Eico ST-70 vs Fisher KX-200
- Thread starter AA6U
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AA6U
Active Member
Unfortunately, I haven't had time to work on them. Since retiring, I have started a home business repairing and refurbishing tube radios and audio equipment and spend a lot of time working on other people's units but not on mine (surprisingly, there are a lot of people who have old tube units that need refurbishing). I have high hopes of getting to those and the other things I've picked up sometime in the near future. The issue is that integrated units like those that need mods take time to do right and at this time I just don't have it. I'll post to this thread when I get to them. Thanks for asking!
Tim D
Super Member
Thanks for updating us. Let us know when you get into it. We love to watch.
primosounds
Powered with pure tube sounds.
Recently, while cleaning out the storage for my "parts" units, i came across an eico ST70 that was in fairly decent condition. Evidently, it had issues with the preamp section because a long while back i had worked on it. Well, I figured what the heck it is like a free amp since i had forgotten i had put it away many years ago. So I decided to completely bypass the tone controls and run the signal from the selector switch to the 12ax7 of the amplifier section. So, using shielded cables i complete bypassed all the circuitry involved in the preamp section. No filters, no switches or potentiometers, no capacitors or resistors, no noisy tubes. I must say that sound was really clean and very enjoyable. I would not recommend this to everyone's rebuild but like i said it was like a freeby for me so i really had nothing to lose except a bunch of circuitry.
PS. This is easily reversible if you just want to try.
klamsoss
Be willing to fail and try again.
I don't mean to hijack a thread, especially one this old, but Primo, do you have notes on the work you did? I'm interested in trying out the pre-bypass thing. I'm going to do some direct comparisons of my Fisher X-100B (which uses the 7868 tubes) and the eico I am buying. The Fisher has been modified to have a preamp-out function, so I can skip the apparently junky preamp in the eico. If they are quite similar in power amp character, I may end up doing a frankenstein's monster bi-amp set up in my system. I have noted improvements with bi-amping using identical solid state amplifiers, and I reason that similar benefits might be possible with matching-sound-characteristic tube amps.
I did this same bypass for a friend years ago. He used it for a number of years before buying a new tube amp. I also built an ST-70 power amp stage for another person using original transformers. It worked really well with his Klipsch LaScala's. Dead quiet and one of the few horn speaker combos I ever thought I could enjoy.
I've done the Tronola mods, and them some on the Eico ST-70. I've got DC on the heaters. I've tried constant current sources on the phase splitter. Dave Gillespie's EFB. Bypassed tone controls & etc. Fabricated a new case. Etc. It's what I listen to every day, and IMO it's as good (if not better) than any integrated amp I've heard. Plus it's not ugly any more. 
Here are pics and schematics.
Here are pics and schematics.
Attachments
nj pheonix
Lunatic Member
IMO
Had both, rebuilt both. Tronola nods on the Eico. Clearly the Fisher was more finished as a whole.
Completely restored the Eico is very good and perhaps PA section better than the Fishers , though splitting hairs.
I have an eico 2080 which basically fixes the preamp sides shortcomings. At that point your splitting hairs. Clearly the Fisher is Prettier. it's a crapshoot because the Kx was a kit and the eico could've been a kit. So depending on who built it. well you never know.
Had both, rebuilt both. Tronola nods on the Eico. Clearly the Fisher was more finished as a whole.
Completely restored the Eico is very good and perhaps PA section better than the Fishers , though splitting hairs.
I have an eico 2080 which basically fixes the preamp sides shortcomings. At that point your splitting hairs. Clearly the Fisher is Prettier. it's a crapshoot because the Kx was a kit and the eico could've been a kit. So depending on who built it. well you never know.
AA6U
Active Member
Thanks for the input. After all this time, both the Eico ST-70 and Fisher KX200 units still languish in the closet, awaiting time for me to either rebuild or sell them (and I picked up an additional KX200 along the way). Retirement did not bring me spare time to work on my own electronics as I had hoped, but at least I am not bored!
nj pheonix
Lunatic Member
Nice toys
(I was referring to your signature equipment)
(I was referring to your signature equipment)
Digging up an old thread, SM, that is one beautiful piece. Looks like it just left the factory. Time machine!I've had both. The Fisher KX-200 goes to Warp 8 on the cool factor for me with the chassis mount bias meter.
