sluckey wrote: ↑Tue Mar 03, 2020 6:15 pm
Just a little sidebar... Back in the '60s hum was not a problem with the AC-4, Champ, or other similar small SE practice amps with minimal filtering. Oh, the hum was there alright, but that cheap 8" speaker could not reproduce it very well, so you just couldn't hear it. Then people started connecting a better quality 12" speaker and all of a sudden there was hummmmm.
Guess what: yet the speaker is sounding awesome, it is (very) very loud...
So I'm thinking about upgrading its filtering as per
sluckey wrote: ↑Tue Mar 03, 2020 2:59 pm
Refer to the service manual you posted.
1. Break the connection between the junction of the rectifier diodes and point B+.
2. Install a 250Ω/10W resistor between the junction of the diodes an point B+.
3. Connect a 100µF cap between the junction of the diodes and ground.
For even better hum filtering, use a choke rather than a 250Ω resistor.
&
xtian wrote: ↑Tue Mar 03, 2020 4:56 pmYou don't need more than 50mA current...
In detail, the plan would be: inserting a 47uF reservoir cap, which is the most the EZ81 is supposed to handle, but I'm not sure about the DSR/resistance value of the choke. I guess the most important the resistance, the better filtering so:
- an Hammond Choke 154H (300 Ohms) should even better suit than Hammond 194A Choke Fender 125C3A / 022707 (167 Ohms) - both being 4H and good for 50 mA,
but the highest(*) the voltage drop, too - right?
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(*) & how much the absolute difference in voltage drop...