Nothing like having a week or two of relatively unscheduled time to fire up the ol' soldering iron and smell that holiday rosin aroma. I have a pair of DIY mono PP IT coupled 2A3 amplifiers (with Hashimoto PP iron!) that were sitting around idle for the longest time (several years) waiting for me to finally get back to them to debug and fix an intermittent noise problem in one of the amps. I wanted to have another pair of amplifiers that would drive my new Elsinore speakers, besides the Moskido hybrid amp and GM70 SET monoblocks. (always like double redundancy). Eyeing the easiest way of pushing up close to the 20W output capability to drive my speakers, I bought a quad of JJ 2A3-40 tubes, reworked the power supply to get 400V across the tubes, changed the driver from a 5842 to a D3A that can swing more volts into the grid, and installed a much more reliable way of nulling out residual hum. If you are using AC heaters on your DHTs (I know, old school), using a Helipot multiturn 50 ohm pot across the filaments one tube of a PP pair (the other tube having a pair of 1% 25ohm 3W WW resistors) allows one to adjust to incredibly low level of hum at the speaker terminals (less than 3 mV). Dead Quiet. Anyway, I have the 2A3s cooking at 85mA per tube, 72V bias, i.e., heavy Class A. I figure the JJ tubes like to run hard anyway (85% of rated dissipation). Anyway, these amps sound really, REALLY good. I did a partial rebuild keeping the 5842 driver at first, which was pretty sweet, but the D3A provides more texture and spaciousness. The amp is much more dynamic than I expected or remembered. In fact, I think the "jump" factor is comparable to my hybrid amp. I think I was using Shughang 2A3C's last these were working at a more conservative bias (i.e. closer to classic 2A3), so maybe the combo of the more powerful JJ version and more aggressive operating point makes all the difference. Definitely a keeper, and will be in the system for a while until I get the urge to switch things out again.
Also, dug out my MAC MR71 tuner which I had sidelined after getting a Sony HD Radio tuner (HD-1D?) a few years ago. I recently found the Sony stopped receiving any HD radio stations (It would lock on momentarily, and then lose the signal to static). Anyway, knocked the dust off the MR-71, reseated the tubes, replaced the burned out lamp for the stereo light, and replaced a weak 6U8A in the MPX section that resulted in poor stereo separation. I get a good signal on a classical radio station in Baltimore, WBJC, 91.5, that has decent 3D sound and great programming. I get great reception on WETA, but crappy 2D sound and poor programming (top 100 classical). Need to explore some decent Jazz stations (any suggestions?).
Also, relubed my Teres turntable bearing. Nice to have a steady speed again. And getting my retipped Benz Ruby III from Soundsmith back in a couple days! Woohoo! Eying one of the new Jelco knife bearing tonearms, but that will have to wait.
Good audio holiday season! And still have time for plenty of listening.
David
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