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A friend of mine built this. I dont know very much about it except it has 3x 3-500z and does around 4kw. Enjoy tell me what you think. and it also has an SSB biasing circuit in it. he doesnt run it on am because he believes in being polite to his tubes. oh yeah They arent Actual eimacs their like knock off 500z's but they work good. he told me a story about him driving down the road. when all of a sudden his buddy calls him on the cell and says "dude your antenna is on fire." He ran a Leesville alt with it too. hasnt powered it up in about 10 years. no use for it and no vehicle to put it in. i keep trying to convince him. and YES it is in a old heathkit box but there isnt anything from the heathkit in there he rebuilt the entire thing.

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sweet,, cooling fan,

It's backwards from everything else. That's not a fan it's a BLOWER
and is configured to suck instead of blow.Much less efficient this way. Quieter maybe but less efficient and if he is claiming 4 Kw from 3x 3-500Z's he needs all the cooling he can get in that small box especially on the filament pins and glass-metal tube seals.

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Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

I don't think I have ever seen anyone use heat sink material for plate caps.

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BC

That tank coil is WAAAAY too close to the metal panel. Tank coils should be at least their diameter away from any metal shielding panels or chassis.The circuit Q would be all shot to hell and the risk of an arc at that power level is scary.

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Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

I know that you always sort of have to 'allow' for some slight swelling when a story like this gets passed around, and I try to do that. Keeping that in mind, here are some observations that I think I can substantiate about your friend's story.

The cabinetry Is based on HeathKit's stuff. If it isn't 'refurbished' HeathKit, it's a direct copy of it. The face may have been home made, but that's about it. (Forgot to get rid of some of the original paint, too.)
That particular cabinet would barely be adequate for two tubes with the chimneys and blower, never enough for three tubes of that size. That says nothing about the power supply being in the same cabinet. The required power supply to furnish the voltage and current for 4 Kw output from those three tubes wouldn't fit in there if you removed the tubes! (Even assuming that's 4 Kw Pep on SSB, just ain't gonna happen. And that's being very generous.)
Probably more important is that thing is an accident looking for a place to happen. It is not safe in any stretch of the imagination. Just too many things being asked to do things they were never meant to do.
I'm sorry, but that thing was never designed to work in a mobile unless that was a truck that carried an AC power generator for commercial supply, and emergency generator, and a sort of large one too. When your friend got that cell call about the burning antenna, he was VERY lucky it was the whole vehicle!
I really do like a good 'story'! But to be even half way believable it has to have some possibility of happening. You might suggest your friend work on it a little bit more, the story I mean. Forget the amplifier, it isn't worth working on.
- 'Doc

Right. The truly efficient way is to run two fans. One that is a blower and another one that draws. A 'push-pull system' for moving air will always be more efficient. Just so long as they are quiet in operation - then it is really done correctly...

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A local old timer built an amp that did like 5kw, it had two 4-1000's in it I think. It was as big as a dishwasher. I think the story about your friends mobile antenna being on fire was just that, a cute story. I'm not buying it, sounds impressive though.

SB-220 with the supply removed and another tOOB jammed in.

It's kinda cute.

I can tell it was not run for too long because there is zero cooling on the filament pins and there is no solder running down.

The cooling and tank coil need to be fixed for this amp to work for any length of time. Looks like the tank coil has a lot of inductance for the job at hand. Since it's crammed right up to the chassis the inductance will diminish. It needs to be in the clear as QRN said.

Not enough air on the front tOOb either.

The toroidal transformers are a great space saving idea.

I can't see the UL sticker??

UL?? What's that stand for "Ultimate Linear"?

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Front/back ratio comes from the antenna. Forward gain comes from the wall socket.