HI Dimitry,
The Hurricanes are exceptional amplifiers right out of the box. Like any good valued product, there is a lot more potential to be brought forward.
The coupling capacitors make a huge difference and one recommendation I would have for you is that if you cannot go Teflon throughout the unit, use the V-Caps in the input stage (the two caps mounted on the face plate up front of each unit) and then a good film cap of your choice for the 8 coupling capacitors. That first stage is critical.
The other areas that I find to be very important is the grid stop and screen grid resistors. Here you want a good carbon resistor.
There are a few other resistor applications that are also very important and this is where choosing teh right components for the proper application come into play.
In my mods, I replace EVERY resistor in the circuit on the Canes. When developing these mods, I spent a lot of time doing single stage upgrades to see what the outcome was. Then, in the end, I found that the sum of the whole was justified. I had over 80 hours of labor in the first pair of Canes I modified just doing trial and error.
As far as the power supply goes, I agree with Jeffrey in that some upgrades here would be justified but I will not do anything that alters the original circuit. There are fartoo many liabilities to consider when you start doing this.
Another thing I do in these mods is remove a LOT of the wiring. I recently finished up a pair that I ended up with 7 feet of wire that was removed.
There is a lot of labor that [can] go into these amps. I realize what I do is more than what others would have the patience to do but I like to address even the smallest details. I want to make sure that every pair that comes in, goes out the door never to return with any "issues". I still spend 15-20 hours in each pair and I have done a good number of these amps. I treat every pair like it is my first. I have 5 pair here now.
For a DIY'er, these amps are intense and even intimidating to work on. There is a LOT of stuff in there. If you want to take on the venture, just take your time and obviously work on only one unit at a time. If something goes wrong, you always have the other half to get you back. Be patient, work in stages and you will end up with one hell of an amp. Most important: Have fun and be careful.
TUBES: Lots of options here. The KT88s that most my customers like are the EH. I am at the point that now I use the Sovtek 6550WE for system testing these amps when completed. I choose these tubes because they are inexpensive and I can easily have 2-4 pair of Hurricanes running at a time. That's a lot of expensive KT88s. For my personal amps (as soon as I get the time to build a few pair for myself) I will be using the Valve Art in one and the EH in the other. Same with the Monsoons I have on the list. YMMV.
The 6SN7 that I like is the RCA, I have a couple Canes running now with these as inputs across the board. You will have to experiment to see what you like.
