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Old 20th June 2012, 09:05 PM   #21
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Just to double check, you did wire the choke between the 220u and the 68u caps right?
This will give you a CLC filter. With 245vAC this should give a idal voltage of 245*sqrt(2)=346V on the first cap. Finite capactance and PT winding resistance will bring this down somewhat. Still if you only have 232 V after the choke and something is drawing a lot of current.
Start by measuring voltage over the cathode resistors in the output stage. They should be 100 ohms per your schematic so each V equals 10mA.

As for the 6N1P's listen to the Gimp I just looked at the datasheet, no direct experience...

/Olof
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Old 20th June 2012, 10:03 PM   #22
tuhkam is offline tuhkam  Estonia
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Yes the choke is between 220u and 68u.
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Old 20th June 2012, 10:43 PM   #23
tuhkam is offline tuhkam  Estonia
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This is the current schematic.

Should I take the high voltage for the output tubes at 220u cap?

Does the "V equals 10mA" also go for the 6N1P? If so, 1.7V suggests a current draw of almost 20mA?
I haven't measued the voltages at EL84 cathodes yet.

The sounds quite good, if compared to it a few days ago. There is a slight high pitched buzz, that gets louder if volume is being turned up and dissapears completely at full volume. It gets also louder if one puts his hand closer to the input wires/pot.
This is most likely normal for a spagetti plate without enclosure.

The heaters are now all on the 3A winding (running 6.22V AC). I did a voltage divider with 2x100 ohm between heater wires and referenced the middle to the ground. Got it a bit more silent with that.
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Old 20th June 2012, 11:59 PM   #24
MelB is offline MelB  Canada
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What is the voltage before and after your choke? Let's see exactly what the choke is doing. Also what is the voltage on pin 3 of the 6N1P?
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Old 21st June 2012, 12:03 AM   #25
MelB is offline MelB  Canada
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Sorry on pin 3 of the power tube.
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Old 21st June 2012, 10:05 AM   #26
7N7 is offline 7N7  United Kingdom
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When you have solved the mystery of the missing voltage, I have another suggestion. In the power supply you have R2, 1k followed by a small capacitor. I suggest that you replace the 1k with 3 330-ohm resistors and between each add say a 22uF capacitor - i.e. a 22uF after the first resistor and after each of the two others. This will greatly improve the quality of your power supply without costing you any additional voltage.

Also do by-pass the cathode resistor on the 6N1P with a suitable capacitor.

Paul
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Last edited by 7N7; 21st June 2012 at 10:22 AM.
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Old 21st June 2012, 01:49 PM   #27
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Quote:
Originally Posted by tuhkam View Post
This is the current schematic.
Does the "V equals 10mA" also go for the 6N1P? If so, 1.7V suggests a current draw of almost 20mA?
On 6N1P cathode you have 1.7V drop over 470R = 3.6mA, not 20mA ("V equals 10mA" comment was referring to EL84 with 100R cathode resistor)

Last edited by dovla; 21st June 2012 at 01:50 PM. Reason: typo
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Old 21st June 2012, 03:21 PM   #28
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Rectifier switching noise might be reduced by replacing the bridge with fast diodes eg UF4007's.

+1 for The Gimps' advice on replacing the 470R cathode resistor (R3) with a cheap red LED that can drop 1.7V across it.
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Old 21st June 2012, 09:00 PM   #29
tuhkam is offline tuhkam  Estonia
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I measured some more voltages now.
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Old 22nd June 2012, 12:04 AM   #30
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OK, starts to look good. Approx 30mA through the output tubes and 3,5mA through the 6N1P.
I would probably increase to somewhere around 40mA in the output.
Now you can start to fine tune. Or be satisfied...
However as you stated C8 should be bigger, C3 is borderline(-3dB around 20Hz)

/Olof
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