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Old 14th October 2005, 12:10 AM   #11
Johan Potgieter is offline Johan Potgieter  South Africa
diyAudio Member
Join Date: May 2005
Location: Pretoria, South Africa

Now your first paragraph (air-flow matters) is a most interesting matter - caused me to contemplate for quite a while. Methinks I must adapt my advice re 2 fans somewhat......

I must admit that I had more in mind the kind of set-up where heat generators are distributed, i.e. there will be a gradient in cooling efficiency, being highest close to the fan and worse further on as the airflow diverges. There a "sucking" fan at the other end of the cabinet/duct will even things out. But in this case the air can be blown directly onto the heat generators i.e. the power tubes. Point taken. Two fans both blowing in would have a better effect (but I am not suggesting that Buliwyf's problem cannot be solved by only one fan; getting a bit pedantic, 2 smaller fans side-by-side will blow a broader stream of air....but OK). Good point by you.

But then: I would like to answer your PS question .... but cannot make sense of it! (Is it the time of night??) Er...what transistors? If you mean the EL84s, I fear I still do not follow. Kindly explain!

(My PS: Greetings to Cape Town - I grew up in Malmesbury.)
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Old 21st October 2005, 03:04 PM   #12
buliwyf is offline buliwyf  Philippines
diyAudio Member
Join Date: Oct 2005
update: I just removed the fans.

last night, after about 15mins of being in "standby mode," (fans running), I turned it on and cranked it up really loud (volume, drive, bass, mid, treble ALL at 10), for "authentic vintageness"

well, the Fuse for the output blew after around 3mins of playing.

could this be because that I cranked the amp up too loud BEFORE the tubes become really hot?

now its acting weird when its still not hot, making strange noises followed by a dive in volume followed by a growing feedback then total silence, then after 2 secs, its gona be normal again.
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Old 21st October 2005, 11:58 PM   #13
Bill*B is offline Bill*B  United States
diyAudio Member
Join Date: Sep 2004
Location: tampa, florida, USA
Just to mention what you may already know - check the spec sheets - some 24V DC fans will run happily at 12V, and the slower rotation speed at that reduced voltage keeps them quiet. Nelson Pass mentioned this in his DIY A75 sand amp, and I've adopted the practice. Bill.
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