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Ebay 300B SE amp information
Ebay 300B SE amp information
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Old 20th October 2018, 02:48 AM   #21
sulcorebutia is offline sulcorebutia  Hong Kong
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Join Date: Oct 2009
Originally Posted by ashok View Post
I bought a 300BSE amp from ebay. It came with no information at all , just board, parts and no tubes of course.
Would anyone have some info on this kit.
Hi-end 300B+6SN7+5U4G 8W+8W Class A tube amplifier kit | eBay

Not sure if it is the same one. Well if it is, you can see one of the simplified circuit down in the description.
300B ?????? ????? ??? ??PCB ??-???
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Old 20th October 2018, 11:20 AM   #22
woodo is offline woodo  Australia
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Join Date: Jun 2018
Originally Posted by wdecho View Post
Though I have a low level of hum which annoys me and haven't been able to resolve this doesn't take away from the sweet sound.

AC filaments? Balancing pots? It is hard, at least for me, to totally eliminate hum with a true triode with 5 or more watts using 103db speakers but with DC filaments and balancing pots I reduced it to an acceptable level. I do believe my build would be quite with 90db speakers. It takes some effort though. I used Arta to set my balancing pots which helped a lot.
I would like to incorporate this into my circuit but it might be difficult given itís a PCB. there may be a way to tap into the circuit for someone who knows what they are doing (ie not me). I would probably need to rebuild the the amp using point to point wiring. refer to thread on SE 6sn7/300b on diyaudioproject.com site. DIY Audio Projects Forum • 300B SET Design Project
btw could you explain ĎArtaí? I would like to follow up.
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Old 20th October 2018, 12:12 PM   #23
woodo is offline woodo  Australia
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Join Date: Jun 2018
Originally Posted by kmtang View Post
The 300B is self-biased that you don't need to worry. Depending on the B+ voltage, say 400Vdc, the idle current shall be 80mA approximately. The OPT should be 2.5 to 3.5Kohm primary impedance.
Thanks. everything seems rather fine except for a low level of hum. thereís enough power with my 89db@1watt two way speakers. i can hear some bass down to 40 hz but canít hear much from the tweeters above 10khz tones ( my old ears most likely). i would like to check the frequency response on a scope though.
opts are mentioned in the circuit above. i use the gsxe 15-3.5k. there not large but seem quite good enough.
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Old 21st October 2018, 08:24 PM   #24
azazello is offline azazello  Bulgaria
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Join Date: Aug 2008
Location: USA
15W OT is small for 300B. You need min. 25-30 W OT. Output power of tube 7-8 W You can multiply to 3-5 time to choice OT.
Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...

Last edited by azazello; 21st October 2018 at 08:26 PM.
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Old 21st October 2018, 10:21 PM   #25
woodo is offline woodo  Australia
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Join Date: Jun 2018
In a future build (this was my first) I might go for larger opts if needed but I am really surprised how good the overall sound is with the 15 watt. I was listening to Led Zeppelin 2 and John Paul jones bass guitar was quite prominent in the sound which I hadn't noticed before with my ss amp. It may not be possible to re-create the organ notes from the big pipes but my speakers roll off at about 50 Hz anyway.
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