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. 





If you build a vintage amp with the sort of power supply you are using in your SET that vintage amp would sound much better.



The three-tube 6SN7 circuit board for the Dyna ST70 converts it to a Mullard circuit, with lower distortion and stronger drivers. Since nearly all the ST70 circuitry is on the single circuit board (for both channels), swapping that board basically gives you a new amplifier ... while retaining the power supply, chassis, and transformers. Lots of ST70 variants, since so many were made and are still kicking around. And the output transformers are pretty good.

Of course, if you are replacing the power transformer and upgrading the power supply, you might as well build on a new chassis, and have an all-new amplifier. Nothing wrong with a 6SN7 Mullard circuit and modern power supplies ... that will take you into the $3000 to $10,000 quality bracket right there.

Actually, the Kootenay, and the the Valhalla amps use a similar circuit for input and drivers (with judicious use of a CCS), and the power supplies are the basis for what we used in the Blackbird 300b amps.  We improved the power supply design for the Blackbird, but the same basic ideas are in the Kootenay KT88 power amp and Valhalla 6L6 integrated amps.   Long tailed pair with CCS and really good power supplies and iron.  As Lynn said, it makes for a really good tube amp.  Not the level of the 300b project, but very nice indeed.

But many of these classic PP still sound fine! Why? Because feedback or because PP has PS noise cancelation?  

Feedback allows the amplifier rejection of that which is not the signal, so generally speaking, yes.

I really liked the 3 6sn7 tube version that tubes4hifi used to sell and perhaps still does.   It makes the amp considerably better. 

The problem with any mod that adds tubes to the circuit is the extra load on a power transformer that might already be 65 years old. Dynaco strikes me as being pretty precious about their transformer ratings- I don't like to take chances with them, especially in light of their age.

This is just me of course but if I'm going to modify a vintage piece I follow two simple rules. The first is don't add any extra load to the power transformer. The second is don't do anything that does not fit very easily into the existing chassis. Violate these and you're likely better off doing the whole thing from scratch.

The really glaring weakness in the ST70 is it should have been designed with dual rectifiers; as a result the 5AR4 is the most likely tube to fail in the amp. Triode Electronics of Chicago has a beefed up power transformer that is a drop in replacement that allows you to add a second 5AR4, thereby keeping the correct B+ operating point and so not stressing the output transformers as well. But you have to find room beneath the chassis for some 500V filter caps. It starts to get a bit ridiculous- at that point why not just do your own chassis so you can lay out things properly?

If an ST70 is properly refurbished but pretty well the stock circuit, it can be surprisingly good against a lot of modern PP and SET amps. Since it really does not have enough feedback, you have to help it along with good quality coupling caps and resistors in the voltage amplifier and driver circuit. The second thing to understand about this amp is because of its power supply weakness, you really should not push it hard (which is better for sound but also keeping that 5AR4 alive). CE Distribution in Arizona makes a drop in replacement filter can that features an 80uf section, which should be deployed after the choke, for the plates of the power tubes. That's about as much extra capacity as you can safely add to this amp without stressing the 5AR4.

The octal boards for ST70 are direct fit and do not stress the power supply.  You can use the diode replacement for rectifiers, but it sounds different.  Basically, the amp is not bad, and a great deal for the money when restored and updated.  A decent preamp and some reasonably efficient speakers and a person can have a very pleasing stereo.  That said, an ST70 is nothing special because there really isn't room to make it special.  I think we agree on that.  You might as well start over and do it right without the compromises.