we have a winner
Yesterday I was able to finish all the wiring. It won't win a beauty contest, but for now it should do. I also temporarily removed the output caps in order to give EC8010 a good sleep...they are in fact insulated at the bottom. 😉
After checking all connections and solder point a few times I plugged the tubes back in and powered the amp up...
with my 70 ohm test cans everything started to work properly, AND, no oscillation!! The ugly tocking sound is gone, the leds light up after a few seconds and everything stays calm.
So my first big Thank you goes to EC8010 you basically led me through this rewiring!
I checked the important voltages with everything being in the ballpark except that all voltages supposed to be around 110V (anode of V1 and the WCF) are now around 140V. The bias of the input tube is at a very exact 3,537V (both halves, so much for led accuracy), so I don't know where the increase in voltage is coming from.
I didn't have much time to give the amp a good listen...to use a Raymond Chandler analogy: "it produces sound...".
When the enthusiasm has settled a bit I will compare it to my other amps.
I did skip the 10nF on the heaters (the tube gods may forgive me), but will for sure implement it in my next amplifier. Or, when the amp has more mileage I might start with other modifications (i.e. fixed bias for the output tubes as Kevin has suggested...) and then put them in.
So thank you everybody who contributed their wisdom/experience...it was of great help!
Yesterday I was able to finish all the wiring. It won't win a beauty contest, but for now it should do. I also temporarily removed the output caps in order to give EC8010 a good sleep...they are in fact insulated at the bottom. 😉
After checking all connections and solder point a few times I plugged the tubes back in and powered the amp up...
with my 70 ohm test cans everything started to work properly, AND, no oscillation!! The ugly tocking sound is gone, the leds light up after a few seconds and everything stays calm.
So my first big Thank you goes to EC8010 you basically led me through this rewiring!
I checked the important voltages with everything being in the ballpark except that all voltages supposed to be around 110V (anode of V1 and the WCF) are now around 140V. The bias of the input tube is at a very exact 3,537V (both halves, so much for led accuracy), so I don't know where the increase in voltage is coming from.
I didn't have much time to give the amp a good listen...to use a Raymond Chandler analogy: "it produces sound...".
When the enthusiasm has settled a bit I will compare it to my other amps.
I did skip the 10nF on the heaters (the tube gods may forgive me), but will for sure implement it in my next amplifier. Or, when the amp has more mileage I might start with other modifications (i.e. fixed bias for the output tubes as Kevin has suggested...) and then put them in.
So thank you everybody who contributed their wisdom/experience...it was of great help!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Delighted to hear that the tick-tocking has stopped and that your LED modification works. Well done.
Just in case somebody is interested...
Now that I have listened to my modified MJ and compared it to my other amps I can say that switching to LED bias in the first stage was well worth the effort:
the amp sounds a good deal crisper now, transparency has improved without any edginess and bass quality is much better.
The reworked grounding scheme also pays off with the noise floor being much lower.
Now that I have listened to my modified MJ and compared it to my other amps I can say that switching to LED bias in the first stage was well worth the effort:
the amp sounds a good deal crisper now, transparency has improved without any edginess and bass quality is much better.
The reworked grounding scheme also pays off with the noise floor being much lower.
An externally hosted image should be here but it was not working when we last tested it.
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