Eico ST-70 vintage tube integrated amp restoration/upgrade

ben62670

HeHe I am glad you are having fun. Be safe with those high voltages.

Fongolio

ben62670 wrote: »

HeHe I am glad you are having fun. Be safe with those high voltages.

Only one little jolt so far when I was setting bias. I touched something near one of the can caps and felt a very uncomfortable tickle. Speaking of which does anyone know of a safe procedure to drain the can caps of their charges before replacing them? I've read the PS can cap is nicknamed "death cap". Sounds scary. Any input is appreciated. Thanks.

Kelvin

mhardy6647

No, the death cap is something else - it's between the line (AC mains input)and ground; your ST-70 may or may not have one. If it does, it should be replaced with a modern equivalent (there's a duty type spec for these caps, maybe X or Y... or Z???).

Time is your friend. If you shut the amp off or unplug it, the caps will drain as the amp consumes the last of its pent-up juice. Folks typically discharge them through a resistor to ground - you can just use a screwdriver, but I guess that's not so good for the capacitor :-) I usually just wait a bit before servicing. Not going to give you advice to mimic me, though.

Don't be afraid of HV but do be respectful. The big power supply caps could give you a good whack :-(

Fongolio

mhardy6647 wrote: »

No, the death cap is something else - it's between the line (AC mains input)and ground(

Oh, ok. I've already swapped that one for a modern electrolytic. Thanks for the info.

steveinaz

Awesome project, you the man.

Tour2ma

Love this thread...

mhardy6647 wrote: »

Time is your friend. If you shut the amp off or unplug it, the caps will drain as the amp consumes the last of its pent-up juice. Folks typically discharge them through a resistor to ground - you can just use a screwdriver, but I guess that's not so good for the capacitor :-) I usually just wait a bit before servicing. Not going to give you advice to mimic me, though.

Always think it's cool to hear an amp "spin down", i.e., the volume fade after the amp is turned off and the big, output caps' charge keeps it playing for a few moments. It's an audible verification of their discharge. Then after they've spun down apply the screwdriver as a double check.

mhardy6647

Tour2ma wrote: »

Love this thread...

Me, too, sort of... I've got an ST-40 and now also an ST-70 down in the morgue. This thread might motivate me to at least toss 'em on the Variac and see what we're dealing with...

Fongolio

mhardy6647 wrote: »

Me, too, sort of... I've got an ST-40 and now also an ST-70 down in the morgue. This thread might motivate me to at least toss 'em on the Variac and see what we're dealing with...

Just do it! You know you want to. And if you could hear the sounds coming from my SDA-1C's in the last couple of days you'd already have the bottom cover off at least one of those old Eico's.

mhardy6647

Fongolio wrote: »

Just do it! You know you want to. And if you could hear the sounds coming from my SDA-1C's in the last couple of days you'd already have the bottom cover off at least one of those old Eico's.

you haven't seen the queue in the basement :-P

Fongolio

Update. The new multi cap cans came in on Friday. In order to install them I had to cut bigger holes in the stainless base. I used a dremel but it was not easy, that metal is hard and it was very slow going. I also purchased some mounting clamps to go with them and mounted the cans to the chassis. Wiring was pretty straight forward except the old cans were twist lock and the ground was through the can body onto the chassis. The new ones needed a new ground wire running to chassis. Done. By the way the new can caps are JJ's.

While I was at it I put in the new parts for the loudness mod. I had used old parts for the mod previously but installed the new caps yesterday.

Power up. Everything working and sounding fine except. Slightly more hum and significantly more hiss. I'm thinking my new ground wires could be the culprits for the hum, but the hiss has me stumped. Not all resistors have been replaced so I'm wondering if I could be picking up some noise from them. Suggestions at this point would be greatly appreciated. New pics up soon. Thanks.

mhardy6647

Old carbon comp resistors can produce all kinds of interesting, static-y noise, so, to quote Donald Sutherland in Animal House... "It's a distinct possibility."