As far as sound quality, I agree with the above. Get both, keep one.
AA6U
Active Member
Cool factor is not an important issue. Eico has always been an ugly duckling among audio equipment. I am looking for great sound. I am just finishing up rebuilding the KX-200 and then I'll get to the Eico and see which sounds better. Another alternative is to dump them both because they use 7591s which are surprisingly expensive (even the Russian 7591s cost more compared to EL34s, etc.) and get a different classic amp with different output tubes. I'm making suggested mods to the KX-200 so that it doesn't burn out tubes as fast as it's reputation suggests.
I am working on a plan, to convert an Eico ST70 to KT88 output tubes. The advantage, beyond much more ready tube options, would be a ton more power. It's possible to get in excess of FIFTY watts per channel, from 20Hz-20KHz, from an Eico ST70, wired in "Hot Rod" mode, using KT88s.
Whether or not this plan works, will depend on whether I can eke a bit more gain out of the preamp and amp driver stages of the ST70. It will need to have a total of about 6dB more gain, because of the lower gain of the KT88. I think that it's at least feasible...
Regards,
Gordon.
Whether or not this plan works, will depend on whether I can eke a bit more gain out of the preamp and amp driver stages of the ST70. It will need to have a total of about 6dB more gain, because of the lower gain of the KT88. I think that it's at least feasible...
Regards,
Gordon.
nj pheonix
Lunatic Member
Gordon,
How is this one different than the hotrod redo you did before?
How is this one different than the hotrod redo you did before?
Same amp circuit- just modded for a little more gain- but in the chassis of the ST70. The question to be answered, is how much more gain can be had- as well as how much can be had from the preamp, too. I need about 3dB more from both, for a total of 6dB. That's only a voltage gain increase of 1.414:1 for the preamp, and the same for the amp- that's not too extreme.
Yes, there will be some different heater/power transformer configurations than stock. That's the main part I am mulling over now, in fact- how to get enough heater current, and how to beef up the power supply filtering (I want a choke in there somewhere). B+ current is fine- Andres' Hot Rod with the doubled-up 7591s proved that. My KT88s actually draw slightly less idle current than his doubled-up 7591s (133ma per channel, as opposed to about 140ma, at idle), so the B+ part of the circuit will be fine. There's also plenty of bias voltage available from the stock PT.
I am also trying to figure out a way to "drop" the output tube sockets down into the chassis- so that I have a chance of getting the top cover back on, with KT88s. I already could fit old-stock 6550s under the stock cover, I think- but KT88s are considerably taller.
AA6U
Active Member
Just finished refurbishing/upgrading the first of my KX-200s and it sounds great. I changed C19-22 from .047uf to .1uf as suggested to increase the bass and biased it at 36ma so it wouldn't eat tubes as it is known to do. Output tubes are a mixture of American and Japanese.
It certainly has great bass balanced with clear, detailed mids and highs. I'm very impressed with the soundstage, and I've worked on and heard a lot of systems.
It certainly has great bass balanced with clear, detailed mids and highs. I'm very impressed with the soundstage, and I've worked on and heard a lot of systems.
nj pheonix
Lunatic Member
I had a couple of x 200s and a Tronola modded at 70.
I could never get the Eico as quiet as the Fisher.
The Eico was no slouch though.
The Eico 2080 sort of solved the noise issue. All the bits are in an st70 but it takes a bunch of work to make it like a 2080.
I very much enjoyed the x200. It has been my favorite integrated that lived here.
I still have st70 iron here with intentions on trying some variation of the hotrod version Gordon wrote about before.
Just not the time or motivation to get to it.
I could never get the Eico as quiet as the Fisher.
The Eico was no slouch though.
The Eico 2080 sort of solved the noise issue. All the bits are in an st70 but it takes a bunch of work to make it like a 2080.
I very much enjoyed the x200. It has been my favorite integrated that lived here.
I still have st70 iron here with intentions on trying some variation of the hotrod version Gordon wrote about before.
Just not the time or motivation to get to it.