Discussion in 'Eico Place' started by Rideoften, Feb 13, 2013.
Can you guys tell me the pros and cons of this amp?
Pros: reputed to be capable of very good sound.
Cons: who knows who built it in the first place, and Eico must have fired the design staff before that series was conceived.
Ride -- It is the baby brother of the ST-70. It is a cathode biased amp instead of fixed bias as used in the 70, and also uses a simplified driver/inverter circuit, rather than the Mullard based circuit that the 70 uses. It has about 20 watts a channel versus 35 of the 70, and of course has smaller OPTs as well. With the simplified circuit, it also does not have the notorious low level noise issues of the 70 either when sensitive speakers are used. Other than that, basic features are basically the same as its bigger brother.
they're great amps once some mods are done such as the loudness circuit mod.i have one and it's definately not going anywhere.theyre great with horn speakers, and even with my radford transmissionlines.
I have mine running a pair of Cornwalls and it sounds great, I have a ST-70 as well and I like the 40 more than the 70. Great little amp if paired with correct speakers.
Good amplifiers with a few serious but fixable design flaws and a face only a mother could love. I'd recommend owning one ST-40 and one ST-70. Kudos to Gary Kaufman for kindly re-habbing mine last year!
looks great :thmbsp:
Thanks for the help guys. It definitely has a face only a mother could love. Looks like a practical unit.
I just put my ST-40 on line as I ready the SE 2A3 amp to move to NH... further details as events warrant
heh, I've packed up the SE 2A3 amp to install it in its forever home... inspired by this thread, guess what I installed in its place?
Do these have active tone controls?:scratch2:
I'll have to look at the schematic, but I cannot imagine that the ST-40 (or even the ST-70) would have active tone controls - these were pretty bare-bones/entry level kits of their day. EICO, as always, spent the parts money on the iron - everything else was pretty much table scraps EDIT - D'oh, "feedback-type" tone controls are proudly featured in the EICO catalog copy!
I wish I could buy a kit or two new at that price.
It's a nice amp. Kegger has a fine rebuild thread on AK on it converting it to triode. I like the converted sound very much. http://www.audiokarma.org/forums/showthread.php?t=211563
The ST70 was my first tube amp,The weird thing it had, was a way to null the bass and treble controls to make sure they were the same left to right.
It would phase invert the left channel against the right,and if set correctly,you would hear very little,until you switched back to normal mode.
I also had the matching ST97 tuner which sounded great,I still have both pieces.35+ years later.
I redid one of these. The loudness switch mod is a must and makes a real improvement in the sound.
I would like to learn about any mods to the ST-40. I still own one (factory-assembled) along with the (Fred-built) ST-97 tuner (minus the multiplexer which I'm still searching around here for). I need to check these out and get them working, just because I haven't yet, not that I do need them.
I've noticed that both the ST-40 and the ST-70 use the 7591 output tubes (probably driven at higher voltage and) with larger output transformers. I guess they're not in a Williamson ultra-linear configuration after all. (The 7591A has a higher ampere thru-put at higher voltages. One thing that puzzles me is why that Williamson circuit has to use the extra taps on the output transformer rather than just a voltage divider on both sides of the transformer?)
How does the phono preamp 'sound'?
It's a feedback tap, isn't it? Not all that different than the UL topology, is it?
As to the phono preamp - never tried it; generally the vintage amps don't exactly excel in the performance of their phono sections (even if restored with fresh capacitors and resistors); they're usually pretty crude and their sonic performance, and usually their technical performance, reflects that. The HH Scott phono sections were something of an exception to this truism... but that's one area where I'd recommend going modern.
Yes, the ultralinear circuit is a local negative feedback source. But if you feed back a portion of the push-pull pair tubes' signals to the same connection you also get negative feedback, just not with whatever alteration those transformer taps provide.
Someday I'll have to connect up my scope to view the difference between the two signals, but to my Dyna Mk II's not the Eico.
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