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Discussion in 'Amplifiers' started by 190, Mar 12, 2009.
whoops I must have blacked out you said it has a coil etc, seems like an input tune to me.
Tuning input cap
The tiny little "slot" in the back of most tube amps (& old tube radios) is your input tune capaciter.
Use it for tuning (highest output - swing) everytime you change something in the "circiut" ie: radio, mini-Scout, papa Scout, wattmeter, low pass filter, antenna.
Change, add, remove any of these & you will need to re-tune the back of each piece of equipment that has one of those capaciters. That includes coax jumpers.
Tune your driver w/ amp in stby, & then tune the amp. Use a watch/type screwdriver for the cap, & be really carefull. The thing you are turning is just a slot cut into the end of a machine screw, & it WILL break if you crank on it!!
As you "un-screw" (counter-clockwise) the post, it compresses the mica wafers that make up the cap, so start the whole process w/ the cap backed all the way out (turn counter-clockwise till tight - won't turn), & usually, as you turn "in", it will have a "sweet spot". Don't mess w/the nut as that is how you mount the cap to the equipment.
Dead-key your mic, & turn the cap clockwise until highest output (w/o modulation-I turn my mic gain down). Turn mic gain back up, re-key & tune the front like you normally would do, & then adjust the cap in the back for highest swing. It should be within a 1/4 to 1/2 turn of where you started, if not the same. (sweet spot)
Don't know if you have a dummy load, as that really helps in the tuning process. Mine has a wattmeter & is oil-filled made by B&W. Normal price on feebay is around $125 - $200 max, & every bit as good as a Bird meter. Best $$$ I've EVER SPENT!!!
Hope this helps.... Let me know if you need more info, or if I didn't make sense.
PM me if you get into a jam (or jelly )
Just my 2 cents.....
On the Scout 20 set the Hi/Lo switch to Hi and then max the two tuning knobs for a peak dead key without any audio. This will pretune the amp. Once you have this done key the amp and say AHHHHHHH while moving the tuning controls slightly to acheive the highest peak reading. Only one of the controls will make a difference in the peak power, the other one will change the key slightly. Once you have the peak reading continue to move the control (that makes the peak higher) clockwise until you see a drop in wattage of about 30 watts or so. You then can tune the input tuner on the back of the amp for max peak from there. The amp then is tuned and will require no further adjustment. If it is in good shape it should run cool and have great audio.
Also you do not want to drive the Scout 20 with the Mini. The driver tubes in the Scout can't take that much wattage for a long period of time. With the price of tubes now it is not something to do. Both are good amps and are reliable. I have owned both and still have several Mini Scouts. They are keepers.