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OVERCOUPELING ?'S

Stellasstillarat

Stellasstillarat

Active Member
Aug 14, 2014
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I normally don't operate on am and only re tune my Palomar 300a about once a week. The operating manual says once the amps tuned for max it's ready to go on ssb and that's exactly how I run it. I do notice after tunning the 300a for max it definitely needs to be over coupled for am use (turning the load knob 1/4" clock wise as per manual installation) other wise the audio reports on am will be "scratchy". As I mentioned I don't operate on am often but emedietly after tunning for max i heard a 1sd227 from Italy. I wanted to make the am contact so turned the load knob a cunt hair clock wise and made the contact. I forgot to return the load knob to it's original position as to achieve max output before switching to ssb.when I switched to ssb i noticed a bit more than 125 watts higher output on ssb with the amp over coupled. Now I know 125/150 watts isn't gonna make a huge difference if any at all on the other end but may help when skip conditions are poor. Can running the amp like this on ssb have a bad affect on my components (tubes) by not having the amp tuned as per manual operating specs (max smoke) for ssb?. I would think it wouldn't mater but I'm not tecnicly knowing that's why I'm asking. Thanks
 

When you tune the amp you tune it for frequency, not mode. Leaving it overcoupled for SSB won't hurt it in any way.

When I tune my Phantom I overcouple it and just leave it there regardless of mode.
 
Excellent. I thought that may be the case but didn't want to chance damaging the amp in any way. I just recapped it cleaned the contacts and lubricated everything. It shocks me how robust these
40+ year old old amps perform. I also own the phantom (10 tube) and it also performs excellent. I'm short on real estate and the 300a 's separate power supply makes it perfect for my limited station space as I leave the p/s on the floor. Many people rag on all the "11 meter sweep tube amps" but, imo there excellent for what thay are. I get great signal and audio reports wheather I'm using the phantom, maco 300 or the 300a in combination with my madison and silver eagle. My madison retains it's audio limiter and i always drive the amps with 11/2- 2 watts. Thanks for responding and happy Dx'ing.
Atlasta said:
When you tune the amp you tune it for frequency, not mode. Leaving it overcoupled for SSB won't hurt it in any way.

When I tune my Phantom I overcouple it and just leave it there regardless of mode.
Click to expand...
 
The extra 125 watts will not be noticed even when band conditions are poor. It simply is not enough difference to matter. Overcoupling the amp increases stability somewhat and tends to increase the linearity of the signal.
 
The only harm you are doing that amp is retuning it every week. Tune it up and leave the knobs alone. If you change frequency a lot some multi colored post it notes can be cut down to make small markers that won't damage the finish on the front of the amp. All you need is a strip of the sticky part that's just big enough to see.

Nothing wrong with sweep tubes if they will produce the power you need without using a bucket full of them. They get bashed on the internet for all the wrong reasons.
 
M0GVZ said:
Tube amps shouldn't need retuning for the 11m band at all. Go to the middle of the band, tune it up, leave it alone.

I don't understand the term overcoupling.

For those who've forgotten how to tune a tube amp, Cpt. Kilowatts excellent guide is here:
http://www.worldwidedx.com/threads/how-to-tune-a-tube-amp.26225/
Click to expand...

Overcoupling is a term used to describe advancing the load control slightly after the amp has been tuned and loaded properly. Advancing the load control until the power output drops slightly will generally increase the linearity by making the amp more stabil. In some cases it can raise the efficiency a tiny amount. We used to do it with an old Harris FM5H FM transmitter that had a 4CX250B driving a 4CX5000A to avoid self oscillation between the driver and PA.
 
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What's funny about over coupling or tuning up in general is listening to other operators explain the tune up procedure. They say things like "start at 12 o'clock" then turn clockwise or counterclockwise to other guys with different amps. Turning the load clockwise on one amp may further mesh the air variable and do the opposite on another. Some stuff I've saw the air variable turns a full 360 and the knob is held in place with a set screw. Who knows what position the bread slicer is at 12 o'clock and what tuning it to the left or right is doing.

Since you have an amp with an owners manual I'd say you're safe to follow the directions. Just don't use the specs out of a Ford manual to help someone with a Volvo. :D
 
I had the amplifier recapped, contacts cleaned,fan greased and anything else that can be done to a 40 year old amplifier. the tune and load knob used to be very stiff and wouldn't move unless you applied quite a bit of pressure to turn them. since I had it restored the tune and load knob very easily turn. It actually tunes up a lot easier then befoer the restoration. unfortunately I occasionally notice the amplifier isnt tuned correctly. I believe this is because the knobs are so smooth and easily move compared to the very tight feeling they used to have. that's why I usually have to retuning approximately once a week. I have noticed pictures of many amplifiers with those paper markings at the proper load and tune setting. I will take your adviceand put those slices of paper at the proper tune and load... points. Thanks to all the info.
543_Dallas said:
The only harm you are doing that amp is retuning it every week. Tune it up and leave the knobs alone. If you change frequency a lot some multi colored post it notes can be cut down to make small markers that won't damage the finish on the front of the amp. All you need is a strip of the sticky part that's just big enough to see.

Nothing wrong with sweep tubes if they will produce the power you need without using a bucket full of them. They get bashed on the internet for all the wrong reasons.
Click to expand...
 
Stellasstillarat said:
.... I have noticed pictures of many amplifiers with those paper markings at the proper load and tune setting. I will take your adviceand put those slices of paper at the proper tune and load... points. Thanks to all the info.
Click to expand...

some people even color code them for each band,.......... YMMV

Ameritron_AL-811X_400x300.JPG
 
[QUOTDainBramage, post: 518609, member: 42889"]some people even color code them for each band,.......... YMMV

Ameritron_AL-811X_400x300.JPG
[/QUOTE]Only
one color needed here. That may eventually change but no ticket limits me to 11 meters. I've seen mamy amps on eeBay with those and other marking mmaterial. I've even seen anps with magic marker to locate proper tunning points for different bands. Probably not a good idea to permanently mark up the face of ones amp. It definitely makes more sense marking when you have several bands to operate on. Thanks for the picture.
 
Stellasstillarat said:
I had the amplifier recapped, contacts cleaned,fan greased and anything else that can be done to a 40 year old amplifier. the tune and load knob used to be very stiff and wouldn't move unless you applied quite a bit of pressure to turn them. since I had it restored the tune and load knob very easily turn. It actually tunes up a lot easier then befoer the restoration. unfortunately I occasionally notice the amplifier isnt tuned correctly. I believe this is because the knobs are so smooth and easily move compared to the very tight feeling they used to have. that's why I usually have to retuning approximately once a week. I have noticed pictures of many amplifiers with those paper markings at the proper load and tune setting. I will take your adviceand put those slices of paper at the proper tune and load... points. Thanks to all the info.
Click to expand...


Most tuning capacitors have a screw on the end of the shaft that controls how hard or easy the shaft turns. If it turns too easy you can turn the screw to tighten it a bit and make it a little bit stiffer to keep it from turning by itself from the weight being off center or from vibrations.
 

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