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Tube Hi-Fi Revisited

2/18/1998 10:14 AM
Mike D.
Tube Hi-Fi Revisited
A while back I posted a question about tube hi-fi, whether it was worthwhile. The responses were unanimous, do it! Recently, I obtained a Dyna ST-70 and PAS3 preamp at a very reasonable cost. I hooked it up, fired up a cd and lo and behold, it did indeed sound a lot better than solid state (Kenwood receiver). Even my wife, the ultimate "non-audiophile", could notice the difference. I tested all types of music, from Mozart to Judas Priest, cd's, vinyl, tapes, and FM. In every case the tube sound was more happenin', sometimes radically so. This is with the same ho-hum Cerwin-Vega speakers with cheapo Radio Shack replacement tweeters. I can't wait to get some real speakers! Thanks guys, I'm a believer.
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2/18/1998 11:00 AM

You may want to do some surfing and find out even more about your ST-70. There are a tremendous amount of mods for that amp which you may find to your liking. If you can read a schematic and solder, you'll find that most of them are very straightforward. If you have a hard time tracking down sources, let me know, and I'll try to help.  
Also, check out Deja News - they have a BBS for tube hi-fi heads. (I believe it's under audio.tubes or some such listing).  
2/20/1998 10:01 PM
Jim Kroger

It's called  
Yeah, improving that ST-70 can  
keep you busy for life. I surely  
can benefit from it more with some  
different speakers.  
I recently dumped a few megs of  
data I'd collected from  
about mods, etc., for the ST-70.  
It's the most popular amp ever made,  
selling about 200,000 between its intro  
in 58 (?) and demise in the late 70s (?).  
The trannies are excellent and the design  
is an excellent one.  
Some people get these sounding near to  
multi-thousand dollar modern tube amps.  
There is an ST-70 web site too, can't  
remember the guy's name. There is a FAQ  
also. Check  
2/23/1998 8:32 PM
Steve A.

>>>Recently, I obtained a Dyna ST-70 and PAS3  
preamp at a very reasonable cost.<<<  
    Wish I knew what I did with my PAS3 preamp and pair of Eico 35's from back in my prehistoric past... One note: the Dynaco equipment was usually (always?) sold as DIY kits, so one would be advised to check through the wiring to make sure that there aren't any cold solder joints, etc. It's probably be a good idea to go through the circuit and reheat all of the solder joints if the work looks at all sloppy.  
    I had thought that I might be able to get good guitar sounds with my Dynaco/Eico setup, but the RIAA curve for the magnetic phono input doesn't exactly make a guitar sing... There was no AMPAGE or killer amp tech books around back then (early 70's), but I think with $5 worth of parts the PAS3 could be converted into a decent guitar preamp! I did manage to slave the Eico 35 power amp to my Fender Pro, but didn't have a good cab to do it justice. (The Eico 35 was like half a Dynaco ST70.)  
    Dynaco rules!  
Steve Ahola
2/24/1998 9:35 AM
Mike D.

I checked the quality of construction on both pieces and it is very good, I got lucky here. The cosmetics are a little rough though, and I suspect that's why I got a reasonable deal ($200 for the ST-70 and $100 for the PAS-3). I know that a lot of people like to modify these units, but I'm pretty satisfied with the stock sound (for now, anyway)  
I also got an EICO ST-40 integrated amp for $100. The owner had modified it by bypassing the preamp section, so the only control on the front panel that works is the on-off switch! I'd like to change it back to integrated, but the preamp tubes are missing and I'm unsure of the wiring. Do you know of a source for a schematic? I've had no luck tracking this model down on the web so far.  
What I've really noticed with the tube gear is how compressed FM radio is versus CD's and especially vinyl. FM sounds like poop. Never really noticed the difference with the solid state gear. Now, it's like night and day. Man, that vinyl sounds good.  
You're right, Dynaco rules! I should have bought this stuff a long time ago. My friends and family are blown away by the killer sound.  
Mike Donovan
2/24/1998 8:41 PM
Mike there is an unofficial EICO home page outthere some where- I think they have the st-40 schematic on it... I got the hf12 from the site, sorry I don't have the address....  
2/25/1998 10:09 AM

I did a net search an found the (unofficial) EICO page. Although the ST-40 is listed there, no schematic for that is posted yet. Seems to me that this amp was similar to its bigger brother, the ST-70, using 7591's, but with slightly smaller transformers and with fewer selector switching options.

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