DIY Audio Projects Forum

Building a 300b
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Author:  steakhead [ 10 Aug 2017, 20:35 ]
Post subject:  Re: Building a 300b

the 5 volt connected to the rectifier tube, is the point of b+ for powering the amplifier, perhaps it might be a good idea to remove the ground, off the 5v
centre tap, then the fuse will not blow.. it might help if you locate a book of some sort, to help you understand power supplies, the author of these books really
don't care how much you read about what they have to say, but the guys on this site, care about your not making sense rational. there is a hole in the bucket.

Author:  clowkoy [ 18 Aug 2017, 19:14 ]
Post subject:  Re: Building a 300b

I enjoy listening to this amp.
I changed the rectifier to 5U4G and it decreased the voltage by about 25 volts.
I have a few observations:
1. Hum level is dependent on the 6SN7. I have 4 Sovteks and 2 JJ's, I can get <2mv on 2 of the Sovteks, the rest varies from 2.2 to 4.5mv. The hum follows the tube.
2. I have to adjust the 300B hum pot every time I change the 6SN7. I thought the pot is only for the power tube.

Author:  Suncalc [ 18 Aug 2017, 20:28 ]
Post subject:  Re: Building a 300b

Can you post your final schematic?

Author:  clowkoy [ 18 Aug 2017, 22:25 ]
Post subject:  Re: Building a 300b

Hello Matt,
It's the one from here: ... ematic.htm
Only changes are: no bypass cap on the 6sn7 470-ohm resistor and 750-ohm 300B cathode resistor.

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