Eico's Owner Group
- Thread starter drtool
- Start date
Hi James- Sorry the reply took so darn long. Not an expert tech here, I hear details with this amp I have heard with no other, but also somewhat agree and possibly in the highs I sometimes want a bit more sparkle on cymbals, etc sometimes? But for the most part, this amp is very special and I'm a huge fan! And that's a thing I "think" I finally discovered/learned from a lifetime in audio, that maybe the midrange is the most important thing to get right? My tubes are getting some good hours on them and that doesn't help in my experience as tubes age.
For the hum, did you replace the PS caps too? Whenever I do a rebuild, I take the time to just order a replacement can multicap from Hayseed Hamfest for the PS, fits my skill level. I of course get a little hum, it's a tube amp, but not hearable at my listening position, even on phono with it cranked to 50% volume. But go up to change a record and you hear hum right by the speaker.
I did do other stuff though on my rebuild. On these, unless you are super tech status, not really possible to bypass the tone controls from what I understand, so those got pots cleaned very well, and carefully set to flat. (I never use EQ) But on uneccessary items you could figure out to bypass, I did that and it likely helped with S/N and possibly hum. The weird balance control, removed from circuit. The function select too- removed from circuit also. That's a lot of switch contacts and wires out of the circuit and I bet it helped..... everything. AK is full of very skilled techs who may offer more enlightenment, I would do the can cap if that has not been addressed.
As you mentioned, ground points, removed/cleaned each one and also reflowed all solder joints. Totally agree, HF-81 is one amazing amp!
JamesML
Well-Known Member
Hi Hob,
Yes, I recapped the power supply. Plus some other electrolytics.
Also, I agree about using HH cans. I've used them in my Fisher equipment (500c,400,X-202-B and X-101-C) with excellent results.
If I'm honest re stuffing of cans, altho it's nice to keep some originality, is a bit too much for me nowadays to bother with. And HH do such an excellent job.
The HF-81, for such an unassuming piece of equipment, is definitely a very nice amplifier. And, it holds it's own alongside with my Fishers.
Happy Listening!
Jim
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View attachment 2407198 View attachment 2407199 Hey, I'm now the proud owner of my first Eico! I picked up an ST40 that looks to be in pretty good shape. The owner sold this as 'restored' and cosmetically, it's in very good condition, the pictures are without doing any cleaning at all. First question, the selector switch spins all the way around and doesn't stop at each setting, I'm thinking this isn't what it should do, but I don't know these amps, comments? It does look like a lot of recapping and resistors have been done and the solder job looks good. Anyone with a good eye that sees anything that looks off, let me know. I would have like to have seen some original tubes, or something besides Russian 7591's. The rest are JJ's except the Hammond rectifier. Somewhere a 'restore professional' is having fun with a bunch of original tubes. The rectifier tube seems loose to me, it goes in with a nice 'thunk', but then wobbles pretty easily. Is this an issue or is it because of the 5 pin configuration? The tube shields are missing, I'll have to look for these, if anyone knows where to find some I'd be grateful. I will replace the 5 amp fuse that came with the amp with the 3 amp fuse it's supposed to have. Flipped it over and wasn't happy with the collection of random screws that were forced into place resizing a lot of the holes. Oh well, it's the bottom plate after all. Inside wiring looks good, again, let me know if anyone spots anything that looks off. (After I put the amp back together I saw my pictures weren't the best) The power cord is still two prong, but I run everything through GFCI anyway. I want to spend a little more time looking it over before I try powering it up, I may have to dig up my variac out of the garage first. Anyway, I'm looking forward to any suggestions then hearing what this guy can do, hopefully soon. Cheers!
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s-petersen
Scott
The selector switch is supposed to stop at each setting, and stop at the ends, there are 2 separate issues there. the ball detent is possibly missing the balls, and the stops may be bent, unless someone took it apart, another possibility is that the shaft has been pushed in and the retainer is broken or missing under the knob. The amp still needs to have some of the old caps replaced, the black ones with the stripes(pyramid caps are original). The tube socket contacts float in the sockets so if the tube inserts with some resistance it is probably ok, if it inserts pretty easy you can retension the contacts with a small pick, prying between the contact and wall of the socket to close the "c"
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s-petersen
Scott
It should be repairable, some pics of the shaft under the knob, and the detent mechanism would help for troubleshooting. Your knobs look in really nice shape, most of the time they turn yellow with age.One way to tell if the retainer is missing or broken is that there should be no play when pushing and pulling the shaft.
I am not positive but there is a chance I have one, but it is a pain to replace.
That cap is original, and should be replaced.
There is an assembly manual in the AK database as this was a kit originally.
Near the bottom of the page is the owners and construction manual.
http://akdatabase.com/AKview/thumbnails.php?album=42&page=2
I am not positive but there is a chance I have one, but it is a pain to replace.
That cap is original, and should be replaced.
