Converting Eico HF-81 to a simple PP EL84 (pics incl.) - diyAudio
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Old 14th June 2012, 07:38 AM   #1
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Default Converting Eico HF-81 to a simple PP EL84 (pics incl.)

I had an Eico HF-81... fully restored it and it was like-new condition after restoring and I sold it contrary to my wish (caught between a rock and a hard friend)!! ... It's been some months and now the buyer (my friend) has blown the amp away so bad I can't fix it using 45 pages of assemble manual and I have no time to reassemble it from the beginning ... many of caps and resistors are blown... some wires are melted!! I took the amp back for a 100$ as is... I think the only parts usable are Choke (tested Ok) , OPTs (tested OK) and El84 and 12AX7s... phono stage tubes are gone... the chassis is fine of course

Now I want to convert it to a simple PP EL84 amplifier, no phono/mic/fm/am/tone control/balance no nothing... just a nice PP project using Mullard tubes and OPTs with a single RCA input... an Alps pot will be used I want your opinion on the schema

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Last edited by ARIYAHOOR; 14th June 2012 at 07:52 AM.
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Old 14th June 2012, 09:01 AM   #2
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23 views and no reply
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any PP EL34 schematic compatible with Eico HF-81 OPTs?
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Old 14th June 2012, 12:41 PM   #3
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Click the image to open in full size. disappointed!
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Old 14th June 2012, 02:16 PM   #4
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You can try the Pilot 232 circuit, just use the amp section and keep the power supply from the Eico.

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Old 14th June 2012, 02:18 PM   #5
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Originally Posted by directdriver View Post
You can try the Pilot 232 circuit, just use the amp section and keep the power supply from the Eico.

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Oh thanks for reply finally
you know, device is malfunctioning and I can't separate PSU from Eico...
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Old 14th June 2012, 02:30 PM   #6
12E1 is offline 12E1  United Kingdom
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Quote:
Originally Posted by ARIYAHOOR View Post
Click the image to open in full size. disappointed!
Forgive me for saying this, but I think that you have unrealistic expectations. Almost everyone on this forum has a life somewhere else that takes most of their time. Many will only look into the forum once a day, and often rather less. Of those who had viewed your thread, I would think that most would not know what an Eico HF-81 amplifier is and so they would not reply (I certainly have never heard of that model). To express disappointment at a lack of response after only 5 hours from your original post seems completely unnecessary.
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Old 14th June 2012, 02:48 PM   #7
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eico_hf81_schematic_full.jpg

hope this helps
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Old 14th June 2012, 02:50 PM   #8
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Originally Posted by 12E1 View Post
Of those who had viewed your thread, I would think that most would not know what an Eico HF-81 amplifier is and so they would not reply (I certainly have never heard of that model).
The HF-81 is probably the most talked about EL84 integrated amp in recent years, at least in the USA. Since the 2006 write up in Stereophile, its price has skyrocketed for a low powered integrated amp. It also inspired many DIYers to modify this gem in various websites. Some audiophiles are excited about it and some are disappointed. I heard one and it sounded good but I think there are many sleepers out there just as good or better. Regardless of one's opinion about its sound, it is certainly the most talked about amp of its genre.

I do understand your point about the OP not being patient enough and I agree.
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Old 14th June 2012, 02:59 PM   #9
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Originally Posted by ARIYAHOOR View Post
device is malfunctioning and I can't separate PSU from Eico...
Okay then, just build it like the circuit and use whatever existing parts you can salvage from the Eico. If you plan to use the Eico chassis then you can't use an octal tube like 5AR4 without drilling a bigger hole for its socket. I would just add a filament transformer so you can re-use the dual EZ81/6CA4 rectifier tubes.

Here's the schematic for the HF-81 and you will notice the Pilot amp section uses the same tube complement as the EICO so it's not that hard to implement the circuit. The Pilot is the best sounding 6BQ5 amp I have ever heard, period.
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Old 14th June 2012, 03:49 PM   #10
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There are lots of EL84 circuits out there. SY's Red Light District, some from TubeCad, the Baby Huey, El Cheapo, mine:
Just what the world needs - another EL84 amp

Lots of different ways to implement this depending on your taste. Even though the designer of the Simple EL84 is a poster on this forum, he doesn't frequent the tubes section from what I can tell. According to his website, he's moved on to class-D amps. You might be able to find him posting in the analog line level section as well.
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