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300b lovers

I have been an owner of Don Sachs gear since he began, and he modified all my HK Citation gear before he came out with his own creations.  I bought a Willsenton 300b integrated amp and was smitten with the sound of it, inexpensive as it is.  Don told me that he was designing a 300b amp with the legendary Lynn Olson and lo and behold, I got one of his early pair of pre-production mono-blocks recently, driving Spatial Audio M5 Triode Masters.  

Now with a week on the amp, I am eager to say that these 300b amps are simply sensational, creating a sound that brings the musicians right into my listening room with a palpable presence.  They create the most open vidid presentation to the music -- they are neither warm nor cool, just uncannily true to the source of the music.  They replace his excellent Kootai KT88 which I was dubious about being bettered by anything, but these amps are just outstanding.  Don is nearing production of a successor to his highly regard DS2 preamp, which also will have a  unique circuitry to mate with his 300b monos via XLR connections.  Don explained the sonic benefits of this design and it went over my head, but clearly these designs are well though out.. my ears confirm it. 

I have been an audiophile for nearly 50 years having had a boatload of electronics during that time, but I personally have never heard such a realistic presentation to my music as I am hearing with these 300b monos in my system.  300b tubes lend themselves to realistic music reproduction as my Willsenton 300b integrated amps informed me, but Don's 300b amps are in a entirely different realm.  Of course, 300b amps favor efficient speakers so carefully component matching is paramount.

Don is working out a business arrangement to have his electronics built by an American audio firm so they will soon be more widely available to the public.  Don will be attending the Seattle Audio Show in June in the Spatial Audio room where the speakers will be driven by his 300b monos and his preamp, with digital conversion with the outstanding Lampizator Pacific tube DAC.  I will be there to hear what I expect to be an outstanding sonic presentation.  

To allay any questions about the cost of Don's 300b mono, I do not have an answer. 

 

 

whitestix
atmasphere's avatar
atmasphere
11,633 posts
 

From this distance, I wonder about circuit stability.

@lynn_olson They were quite stable and reliable. But the circuit is carefully designed around some serious issues with phase margin, which is why you really don’t want to try any serious mods other than updated coupling caps unless you do the math and think it thru.

The Dynaco ST 70 had good transformers, but the driver section was barely adequate and if you replace it with one of the more modern boards, especially the all octal tube ones, the amp is greatly improved. The small chassis limited the quality of the power supply you could fit in there though.

@donsachs The real weakness of the ST-70 is the rectifier. Its not got enough current and so is the most likely tube to fail in the amp. If you replace it with solid state the B+ will be too high. It is possible to use dual rectifiers but you have to replace the power transformer to do so. Triode Electronics of Chicago makes a power transformer that drops into place. You can use the filter can location for the other rectifier; the power supply caps can be installed beneath the chassis.

There are adapter sockets on ebay that allow you to run a 6GH8 in lieu of the 7199; that gets you a far more common tube that also runs the amp with a bit lower distortion.

markusthenaimnut's avatar
markusthenaimnut
354 posts
 

I’ve said it before and I’ll say it again. This is such a great thread.

Oh! And hi @eddie138 ! Nice of you to drop in!

donsachs's avatar
donsachs
250 posts
 

@atmasphere Actually, I have rebuilt a few ST-70.   I agree, the rectifier is inadequate, but so is the driver section, which is at clipping at or just before the output section clips.   I have heard a couple of drop in boards and the octal version was by far the best.  Much better amp with 6sn7 input tube and 6sn7 drivers.   Still, the small case keeps you from installing a really nice C-L-C supply built with only film caps rather than lytics.  When modded it is a cute little amp, but hardly worth the trouble compared to other designs in my book.  I recall another vintage amp or two that used 6GH8 or similar for driver section, probably Scott, but too long ago.  Yes, we re-wired the sockets to take more common variants of the triode/pentode combo tubes.  They are all nice little amps, but not in the same universe as the topologies we are discussing in this thread.   However, would make nice little systems though with good speakers.  

I recall a Fisher flagship el34 amp that was really rare that actually sounded quite good when restored as well.  So long ago I forget all the model numbers!  When I was doing all the vintage work I could probably have rattled off the model...

lynn_olson's avatar
lynn_olson
274 posts
 

Without making a big deal of it, Don and I have definitely taken the Blackbird several steps (with new parts, and some new circuits) beyond the amps at the show. You guys are in for a treat.

atmasphere's avatar
atmasphere
11,633 posts
 

@donsachs Unless the power transformer is replaced, I think its a bad idea to drop in a board using 6SN7s as much as I like that tube. 6SN7s have a 600mA filament; running 4 of them is 2.4 Amps! The transformer would burn up in due time.

Yes, you can install a supplemental transformer...As much as I like the ST70 (it has decent output transformers) IMO when you get that far into it, I feel like starting from scratch with a chassis that is large enough to really do what you want is a better move- and leave the ST70s for what they are good at: inexpensive and competent tube power.

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