Author Topic: 2A3 PSE circuit design  (Read 284 times)

Offline Andresound

2A3 PSE circuit design
« on: January 05, 2019, 12:07:56 PM »
Hi guys, its been a while. Compliments of the season to everyone. I am looking for a simple circuit for stereo parallel single ended using 2A3ís without the need for interstage trransfomers. I would like to build this for a freind. Source components would be a computer analog. I have enough vintage pre and rectifier tubes. Any suggestions would be welcome. If PP is easier.. then I will look at that too.

BTW.. it will be a single chassis for both channels

Offline handsome

Re: 2A3 PSE circuit design
« Reply #1 on: January 05, 2019, 02:21:13 PM »
nothing wrong with going by the datasheets: 1.25k output transformer, ~300V HT for cathode bias ~250VHT for fixed bias both at ~130mA. You need to swing 45V for full power:  6SL7/12AX7 voltage amplifier feeding a 12AU7/6SN7 cathode is one way of doing it.....

Offline Andresound

Re: 2A3 PSE circuit design
« Reply #2 on: January 06, 2019, 08:55:13 AM »
Thank you for the info. Do you have a particular circuit in mind?

Offline handsome

Re: 2A3 PSE circuit design
« Reply #3 on: January 06, 2019, 10:00:05 AM »
no particular circuit. setup your 12AX7/6SL7 as a common cathode amplifier - look at the datasheets and choose an operating point depending on how much gain you need (there are lists of operating points with gain, load resistor, HT voltage etc). Then have that stage feed a 12AU7/6SN7 cathode follower that is biased to at least 5-6mA (more could be better). And finally have that stage feed your 2x 2A3. 2A3's: set them up according to the datasheets ( i think its 60mA at 45V bias?). The reason i added a cathode follower is that paralleled 2A3s will have twice the capacitance of a single one and you need some current to drive that - 12AX7/6SL7 could be marginal in that respect. 12AT7 could be an option but you might not have enough gain - is this to be an integrated amp or a power amp fed by a preamp? Cathode biased output stage is simpler (less parts) than a fixed bias output stage. Peruse any of the"standard" 2A3 designs and you will quickly work out what you need for power supplies etc. 

Offline Andresound

Re: 2A3 PSE circuit design
« Reply #4 on: January 09, 2019, 08:28:26 AM »
 Intergrated