hunter 2000b question

[kb3ouk]

that's the only thing i hate about oil filled dummy loads, heat them up too much and bad things happen. usually for me it's nothing more than boiling some oil out the vent holes in the lid.

[w1vtp]

well, friday night i figured out what was causing the problem. i wasn't looking in the right place. i noticed the power output was being screwy, and all over the place. that's when i noticed the smoke coming out of my wattmeter. evidently, the directional coupler in that thing, even though it was good up to 200 watts, couldn't take 200 watts of carrier for more than 3 minutes. took the meter out of line, everything was good. last night keyed it up and left it sit for about 5 minutes, the output was steady.

Escaping smoke will do it every time.  Did you capture the smoke so you could stuff it back into the components it came out of?  That can be as tricky as soldering surface mount components with a 150 watt iron 

Seriously, testing equipment failure can really confuse the heck out of any troubleshooting effort

Al

[w1vtp]

Just watched your vid on utube

Noticed some downward deflection of the plate current.  I'm guessing it's the ALC in ur 901 kicking in on peaks.

Also, what was that gawd-awful noise on your RX during standby?  Is  your line noise that bad?  If so, time to go out with a sledge and hammering some utility poles while listening to the noise to see if you can find the right source of the noise

GL es 73, Al

[w1vtp]

Here ya go

http://www.k7jrl.com/pub/manuals/hunter/2000b/2000b.pdf

Al

[kb3ouk]

yea, that's normal noise here. wouldn't help to go around checking different poles, every one of them around here is probably at least 30 to 40 years old. and the wattmeter in the video is the one that i burned up. what got real interesting was letting the amp keyed for a few minutes and watching the needle dance around from the toroids inside absorbing power. that's what i found was wrong with it, the coupling toroids were kept from touching each other by globbing hot glue around them, and i vaporized the hot glue, causing the smoke. scorched the enamel off the wires around the toroids, too.

[kb3ouk]

would anyone happen to know what the input impedance for this amp is, or how to figure it out? i'm wanting to build a small exciter to drive it, would prefer a no-tune broadband solid state design, that is capable of 15 to 25 watts. reason i don't want to have to tune it is because it is a pain to run my ft-901 into it becuase when i change bands i have to tune the 901 into the dummy load, then tune the amp. after i tune the amp, i have to go back and RETUNE the 901 because the amp doesn't have a tuned input, so the 901 isn't seeing a 50 ohm load like it was into the dummy load and won't put out the full amount of power that it's capable of putting out with 100 ma on the finals like the manual states, so i have to retune it so that it is putting out the full amount of power. Then i have to switch over to the antenna, possibly tune the antenna tuner, then retune the amp into the antenna, then finally retune the 901 for a THIRD time. if i use my 718, then the only things i have to tune are the amp and sometimes the antenna tuner. but the problem with the icom is it doesn't like the high SWR it's seeing at the input to the amp, so it only wants to put about 10 watts into the amp, which isn't quite enough to drive it to full power. it needs about 15 to 20 to drive it to 180 watts out.

Note: the manual says it was designed for exciters with a 50 to 70 ohm output, so maybe something is out of value from being old?

[KX5JT]

Input impedance should be 50 ohms. 

Shelby, be careful.  You made this statement :

"but my little MFJ tuner that i just put after the amp handles 150-200 watts of carrier easily"

I started running AM much like you, with an amplifier.  My tuner at the time was an MFJ-962C.  It was rated for 1500 watts PEP. (fine print in the manual revealed that was 1500 watts PEP DC INPUT and for SSB , not heavy duty-cycle modes).

Anyway, I ran 100 watts carrier from my DX-60 into the SB-200 into it thinking I should be fine, no problem.  It was APPARENTLY OKAY for the first year, then the roller inductor started arcing right were the roller made contact on 3.885 AM.  This was a slow and insidiuous process of heating up and running RF through that tuner and it took a year. 

Your 200 watt carrier should give you 600 watts PEP assuming 100% modulation.  You're already twice passed the STATED rated power handling for the tuner and I promise you that MFJ OVERSTATES their specs. 

The point of my post?  Use that "little MFJ tuner" if you want too but be looking for something bigger because it will fail at some point if you keep pumping 200 watts of carrier into it.  I believe you already have some experience with AM carrier ratings vs. PEP ratings.