There is an assembly manual in the AK database as this was a kit originally.
Near the bottom of the page is the owners and construction manual.
http://akdatabase.com/AKview/thumbnails.php?album=42&page=2
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s-petersen
Scott
Because the switch can be taken apart, the shaft and detent unit can be removed from the switch wafers(being careful not to get them out of sync)
and repaired without unwiring the wafers. Use a felt tip pen to mark the shaft and wafer to reassemble them
and repaired without unwiring the wafers. Use a felt tip pen to mark the shaft and wafer to reassemble them
Once I had the construction manual and exploded diagram I was able to get the selector switch working (thanks Scott!). I did find some West-cap paper and oil capacitors connected to the selector switch, so they need to go as well. Off on Friday so I'll have a chance to go over everything in more detail then and get the caps already identified swapped out as long as I can get them in time.
Your comment on the yellowing of the dials got me thinking and I remembered this from a while ago: http://www.retr0bright.com/
A group of chemists and enthusiasts came up with a diy process for reversing the yellowing. I haven't had to try it but it sounds like it would be worth a try.
Your comment on the yellowing of the dials got me thinking and I remembered this from a while ago: http://www.retr0bright.com/
A group of chemists and enthusiasts came up with a diy process for reversing the yellowing. I haven't had to try it but it sounds like it would be worth a try.
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s-petersen
Scott
I have a ST 40, and 70, and ST84 that could use the treatment
A quick once over this evening and I think I have my work cut out for me. Capacitors marked C36 on the construction drawing call for 20uf/400V has a 47uf/450V cap in place and C37 called for a 30uf/300V cap instead there's a 80uf/450V cap. Can't be right for what I believe is the rectifier circuit? The wires for the loudness switch are tucked away nicely in the back without being hooked up. A big empty space was a giveaway that a 16ohm wire wound resistor is missing, oops. Checking some random points in the amp against the construction drawing shows some 'differences'. I'm glad I didn't try to power this thing up. Nothing hard to fix but now I don't trust anything about this amp and I may have to go over the wiring piece by piece to make sure nothing else is missing or off : /
Wheel-right
New Member
Got myself a HF-87 this week, found it on Reverb, looked clean so grabbed it. Some pics from Reverb then a few after taking the bottom off, a great surprise that it has had much done to already, bypassed selector switch, new controls, caps and much more. Still going to move the inputs to the back but then use it for awhile. Still gotta get tubes since it was sold without, oh well it was good deal anyway. Posted this elsewhere so sorry for the double up. Thanks Rob
Wheel-right
New Member
So it appears this amp is a factory wired unit with the combination of the date and initials inside and also it has riveted fasteners all around. All good stuff so I guess I picked a good one which is great cause I hoping to take this one to the end. Could use some new sockets as the pins are a little loose, lotsa years of use but still this seems to have been taken care of.
Dandy
Addicted Member
Hi Dav3, I've just dropped by here as I listen to my modified ST40. Seeing your post, I wondered if you'd got the correct electrolytic caps in place and if your amp is in regular service by now? If you haven't done so, I would suggest replacing all those black coupling caps with yellow markings too, because of their age.
Sorry for the late reply, I've been off the site for a while. I took the ST40 off-line as it was starting to miss behave and it was time for more work. I have a box of caps ready to go, including the 30uF 400v that I stupidly ordered to big to fit : /
s-petersen
Scott
What ended up being the issue with the detent for the selector switch?
HI all. I've had this ST40 for over half a year. Bought it from a local tube amp rescuer. There are probably different versions. Mine has the late 60s 7981 tubes. I had some questions for a while but now think it is excellent and pairs well with my super Heresy 1.5 speakers. Possibly the recent line conditioner helped. Maybe the large capacitors I put in my speaker crossovers needed time to break in. Maybe just good ear days, but I'm very happy with it. I had a lot of solid-state stereos over the years, some were pretty good, but this may be the best system I've had and I'm probably not done.
Dmartn149
Super Member
Hi, welcome. I haven't posted in this thread in many years. I recapped an ST70 that had been built by my Father in law. He was a pretty careful and meticulous man. Even so, I found a few connections that had never been soldered. My advice to anyone working on an old kit amp is to carefully check all connections.Hi, looks like no one new has been here in years.. Working on 2 HF-12s.. One Early V2 12AU7 One Late V2 12AX7 Dad built the Early one before my birth and I just purchased the late model for $60. Recapped replaced a lot of out of spec resistors and all tubes (new not NOS) Trying to decide if I want to convert the early to late but would need a new bass pot 1M LT with long shaft..
Dandy
Addicted Member
Hi folks, ST40 owner here. As I was one of those who asked the mods years ago for a separate Eico forum here, could I remind us that this so we can post separate threads on different Eico products here. It's easier to find discussion of different models if each unit under discussion has a different thread. And more threads makes this section more interesting!