Fongolio

Update. I ordered new resistors for the entire Eico unit. I'm about half way done replacing and the hiss problem is way down. As is the hum noise. I also did a couple of modifications while I had it open. The two phono inputs were 47k loading and 100k and since none of my carts prefer the higher 100k loading, I switched the resistors to 47k on that input as well. I have two turntables hooked up to it and now both sound really nice. There is a third input for tape (originally designed for reel to reel) that is basically useless so I converted that to a 47K phono input as well. I also changed the old two prong power cord for a proper three prong and ran the ground wire to chassis. This may account for some of the decrease in hum which is inaudible at anything below 12 o'clock on the volume dial.

On a side note, I purchased a new/used arm for my Thorens TD160. It's a Mission 774. The Thorens required extensive chassis modding and I needed to construct a new arm board for the Mission to sit on. The dremel came in very handy for this work. End result the arm is installed and fitted with my very high compliance Audio Technica AT20SLa cart. The arm is extremely low mass and fitted with a silicone damping trough and paddle. It sounds exquisite. Unbelievable detail and amazing tight defined bass. It makes the old Audio Technica cart sound very nearly as good as my $1000 Benz Micro Glider M2 on the Pro-ject 6.9 table. I purchased the Mission arm from a guy on Canuck Audio Mart for $225 which is a steal considering how good it sounds. A very significant upgrade from the stock Thorens arm.

Tour2ma

LOL... three phono inputs...

Thanks for the "bonus" tone arm update... Please post a pic or two when you can.

Fongolio

Update. The new resistors are all in. I also changed the diode/rectifier for a more modern diode. I re-wired a few things like the feedback and the grounds to the new can caps. The phono section is now almost totally hum free. I say almost because when using my MC step up transformer for the MC Benz cart I do get some hum at about 12 o'clock on the volume dial. Hiss is dramatically down. What is up is bass slam. This unit now sounds insanely good. Amazing detail, bass, wide sound stage and 3 dimensional imaging (the SDA's are contributing to that as well). The only things left to change are the rca inputs and the speaker terminals which I'm in no hurry for since it sounds so spectacular now.

I've attached a couple of pics of the underside completed. My solder job wasn't so pretty in some places but every connection checks out good. In the top pic you can see the new can caps and their clamps. It's really amazing when I look at the before pics and remember how it was when I brought it home. I've also included a pic of all the parts that were removed and replaced.

Last is a couple pics of the Thorens table with the new arm board I built for the Mission Arm. The arm is a huge upgrade from the original Thorens and it sounded pretty good by itself. That's Joe's "The Clamp" on the table as well. I just got that last week and can say it works as advertised. Very nice addition to the table.

FTGV

Nice work!The underside of that chassis is rather busy looking.

Fongolio

Tour2ma wrote: »

LOL... three phono inputs...

I always have two tables connected and the third is in case one day I buy a multi arm table. Then I don't have to fool around switching phono cables every time. Future proofing.

geoff727

I gotta say, it looks like you are really having fun!

G~

Fongolio

There is a little bit of trouble in paradise. Eico recommends biasing the output tubes to 0.38 volts which I had no trouble doing before the resistor mods. Now, I can't get either channel to go that high even with the wiper maxed out. 0.17 volts is the highest I can achieve on the one channel and just slightly more than that on the other. Anyone have any ideas? I've checked the resistor values and they measure correct. The weird thing is that it's both channels. Should I be worried when it plays so nice? I've set them both to 0.16. Setting the balance on them works fine. Any input greatly appreciated.

Kelvin

Fongolio

I see I never finished updating this thread. The biasing problem turned out to be the Mullard 5AR4 rectifier was only half working and was fixed with a new Shuguang 5AR4 rectifier tube. I'll replace it with a Mullard original when funds allow but the Shuguang has been in for months and is working perfectly. I also replaced the ancient original diode with a modern 1N4007. The unit remains balanced and biased to the recommended 0.38v with tweaking only required once every 6 weeks or so. Very stable and it sounds fantastic. I use it daily with no problems whatsoever. It's been a great addition to my setup and has already brought me many hours of audio nirvana.

saemark30

How do the mods sound?
I like the ST70, the phono is a little on the dull side on mine.

