My Eico HF-81 upgraded

[ferdinand]

Hi everyone, greetings from Buenos Aires

This is my heavily upgraded Eico HF-81. As you can see from the pictures it has Mundorf Silver Oil caps in the phono section, new RCA plugs, new wiring, Fischer & Tausche power supply caps, NOS Pyramid coupling caps, GE EL84, Telefunken 12ax7 and 12au7, Mullard EZ81 rectifiers.

The most important thing though, it has the original output transformers. Haven’t found yet who built them, but they are quite mystical

It just sounds so good, I’ve owned Accuphase, McIntosh MC30, class a Luxman, and many other amps (integrated and separated) but no other piece of gear sounded as good as this little devil.

It’s 15w do magic, I can’t find a better word, just a magical amp.

 

[nerdorama]

Haven’t found yet who built them, but they are quite mystical

Hi ferdinand,
There should be an EIA code stamped on the end bell of the transformers. There should be a 6 or 7 digit number and the EIA which identifies the manufacturer will be the first 3 or 4 digits. If you can post the numbers on the transformer, we can help you figure it out.

This page has some of the more common codes.

Commonly Seen EIA Codes

You can download more complete lists here. Look at one of the lists from the late 1950's or early 1960's.
John

 

[ferdinand]

Hi ferdinand,
There should be an EIA code stamped on the end bell of the transformers. There should be a 6 or 7 digit number and the EIA which identifies the manufacturer will be the first 3 or 4 digits. If you can post the numbers on the transformer, we can help you figure it out.

This page has some of the more common codes.

Commonly Seen EIA Codes

You can download more complete lists here. Look at one of the lists from the late 1950's or early 1960's.
John

Hello John! That would be great, I've been wondering about their origin for quite some time.

Here are the pictures and their codes

Power Transformer: S-30021 798918
Output Transformers: 32013 960, both

I've read the EIA Code's list from the lates 50's and I've found the following. What I do not know is if the code is the first or the second line stamped on the transformers

300: Speer Resistor Division, Speer Carbon Company, Bradford, PA
320: Trav-Ler Radio Corporation, Chicago, ILL
798: Supreme Transformer Corporation, Chicago, ILL
960: Ontario Industries Inc., Hornell, NY

Thanks!

 

[nerdorama]

The first line appears to be the Eico part number. I've never see 960 before. Usually the second part of a 6 or 7 digit EIA number is a date code, generally the year and month. I wonder if 960 is actually a date code, 9th week of 1960.

 

[ferdinand]

The first line appears to be the Eico part number. I've never see 960 before. Usually the second part of a 6 or 7 digit EIA number is a date code, generally the year and month. I wonder if 960 is actually a date code, 9th week of 1960.

So it is still a mystery who built them

 

[danno2000]

The 30021 power transformer were built by Heyboer in Michigan. Below is a replacement one from Heyboer which can take higher AC in compared to the orignals from 1958-60 which were designed for 110v. You can even get them to make the -1 version which has more steel and the heaters are rated for a bit more current, making the transformer run a bit cooler. I have used dozens of these over the past 20 years for restorations. Yes the other number is the correct output transformer...not sure who made them back then. Hope this helps.

 

[nerdorama]

Did Supreme Transformer Co. become Heyboer?

 

[spantou01]

I thought enquiring minds in this old thread might want to know. I was reading it this morning and it prompted me to wonder about the transformer numbers on a home built Amplifier that was sold to me as a mono EICO HF81. The numbers seem correct for OEM EICO transformers. However, no EIA codes for manufacturer and date. (Except a “0”)

 

[spantou01]

I got my other EICO HF81 out to check and found:

Output transformers: 32013 (nothing else)
Power transformer: 32021 and 960 in line below.

 

[nerdorama]

I think the 32xxx number are Eico house numbers. I have Eico transformers with this sort of number.

 

[airscapes]

The 30021 power transformer were built by Heyboer in Michigan. Below is a replacement one from Heyboer which can take higher AC in compared to the orignals from 1958-60 which were designed for 110v.

Just picked up one of these.. No expert here and wondering if I will need to run this on a Varac? I have 2 hf-12s which these seem to be just packed into a single cassis. I run the HF12s on line voltage and the power transformers run under 150F in one and 125 in the other. I know this forum seems dead but hopping someone familiar with the HF-81 is still around as I will need help with the rehab.
Thanks in advance!
Doug

 

[tubeactive]

When the HF-81s came out, wall voltage was probably 115-117VAC. Today, we see 125VAC at the wall outlets.

A Variac is essential for cooler running and longevity. You could also rig up a "bucking transformer," using a filament transformer.

I use a Variac at 114VAC maximum into my HF-81. If I run it more than 4 hours, I turn it down to 112VAC, as the power tranny does heat up.

I recommend using tested and matched 6CA4/EZ-81 rectifiers. Likewise, for the output tubes. The coupling caps going to the EL84s should be tested/matched in capacitance value.

I set mine up to have 3, stereo phono inputs.
I changed the Mic and Tape Head inputs to magnetic phono inputs. With the Tape Head Speed switch, I installed two different phono playback curves. I like old records...

 

[airscapes]

When the HF-81s came out, wall voltage was probably 115-117VAC. Today, we see 125VAC at the wall outlets.

A Variac is essential for cooler running and longevity. You could also rig up a "bucking transformer," using a filament transformer.

I use a Variac at 114VAC maximum into my HF-81. If I run it more than 4 hours, I turn it down to 112VAC, as the power tranny does heat up.

I recommend using tested and matched 6CA4/EZ-81 rectifiers. Likewise, for the output tubes. The coupling caps going to the EL84s should be tested/matched in capacitance value.

I set mine up to have 3, stereo phono inputs.
I changed the Mic and Tape Head inputs to magnetic phono inputs. With the Tape Head Speed switch, I installed two different phono playback curves. I like old records...

I just checked and for whatever reason line voltage was reading 116v with my meter.. normally it is 121 as per most of my UPS displays
I will probably ping you when I get round to restoring for details on the changes you made.. Could be the fact there is no power at that end of the basement and my power strip is plugged into a 15-20' tension cord..