Beautiful! So, I'll share a bit about my Icon HP amp.
It's treating me very well. As I previously stated, I did do a coupling capacitor upgrade. I went out and bought a good quality Mundorf silver in oil cap and took it to a local shop to have the caps soldered in. The engineer saved the stock caps so I could see the difference. The stock caps were the size of navy beans. Very small. The caps that I replaced them with 3 times the size. I asked the engineer about this difference and he thought that this was surely a good upgrade to make. He believed that the stock caps would be a point of congestion and the new caps would allow for more current flow and more importantly a better sound.
Tube wise, I first began with a Chinese made 6SN7 by Sophia. I think the tube was ok but I found the sound to be grainy. After a few months I decided to venture out into the world of NOS tubes and bought a pair of Sylvania tubes from the late 50's. I also upgraded the 12AX7/ECC83 tube to a Mazda France tube, silver anode, from the mid 60"s. This is what I'm currently running and I'm very happy. A full warm sound, not too lush. Very detailed and focused.
Which brings me to ask a question of you.
How do you like these tube equivalents? I was totally unaware that the S6N7 could be changed out for another tube. I'm also noticing the tall bottle. How does this upgrade effect the sound? I'm very interested in hearing your thoughts. Also, would you share what parts are involved in your tube upgrade? If I wanted to try this out myself, what equipment would I need to seek out?
Yes you can run 6SN7 equivalents. For excellent sound that costs very little, check out the Russian 6h8c / 6N8S tubes. Stay in the 1950's and 60's though. Meltz versions are the expensive rare highly sought versions, but I use tubes made in the Russian 'FOTON' factory from the 1950's. You can get a dozen true NOS package seals never been broken for 20 bucks. These Russian tubes are the exact equivalent to American 6SN7.
The predecessor to the 6SN7 here is the US in the 6F8G. They are essentially the same tubes spec-wise. They are much larger physically, and have the ground pin is on top of the tube. Adapters to use these in the 6SN7 slot are ubiquitous on eBay. Only downside to the adapters is they come from China and make take a few extra days of shipment.
When everyone was going crazy over 6SN7, sending the prices through the roof for NOS, savvy tube collectors were grabbing up the 6F8G. Unfortunately, the collecting world caught up, and now the 6F8G has gotten much more rare and expensive. But for my ear, they are preferable to the 6SN7. The still have all the tubey goodness of the 6SN7, but seem to possess a bit more sparkle up top and make for a more 'live' sounding stage. They also seem to be a bit better at micro detail; delineating mid-range detail on a tick higher level.
I own lots of top notch 6SN7 and 6F8G. My favorites of each are the World War II era versions. Which means look for their military designations... VT-231 for 6SN7 and VT-99 for 6F8G.
RCA is a reasonable jump on spot for 6F8G. Sylvania ones sound nice, too. The most coveted, similar to the 6SN7 collectors, is the Tung Sol VT-99. They come with a couple different plate styles, but as long as they are the same in both spots, I don't fret over that as long as they are well matched and both VT-99. It may take a couple C bills or more to get into Tung Sol.
But again, RCA sounds great and you can get a nice pair of VT-99 for under $100.
Other ones that are rare but sound good are National Union and Ken Rad. Both in good shape (especially two reasonably well matched examples) are getting harder and harder to come by.
Now on the flip side, some issues you may run into with them is poor grounding/noise and microphonics. The next generation 6SN7 was improved in both regards.
