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Eico HF-81 Tube Amp to Restore

T

tube-a-lou

Addicted Member
Hi all,

Well the Eico HF-81 came in the mail today, it's in pretty nice shape
little bit of rust and tarnish but that will clean up, inside a little different
the rectifier side has to be redone and I'll have to check each and every
solder joint. I already started doing a little rewiring work and cleaning
and I ordered parts for it. I will not plug this guy in till all is done so I
hope all the transformers are okay. If you guys have any tips on the amp
let me know, here's are some pictures. The last picture I'm trying to decide
which cap I should use/get, I already have a pair of F&T 50+50 500volt caps
the one in blue which I would glue to a wafer and then screw it down to
the chassis, then add a 22uf 450volt cap underneath. I would be saving
$35.00 dollars on a new AE cap which would only keep it looking vintage
but I'm thinking the F&T might be a better cap?

Tube
 

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yeah save your $ on those AE caps. Use either JJ or singles under chassis. I have the HF85 which I completely stripped down to nothing and re-made with all new wireing, Cs and Rs. RIAA network and tone PECs, both home made on perf bds. New 2p 6pos rotary selector switch replaced the old mess of wafers. changed it into a 2 input CD and 1 or 2 Phono inputs. gutted all ref to ''tape''.
Would like to get my hands on an 81. That vintage Eico stuff is easy to work on and get excellent results sound wise.
keep us posted on progress.
 
Great to see this project start. Thanks for the first report. I know what it feels like to be committed to an amp, without knowing if the OP transformers are working.

I would be conservative with all orig components that check out okay because you want to hear the original sound. OTOH, consider replacing the tube sockets with good quality replacements. I had mysterious intermittent problems with my Eico ST40 till I did this.
 
The tube sockets are not good, thanks for that info. I did take a ohm reading of the
OP transformers and I got readings, so I think there good. I'm going to put in a power
switch in the back to not use the front treble switch which it a odd design, I see a lot
of them with switches put in the front drilled in and it doesn't look that good. Dandy
I'm only at this point going to put in new .1 coupling caps and new electrolytics and
test the resistors and change some wiring.

Tube
 
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I usually prefer to keep these things as stock as possible (with exception for bad components like capacitors and resistors) other than that I would try to not juryrig any new power switches or change out any of the old tone controls or mode switches because then when you get into changing out the old switches and modifying this and that then you have something that looks like someone without any experience was screwing around in the unit and chances are if you go to sell it in the future the next person might of wanted to have those old switches in there because of how they worked or sounded compared to the new ones, and then you won't be getting top dollar out of the unit because you modified it to something YOU liked and not necessarily to something someone else would like. Also if you just clean those switches by shooting some Deoxit into them and then rotating them a few times and then let it dry before applying powe to it then you should have your switches functioning like new again. But that's just me, as I wouldn't have the patience nor the guts to try and completely gut a piece of equipment like this that more than likely took at least 3 days worth of manhours to build in the first place all to just install inferrior Chinese components into it and not even take all of the care and dedication that the original builders to build the original. That's just my 2 cents.
 
and my 2 cents is modify the heck out of it to your hearts content and make it the way YOU want it. These things are not made of gold, altho some seem to think so.
If a purist wanted it he had the chance to have it and didnt take it. Someone else did.
I say the owner has the right to do as he pleases. Let the purist get that crud encased piece of rust and just love the heck out of it. But Its never been modified!!!
You may can tell I have strong feelings on this issue. Sorry for the rant.
No offense to any purists either as I understand where they are comming from.
Went down same path doing old car restoration. Ended up with present feelings.
 
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Tube, what you are planning sounds right to me, at least till you are more familiar with it.

I also went halfway recently with my Dyna SCA-35, but it had already been badly hacked about by previous owners, who had also hacked up the replacement boards. I used as much as I could of the original front panel components and the stock phono preamp board and it works well.
 
Okay, so I did the switch today and did a little rewiring here and there. the next thing is
in the front and right side there's two .25uf@200volts caps, these are a paper type so
Can I use a .27uf if need be because .25 so far is a no go. Oh on the switch I have a
source of good USA parts and that's what's going into the amp if I could do it. I'm not going
to change all the parts inside, I've read that the Sprague Disc cap are some of the best sounding
around and a few other things Will stay.

Tube
 
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ferninando said:
yeah save your $ on those AE caps. Use either JJ or singles under chassis. I have the HF85 which I completely stripped down to nothing and re-made with all new wireing, Cs and Rs. RIAA network and tone PECs, both home made on perf bds. New 2p 6pos rotary selector switch replaced the old mess of wafers. changed it into a 2 input CD and 1 or 2 Phono inputs. gutted all ref to ''tape''.
Would like to get my hands on an 81. That vintage Eico stuff is easy to work on and get excellent results sound wise.
keep us posted on progress.
Click to expand...

I did an 85 all the way down too, I think they are worth it, and so is the 81. New sockets and all. You here folks talk about tube gear being high maintenance, but if you do it right, it's really not. I can't remember the last tube piece break down I've had.:scratch2:
 
I've had very good luck restuffing can capacitors. There are plenty of skinny radial lead replacement caps to choose from, and they can be paralleled to give you exact values if you wish. It seems more convenient to keep them all above the deck.

I cut the cans with one of those Japanese style flush cutting hand saws. I drill the bases for the leads with a 1/16" drill bit.

Clean look, reliable parts, fewer pieces below deck.
 
That's what I did on my Fishers I'll have to look for those if there skinning enough,
But what about the .25uf 200 volt caps is .27uf okay?

Tube
 
27 should be fine. Assuming the original cap had a tolerance or +/- 20%, a 27 would be within the original spec.
 
.22 would probably be alright as well as .27. If you look at caps rated for AC you'll find some options at .25uf. Search mouser for .25uf/250v AC film caps and see what happens. The DC rating will be substantially higher than the AC rating.
 
I used .039uf in my HF81 I just re-did (because I had some really nice polystyrene .039 @ 400v caps). It worked just fine. From what I heard afterward, I suspect it may have helped the bass response (the slightly larger cap value allowed the amp to maintain open-loop gain to a slightly lower frequency, which made for more available feedback at the lowest frequencies- which should act to lower bass distortion and make the bass response flatter).

In most cases, with most amps, as long as you don't go more than double the original coupling cap value, things are usually OK. These HF81s are not that particular about cap values, in that position.

Regards,
Gordon.
 
Thanks guy's, I just spend about 45 minutes cleaning the brass front plate and it does
look better! Boy that stuff I used cleaned it's great, but it's a little strong! Never-Dull


Tube
 
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For now I'm going to use the F&T cap, I'm going to figure a way of putting it in
without drilling holes in the chassis.

Tube
 
You could try removing the steel plate with the twistlocks on it from the old can cap and glue it to the F&T. Be better than gluing it to the chassis.
 
Here's some pictures of some work so far, First picture is new switch and
cord which on the Eico is real easy because of the screws second pic is
the new 180 ohm resistors, I've read on the Earthlink website that 180 ohm
help the tube bias better, we'll see how this works out. The one thing I'm
doing is going over a lot of solder joints and resetting wires that they look
a lot neater.

Tube
 

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