DIY Audio Projects Forum

Another 300B SE Thread...
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Author:  whaleman [ 14 May 2019, 20:41 ]
Post subject:  Another 300B SE Thread...

So I was looking for a 300B SE straight forward and simple schematic and found it on this site. So here goes my JC Morrison 300B SE implementation. It works wonderfully with zero hum and plenty of gain. Bass is quite good as well. I am sharing my experience so perhaps others can give it a shot. It worked without any glitches on the first try, once I got the right mains transformer. My schematic is just slightly modded as I built it as a power amp and some of the 6SN7 voltage needed a little tweaking. If some are interested, I can share more detailed pics.


Author:  tubo [ 24 Jul 2019, 22:49 ]
Post subject:  Re: Another 300B SE Thread...

Hello Whaleman,

Great Job. The amplifier looks beautiful. Do you have any complaints as to how the amplifier sounds? I’ve been wanting to build the same 300b amplifier and I have most parts except for the output transformers.

Will a 5k single ended transformer also work good without tweaking the voltage on the 300b? Also how did you do your grounding?

Looking forward to hearing from you..

Thank you

Author:  Woodo [ 25 Jul 2019, 03:53 ]
Post subject:  Re: Another 300B SE Thread...

Hi, I assembled my first 6sn7/300b valve/tube amplifier from a similar circuit on a ebay pcb last year.. Lower transformer secondary voltage 320-0-320v and slightly different operating points. I found the sound quality quite good and really enjoyed it. A tech I took it to suggested there some biasing improvements that could be made which I didn’t really understand at the time so did not do. I read the following thread which captured my imagination viewtopic.php?f=9&t=2699 and decided to assemble the slightly tweaked circuit at page 33 viewtopic.php?f=9&t=2699&start=320#p28729 as closely as possible noting the differences in my hardware which I re-used from the previous amp. I completed it some time back and it sounds very detailed and articulate with power to spare with my two way speakers 89 db @ 1 watt/m. I have some issues with the 5v filament transformer which should be resolved when i get the right transformer.

Author:  tubo [ 27 Aug 2019, 07:19 ]
Post subject:  Re: Another 300B SE Thread...

Hi John,

Thank you very much for responding. I just finished a diytube get set get go amp and it sounds nice. I look forward on building the morrison 300b. Thanks for sharing.

Author:  Woodo [ 27 Aug 2019, 17:20 ]
Post subject:  Re: Another 300B SE Thread...

hi turbo, thanks for the comments. just for interest, the filament regulator oscillation I was having and mentioned in the thread, if you can call it that, is resolved since installing a different transformer and the amp is quiet now. I read about the gsg amp a while back, Sounded like an interesting project. I’ll have to refamiliarise myself on that one.

As for your query to whaleman about his grounding scheme above, i went through my own hum and buzz solving odyssey. I found the following advice is very instructive and helpful viewtopic.php?f=9&t=4542&start=30#p38008 from @suncalc recognising there are other schemes too that may work.

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