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Old 24th September 2011, 11:39 PM   #131
rsdio is offline rsdio  United States
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Quote:
Originally Posted by Backbones View Post
the heatsink I think beyond 300mm (from front to back) consists of two 200mm heatsinks bolted together. I never did find out how this altered the heat dissipation characteristics. Instinctively (not scientifically) I would prefer the heatsink to be a single unit.
I think it depends upon how many power transistors are in your circuit, and whether they benefit from matched temperatures. If you have many power transistors that are independent, then cooling might be better with separate heat sinks.

The ADCOM GFA-555 has four circuit boards with (I recall) two power transistors each. There are four separate heat sinks on the back of the amplifier chassis, two per channel or one per board. I noticed as I took off the chassis cover that the heat sinks are actually separate, and merely bolted together by the screws that hold on the bottom plate and top plate. I do not know whether Nelson actually designed these aspects of the enclosure, but it seems like a relevant observation.
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Old 25th September 2011, 12:45 AM   #132
Variac is offline Variac  United States
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Hmmm wonder if Nelson will add to the Burning Amp story at this year's event.
Oh wait! He already did! But we can hope for a little spin on things can't we?
I just sayin' why wouldn't he, he's on fire with this new board!
Mark
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Old 25th September 2011, 02:16 AM   #133
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No, I'm just fine. It's the board caught fire.

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Old 25th September 2011, 02:42 AM   #134
Variac is offline Variac  United States
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I thought it was the Beard
Fear it!
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Old 25th September 2011, 06:19 PM   #135
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Quote:
Originally Posted by rsdio View Post
The ADCOM GFA-555 has four circuit boards with (I recall) two power transistors each. There are four separate heat sinks on the back of the amplifier chassis, two per channel or one per board. I noticed as I took off the chassis cover that the heat sinks are actually separate, and merely bolted together by the screws that hold on the bottom plate and top plate. I do not know whether Nelson actually designed these aspects of the enclosure, but it seems like a relevant observation.
It is a design matter really. The position of the mosfets on the BA-2 power board are not set by me which means that when I line them up against the two heatsinks bolted together at least one will end up close to the edge of the join. I'm sure this means that the ability of the heatsink to dissipate heat will be impaired because the mosfet is close to the edge. Of course you could cut the board in two and have three on one side and three on the other but it would all be very messy.
Chris
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Old 25th September 2011, 06:26 PM   #136
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Quote:
Originally Posted by Variac View Post
Hmmm wonder if Nelson will add to the Burning Amp story at this year's event.
Oh wait! He already did! But we can hope for a little spin on things can't we?
I just sayin' why wouldn't he, he's on fire with this new board!
Mark
It would be great to get over to the BAF but with my bad back and fear of flying it just ain't going to happen this year. Any chance of a EuroBAF, maybe at the Munich show. Good reason to visit a great German city. Does Nelson travel well? Fantastic beer.

I'll take the train from London
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Old 25th September 2011, 08:38 PM   #137
Zen Mod is offline Zen Mod  Serbia
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frankly , only fear I have right now , is flying with my (now again) bad back .....

just finished skype-ing with Mighty AR2 , hoping to see him and all BAFling Greedy Boyz soon .....

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Old 25th September 2011, 10:47 PM   #138
Botte is offline Botte  United States
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Default Gain different than expected

Hi Guy’s,
I fired up the BA3 input board with the FQP3N30 and FQP3P20 and I have only a gain of ~8X. I was going to reduce the gain so I started with R10 and R11 of 50 ohms and I had a gain of about 3.5X. So I started cutting back to the 22 ohms specified and could only get a gain of a little better than 8X. Is this just the difference in the Fairchild VS Toshiba parts? I thought they were equivalent maybe I should start hinting for the Toshiba's, any ideas?

Thanks,
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Old 26th September 2011, 03:22 AM   #139
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There's quite a lot of degeneration on the Mosfets, so it's probably not that.

Are you using the 2SJ74 and 2SK170?

If you want a little more gain, just increase the output load resistor a bit.

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Old 26th September 2011, 03:26 AM   #140
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For those of you who are not attending BAF, you will delighted to know that
I will be presenting the BBA-3, the balanced version.

Not to despair, I will put it online very shortly after. In the meantime,
hands-off to the usual smarty-pants who are probably already working on
this...

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