Help me assess my Eico HF-81

[CZ4A]

I found this HF-81 on Craigslist and bought it as a package deal with a Fisher Model 90-T tuner for $260. I wanted a decent project amp to start my foray into room tube hi-fi (I have a couple of modern tube/hybrid headphone amps). The amp is complete except for a missing bottom plate. The tubes are a grab bag both in terms of brands and in life left.

Now, onto the n00b questions! It looks like this Eico has already been recapped once, but would it be worth it to replace the rest of the vintage caps, including the disc caps? Any good simple modifications I can make to improve the sound? How do I go about obtaining a new bottom plate? Would automotive plastic cleaner be good for getting rid of thew white residue on the knobs? Is it worth it to replace the RCA jacks, or will a simple sanding + cleaning do?

Please note I haven't powered the Eico on yet. I need to buy or borrow a variac. Given some of the modern caps and that the Fisher has a Monster-brand cable in the multiplexing jack, I wouldn't be surprised if they were being used until very recently.

 

[ferninando]

It is old and requires a total restoration. The assembly manual is a necessity. Get one.
All caps should be replaced.. Many Rs are probably out of spec, so I would replace all resistors as well with
new carbon films.
That is MY standard procedure on a unit such as this. Not everyone does it.
Leava any mods till after resto then see how good it will sound.
Tone PECs should be re-made into discrete components. the parts values are in the schematic
Build them with perf board.
Clean and lube all pots and switches.
Prepare enclosure for new paint and strip and polish the brass faceplate. Do NOT use steelwool.
You have a big fun project ahead of you.
I have refurbed/restored 2 Eico HF85 preamps, one being a real chicken coup pull-out,
requiring total teardown and rebuild with everything new, and 2 HF12 mono intg. amps in the same manner as described above but no teardown, just Rs and Cs.
Eicos are easy to work on and the results are worth the effort in sound enjoyment.
But this is only what I would do. I could restore Eicos till the cows come home.

 

[CZ4A]

Thanks for the advice! I was thinking a full recap (except maybe the two or three obviously modern caps, depends on brand and how they test), checking the resistors, and a cleaning are needed. I've already removed the enclosure parts so I can have them stripped and repainted.

For anyone else reading- do you have the dimensions of the HF-81's bottom plate? That's the only part missing from this amp. I am thinking of working with one of my automotive buddies to fab one up from thick sheet steel or aluminum. A photo would also be helpful for the placement of vent holes and the rubber feet.

 

[ferninando]

eico used steel plate for the bottom, I would use alum.
just measure size of the enclosure when assembled. I thing there foot screw holes, use use those dims for the bottom.
U can see where/how it fits.
I would replace ALL caps and not count on what someone else has done. But thats just me.
I want/make everything new as much as possible. So I now exactly what I have.

 

[Dandy]

+1 on not assuming anything about the new caps. If you keep them, check that the 'repair' soldering is good. Just to be clear, you can leave the circular ceramic caps for now. They will be okay.

Also, I suggest doing some reading up on others' restorations. Some say that a complete replacement of passive components affects the sound.

 

[ferninando]

It does not now sound like it did when it was new and never will so don't be concerned about that.
All the old parts have drifted and aged.
replacing the passive components with new ones will affect the sound for the better or just
not at all.
you can only tell if you listen to it before changing anything then change one thing at a time and listen and repeat until you hear a difference
for the worse then put that part back and continue until you have replaced all the remaining parts and then listen to it. then change the part that made it sound bad
with a new part and see if it stil sounds bad.
I have never done a total parts replacement and had an amp sound bad.

 

[Dandy]

I agree in general, but the HF81 for better or worse has a reputation for a 'magical' sound, which is partly attributed to the kind of original parts used. This has also contributed to the higher prices they go for there days. So, I agree with ferninando in saying do the update in stages.

 

[specialidiot]

paging jaymanna..... he rebuilt my HF81 in a most radical way, it's essentially an all new unit and yes it is magical. All of those pesky wafer switches were completely rebuilt, and anything not needed was removed.

It started as a basket case and is now a work of art. One of the features is solid state screen voltage regulation. He's a mad scientist, for sure. I'm mostly using RCA cleartops for 12ax7s, Mullard EZ81s for rectification, and the power tubes are the rusky 6p14p variants of el84.

The case was destroyed. AKer Ejfud put this together:

I now use it at our lake cabin driving a pair of Kardignia speakers built for me by RayW. It's an AK collaboration, for sure.

 

[mhardy6647]

I... I didn't know that an EICO could be made beautiful.

Wow.

 

[CZ4A]

That case looks amazing. It goes so well with the faceplate. I'll probably need a case made for the Fisher tuner when I get around to it. It originally came with the Eico's mesh like you can see in the first picture! The temporary Fisher cover had sides that look like they were cut from another Eico's mesh. I'm thinking of using those pieces for ventilation of the bottom plate I need to fab up.