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eBay 6SN7 / 300B Amplifier PCB Kit
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Author:  Gio [ 07 Oct 2018, 08:17 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

Increasingly, I'm liking the AN drivers better. Better value IMO here in North America. However, shipping may be rather expensive to Australia as they are much heavier than the comparable fostex drivers so you will have to look into that.

Author:  Woodo [ 10 Oct 2018, 17:40 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

i see in Aust. has some options for efficient full range speakers but not audio nirvana. although i am sitting here listening to Yes’s Keys to Ascension as loud as i would ever have listened with our Pioneer class d theatre amp with 20 times more watts. the efficiency of the b & w 706 s2 speaker are specified as 89dB from memory. both amps sound quality is good in my estimation but i feelimagine the valve amp sound is more pleasurable. it would be good to compare with other valve amp builds. the shielded signal wires reduced hum a bit, a low level remains which is hardly noticeable i may have to live with.

Author:  Woodo [ 13 Oct 2018, 02:38 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

Thought I would post the voltage measurement for comment. Not 100% sure how to go about it but comments welcome to aid learning.
Left measurement before right.

6sn7 triode 1: confusing because I think they have swapped triodes compared to traditional circuits but pin 2 to across cathode R 71.4 and 75.1 v
6sn7 triode 2: pin 5 across cathode R 230.9 v and 225v
6sn7 heaters: 6.7v both
300b: pin 2 plate to end of cathode R group 360v and 360.2v
Heaters 4.7 v both

Suggestions on other measurements I should take or better ways to take the measurements welcome. From the circuit should I use different bias points? Pretty happy with the sound but good to know if. Hold be improved. There's a possibility to increase B+ as the tranny allows 380v. I am using the recommended 320v by the pcb supplier but would be willing to give it a try if sonically worthwhile.

Author:  Woodo [ 09 Nov 2018, 19:06 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

i made some further measurements as follows - left, right
6sn7 (1) grid to cathode 0v,0v ?, plate to cathode 72, 76v, across 750 cathode R 2v, ?
6sn7 (2) grid to cathode 72.1, 75.8 v, plate to cathode 232, 226v, across 15k cathode R 77, 79.4

300b grid to cathode, 55-60v, 56-61v (pin 1-pin 4), across cathode R group 56.5, 61.5v

300b, plate to cathode/heater 306-302v, 307-302v, plate to across cathode R group 365, 365v

As i hear a little hum in both channels i measured about 3 mV across left/right speaker outputs.

Happy to receive comments on significance of measurements, suggestions etc. Thanks

Author:  Woodo [ 09 Nov 2018, 19:15 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

After putting in quite a few hours am still mighty impressed with the sound of this amp even though it has been built with budget components. on certain skilfully recorded albums i feel sure there are instruments and nuances in the music i have never heard before when played on my theatre amp.

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