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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 10 Oct 2019, 07:37 
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Joined: 13 Jan 2018, 21:33
Posts: 312
Location: australia
“While I had Qians amp I increased the snubbing around the filement rectifiers. Though the hum from the amp was only low I thought it worth while to see if I could reduce it more. I put 0.01uf polys between all legs of the rec. bridges. Qian tried serveral times to find a hum and could not. “

@mwhouston, Hi Mark. I still have (just) audible noise I suspect from the heater circuitry. Above do you mean you placed the caps across the + and - of the bridge rectifier? Are there any other sites you have snubbed that you found necessary?

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PostPosted: 08 Nov 2019, 15:25 
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Joined: 26 Jan 2011, 08:57
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May I ask the board about the 300B schematic?
I see it is one channel.
How do I tie the second channel to the first?
Thank you.


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PostPosted: 08 Nov 2019, 18:55 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
Both channels are shown in the schematic in this post: http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=2699&start=131

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PostPosted: 08 Nov 2019, 19:05 
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Joined: 26 Jan 2011, 08:57
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Thank you very much.


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PostPosted: 09 May 2020, 22:48 
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Joined: 13 Jan 2018, 21:33
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Location: australia
Woodo wrote:
Thought I would post the circuit as currently stands for my build of this great sounding amp and prepare to move on to next project albeit slowly which I hope will be simpler and cheaper on vacuum tubes at least. Some differences to the circuit on page 33 are noted in the schematic. Have to order a new filament transformer that will reach 5v quietly. May try going back to the capacitors in the original circuit after the transformer arrives and put into the box . Thanks for all the input everyone. :up: If mistakes are spotted, happy to receive input.


A neater version of the circuit in microcap. 5v filament circuit as before. Still to locate the bridge rectifier and LT1085 in the component library. Still sounding good. I still get some buzz on startup which dissipates after tubes warm up, circa 2 min.


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PostPosted: 30 May 2020, 05:37 
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Joined: 07 Feb 2016, 13:01
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Woodo wrote:
Woodo wrote:
Thought I would post the circuit as currently stands for my build of this great sounding amp and prepare to move on to next project albeit slowly which I hope will be simpler and cheaper on vacuum tubes at least. Some differences to the circuit on page 33 are noted in the schematic. Have to order a new filament transformer that will reach 5v quietly. May try going back to the capacitors in the original circuit after the transformer arrives and put into the box . Thanks for all the input everyone. :up: If mistakes are spotted, happy to receive input.


A neater version of the circuit in microcap. 5v filament circuit as before. Still to locate the bridge rectifier and LT1085 in the component library. Still sounding good. I still get some buzz on startup which dissipates after tubes warm up, circa 2 min.


can I get wattage detail rates for all resistors used?

Woodo wrote:
Thanks Koichi. The buzz is almost inaudible now and the amp is sounding great to me now so I might leave things be until I procure a filament transformer that can do the job as intended. I have emailed Hammond to get an opinion on whether the one I have (266LA12) is up to the task or is perhaps faulty and should be replaced but no word as yet. The only other change I have made is to remove the 100 ohm resistors in the secondary wires, as this didn't improve the buzz anyway. I might have mentioned it but I put one of the 100 ohm resistors and spare 39 uF capacitor for additional filtering of the b+ to try and reduce the hum (this was before I found the regulators tone making the noise so made no difference to the buzz). I may return things as they were to be as faithful as possible to the original. The b+ is about 420v now. I replaced the dropping resistor with a 10k to the 6sn7 supply so this is 300v now.


Is your amplifier quiet and free of hum? which solution did you use?


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PostPosted: 02 Jun 2020, 16:38 
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Joined: 13 Jan 2018, 21:33
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Location: australia
I generally followed the circuit as posted At the beginning of the thread for resistor ratings. I’ll update my circuit with those used. I had a look at my empty mouser bags and the plate, grid and driver cathode resistors are 1 watt. The 300b cathode resistor is 10 watt, I had difficulty finding a 7w as per circuit. That one gets very hot. I didn’t check power dissipation but I used 1/2w resistors in the filament regulation circuit. As for hum there’s a bit of a buzz at startup but around 2 minutes subsequently it becomes inaudible. I ended up replacing the filament transformer with a toroidal 30VA 6v dual secondary unit. Seems to work well. I haven’t tried adding any bypass caps as suggested yet so that’s next.

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