CW/SSB AMP TUNING ON AM RIG?

[Stellasstillarat]

Quriousity question. I know many cber's use amps like the heath kit 220 and the like on ssb. How does one tune these amps? I know if someone's using a modified ham/10 to 11 meter transceiver thay can easily tune it on cw as those radios may have cw but, how do thay tune them if there using a rig without cw ie cobra 2000, uniden Madison ect. ect? Also. Can these cw/ssb amps be moded for am use? Thanks

 

[binrat]

Low power when tuning and then let it rip.

 

[vkrules]

Seriously ?. Why do you think it needs modifying for am.No offence meant but I think you should stay away from these amps until you do some more reading.

 

[bob85]

tuning a tube amp on low power then letting it rip is a great way to damage your amplifier, tube optimum load impedance changes with drive level,

tuning at low drive then turning the drive up without retuning at the high power level will cause the load cap to be set too far meshed ( too much capacitance for the load ) which can cause arcing & high grid current, DON'T DO IT

whatever method you decide on ALWAYS do your final tune at the power level you will be running at or close to it.

 

[Crusher]

Hey Bob85, wait until they used that super hack packed modded export radio and then use a small class C amplifier to drive that amp tuned like that. Looks like an electrical storm inside tube amp as the tune and or load caps arc. I have even seen a vacuum variable tune capacitor light up like a light bulb. LOL. Almost looked like a strobe light.
Good to see you back on the forums.

 

[binrat]

Bob85, my comment was meant to be sarcasm. There is a lot more needed that what I stated.

 

[bob85]

That's very nice of you binrat ,

a guy comes here for advice and you tell him to do something that will very likely damage his amp,

plenty of folk do think that's a good way to tune a tube amp so you had me fooled too,


hey crusher,
its good to see you out here, keeping an eye on us small amp guys,
hope all is well there m8

 

[vkrules]

Perhaps the answer should be "put your hands in your pockets and move slowly away from the amp".
Back on topic No CW you use AM!!!! no mods needed..

 

[Crusher]

Generally tune up on low first, hit the tune and load caps few times each. Tune for maximum peak watts. Then put on hi side and retune the tune and load caps. You need to keeps these keys short while tuning. Tune up, let it sit for a few seconds then do it again. Reason I do it this way, while amp is mistuned higher grid currents and possible over dissipation. Once amp is tuned, I usually back down drive just a hair. Depending on amp and who's been in it. It may have a very high Q tank circuit. So once you move up or down say 6 channels you may have to retune amp. Usually just have to tweak the load cap a bit.

 

[Crusher]

And seriously, those "modified 10/11 meter rigs if they aren't kept near stock. You will run into problems. I have had 3 separate guys over here with either SB220's or Drake L4B's. Using a export or 959 radio that has been peaked and tweaked so much they transmit all over. No band pass filtering. Seen the tune and load caps arc like crazy. Melt fins. On a 4 tube 572b, the doorknob cap exploded. Point is use a clean radio. Or at least a low pass filter after radio to cut down the parasitics.

 

[Shockwave]

The CW-Tune / SSB switch on an SB-220 is very different than the Hi / Low switch you may see in an 11 meter amp. The junk designed for this band usually places enough resistance inline with the RF from the exciter that is causes a significant reduction in the drive and output power of the amp. The problem with that switch is it often wrecks the input impedance to the amp and always alters the output impedance that the amp needs to be loaded into as Bob describes.

Amateur equipment is designed a bit better than this and that includes the old SB-220. That switch which has been mistakenly called a Hi / Low switch is actually just reducing the plate voltage and dissipation on the tubes without altering drive level or circuit impedances. Since plate voltage is reduced, plate current is also reduced proportionally and that causes virtually no change in output impedance. That means your SB-220 can be safely tuned with the switch in the low plate voltage position and then switch to the higher SSB voltage without the need for much if any retuning.

There is still more to consider here. Since the bias in the SB-220 is fixed by a 5.1 volt Zener diode, a reduction in plate voltage also causes a proportional reduction in bias current which lowers the class of operation below AB1. That reduces plate dissipation and increases amplifier efficiency. What do you think happens to the plate dissipation of the tubes when you run AM with the SB-220 in the SSB mode?

