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Tube mono-block amp with SIX 6L6 outut tubes

Well... overcurrent on a mosfet output device is usually pretty safe for quite a while. Second breakdown is the problem with bipolar. Their rating at high voltage is much lower than their power ratings would imply.

I designed mosfet amp in the early 80s. I tested it by putting in a full level signal with an output s/c. The only protection was a zener across the gates to limit the current to the device ratings. I left it cycling with its

90 Deg heatsink thermal cutout for 3 days. No problems.

-- Kevin Aylward

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- SuperSpice
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Reply to
Kevin Aylward
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The final triodes (6080) are special high-current tubes. The amplifier designer rated the thing at 25 W into a 16 ohm voice-coil speaker.

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-TV
Reply to
Tauno Voipio

Ya, BJT amps tend to have oversized output devices as compared to what their rated maximum "RMS power" output would imply. 75 watt-rated devices in 25 watt amps. The problem is risk of second breakdown when working into reaactive loads, not de-rating BJTs appropriately when they're handing significant powers into reactive loads common newbie mistake

Reply to
bitrex

Used to be true -- modern MOSFETs are more than current-dense enough to exhibit 2nd breakdown. I shouldn't actually say modern, because apparently SuperJunction process has... PTC source connections or something? I haven't seen one without a square SOA yet I don't think. So by now, it's actually previous generation that you have to watch out for. I forget if lower voltage (SJ goes away under ~400V I think it was?) processes are still prone.

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/
Reply to
Tim Williams

Exicon are the audio mosfets of choice today, apparently. They are laterals.

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They have the usual power limited SOA.

I don't know who actually makes them, but my guess is someone like XFAB.

Standard fab vendors will make any asic for any fabless company, even if the asic is just the one big transistor!

-- Kevin Aylward

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Reply to
Kevin Aylward

Back in the late 60s early 70s, I had several (self refurbished) mono-block power amps that used four 6L6 output tubes. I did not even know about matching those tubes. I just put in any tube marked as a 6L6. I recall having both the glass (GC) types mixed with the black metal ones. I always had good sound and lots of power. I do recall that replacing the metal cased ones with 6L6GC did increase my power though. But until I could afford new tubes, I used what I had. And even with the new tubes, I never matched them.

Reply to
tubeguy

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