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Suggestions for a Medium Gain Guitar Amp Topology...
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Old 20th February 2018, 10:39 PM   #61
Andrew Eckhardt is offline Andrew Eckhardt  United States
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" and the OPT is now a magnet"

I snorted.
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Old 21st February 2018, 01:17 AM   #62
Tubelab_com is offline Tubelab_com  United States
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Quote:
" and the OPT is now a magnet"
I bought about 200 surplus OPT's from an Ebay seller when the ADA plant burned ans ADA subsequently closed down. These were in the delivery pipeline indicating thar ADA was looking at making some medium power push pull tube guitar amps.

I have used over 100 of those OPT's over about 15 years. This is the second one I have killed, and it still may be possible to degauss it. I have done that successfully with a variac, but not with a transformer this bad. There could also be some internal damage from the lightning bolt that tried to eat it, but it still has the correct DC resistance. I had the amplifier up and running with some of the biggest TV sweep tubes I have in it. I was getting about 160 watts per channel on 600 volts of B+ when I decided to turn the power supply up a bit more......BOOM......PSST, silence, smoke.

The other one? "and the OPT is now a fireball."

Nearly 15 years ago I decided to wire a pair of the same big TV sweep tubes up to one of my new OPT's and feed it with a big industrial control transformer. The 600 volt transformer made about 750 VDC once rectified and filtered. This time it was a guitar amp, the biggest tube based guitar amp I had tried up to this point. I had checked all the details, powered things up with a variac, and was somewhere north of 600 volts of B+ with over 150 watts flowing out when my 50 watt load resistor (a missed detail) blew leaving the amp without a load. The OPT instantly tried to eat all that power, but couldn't digest it all, turning some into FIRE!!!!! The resulting fireball was extinguished when the 20 amp circuit breaker that fed the whole room tripped.

That OH SH!T moment prompted me to get a fire extinguisher, add a 15 amp breaker and a kill switch to the workbench power feed, and buy a pair of 8 ohm 500 watt resistors.

Uber crazy experiments also prompt a 1/4 inch thick sheet of polycarbonate plastic between me and the amp under test......

Uber crazy experiment? Take one transmitting tube removed from a 500 watt AM radio station (glowing!), with vice grips and hose clamps for a socket, add a 1500 volt 1/2 amp power supply from a Motorola VHF base station fire department transmitter (standing on end, 70 pound power transformer behind the yellow meter), wire these up to one channel of a HiFi amp that I had built, drive it with the output of an ADA MP-1 tube guitar preamp, connect the output of this mess up to a DIY cabinet containing a pair of Electro Voice guitar speakers, and set the MP-1 on program 10, a patch that I just called "JIMI." Result, lots of loud coming from a single ended triode amp that made over 200 watts! This one didn't blow up and sounded good too.

There are some pictures with the "blast shield" removed for clarity. I'm nowhere near this thing with a guitar for those pictures. The 500 watt resistor is in front of the OPT next to the grey meter. There is a 16 uF 7500 volt capacitor behind the tube. Power (1500 volts) flows to the cap through a Radio Shack clip lead (yellow). Don't try this at home!

I saved all the big parts so I could build one of these amps, but do I need a 200 watt Champ? Maybe someday.......
Attached Images
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File Type: jpg 833AFreqRespTest2.jpg (532.6 KB, 67 views)
File Type: jpg StratFeedback1.jpg (744.8 KB, 67 views)
File Type: jpg 200Wattsa-2.jpg (137.8 KB, 63 views)
File Type: jpg RedGlow.jpg (989.5 KB, 61 views)
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Old 22nd February 2018, 09:08 AM   #63
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by Tubelab_com View Post
That OH SH!T moment prompted me to get a fire extinguisher, add a 15 amp breaker and a kill switch to the workbench power feed, and buy a pair of 8 ohm 500 watt resistors.
Man, I wish you'd write a book.
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Old 22nd February 2018, 09:18 PM   #64
Tubelab_com is offline Tubelab_com  United States
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I could never write a book. I have fought ADD, ADHD, or whatever they call it now, for my whole life. My attention span is too short to READ a book, let alone write one. Reading short magazine articles and writing forum posts are about my limit.

I think there have been two or three books that I have read from cover to cover in my lifetime. They were written such that you could read a bit at a time over a month or so.

Your books and Morgan Jones are like that. I have never "read" them, but I have learned from them.
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Old 23rd February 2018, 01:58 AM   #65
PRR is offline PRR  United States
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> I could never write a book.

I believe you have.

You have 9,000+ posts here. Many of them run 400+ words (may be your attention-span). That's 3 million words. A book can be 100,000 words. D.Self's Audio Power Amplifier Design 6th seems to run 450K words. Even editing out (there's people do that for you) redundancies you have six or a dozen books here.
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Old 17th April 2018, 11:59 AM   #66
thoglette is offline thoglette  Australia
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Originally Posted by PRR View Post
Even editing out (there's people do that for you) redundancies
Yup. You just need to find someone you can work with to collate the words; sketch out the topics you want and put all the words together. A co-author really.

Then you could do with a good and brutal editor/publisher to push you both on "why are you asking me to publish this?"

Two different skills but not in short supply.
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