Since the bias current is already high on the SSB position, when you combine that with the AM carrier you get some fairly large demands placed on the tube anodes and plate supply that is already a bit lacking on the SB-220. Good advice is to never run the carrier past about 300 watts regardless of where the mode switch is. Any more than that and you'll never have the headroom required to properly modulate the carrier.

Even better would be to have someone knowledgeable modify the bias circuit so that more negative bias were applied to keep the tube hovering around the low end of class B in the AM mode. Something around 12 volts rather than 5 would be appropriate. Never forget you are dealing with a piece of equipment that can easily electrocute you. The bleeder resistors in these amps are old enough now that they can fail at any time. I've seen more than one with all the bleeders removed after one failed. Very bad!

 

[Shockwave]

And seriously, those "modified 10/11 meter rigs if they aren't kept near stock. You will run into problems. I have had 3 separate guys over here with either SB220's or Drake L4B's. Using a export or 959 radio that has been peaked and tweaked so much they transmit all over. No band pass filtering. Seen the tune and load caps arc like crazy. Melt fins. On a 4 tube 572b, the doorknob cap exploded. Point is use a clean radio. Or at least a low pass filter after radio to cut down the parasitics.

Just as good is when someone puts a 2 pill transistor oscillator in front of an SB-220 to drive it. The old Palomar TX 100 was a favorite oscillator at one time. Guys would spend hours inside the SB-220 trying to figure out what kept letting the 47 ohm 2 watt smoke out of the parasitic suppressors, never once considering it might be that junk driver. Some figured out it would hold together using 4 watt metal film flame proof resistors never realizing they just succeeded in keeping the dirtiest signal on the air with 13db more "everywhere".

 

[Captain Kilowatt]

Quriousity question. I know many cber's use amps like the heath kit 220 and the like on ssb. How does one tune these amps? I know if someone's using a modified ham/10 to 11 meter transceiver thay can easily tune it on cw as those radios may have cw but, how do thay tune them if there using a rig without cw ie cobra 2000, uniden Madison ect. ect? Also. Can these cw/ssb amps be moded for am use? Thanks

Bottom line is a carrier is a carrier regardless of the method of modulation superimposed on that carrier. IOW without applied audio CW, AM, and even FM are all the same thing......dead carriers. Use whatever suits your fancy to drive the amp while tuning as all that is required is a constant level carrier. The actual ho-to of tuning the amp has been explained above.

 

[Stellasstillarat]

The question was purely curiosity driven. I have no interest in using/purchasing a ham amplifier to run in concert with my madison or Washington. Im exstramly happy with my 300a. I can't imagine anyone using a 2 kw ssb amp on 11 meters making any more contacts than me my Washington, 300a and my 99a 13 ft off the ground. One cq dx and a half dozen stations are calling back. Qso's all over Europe and east to west north to south and all points between. I know there are many power hungry chicken b anders using these types of amps with cb radios hence my "curiosity" questions. I personally think anything above 2- 300 watts is over kill. Thanks mr. Know it all.if you would've read my question correctly maybe you wouldn't have been so sarcastic but I've noticed your answers to questions asked by people who are ignorant on the communications area are often snotty. We all can't be Marconi's out of the womb like you. Thanks anyway.

Seriously ?. Why do you think it needs modifying for am.No offence meant but I think you should stay away from these amps until you do some more reading.

Seriously ?. Why do you think it needs modifying for am.No offence meant but I think you should stay away from these amps until you do some more reading.

 

[Captain Kilowatt]

Well I thought it was a perfectly legit response considering that AM,FM,CW etc are all carrier modes and everyone (should) know(s) that you tune an amp with a carrier.......any carrier since we are tuning for frequency and not mode.Since an SSB radio also has AM mode it has a carrier available to tune the amp with.

And speaking of snotty responses, I have noticed a lot of yours in the last several months have taken that tone if something does not agree with your ideas so maybe a lot of folks should take a deep breath and hold it for a minute before replying to something they don't like.