Audio and Electrical Engineering
EICO HF-87 Restoration Project
The EICO HF-87 was a kit amplifier sold out of New York back in the 1950s. It is highly regarded as one of the best of these types of amplifiers, easily eclipsing the better selling, yet inferior, Dynaco Stereo 70.
This is not a faithful restoration project, as the olive drab finish of the original unit just isn't my style. In case you don't know, let us take a look at what an original EICO HF-87 looks like:
I've had my EICO HF-87 since the 80's and I love it. It has been a fabulous amp. Still after 50 years of service, the power transfomer failed. So I rebuilt the amp when swapping the failed power transformer.
It is worth noting that in addition to not keeping the stock finish, I also did not maintain the original schematic— I designed my own. Again this is a highly regarded amplifier and many may not approve, but the simple fact is, it sounds better now.
This amp is used with my Mac for music while I'm on the computer. I built a switchable bias system that allows me to switch between 1/3 and full power dissipation on the output tubes, as well as being able to select EL34/6L6/KT66/6550/KT88 output tube modes. I kept the original mono/stereo switch from the original circuit as I don't think all stereo recordings are great— some bad mixes sound better in mono.
Photos
The wonderful original EICO output transformers, stripped for painting.
The HF-87 chassis stripped and sanded down to bare metal.
The bell ends stripped and getting ready for clear coat.
A thick lustrous glaze of copper paint applied to the chassis.
Close-up of the copper paint.
The EICO transformers back together and ready to place on the chassis.
Thank you UPS.
Transformers in place on the HF87 chassis.
Tube sockets and wire taps awaiting parts.
Starting to wire the outputs.
A shot of the back of the amp.
Bottom panel.
Label I created. You can download the EICO logo I used here for your own personal use.
Doing some testing and listening.
The final amp driving a pair of Monitor Audio RS1 Silvers.
Ditto.
EL34s in the dark.
