Dimitry, did you buy these amps? If yes, are you happy with them?
Yes I did. I am very happy with them.
However, there were growing pains - the previous owner was compulsive/obssessive and he apparently tweedled the bias all the time, often blowing up the tubes. A couple of sacrifice tube resistors in these amps needed to be replaced. One tube was not connected to the meter, which due to a design flaw simply "holds" the previous tube's current - very dangerous, as you are fooled into thinking the tube is biased just the same. Finally, the fuze holder on one was not screwed down all the way, causing the amp to switch off randomly.
Now all is fixed and they are fabulous and very stable. Love them. My particular pair has silver wiring and Relcap Multicap for coupling. I plan, sometime in the future, to send them to the "extreme" shop for $5k's worth of TLC. I think, for me, these are the final amps.
Bill Baker at Response Audio will do a FINE job of making them better, but YOU or someone who knows how to solder can make them sound a good bit better by further upgrading the 10 0.22µF couplers per amp with SoniCap Platinums. The Platinum uses a film that's an alloy of teflon; they sound VERY quick, clean, smooth, detailed, and tonally neutral while being significantly less expensive than the V-H teflons that Bill uses. My ASL dealer loves the sound of Jensen paper-in-oil-copper-foil caps, but others tell me they sound artificially warm.
I just received a new pair of 'Canes and have chosen the Platinums for the 1st position and Cardas Golden Ratio solids (which are close to the SC-Ps sonically) for the 2nd position.
What are you using for 'N7s and '88s? I'm collecting new and used 'N7s, but, not being a GEA, it takes me a long time to determine the character of the input tubes. I'm still using the stock Chinese '88s, but probably I'll buy a set of the Penta '88SCs with closed plates; they're getting rave reviews on the Tube Asylym.
Dimitry, I summarized my thoughts on couplers for the 'Canes here http://www.audioasylum.com/forums/tubediy/messages/94704.html . If you were ready to spend upwards of $5K at Bill's, you definitely can afford the SoniCap Platinums. And...they're $23 each less expensive than the V-Cap TFTFs, = $460 for the 2 amps.
Do you have detailed notes on modifications already performed? If so, if you share them, probably I can give you more to consider. Pls e-mail me at jeffreybehr(at)cox(dot)net. I've ordered the couplers and other parts and am currently co-designing a serious upgrade of the main PS. I'll let you know how that goes with my advisor who has LOTS more experience at this than I.
Where are you? Maybe I can physically help you improve your amps.
I've bought about 4-dozen* 'N7s, NOS and used, and I know they work in the amps, but I've yet to characterize them.
* Just another example of why my wonderful wife calls me Mr. Excess.
Wow, you seem very involved in improving your amps. Keep me posted on you endeavors. I am a sometimes tweaker, but some of the things you are contemplating are a bit above my level. However, there is always something to learn from knowledgeable people ! I am in Massachussetts, by the way. If you decide to go commercial, let me know. I am especially interested in you 6SN7 experiments.
On 6SN7s, here's what I wrote to my audio buddies tonite:
"Wow are my ears and brain (?) tired. Just listened carefully to a half-dozen samples of 'N7s in the frontend* of the 'Canes. Of the 6 samples, I made notes on only 4, that is, I think I heard character in only 4 tubes--3 were a little edgy/bright, and one seemed a little warmer. After listening to all 6, several more than once, I replaced the 2 Chinese inverter/driver tubes** with RCAs and left them in; that seemed to increase the spaciousness a bit.
I hope Pat's coming over tomorrow to help!
* 2 Voltage-gain stages in series...cascade, I believe it's called.
** one section of the dual triode is half of the amp's long-tail phase splitter and the other section is the cathode-follower driver."
Listening carefully to stuff like this is WORK for me. Oh well...it must be a labor of love or I wouldn't be doing it.
My 'Cane mods are in 4 general areas--the coupling caps, the decoupling (= frontend) dropping resistors and storage caps (currently 4 'lytics), the main PS, and the grounding wiring and rest of chassis. For the decouplers, I'll be tossing all the 'lytics and replacing them with Solen 'propylenes bypassed with SoniCap-2s. I've ordered them, but I'll soon be determining if the sizes I chose will work. On the PS, I'll be increasing the total capacity a little and putting most (about 80%) in the 1st pole and using only 200µF of Blackgate 500s in the 2nd pole, probably with a little MC-RTX bypass.
I'm going to try to install one piece of 14g. solid copper wire as the ground wire and run it around the chassis instead of having all those little (18g.? 20g.?), stranded wires running all over. I thought about using solid silver but decided that was overkill. I will be using double-20g. solid-silver conductors in teflon airtubes for signal or high-Voltage wiring I feel like replacing. Probably will be replacing few resistors, as resistors generally have far less character than caps, and the resistors ASL uses are plenty good enough for me.
Did you get details on your amps' mods done by Mr. Bogdan?
Sounds like you have great plans !
The modifications on my amplifiers were all coupling caps (front and side, so to speak) to MIT RTX and silver wire to from the jacks to the front end. I don't think he did anything else. I replaced the binding posts, some of which had cracked bases (flipping them over, if you are not careful, can put a big bending moment on the posts), with the same kind from the manufacturer. The tops of the transformers have scuffs on them (apparently from several trips to the repair place, where the amps were placed upside down to work on them), which I need to paint.
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.
I agree Dennis. I too prefer designs without feedback but also find that some system combinations can do quite well with feedback. This is why I have feedback (a small amount - less than 5dB negative) in my 300B amplifiers that is also switchable to take it out of the circuit.
With the Hurricanes, there would be no need for feedback but with SET designs, the speaker choice now becomes much more critical.