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Old 21st July 2009, 03:31 PM   #1
Brit01 is offline Brit01  United Kingdom
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Default Pete Millet HA-2 headphone amp

Guys,

How would I incorporate an extra jack for 32 ohm headphones?

This is designed for 100ohms.

Also would like an output to use this as a linestage if possible.


Pete Millet used the 6080 in a couple of his projects, the HA-1 and HA-2 headphone amps, the data is still available on his personal archive of the Wheatfield Audio website at http://www.pmillett.com/wheatfield.htm
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Old 21st July 2009, 03:57 PM   #2
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Hi!

You'll want to use at least 250uF as your output dc decoupling capacitor instead of the 47uF in the schematic. 600uF would be even better for 32 ohms.

It should be fine as a line stage too. Just put in a switch so you can choose between a big 250+uF cap for headphones, and a small 0.1 to 0.47uF to feed another amplifier.

Do a search on "Cheapfield" here if you're interested in my own follies. Finishing the HA2 up will be my next project. I just moved to a well used house, so all my DIY efforts are doing there for now.
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Old 21st July 2009, 04:26 PM   #3
Brit01 is offline Brit01  United Kingdom
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Perfect. Thks very much. That is what I was thinking exactly but as I'm a beginner didn't want to jump the gun.

Already got some 440uF and 680 uF caps in the post


And got some nice PIO 1uF caps on the way although I have some RTI and Auricaps in my house to test.
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Old 22nd July 2009, 02:31 AM   #4
Brit01 is offline Brit01  United Kingdom
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I thought my big 6.3V tranny would be up to supplying the heater on a 6080 and 6sl7gt but i was wrong.

It's voltage is dragged down to 5V when I put these 2 in parallel.

I have a 4Amp 12.6 V tranny but I understand I can only put 2 6.3V tubes in series when they draw the same current.

Is there is a method to put the 6080 and 6ls7gt in series from a 12.6V tranny?
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Old 22nd July 2009, 05:09 PM   #5
Brit01 is offline Brit01  United Kingdom
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Is there is a method to put the 6080 and 6ls7gt in series from a 12.6V tranny because they have such different heater current requirements?
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Old 22nd July 2009, 05:19 PM   #6
rknize is offline rknize  United States
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When you put heaters in series like that, they have to have the same current rating. Otherwise the effective voltage divider that the two filaments make will be uneven.
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Old 22nd July 2009, 05:46 PM   #7
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Is it center tapped? You may be able to rectify it to DC, but then it may be cheaper to get another transformer. I have the opinion that tubes are happier with AC heaters.
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Old 22nd July 2009, 05:50 PM   #8
Brit01 is offline Brit01  United Kingdom
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Non CT.

I've been very happy running AC with previous projects.

Yes looks like new trannies will have to be built.


I might as well go for one with 5V so I can utilize the 5U4GB I have.
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Old 22nd July 2009, 06:20 PM   #9
kuroguy is offline kuroguy  Germany
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You can put different current heaters in series. It requires the addition of a shunt resistor across one of the heaters.
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Old 22nd July 2009, 06:45 PM   #10
Brit01 is offline Brit01  United Kingdom
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Quote:
It requires the addition of a shunt resistor across one of the heaters.
This is a new concept to me. Would you be able to point me in the right direction?

Thks
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