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 Post subject: EICO 145 Question
PostPosted: Mar Sun 04, 2018 11:51 am 
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Joined: Feb Sun 01, 2015 9:37 pm
Posts: 381
Location: Laflin, PA
I picked up a EICO 145 from EBAY. The thing has been butchered in pretty good by someone. I removed some strange parts that I had no idea why they were there. They include a push button (that replace one of the ground input plugs), a relay, a selenium rectifier and some assorted cap and a high wattage resister. I just rebuilt the thing back to what was original.
My question(s):
When the volume is turned all the way down I still hear a hum from the speaker (when on signal tracer), anyone think this is normal?
What size electrolytic caps has anyone used? The caps when I got it were 40 mfd and the schematic shows 10 mfd (or higher).

Other than the low hum with the volume down the amp has plenty of gain and seems to be working correctly.

Recommendations welcome on this unit.

Thanks for reading!

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 Post subject: Re: EICO 145 Question
PostPosted: Mar Sun 04, 2018 12:58 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
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Location: Sunbury, Ohio 43074
A few general comments ... please post a link to a schematic for your unit to recieve more specific help unless someone already has one.
You mention a hum from the speaker with the volume all the way down. Is it 60Hz hum or a higher frequency? How loud is the actual hum?

You mentioned replacing the 40mfd caps ... presumably the power supply filter caps? If so, 40mfd should work, again without seeing the schematic, difficult to be certain. In some cases too high filter caps can lead to too high voltages. Mostly not, but just guessing in the dark here ...

Also, in the case of hum in such an elderly unit, check all system grounds, especially those that bond to chassis, for corrosion or make sure they are otherwise tight and secure. I usually re-bond any chassis grounds by removing, wire brushing the area, reinstalling with a star lock washer for secure ground.

More specific help with more specific questions :)

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 Post subject: Re: EICO 145 Question
PostPosted: Mar Sun 04, 2018 1:27 pm 
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Location: Laflin, PA
Barry H Bennett wrote:
A few general comments ... please post a link to a schematic for your unit to recieve more specific help unless someone already has one.
You mention a hum from the speaker with the volume all the way down. Is it 60Hz hum or a higher frequency? How loud is the actual hum?

You mentioned replacing the 40mfd caps ... presumably the power supply filter caps? If so, 40mfd should work, again without seeing the schematic, difficult to be certain. In some cases too high filter caps can lead to too high voltages. Mostly not, but just guessing in the dark here ...

Also, in the case of hum in such an elderly unit, check all system grounds, especially those that bond to chassis, for corrosion or make sure they are otherwise tight and secure. I usually re-bond any chassis grounds by removing, wire brushing the area, reinstalling with a star lock washer for secure ground.

More specific help with more specific questions :)


Actually I have done all of the above with this unit. I was actually wondering if anyone had this unit and noticed the hum when the volume was all the way down. Yes those are electrolytic(filter) caps I was talking about the build instructions indicate two 10 mfd but when I got the butchered unit they have replaced whatever was original with the larger values (which were bad). I was thinking the hum did not sound like 60hz more like 120hz. I did the test lead grounded to the chassis and tried all the grounds to see if that made any difference.

I was watching a video on You Tube about this EICO and I really think I was hearing the same hum on his video.

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 Post subject: Re: EICO 145 Question
PostPosted: Mar Tue 06, 2018 12:04 am 
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Joined: Jun Fri 19, 2009 6:34 pm
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Location: Long Island
Actually the manual calls for 8-uF electrolytics. 10-uF would be the modern day replacement value. 40-uF is over the top and could be part of the problem if it is raising the B+ voltages too much.

The unit is designed with the chassis as common, and one side of the heater circuit is connected to it. So a very small amount of residual hum is possible if the volume control is full up. I had a 147A which is a somewhat later version and it had a small amount of residual hum as well. These are simple amplifiers without feedback, so any hum or noise added by the circuitry will appear at the output.

Since the unit was most likely a kit, it may be worth downloading the assembly manual if you don't have it already and checking that the wiring was routed correctly. In particular, the heater and AC power wiring should be kept far away from the low level 6SJ7 stage. A tube with high heater to cathode leakage could also be causing the problem.

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 Post subject: Re: EICO 145 Question
PostPosted: Mar Tue 06, 2018 1:14 am 
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Joined: Feb Sun 01, 2015 9:37 pm
Posts: 381
Location: Laflin, PA
Chris108 wrote:
Actually the manual calls for 8-uF electrolytics. 10-uF would be the modern day replacement value. 40-uF is over the top and could be part of the problem if it is raising the B+ voltages too much.

The unit is designed with the chassis as common, and one side of the heater circuit is connected to it. So a very small amount of residual hum is possible if the volume control is full up. I had a 147A which is a somewhat later version and it had a small amount of residual hum as well. These are simple amplifiers without feedback, so any hum or noise added by the circuitry will appear at the output.

Since the unit was most likely a kit, it may be worth downloading the assembly manual if you don't have it already and checking that the wiring was routed correctly. In particular, the heater and AC power wiring should be kept far away from the low level 6SJ7 stage. A tube with high heater to cathode leakage could also be causing the problem.


I used the 10 uf caps like it was showing in the schematic. I tried replacing them with 20 uf and it actually sounds better. I did download the build manual and rebuilt the unit back to the original design. I did make sure to keep the heater and AC as far as possible from the amplifier which was the way it shows in the original kit manual. The tubes are testing as good on my EICO 666 but that is never a 100% that they are not having problems. I had wondered about the 6X5 since they have a history and the unit was run with 40 uf caps when I got it. THANKS FOR YOUR INPUT!

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