Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Tue 26, 2021 10:39 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 17 posts ] 
Author Message
 Post subject: Looking for Eico HF-20 schematic please.
PostPosted: Jul Fri 16, 2021 11:32 pm 
Member

Joined: Jun Fri 26, 2020 9:35 pm
Posts: 76
Location: 98020
Hello-

I am looking for a schematic for an Eico HF-20 amplifier. Also, was Eico a supplier of kits, similar to Heathkit, for customers to build their own items? The quality of the solder work in this particular example does not look factory-level to me, but I am not familiar with Eico products; this is the first I have acquired.

Thank you-

Troy
Edmonds, WA


Last edited by soloapollo on Sep Fri 03, 2021 11:16 pm, edited 3 times in total.

Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Jul Sat 17, 2021 12:27 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5272
Location: Rochester NY USA
Yes, EICO sold mostly kits. It's in Sams 479-5 - I haven't scanned that one yet, someone here may have it. The EICO schematic is attached below

Attachment:
HF20S.gif
HF20S.gif [ 704.87 KiB | Viewed 965 times ]

_________________
My web page: https://bit.ly/2rxq4qx


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Jul Sat 17, 2021 5:04 am 
Member
User avatar

Joined: Nov Sat 07, 2009 11:37 pm
Posts: 2922
Location: Sayreville, NJ 08872
I have the complete operating and assembly manual for the HF-20. Don't recall if Eico issued any service bulletins or service addenda on this model. Would have to look in the file.

_________________
Pete, WA2CWA - "A cluttered desk is a sign of genius"
https://www.manualman.com


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Jul Sat 17, 2021 12:12 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 10765
Location: Beaver Falls, PA. USA
That's a great little amp; I have rebuilt several of them. As with any kit, watch out for poor solder connections.

_________________
Tim KA3JRT


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Jul Sat 17, 2021 1:15 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 18804
Location: Utica, NY 13502 (USA)
An Eico HF-20 is an integrated mono amp having multiple inputs with built-in preamp, volume, and tone controls. I always thought a so-called "monoblock" referred to a basic power amp which lacks those features. I could be wrong.

Dave


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Sep Thu 02, 2021 1:55 am 
Member

Joined: Jun Fri 26, 2020 9:35 pm
Posts: 76
Location: 98020
Hello-

With many thanks for the schematic and advice, I now have this Eico restored and playing almost perfectly. Except... once I started playing it, it became noticeable that some very strange noises would be audible if the chassis was even slightly jostled (think turning a knob; didn't matter which one, or sliding it an inch sideways). Today I took the bottom cover off and lightly touched components with a bamboo chopstick to see if I could figure out any that caused the noise.

Well I did find the guilty component. Except it's the only part in the whole amp that I am not sure just what it is, or what to replace it with. It looks like a 4-lead ceramic capacitor, except it is rectangular in shape (I have only seen round ceramic caps, and those only with two leads). The part is soldered to R14 (see schematic already posted above) and simply labeled "LOUDNESS" on the schematic.

The actual part itself has "1 2 3 4" numbering the leads, and it looks like "PC 324" printed on it, which does not help me identify what it is. I see nothing in the parts list that seems like the right component.

SO- what is it, and what should I replace it with? I am assuming that this exact component is long since obsolete and no longer available. A suitable substitute would be OK with me. Except for that one part causing nuisance noises on occasion, the amp really is performing great and I very much like the way it sounds.

Photo of part below.

Thank you and best regards-

Troy
Edmonds, WA


Attachments:
IMG_0013 (2).JPG
IMG_0013 (2).JPG [ 907.95 KiB | Viewed 721 times ]
Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Sep Thu 02, 2021 2:23 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3791
Location: Oak Creek, WI USA
The construction manual for this amp calls out the R14 Loudness control as a 500Kohm Compentrol, which would have been made by Centralab. Apparently that little couplate is actually part of the pot itself, and is probably a couple of little caps that handle bass and treble boost at low volumes; that is why it is tied to the taps in the pot. Not sure if replacements or NOS are available anymore.


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Sep Thu 02, 2021 4:44 am 
Member

Joined: Jun Sat 15, 2019 7:43 pm
Posts: 1469
This should help.
Attachment:
PC324Couplate.png
PC324Couplate.png [ 203.41 KiB | Viewed 707 times ]


DM


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Sep Thu 02, 2021 12:30 pm 
Member

Joined: Jun Fri 26, 2020 9:35 pm
Posts: 76
Location: 98020
Oh wow- thank you! Yes, that definitely helps a lot. Don't think I would have figured out that network myself from the failing original part. Is this information from an old CentraLab catalog? They definitely crammed a lot of components into that small wafer. I imagine that compactness may have contributed to the eventual failure.

