Eico HF-85 preamp questions

Hard to roundup all the threads to weave a tapestry that covers it all? lol I've killed alot of time sifting through Yahell Eico group and here for all of it. Sam ya' did a nice job of rounding up those threads. Maybe just my ineptitude at searching and saving? I've been wondering it if it would be possible/desirable, aw hell I just wanna know, if the last stage could be modified to have a cathode driven lower impedance out? Pros/Cons, opinions?
 
what if all the pots are replaced with new ones without taps, no ldns sw. no tape sw, no tape in/outs just line/cd and phono ins and new rotarys. that was my plan to do. but ti sounds like theres other things need fixing or changing to correct gain defects and all. lots more than I had planed to do. and then it will hum probably anyway.
It just sounds like a big headache at this point. maybe I need to put it down for 6 mos and come back later. with a new perspective. O' decisions decisions.
 
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ferinando
I wouldn't throw in the towel so soon. I think what you've outlined what you want is not so far away from from where we are and may make it easier to achieve your goals/objectives.
 
Whoever finds these first, please post here for posterity. I'm a member of the Eico group so I'll take a look over there. I need to go back into my 85 and make these corrections too. Here's my favorite tube pre, pretty much stock except for DC on all fils except the rectifier.. :yes:

FYI, Jay - you can get transparent heat shrink tubing that'll fit K40Y caps and allows you to see the values & power rating after it has been shrunk.

-D
 
Just an update, no questions this time.

The "Metallic Satin Nickel" Rustoleum paint isn't exactly like fresh cadmium plating, but it's a pretty decent cosmetic match. Far and away better than the splotchy mess of discolored cadmium plating I had before, even if it wasn't exactly my best paint job. The only part that's visible when the cage is on looks great, so that's the big thing. I think it's a bit better match than the stainless-look Krylon paint I used on the SCA-35 chassis parts, though that looks good too. As this one wasn't rusty, just splotchy, I only painted the visible surfaces. The intact bare metal finish is still there to make good ground points on the underside.

The tube sockets were all in pretty good shape, but a bit of a cosmetic mish-mash. Fortunately I had three nice nine-pin sockets and one nice seven-pin socket that matched the original shielded sockets.

While they aren't pristine, the original screws are in pretty decent shape, so they're being re-used.

I added some rubber grommets to the holes where wires pass through the chassis. I never liked the notion of sticking wires through bare metal holes, no matter how well beveled.

As I would like to use a power cord with a strain relief rather than the grommet and knot method originally designed by Eico, I need to get a unibit out and open up the power cord hole a bit. It's almost big enough, but not quite.

Fortunately I have a few good courtesy sockets tucked away, especially as I can't find the bag of repops that I bought from Jim McShane a few years ago. As seems to be the case with any tube gear, one of them was shattered.

Still need to go through my supply of metal-film resistors to see what I have on hand and what I need to order. Caps, too. While the original can cap is long gone and unavailable to be re-stuffed, I keep a supply of cans from scrapped gear around for just such occasions. One of them was just the right size to tuck under the cage.

Also still need to make a new upright RCA jack holder to accommodate the changes I'm making to the inputs. Maybe I'll get lucky and find that my dad has some suitable material in his scrap pile.

I'll try to get a picture of the partially-assembled chassis posted soon.
 
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Any thoughts on values for the filter caps in the power supply? I can go down to 39uF or up to 47uF on the 40V/350V caps, though the only ones that will fit in the can at 47uF carried by Mouser are United Chemi-Con, which I haven't used before. Nichicon makes a 39uF that will fit. I already have a 22uF/400V sitting here, so that's going to replace the 20uF/400V.
 
ferinando
I wouldn't throw in the towel so soon. I think what you've outlined what you want is not so far away from from where we are and may make it easier to achieve your goals/objectives.

of course you are rite there guitbanger. after sleeping on it overnite , Ive decided to go with my orig plans and all the gain issues be dammed. Ive done one of these for a friend in a like fashion and it turned out OK even if it had gain issues. My friend says its the best preamp he's had, like Marantz 7 and several other hi-end jobs.
Of course a complete recap will be done and resistors as well just maybe not all.
After all, this is supposed to be fun.
 
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what if all the pots are replaced with new ones without taps, no ldns sw. no tape sw, no tape in/outs just line/cd and phono ins and new rotarys. that was my plan to do. but ti sounds like theres other things need fixing or changing to correct gain defects and all. lots more than I had planed to do. and then it will hum probably anyway.
It just sounds like a big headache at this point. maybe I need to put it down for 6 mos and come back later. with a new perspective. O' decisions decisions.

I removed all the stuff you mentioned in your things to do list, If you do take all that stuff
out of your HF-85 you will gain a lot of room in your chassis and that will make it easy
to re-wire all the tube heater filaments wires further away from other components, I also
ran the AC in line in at the corner where the transformer is and removed the AC power
on/off switch up at the front of the pre, I just use a power strip to turn on the HF-85 and
the Magnavox 9303 amp thus keeping the 120 AC volt wires short and direct to the
transformer.

