I believe these are the same tranny sets that are used for the 50 watt Plexi kits, but you should email Nik and see what he says.
I cannot hear what you hear with your amp, but these do have A Lot of gain, and consequently can be quite a bit "noisier" than most amps. Have you played around with lead dress at all?  The NFB wire/circuit can be a big source of "hiss".
Good Luck

Well then, it was a good catch on your part. You might want to contact Nik to see if you can push the rating passed 1A at all. But in the mean time, see what a 1A Slo-Blo will do.  Have you powered up this amp yet?
Good Luck

Yes, you are correct.
But why does your amp have a 2A fuse?
Is this amp presently running at 120, and  being rewired for 230V?

I guess I don't understand your question.
1.  What difference does it make whether the rectifier diodes are tube or solid state?  The VVR installs after rectification.
2.  What is wrong with installing the VVR per the diagram you provided?

This is kind of funny, but also interesting.  I know what this sounds like through a speaker, but I never use a dummy load, so I would not have known what to think. This is a good lesson to keep stored in the "memory banks".
Good Job

That is filtering for the B+ rail.  It is part of the rectifying process....AC to DC.  One cap is twice the value of the other. Some might say this will give the amp a "stiffer", "punchier" feel.  It is hard to say, that is pretty far down the filtering line, and it looks like the JTM 50 already has more filtering in the preamp than does the JTM45. It is something you could try on either amp.....
Good Luck

As hywelg mentioned, Teflon wire can be murder. Solid wire has good memory and so does "regular" plastic insulation. So try some different wire. Maybe switch to 20 AWG for the pre tubes.
Good Luck

Well Done!
If not tubes, it sounded like a lead dress/proximity type problem. Nik is a very knowledgeable and helpful guy. I would be interested in seeing some pictures of your solution........
Good Luck

Did you try replacing the tubes?
Lead dress issue?
Pictures?
Did you build it?
Good Luck

I installed a larger value bias resistor in my clone. Just seemed like it was biased way too hot with the stock 250 ohm resistor.
Good Luck

There isn't a good solution.
You probably need a 1-10 watt amp.......
I would start with a less efficient speaker, but you may not like the tone.
You can try one of several different attenuators, but you may not like the tone.
You can install power scaling, but you may not like the way it makes you have to change the EQ as you +/- the power scaling.
I have never thought those Pentode/Triode switches sounded good.
Just try it for a few weeks, the way it comes to you, before you start to make changes. After you get acquainted you will be able to make a better decision as far as "Volume" is concerned.
Good Luck

Do you realize this thread is Two Years old.?
But yes, you have it right. Follow a path that is close to what "roe" recommended. You should probably go one at a time and see how things progress.
Good Luck

You should give Nik a call...
But from a quick glance...The OT can probably function with either EL34 or KT66 as far as the impedance that reflects back from the Speaker-OT-Tubes.
You will have to check the current draw difference between the 66's and the 34's. At a glance, everything else looks pretty much the same, but I have to get out of here.
Send your question to Nik...
Good Luck

Which one of Nik's 18 Watt layouts shows a FX Loop.?

It basically ties the screens to the plates, creating a "triode" tube. That cuts down the power, but I have never really liked the effect. But it is an option, and you do not have to use it if you do not like it....
Good Luck