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Buddy of mine pretty big amp

B

bigred222

Key Up City Radio
Aug 28, 2006
1,155
53
58
34
Stamford, CT
www.cbjunk.com
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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Not that it makes much difference at all, but 'Eimac' hasn't made any glass tubes in ten years. Eimac 3-500s have a date scratched on the 'plate' at the bottom of the tube elements. No scratched date, not an Eimac glass tube. Bunch of tubes with the 'Eimac' name on them around. Don't bet on them being made by Eimac.
- 'Doc
 
Shouldn't that amp top out at about 1.5kW ? Didn't think you could get close to 4kW out of those tubes.

Still a cool project. I'd like to try my hand at a mosfet based amp one of these days, but I still have a lot to learn.
 
QRN said:
4Kw is pushing things but a pair will do 2 Kw easily enough so I would expect to see three tubes doing 3 Kw without breaking much of a sweat.
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That's an interesting amp, however in my experience 3-500Z tubes are not a good choice for a mobile amp. I knew one fellow who ran them and saw 5 grand out of three and he sounded great but, everybody kept cutting his radio off locally and DX. On the shoot-out line, it was like he never even keyed.

This amp has a tri-filar filament choke, the black relay on the bottom seems to be the control relay, the big one on the other side is the antenna switch. Looks like some kind of bias circuit on the heat sink in the lower right hand corner. Not really sure what's going on with the paralled resistor bank.

The 3-Phase torroid power supply (orange donut and other black torroid) coulda /shoulda been a Peter Dahl 3-phase type. At the frequency that the alternator input runs, you barely need that much capacitance to filter the B+.

The tank coil is touching the side of the RF deck, that is not good. Maybe, somebody was trying to shield the meter by putting that plate in the slant, I would take that piece of metal out.

If this was to be a 4000 watt amp, I as the builder would have used larger flat copper strips to connect the tubes to the B+ supply and construct the parasitic supressors.

All in all, I'm sure that it's a good amp, too bad that it is just sitting around, someone should build a fixed-station supply for it. 15 volts at 15 amps for the filament and 3000 volts at 2.5 amps ccs is all you need.
 

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