I also used a lot of shielded wires and grounded one end of the outer conductor to chassis
ground, you can get these units very quiet and still keep AC on the filaments and once
you remove all that stuff it will be easier then you think.
The alps volume pot helped mine a lot and I really like the way those pots feel and with
very nice tracking at low volume.

Most of you know that the tape out jacks are controlled by the volume pot and bypass the
tone circuit in these units, I think the sound is far cleaner sounding and definitely has
better detail in the music, so I don't even use the tone controls on the HF-85 and now
knowing how much better it sounds using those tape out jacks I would not have wasted
my time with the tone circuit and the PC boards I built for the tone controls.

I think it's worth the efforts you will put into it and yes that Eico HF-85 can run circles
around at lot of other preamps.
 
I removed all the stuff you mentioned in your things to do list, If you do take all that stuff
out of your HF-85 you will gain a lot of room in your chassis and that will make it easy
to re-wire all the tube heater filaments wires further away from other components, I also
ran the AC in line in at the corner where the transformer is and removed the AC power
on/off switch up at the front of the pre, I just use a power strip to turn on the HF-85 and
the Magnavox 9303 amp thus keeping the 120 AC volt wires short and direct to the
transformer.

I also used a lot of shielded wires and grounded one end of the outer conductor to chassis
ground, you can get these units very quiet and still keep AC on the filaments and once
you remove all that stuff it will be easier then you think.
The alps volume pot helped mine a lot and I really like the way those pots feel and with
very nice tracking at low volume.

Most of you know that the tape out jacks are controlled by the volume pot and bypass the
tone circuit in these units, I think the sound is far cleaner sounding and definitely has
better detail in the music, so I don't even use the tone controls on the HF-85 and now
knowing how much better it sounds using those tape out jacks I would not have wasted
my time with the tone circuit and the PC boards I built for the tone controls.

I think it's worth the efforts you will put into it and yes that Eico HF-85 can run circles
around at lot of other preamps.

Interesting, I always considered the active tone controls to be reason for the performance of this and the 81. I'll have to try the tape outs.


Sam, Cheni-Con is an excellent quality cap. Every bit as good as Nichicon IMO.
 
I was reading a post in another forum or maybe one of those yahoo groups and others
had mentioned that they were getting better results from the tape out jacks, I suppose
it makes sense they're is less in the signal path.:scratch2:
I am absolutely getter cleaner more detailed sound from those tape out jacks.
 
thanks brokenhill. good info. one question tho. do you use shielded for more than just low level phono lines and the like, or any line carrying an audio signal to insure no noise gets into things.?
I'll have to consider useing the tape out as a "tone bypass". But I too like the tone controls. but with new pots not concentric but ganged.
 
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thanks brokenhill. good info. one question tho. do you use shielded for more than just low level phono lines and the like, or any line carrying an audio signal to insure no noise gets into things.?
I'll have to consider useing the tape out as a "tone bypass". But I too like the tone controls. but with new pots not concentric but ganged.

What about the knobs? Where do you get the ganged pots?
 
Mouser has ganged pots in both audio and linear taper. Shaft extenders are available, though I'm probably going to use cleaned-up originals in this 85.
 
thanks brokenhill. good info. one question tho. do you use shielded for more than just low level phono lines and the like, or any line carrying an audio signal to insure no noise gets into things.?
I'll have to consider useing the tape out as a "tone bypass". But I too like the tone controls. but with new pots not concentric but ganged.
I used shielded in most places, when I built the little circuits using discrete components
that replaced the stock molded PC components that are used on the tone controls I
used shielded conductors on all seven contact points on the new replacement boards,
those tone printed circuits or PCs is where I was getting most of the un-wanted hum
and noise from.
I removed all phono circuits from the preamp, there is just one set of RCA jacks for
line in and yes they have shielded conductors, this would be the same as the AUX was
when it was wired to the selector switch and that has been removed too.
It's a bare bones preamp, less stuff to cause trouble, and much easier to work on now.

If I ever get the urge to listen to any phonos I have a Fisher 400 or other amps I could
do that with.:D

I also like tone controls but when music can sound soo good without them then I don't
miss them, you can leave the normal line out with tone controls intact and full functioning
and have leave the tape out jacks too, try them both and decide which line out you like
more.
 
What about the knobs? Where do you get the ganged pots?

from 'radio days' or 'AES'.. shafts are short and need couplers and ext. shafts fashioned(from radio days also).
kniobs get new from AES(not original). those old knobs looked godawful anyway. You can pik what you like best. tone controls are not concentric, but ganged now. the old TC pots were lousy too. IMO
linear for tone and your choice for the vol., but suposed to be audio taper.
If you go for the ALPS pots then you're on your own ofr shafts.
 
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AES is where I got the tone pot replacements I used, then I made aluminum shaft
extensions with little set screws to join onto the shorter shafts of the new tone pots
and ALPs volume pot.
AES has a lot of different style knobs too, if you go with newer tone and volume
pots and can tolerate the different look with non stock knobs then go for it.
 
brokenhill, do you have a pic of the ALPS shaft/coupler/extn?
were the shafts the 1/8" or 1/4"?
All the ALPS pots I see have thin shafts. mite be looking in wrong place.

edit: my mistake. I see many 1/4" shafts but wrong values.
 
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