I can make a replacement using discrete components, but it definitely won't be as small as the original wafer. Good thing there is plenty of space in there, so that won't be a problem.

My only other question is if it matters if I use ceramic disc or mica caps for the replacements?

Thank you again and best regards-

Troy
Edmonds, WA


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Sep Thu 02, 2021 1:25 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 10765
Location: Beaver Falls, PA. USA
Hi, Troy... Ceramic disc or film capacitors will be fine for the 4500 pf capacitors; 0.0047 mfd will be the closest available value. Mica or ceramic discs will work for the 100 pf locations.

_________________
Tim KA3JRT


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Sep Thu 02, 2021 3:29 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13327
Location: Fernandina Beach, FL
Please be sure that the Couplate is actually bad, not just a connection or the control itself. Unlike others, I actually do appreciate what it does. And being ceramic, it is often very reliable. Poke around before you remove it. But yes, discrete components can be used to duplicate is function.

_________________
Don


Top
 Profile  
 
 Post subject: Re: Eico HF-20 monoblock amp schematic?
PostPosted: Sep Fri 03, 2021 2:53 am 
Member

Joined: Dec Mon 23, 2019 5:52 pm
Posts: 626
Compentrol


Attachments:
compentrols 001.jpg
compentrols 001.jpg [ 842.67 KiB | Viewed 642 times ]
Top
 Profile  
 
 Post subject: Re: Looking for Eico HF-20 schematic please.
PostPosted: Sep Tue 28, 2021 6:06 pm 
Member

Joined: Mar Tue 03, 2009 11:12 pm
Posts: 2009
Location: Great Bend KS
To me it looks like those two black leads could use a resolder.


Top
 Profile  
 
 Post subject: Re: Looking for Eico HF-20 schematic please.
PostPosted: Sep Wed 29, 2021 12:22 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13327
Location: Fernandina Beach, FL
SteveT wrote:
To me it looks like those two black leads could use a resolder.

I certainly would try that first before attempting to replace the Couplate.

_________________
Don


Top
 Profile  
 
 Post subject: Re: Looking for Eico HF-20 schematic please.
PostPosted: Oct Sun 03, 2021 1:49 am 
Member

Joined: Jun Fri 26, 2020 9:35 pm
Posts: 76
Location: 98020
So just an update, in response to recent postings.

The solder joint was not the problem; cleaning that up resulted in no improvement. The couplate was faulty. I built a new one using discrete components, per the provided schematic, and installed that. Now the amp functions perfectly and I am quite pleased with the results.

Thank you all for the advice, suggestions, information, and tips. The end result of all of this help is another 60+ year old amplifier that is in regular service again. Very much appreciated!

Thank you and best regards-

Troy
Edmonds, WA


Top
 Profile  
 
 Post subject: Re: Looking for Eico HF-20 schematic please.
PostPosted: Oct Sun 03, 2021 1:57 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13327
Location: Fernandina Beach, FL
soloapollo wrote:
So just an update, in response to recent postings.

The solder joint was not the problem; cleaning that up resulted in no improvement. The couplate was faulty. I built a new one using discrete components, per the provided schematic, and installed that. Now the amp functions perfectly and I am quite pleased with the results.

Thank you all for the advice, suggestions, information, and tips. The end result of all of this help is another 60+ year old amplifier that is in regular service again. Very much appreciated!

Thank you and best regards-

Troy
Edmonds, WA

Thanks for the update, Troy. Yes, I have seen a Couplate become defective but it is not the norm. But your trouble shooting skills resulted in success! The one that I found to be defective was replaced with discrete components (both channels; it was a stereo amplifier).

Enjoy!

_________________
Don


Top
 Profile  
 
 Post subject: Re: Looking for Eico HF-20 schematic please.
PostPosted: Oct Sun 03, 2021 3:37 pm 
Member

Joined: Jun Fri 26, 2020 9:35 pm
Posts: 76
Location: 98020
Hello-

I don't know if this extra information will help explain the potential cause of the couplate failure, but for a number of years before I acquired the amp, it was stored in a backyard plastic storage bin, which is where it was when I received it.

The amplifier was protected from rain, but it was allowed to alternately freeze and roast with the changes of the seasons here, as well as be subjected to wide swings in humidity. This seems to me an excellent recipe for an uncommon component failure.

-Troy
Edmonds, WA


Top
 Profile  
 
Post New Topic Post Reply  [ 17 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: Hi-Fi in Fiberglass and 4 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB