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Eico HF85 clone?

ferninando

ferninando

Lunatic Member
Since the Eico HF85 preamp prices are so astronomical and appear so infrequently for sale,
it seems reasonable to try building a clone of one.

Has anyone ever done that?

Now I have gutted one and rebuilt it with all new parts with great results.
I have also refurbed one with a recap with new pots , also very successfully.
both noise/ hum free. See my rebuild below.

So what are the opinions on cloning one and making such mods as deemed
necessary?

Will I be the first to do so when I get around to it?
Hope not.

What do the AKrs say?
 

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I rebuilt a pair of WA-P2s,, and scratch built a stereo RCA Phono pre and PS... that's my experience with pre amps... Do these Eico's have PC boards, or P2P wiring? This looks like a good project, looking forward to your build...
 
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It's P2P.
I made tone PECs with pref proto bd and discrete comps..
the project is very early point now and will be awhile before starting.
I'll post a thread then.
anyone careing to see pics of my 1st build I have a ton so just ask.
 
I would like to see the pictures and progress of the clone . The schematic isn't too complicated after you pick apart the phono and tape inputs. Also preamps are great build items since they only need one transformer and are small and light weight compared to amps but also can drive you nuts with chasing down hiss and hum. I usually purchase allied electronics tube transformers(made by Hammond) for preamps since they are cheap and are usually in stock. Back to the HF86 the schematic is easy to find but the PEC doesn't appear to be. When you get to building the PEC's can you post the schematic you used? I think I will be building one in the future minus the loudness feature, tape, and mic inputs.
 
clone pics will be shot.
tone pec schematis is same as the hf 81 amp and I do have schematic.
I built discrete PECs for the earlier build . Illl ook for the schem and post it here. a pic as well.
Had to replace a PT for the one I did for a friend as i burnt his up.
Replaced with a hammond and it works fine and Plan on using the same for the clone.
$60 from AES

hf85 photofax has scheatic for the 85 tone pecs.
I cant seem ot be able to upload the pdf file of sams.
Ill try later.
 

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Since I am a died in the wool DIYr I make them for free for me all day long.
I cant stand paying someone to make stuff like this for me.
other more complex things OK I pay.

here's a hf85 schem with the PECs comp. values.
 

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I have a thread here somewhere when I took one down to bare metal and rebuilt it ditching the PECs for good stuff, and fixing the loudness circuit, DC fils,etc........... Great preamp, the 81 has the same thing, I think it's the active tone circuits that make them so listenable.
 
yeah, they are baxendals.
Yes Jay, they are very much great little preamps.
I just wish more were for sale around the country.
I have a standing ebay search for them but never any under 300.
I want junk ones to rebuild. Mine was given to me by a good friend.
I had refurbed his nice orig. my 1st shot at one.
I removed the ldns altogether. no ill affect.
 
Not to knock you building something from scratch, but for me the HF-85 wouldn't be it.

To much gain and a more complicated circuit then it needs to be, I'd look for something with lower mu tubes in the circuit..
(the HF-85 sounds fine, but there are better sounding and performing circuits/tubes, I prefer something like 6DJ8 based)
 
If I knew what those circuits/tubes were I would certainly explore it.
But not being quite so knowledge about all the choices , I tend to
go with what I've got some experience with until something better comes along.
I am open to suggestions
If you tell me the 2 or 3 top choices I could make I'd appreciate it and would definately
do some sole searching.
Thanks for your interest and suggestions.
 
Kegger, do any of the better circuits exist in commercial products or just in
DYI builds?
Any of them have names?
I did do a search here with no circuits/schematics so dont know exactly which way to go.
any direction appreciated.

Also, if the 85 has too much gain, what is the way to reduce it ?
How does excessive gain manifest itself?
Audibly?
Electricly?
 
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I have tried 5751s in the line stage of my 85 as suggested by an akr
back when I did the build(not a clone) but didnt notice any change or improvement or anything.
 
Yes there are a crapload of commercial product preamps running the 6DJ8, it's pretty much a go to tube for "high end" preamps.
(Juicy Music, Anthem, Audio Research, Bat, Audible Illusions Modulus 3A is also a well known and respected preamp by many)

Keep the heater voltage normal, current between say 5-8ma and plate voltage about 100v they'll last long and perform well there.

Attached is a "basic" line/pre amp schem for a simple 6DJ8 based unit, can run with or without the feedback, better specs with it.. :)


6DJ8 BASIC linestage_M1.gif
 
That 6DJ8 line/pre amp schematic is a simple circuit, since that tube is a twin triode
would one tube work for two channel stereo?

I have one of those Guanzo 2.0 Chinese tube preamps sitting around here that I am
not using, I was thinking I could use the power supply and adapt it to this simple 6DJ8
preamp circuit, below is a schematic of that Guanzo power supply circuit.

Would that work well or should I just scratch build a power supply?

guanzo_6n3_psu.jpg
 
Yes, and that Power Supply "should" work,

Couple things, to get/keep the voltage near about 180v, change the (2) 2k resistors to 1k..
In that schem it shows your caps at 200v, if that's correct then just change those resistors...

But if those caps are voltage rated higher(as quite often not same as schem) then I'd add a cap to the input side of the filter as schem attached.
(I'd use a 400v rated poly cap for the 4.7uf, that should get the voltage near 200v, and clean things up a bit)

P.S., you may want to start a new thread, unless ferninando doesn't mind the offshoot topic in his thread..

guanzo_6n3_psu_m1.jpg
 
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