bearfootIII base tube amp ...transformerless!!!!read on(pic)

[Dave Berry]

Understood. I just figured an operators manual was sent out with the box originally from the manufacturer. Not asking anyone to draw anything up for me just trying to find original paperwork. Thanks for you post

 

[Dmans]

Dave Berry,
I would be REAL surprised if anything came with this amp when new. As was the case with many 11 Meter Linear Amplifier manufacturers (All lLLEGAL at the time) the less of a paper trail the better. Good luck and BE SAFE under the hood of this Widow Maker!
73's
David

 

[nomadradio]

I have had my eye out for any paperwork on this one for a long time.

There is a dodge that removes the shock hazard.

Mostly.

It's called an isolation transformer. The voltage ratio feeding in to feeding out is one-to-one.

Powering it from one of those will isolate it from the hot side of the wall socket, same as the built-in transformer does on most other sweep-tube amplifiers.

But the minimum rating for it should be around 800 Volt-Amps. Or Watts, whichever number they use for the specs.

Doesn't make the high voltages inside any less dangerous, but it removes the risk that the metal cabinet can become hot with dangerous voltage.

73

 

[kopcicle]

Last one that came through here got a junque boxen power supply (color TV trans and a doubler) , more conventional filaments (6.3 or 12 don't remember) and happily went down the road.
Widow maker indeed.

 

[Dave Berry]

Dave Berry,
I would be REAL surprised if anything came with this amp when new. As was the case with many 11 Meter Linear Amplifier manufacturers (All lLLEGAL at the time) the less of a paper trail the better. Good luck and BE SAFE under the hood of this Widow Maker!
73's
David

Thank you

 

[Shockwave]

Being that RF MOSFET technology has reached the point where these transistors can now be powered directly from rectified line voltage, how long before we see the transformerless solid state base amplifiers?

 

[oldtymer]

I had one of these many years ago when I lived in NJ.
Had 3 30kd6 tubes, 4 position rotary switch to select drive power.
Used it with a Uniden Grant, great ssb combo.

 

[Tallman]

Never heard of this one, but SBE made a no-transformer sweep-tube amplifier in the early sixties. Well, it had a small transformer for the tubes' heaters, but used a voltage tripler circuit, direct from the 120 Volt AC line cord. The negative side of the power supply was NOT grounded to the metal chassis. A bunch of disc capacitors would make the chassis an effective "RF" ground, since you are NOT permitted to hook either side fo the 120 Volt AC line circuit to anything on the outside of a cabinet. Table radios and televisions used this trick, with the antenna connections isolated with small capacitors and/or transformers to isolate the external connections from the "live", or "hot-chassis" ground circuits inside. Cabinets and knobs would be made of insulating plastic.

The filter capacitors have to be large to keep the DC voltage from dropping under load. Filters used with a transformer-type supply need not be so large.

Sounds like this guy hooked the four 31-Volt tube heaters in series, and runs them directly from the 120-Volt line.

Ken-Rich used the heaters-in-series trick to keep from having to use a heater transformer in some models. Worked okay with barefoot drive, but larger boxes would experience breakdown between the heater and the tube's cathode. But only in the final stage. Seems the cathode was insulated from the heater well enough for 120 Volts AC, but not for that PLUS the driver's RF voltage.

A barefoot-drive box probably won't have that bad habit.

Just make VERY, VERY sure you have a VERY good ground on this box, and a proper-size fuse in it. For my money, any "transformerless" design like this should have a fuse in BOTH hot and neutral sides of the AC line cord. The third-prong safety ground should NEVER have a a fuse in line with it. The risk is that if one of those disc capacitors should short inside, the full 120 line voltage could appear on the outside of the cabinet. Very dangerous, and creates a NASTY hazard. Making sure the case has a separate (solid) ground will at least cause the fuse to blow before it can create that kind of shock hazard.

Had to wonder, how much cheaper the enormous filter caps really are, in comparison to a transformer plus smaller filters? I suppose if you have the filters already, and don't have a transformer this would make it a lot cheaper.

73

It should be connected to a GFCI plug as well.

 

[Handy Andy]

Ranks right up there with the Black and Decker Drills - "Double Insulated"

 

[sherman north]

What would cause a Bearfoot lll not to get out to far, the 3 tubes light up ? I know nearly nothing about these amplifiers. Any help will be better than none. The cb gets out a few miles and that's it.

 

[sherman north]

Email me at uhsnoebird@gmail.com if you have any answers on the Bearfoot lll that I stated in my last post. Thank you

 

[Shadetree Mechanic]

Antenna problem?

 

[nomadradio]

I would start with a wattmeter in line with the amplifier. Can't tell much about one without a way to read the output power.

73

 

[W4KVW]

The meter on the box is set from an internal adjustment trimmer. It shows whatever that adjustment was set to show. It's commonly called a 'relative' meter. Means that a reading farther to the right is more power, to the left is less.

You really need a wattmeter in the coax line to tell what it's doing.

The internal meter is mostly decorative. Not a wattmeter.

Had one of these come in the shop a week ago. Told the customer I wouldn't work on it. Too much product liability.

He was amused that we call that one the "widowmaker".

73

A Relative Meter? Does it let you adjust it for just some relatives or does it detect all of them so we don't answer the door when the ones we don't want to see show up? LOL Those would sell better that friend chicken on a hot Saturday in summertime. hehe haha

SIX-SHOOTER

 

[sherman north]

I would start with a wattmeter in line with the amplifier. Can't tell much about one without a way to read the output power.

73

I'll be getting that short cable that I need too join the watt meter & the antenna tomorrow is what usps.com says online.
Will give you the results of the wattage soon.