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Hello,
I'm sure this topic has come up many times. I did some searches but haven't found anything that is quite like the problem I am experiencing. I've got a low frequency hum coming from my Eico 2036 integrated amp. Here's the facts:
1) it only occurs at startup and gradually goes away over about a 5 minute period.
2) only the right channel is effected
3) changing tubes around has no effect, stays with the right channel
4) switching to a different source has no effect
5) it responds to the volume control, open the pot up and it gets louder, close it and the hum goes away
6) I've sprayed Deoxit on all of the controls
7) I bypassed the channel blend and tape monitor switches, still got the hum
Does anyone out there have any idea what's going on here? Any help would be much appreciated. Thanks.
Bill
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Honest amplification is better than excessive 2nd order distortion anytime.
Bill
The fact that it gets louder with volume eliminates the possibility of a filter cap.
What you most likely have going on is a slightly leaky coupling cap that is leaking DC voltage for a few minutes and then corrects itself.
This does happen on occasion..If you have the original black caps in the unit,I can almost bet one or two are leaking DC...Its easy to find but start with the output tube coupling caps from the driver.Lift the one side of the cap that goes into the output tube on each tube..Plug the amp back in and measure the DC voltage to ground on the open end of the cap.
If you read one or more volts DC,change that cap.
Honest amplification is better than excessive 2nd order distortion anytime.
What type of meter do you use? I imagine it could affect the reading.
-reub
Just use a regular DVM..You basically want to see if any of your caps are leaking DC.Since I believe his unit has all the old paper caps,the bumblebees had a tendency to leak..Even the old black and yellow Pyramids would leak a bit.It only has to be one or more volts to be an issue.
Honest amplification is better than excessive 2nd order distortion anytime.
Thanks Mike. On this particular amp the volume pot is located right after the selector switch so the tone control circuits and driver/phase splitter is located downstream of the pot. If that's the case, wouldn't a leaky coupling cap cause a hum that is not controlled by the volume pot? The phono stage is located upstream of the pot but I've got the selector switch set to "tuner" or "aux" when I'm using the amp.
It can be any cap,anywhere in the circuit.I just said to start with the obvious but you can have problem back in the preamp stage even.
Do this.I haven't seen this amp's schematic but assuming its a 12ax7 or 12au7 driver phase splitter that drives the output tubes,short the input grid to ground on the DPS tubes and then plug the amp back in and see if you hear the hum..This will at least eliminate the possibility of it being in the amp section.
Here is what you do..Just check and see if there is any DC voltage on any the grids of the 12AX7s or 12AU7s..If there is,you have to change those caps.
If you want,email me tomorrow after school..I get home at 530est.
merccougar89@yahoo.com
Honest amplification is better than excessive 2nd order distortion anytime.
Edits: 03/09/14
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