The main difference between SS and tube rectification is you can run way more filter capacitance with SS - with a tube reg, you are limited to a modest value due to the inrush current and need chokes (inductors) to smooth things out. Modest = 20-60uf for the first cap depending on the tube - that ain't much! Too much inrush when the caps fill and it will kill the tube. Plus there's a limit to how much current can pass through the tube so it can limit the potential power. So for best results SS then a bunch of capacitance to get a stout power supply. If you design around SS from the start you have next to no voltage drop and can run higher B+ voltage for a little more power (the drop in SS cans have a built in voltage drop to match the voltage of the tube they replace). If the Miller Autobias is based on the AB-Q modules (which it appears to be) it's a great system, I've used them in my homebrew designs. Set and forget and built in warmup mute.
Jay - my question is how does the Miller sound against the "get dynco" or the Bob Latino "tubes4hifi" upgraded versions of the ST-70? All three companies sell these upgraded clones but aside from the rectifier debate, I'm not sure what the differences are. I'm interested in buying/trying one of them but it's hard to make a decision of which one as they all get glowing reviews.
If you're going to exchange a GZ34 tube for a WZ34 Copper Cap it would be wise to get a slow start if you don't want to fry the EL34s. SS does not warm up.
Great review Jay! I have one of these upgraded amps and I can truthfully say it is the best sounding amp I own. I know Bryan personally and think he is a brilliant engineer, no bias intented (excuse the pun). First, by responding to a local add for a restored Fisher X100, then picking up some monoblock W4s, Maggies, Dynaco MK3, etc... His ST70 is in a league of its own. I've heard and seen the progression of this upgrade and it is truly a remarkable amp. Your review is spot on in my opinion, that it retains the tube amp magic while having an accurate bass response, power and authority by the improved rectifier circuit. The amp is super quiet too and stable. He showed me on a distortion analyzer they operate something in the low hundreths of a percent and other improvements to lower the noise floor. For me, it is the best of hifi. A tube amp where important and SS in critical places outside the signal path, check out all those filter caps! The preamp section is improved. I prefer the 6sn7 as opposed to the smaller driver tubes.
Awesome! - I've been interested in doing some DIY stuff for a while. Orchard Audio was one of the first that I recall offering kits .. but this one .. This seems special. Great video also .. " Kidney? " haha.. Got me on that one. =)
I have the Dynaco MK III monoblocks and upgraded all the components. Still may make more upgrades. Love the sound, made me fall in love with tubes. Don’t need more power as I have VTL 450s for that
The best st-70 is stock. Use a 6gh8a or 6u8a with an adapter. As log as you renew the capacitors Audio and Ps. David Hafler was a great engineer. The limiting factor were parts. Audio Research did an extensive redesign years ago and it was good. But yet the stock unit was better in my opinion.
I do agree with you !..............these modifications are different circuits and NO longer a ST70 .......When modified I don't call it a ST70 ...........this Miller is full triode and no Haffler circuit ( penthode/triode ).
@@Jayiyagi I haven’t. But I have been restoring and modifying for 50 years. There are numerous replacement boards that use multiple tubes. I have customers that insist on changing the design. The results I saw over the years was mixed. This might be great I don’t know. And it’s all subjective anyway. From a design standpoint the stock ST~70 is a very good one. I have serviced and owned many of these. Go my self I use a Radford STA 15. It’s reall the only amp drives the Quad 57 almost perfectly. It also uses a pentode gain stage. But the overall design was really in a class by itself. It uses a gz34 rectifier as well. The STA25 got rid of the rectifier and used a ss rectifier. It wasn’t as good in my opinion. ARC used and still uses ss rectifiers in most. Requires a thermistor in the ac side at least. Radord they needed one in the b+ supply to delay the voltage until tubes are warm. There ways around this. David bernings EA -230 uses ss rectifier. The 6sn7 grids needed protection diodes because there was no delay on the b+ application. It’s just different. See if you try this on a set of quad 57s. If it drives then it will drive anything. The load varies from 32 ohm down to 2 ohms across the audio band. The stock St 70 was good but tended to ring a bit on square waves causing brightness. But other wise good. The EA 230 was better. But the Radford is the best. Even beats the quad II. It’s all subjective of course. Thank you.
You are 100% correct. All of the “modders” trying to make it better only succeed in making it sound less musical. The ST70 was an excellent amp. Just replace parts that have worn out over time with proper replacements and enjoy the glow!
Early in my audio hobby I was lucky enough to come across a pair of upgraded Dynamo MkIII mono tube amplifiers. They were amazing but like a fool I let them go and have never seen a pair again. Big mistake!
Jay...those replacment banana posts aren't much better than original...put a pair of decent binding posts on...how much do you get paid for promoting this upgrade kit❓🤣...if it's so good and better...then why don't you throw away your original🤣
If we want to understand why everywhere solid state replaced in design tube type rectifiers it would be educating to compare the effort to assemble tube with socket in chassis to alow easy tube replacement and connections and dedicattion of more space and more chassis surface in compare to solid state bridge. Are there any downsides of solid rectifiers? I think I saw some overheated, in case of overload bridge may break and needs to be replaced by qualified service On one side price of bridge is many times lower than tube on other tube would not damage in part of second
Check out GR Research, Danny's take on the ST70 and his tweek, adding tube connectors which elevates the top end, yep you heard right his legend tube connectors.
Exactly what I said to Bryan Miller. It maintains that middle frequency “Magic”, with better bass control and extension. The soundstage is better exhibited! It’s all about the music!
I have a Bob Latino redesigned ST-70 driving Quad ESL-57. OMG !!! In heaven. An excellent first tube amp w/o breaking budget. “OTL” amps are supposed to be the cat’s meow, but $$$$
Jay, It’s a Different product. It’s like a McIntosh MC275 point-to-point wired amp from the 60’s is replaced with all circuit boards…Oh, this happened in the 90’s yet the McIntosh MC275 (point-to-point) is the mored desired amp.
There are still to this day very few transformers that can match the Acrosound and Dynaco transformers designed by David Hafler and his partner Herb Keroes. They are legendary.
I don’t like the way you talked about the sound without any measurements. I don’t think the 3-tube preamp board is any better than the original one. The “good” base you mentioned may be the result of high distortion at base frequency after you “upgrade”.
Jay you should try out one of the prebuilt Elekit integrated amps out of Japan. I’ve never had a 300b with so much bass/punch. Only upgrade was the small 12v tubes
I was excited to see this pop up. BUT, i am not putting solid state anything on my ST-70. I agree with other commenters, you can not really call this an ST-70 Design with the changes miller has made. Disingenuous to call it a ST-70
I actually own the BEST tube integrated amp ever made. The Audio Matiere Majuscule. It runs triode and pentode simultaneously. This gives all the magic of tube with tight bass
