TheRadioBoard

I just finished my first amplifier. It uses 12U7s an 12K5s (based on the 30V Sopht amps circuits out there on the web.)



It's for desktop use with the computer sound output or my Mp3 player. I set the outpul level adjusted so that the amp can be cranked to max without distortion. Perfect for background music in a quiet small room application.

The power supply was a modified version of this


from this thread http://theradioboard.com/rb/viewtopic.php?t=1838

I used a 12-0-12 transformer with RC pi filtering on both the 30V and 12V legs. I planned to use the 12V for both filiment and screens but the filtering wasn't good enough for the screens and caused buzzing. Instead of reworking the filter I hung a 12V voltage regulator off the b+ and used that for the screens. I put a 5V regulator off the 12V and tied it to the female half of a USB cable for charging the MP3 player

The output iron is a pair of Bogens. The case is bigger than I wnted it to be but the power xfmr is largish. The 12K5's suck up some juice!

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Mark

I want to meet the man that put the cat IN the bag!

Nice amp duck. That one will serve you well for many years.
I have a similar project..... in a cardboard box. I wonder if I'm going to finish it, ever.
Nice charging solution for the *pod too.

Only thing is that with a 120mA transformer secondary, you will never see 150mA output, especially with a bridge rectifier setup. 50 to 60mA would be more like it.


And since the VR tubes draw some current, I would make it a 50mA supply at maximum.

Transformers are rated in secondary currents using a full wave center-tap rectifier configuration, not a bridge, unless specificially specified.
Curt

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Curt, N7AH
CW forever
Connoisseur of the cold 807

LOL

Curt the tubes used are 12v space charge car radio types... I don't think he used that 720v xformer...

Tom