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Thanks for sharing.
I am sorting out the best or a better tube configuration myself with the tubes I bought already. With the experiences you all shared with us here, I am gradually reaching a conclusion, and I hope to report my configuration after this weekend.
At this moment, I am satisfied by the following tube configuration of my 339:
Power tubes: RCA 6AS7G, these make the music smoother
Driver tubes: 6SJ7 WGT, these make the music lively, high more sparkling, more details.
For the power tubes, I have tried the following:
7236, Sylvania 6080 Gold tube, Russian 6H13S, and of course the Chinese power tubes that came with the 339
For the driver tubes, I have tried the following:
6SJ7 metal, 6SJ7GT mesh plate, 6SJ7GT solid plate, 6SJ7WGT, a Russian version of EF86, 5693, and the driver tubes
We all know that 339 generates a lot of heat. So much that touch the solid metal part between the two power tubes is adventurous.
Even though 399 seems to be well built for high temperature, I feel that running at a lower temperature is a good thing for this amp or any amp. To achieve this goal, I found a small fan and put it on top of the heat vent between the power tubes. It drastically reduces the temperature of my 339. Now, I can leave my figure on the solid metal part between the two power tubes for a long time, it is warm, not hot anymore.
This is a AC Infinity MULTIFAN S1, 80mm. It uses a USB power plug to get power of a laptop or a powerful USB charger. I am powering this fan with the USB charger for my ASUS phone. The fan covers the heat vent of 399 very well, and I place the fan in the direction to suck the heat out. It is quite, it has its own switch to turn on and off and to choose among three levels of fan speeds.
This fan costs about $10 on Amazon
By searching, I found that this idea was already mentioned long time ago in Post #364 by keph
The RCA 6AS7G is a great power tube for this amp and was noted as a favorite by the time I decided to buy it myself.
My observation regarding the 6SJ7WGT tubes matches yours. These tubes are very good for classical music due to the extended highs and great details. They also improve the texture in the vocals in my opinion. The only caveat is, they can sometimes produce a low hum and some wireless interference with the Tung Sol 5998, while the RCA reds are completely silent. I think, the 6SJ7WGT tubes synergise very well with the 5998s and the 6AS7G. I have heard both, but I think the 5998s with their extra power open up the soundstage and improve the bass as well.
Parts are in for the current pending orders and the adapters should get built and sent out this week.
Tung-Sol 7236 Tube Variations:
There seem to be at least 2 versions of this 7236 Tung-Sol tube - One with black label on metal base and another with red label on metal base. The third (more rare version) has a white label. I got one with red label. Anyone knows the difference?
i have a pair with white and a pair with black writing. Can't hear any difference, both extremely linear sounding tubes; i wrote about a few combinations a few pages back, 7236 was one of them (trying to find time to sit down and analyse more combos). Struggling to find red label ones, only seen once on ebay.
Everyone that ordered tube adapters on the yuking website should have received them by now. If you didn’t let me know. There are more available if anyone wants them.
If you're still interested in a "red label on metal base" Tung-Sol 7236, I bought mine from this eBay listing. I expected to receive one with a white label as shown in the photo, but they sent me a 7236 with red label. Wish I had a white label 7236 to compare it to. I suspect that the only difference is the manufacturing year, but cannot confirm this.
I have a few 7236 tubes with all three label colors (black, red, and white). To me, they sound not that much different from each other.
Thanks! Do you know why the label color is different? Rumor has it that Tung-Sol manufactured 7236 tubes between 1960 and 1965 for Joint Army Navy. The label colors (and batch numbers) represent different manufacturing periods. Unfortunately, I am unable to confirm this. But it's good to know that at least the difference in label color does not translate to audible difference.
Thank you for letting me know the time spanned for them to make 7236. As for the color and the time period, I saw
black label for the years 62, 63, 64
white label for years 60, 61, 62
red label for years 65
There seems to be a pattern there...
Can anyone comment on how the AEON Flow Closed pairs with the 339? I read some where in this thread that low impedance HPs and OTL amps were not a good match. The AFC is rated at 13 ohms and 92db/mW.