Posted by Damir [ 213.202.107.21 ] on July 03, 2006 at 07:08:35:
In Reply to: Re: SE 300B Project, Part 13 - The finished amp posted by 2wo on July 02, 2006 at 15:57:04:
Hey, thanks...I also worked on high temperature and humidity...huh.
The whole saturday afternoon and evening I drilled over 300 holes in the lower cover (ventilation)...first fi 3mm, then enlarge them to 4,5mm, then de-burring...
This is more tin-smith then electronic work, haha...
When I was finished, I mounted the lover cover (tightly), mounted 5 feets (weight!), and bring the amp in the main room. Just listening the music when I have some time - I`m tired of tinkering :-).
The sound is very good, little on the "soft and warm" side, but not too much that we can say "colored"... Clean, detailed, very nice! I think that it just started to "open up". Interestingly, two guys with large experience in the amps building privately suggested me 300h burn-in like their experience. They don`t like the forums, I don`t blame them... 
I measured 5,7 & 6,6 mV of hum on speaker terminals - not overly good, but probably normal for the stereo amp with very small steel chasis. Most of this hum comes from the AC heating, and a little from electromagnetic interactions. Even shorted input grid on 300B doesn`t change the level of hum. Interestingly, one "Svetlana" tube with the hum pot in the middle shows almost 50mV of humm- large "off center"! I needed large turn of hum pot to find the minimum hum. However, the hum isn`t noticeable in the listening position, but people with very sensitive speakers better use bigger chasis of non-magnetic metal, monobloc construction, partitions, and DC heating like reccomendable option.
I`ll do some other measurements, when I find some time. And yes - the amp weights exactly 20 kg ...
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