 50.  I am liking the tone of the 183 much better.  How close to the 183 can I get without adding all those filter caps? Any suggestions please?

@ babybear, it sounds like you are reading both tubes at once, or possibly reading ac current, which is possible if you are reading both tubes via the reds. you will want to insert a red probe in one red socket at a time, and the black probe in the center black socket. Also you will want to make sure that all front controls are set to zero and that you have a speaker or dummy load plugged in. You will want to set your multimeter to the mV or smallest scale on the DC side. You will want to adjust your current to somewhere between 35-40 mV as a starting point. You can adjust up or down to taste, with 47-48 mV (mA in reality) being the upper safe limit for most 6L6 tubes.

@plasticvonaband, I didn't plug to red probes in. I did one at a time, one red probe, one black probe. I left the black probe in the black test point at all times, then switched between the two red probes, back and fore to test the bias. It does sound like two power tubes are being tested together, but surely turning the bias pot up and down would change the readings, but it didnt. I set the multimeter to mV as required. Left the speaker in cos it's already in a combo build, all dials were zero. Is there something I'm missing? I'll try and take a photo to see if anyone could help.

If you're getting 170 mv you're basically destroying those tubes. You'll need to check the wiring around the power tubes and/or the transformer extra carefully, find what you've done wrong and fix it. Then most likely replace the power tubes. It probably needs to go to a tech for this.

i agree. sounds like something is amiss somewhere in the bias circuitry, or maybe in the power supply circuit somewhere. either way, there is way too much current goin through there. if you can, try posting some closeups of the wiring of your tube sockets, but sduck is prolly right, you may need to take it a tech

++1