My OTS has both 220 and 240v taps so you could swap. No 230v though.

Regulator is out for the reason of expense. I am considering building a Variac into a rack box with digital input and output voltage readouts. Does anyone know what sort of rating variac I would need? I reckon 3A should be enough surely?

Conclusive proof this evening that only a couple of volts drift affect the amp tone.

We started our rehearsal with 242.5 volts (UK) and it sounded great, then after a while between numbers I was just playing about, clean, and thought it had lost its edge checked my guitar to see if I had nudged the tone pot, but no, checked the plug in voltmeter and lo the voltage had dropped to 240.2

Then later it was down to 238.7, what a difference!!!  lifeless and dull. Now I need to see how the bias drifts over than range. So I will take my DMM with me as well next time. Or maybe theres more to it than that?

Go with what HAD did. Especially the lead dress around v1 and v2, very important aparently.

If you are reaching behind the amp and twisting a knob between the power valves you are indeed adjusting the bias. If however there is a knob on the rear fascia, that will either be the FET level control or the OD Trim. To my knowledge Nik has never put the bias adjust on the rear plate.

As regards my settings, not much point me passing them on as I have changed quite a few components and I run a 12AT7 in v2. I rarely use my clean channel on its own, I use it as a pedal platform so I like it quite neutral, ie not overly bright, mids backed off, bass not too prominent.

If you are getting feeback on the clean channel you are doing better than me or you have the master cranked.

Take it to Sebago, have it checked over, not only as a tech can do, but also someone who has an ear for how these are supposed to sound. Then talk to the guy about what you want from this amp. Bear in mind you should take your guitar with you as pups make a big difference. And I think you'll find its not always possible to set it up to be perfect for both H/B's and single coils.

I wouldn't, unless you play on one for a fair time. It might be that this style of amp isn't for you. The clean can be very revealing of poor technique and, depending how its setup the OD can be really poor for rhythm playing, its intended as a lead channel.

There is nothing fundamentally wrong with your amp, unless someone has thoroughly messed up. If you don't know what might have been modded take it to Sebago Sound and have him tweak it to suit you. To be honest you are going round in circles, but you do need to be able to describe what yours is lacking and what you want from it for Sebago to be able to come up with the goods.

Probably Dale RN65D's though I think Nik only uses those on the plates?. Carbon film type, but you should really go for at least ½w in there, better still 1w.

No, the CRS I tried was flat and dry to my ears, and the OD channel was really only suitable for lead work, it didn't sound good for rock rhythm.

If you change the LNFB on V1b then you ought to put the options on a switch. One option is 10Meg - cap- 10Meg, another is no FB. And of course you can change the cap value.

If you want to change the feel of the amp and loosen it look at changing the slope resistor as Doc has suggested many times.  I also like his treble bleed mod for OD, it allows you to set the clean channel brighter without compromising the OD tone too much.

And I don;t get the sustain/feedback OD thing either, though for me its not that important, I like the OD to be just a slightly driven clean, I have a 12AY7 in v2 and for me its better, less gain and distortion. I need to buy a load of different balanced PI tubes and spend some time trying to the get PI balanced properly though.

Minuscule changes. I have mine on a switch and I would not be able to hear the difference if I was to stop listening for 5 minutes to make the changes.

Looks to me like the two 22Meg local negative feedback R's have been removed, but the cap was left in place, not connected.

One of the later models puts this on a switch which would have been the sensible thing to do.

He won't thank you for an HRM. Anything with a decent clean channel will do.

Not for taming volume no. The C-lator is only necessary if you want to run effects. It has some effect on the amps response and is a different master volume thats all. It isn't necessary to run effects either, lots will work without it. (Nova reverb works fine for me, Pickmaster uses some without  a *lator).

Triad mode is useful for an overly bright amp, its not good at all as a volume switch as it makes the amp duller.

An attenuator will only take some volume off before it has an effect on the tone. I don't know about the Weber Mass, I use a Hotplate which is fine live to -8dB but for recording you'd not want to go below -4dB, but only with Fender style amps, it doesn't work well with EL84 amps, the Airbrake works better. And the Marshall Powerbrake works well with Marshall amps but not with Fender style amps. All attenuators are not created equal. If you have plenty of cash you will be able to experiment, otherwise look to the Fuchs Casino range, Blackjack21?

wyatt is right. Stop chasing low power in a high power amp. It aint there.

If you want a low power amp get one designed and voiced to do the job. I have tried Powerscaling, attenuators, pentode/triode switching, pulling output tubes, and everything has an effect and always not good. Attenuators down to around 6dB are OK, powerscaling in moderation is OK, lower sensitivity speakers (but you'll not get the speaker you 'prefer' in a lower power version, so another compromise), etc etc.

But actually, the OTS is already well suited to lower output volumes because of the way its designed, the output section is designed to run clean all the way up. You just need to voice it slightly differently for lower colume and possibly a few other mods to increase the touch sensitiyity in the pre-amp.

You also need to route the V1 and V2 plate and cathode wires close to one another. Search lead dress on TAG. I also re-routed the heater wires up in the air

One other thing I did over Christmas when I did a load of rewiring and mods was to orientate the signal caps correctly.  Again search TAG for info. All those changes made a huge difference my amp is a lot livelier now.