Fongolio

saemark30 wrote: »

How do the mods sound?
I like the ST70, the phono is a little on the dull side on mine.

Every day that I sit back and listen to it, I'm blown away that a 50 year old piece can sound so good. The mods, including the loudness switch fix, really bring the phono section to life. Bear in mind too, that most of the tubes are original Eico Mullards except for the converted 12AX7's which are original factory Svetlana's.

saemark30

Has you looked at the Tronola mods.
http://tronola.com/ST-70A_mods_package.pdf

Improved low end, power and S/N ratio.

saemark30

This mod also changes the 12DW7 to 12AX7.
But the gain of the preamp is increased and the power amp is decreased.

Fongolio

saemark30 wrote: »

Has you looked at the Tronola mods.
http://tronola.com/ST-70A_mods_package.pdf

Improved low end, power and S/N ratio.

Yes, I've done all those mods. HUGE improvement. Totally worth the time and erffort.

saemark30

I have to put that on my to do list.

Gatecrasher

I know for a fact that Eico amp is a very nice-sounding unit.

I grew-up with one.

My father built one of the kits in the late 50s - early 60s? He was in his 20's.

I'll have to ask him the exact year but I used to crank it up all the time and have seen of our black & white family pictures from around 1961 or so with the amplifier in the background. It was fairly heavy and had a nice extruded aluminum faceplate and rigid chassis. The same knobs and everything.

It would heat-up pretty-good too I remember, but never failed. I don't think it ever broke the several decades he had it.

He had it connected to a pair of huge home-made bass-reflex cube speakers he built with Pyle drivers. They had big horn tweeters too and were covered with woodgrain Formica. He had an old Garrard turntable and in the later 60s added an 8-track deck to it.

The system was mighty-fine for it's day and all my friends in the 1970s were amazed at how good it sounded. It cranked and had a lot of punch.

I'm going to copy the pics and ads you posted and e-mail them to my Dad (who is now 75 years old). He'll get a kick out of them.

Pretty-cool and if I would have seen it probably would have bought it too!

mhardy6647

heh. Thanks to the huge generosity of two generous people, I just joined the "other" ST-70 club myself. A local hi-fi colleague (the fellow for whom I re-habbed a Marantz 8B years ago) gave me an ST-70 way back in December 2010. A couple of weeks ago, local hi-fi tube guru Gary Kaufman (www.the-planet.org) kindly rehabilitated it for me. He says he enjoys fixing up ST-70s (and he knows me well enough that it'd be a long, long time before I worked up the gumption to tackle the re-hab myself!).

Picked it up yesterday and spent a little quality time listening to it today.



(speakers are a pair of EPI 110C, from my favorite local emporium)



Gary also kindly rehabbed my other EICO carcass - the ST-40, mentioned earlier in this thread, found on the scrap metal pile at my favorite local emporium. It sounds great. They both do.



(I did a cursory front panel & knob cleaning of the ST-70 today; haven't done the ST-40 yet - which is probably fairly obvious from the photo)

Fongolio

They've got to be the ugliest great sounding integrateds ever. No matter how superb mine sounds now it still looks butt ugly but I don't mind. It brings me hours and hours of enjoyment. Congrats on getting both your up and running. What all was done to restore them? Caps, resistors and the works? Are you running stock tubes on both units? Did your man do any of the mods? Craving details here!!

Gatecrasher

I don't think it's that ugly. I always liked them. I did see someone on eBay selling aluminum inserts for the Eico knobs a while back though. Would probably make it look a little nicer.

The part I always liked was the sound from these amps.

TNHNDYMAN

^ Mr. H-
What do you use to clean the front panels?