| Author |
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Thunderbolt
| | Posted on Wednesday, August 22, 2001 - 6:31 pm: | 
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I just got an old tube amp in great shape. was told it was a Johnson but there is no label.It is a 1 kw.It has 4 8908 tubes driving 6 8908 tubes.The driver side has 2 knobs the say (plate) and (coupling).the final side has 2 knobs that say(antenna) and (plate).what do these do and how do I use them? It transmits fine they way they are set but dont know what they do.Also there is a knob inside the amp floor on the driver tube side.What does that do? this has SSB and AM,HI and LOW switches.No preamp.2 meters,one for each side |
307 (307)
| | Posted on Wednesday, August 22, 2001 - 7:11 pm: |
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Hi Thunderbolt. There are several ways to tune the amp , however do not mess with the one inside the amp. Chances are it is the bias adjustment and if you mess with it the tubes will "cherry up" and you are out a bunch of money. The best way to tune it is to key up and with an "Auuuuuuudio" going into the microphone , adjust the plate and coupling for max power output then quickly peak the antenna and plate for max power. Don't get into a habit of always tuning. The rule is to tune it up as fast as possible |
Thunderbolt
| | Posted on Wednesday, August 22, 2001 - 8:57 pm: |
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Thanks 307.I will do that .I guess after that I will keep it at that adjustment all the time right? with the same radio.I am running an RCI 2950dx into it dial all the way back.How many watts do you think I should dead key into it? I am swinging about 20 on AM and about 27 on SSB.The amp did pop the fuse when I turned the RCI up.Also it has been in storage for about 15 years so is there anything to worry about? |
Hook
| | Posted on Wednesday, August 22, 2001 - 10:21 pm: |
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I learned another way a couple weeks ago that works great for me and is alot faster....turn mic gain all the way down and tune with just a carier. Once peaked,turn down the output about 20%. If you want.. make some small marks with a pencil and tune the other way...will most likely be right where you had it. Tunes faster for me because I'm not fighting against myself.There is no way you can AUUUUUDIOOOO consistantly,your voice will vary from begining to end so your tuning will be off.I had trouble getting tuned before, now it only takes a few seconds AND you are not AUUUUDIOOO'ing across the world  |
Anonymous
| | Posted on Saturday, August 25, 2001 - 12:43 pm: |
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another thing to remember...don't fall into the "tune every day" trap. I've seen folks who retune the amp EVERY time they turn it on. This is destructive. After using an amp for a while, you should be able to remember where it runs for any given bandspread. You shouldn't have to move it more than a fraction of a turn on the TUNE when going from one end of the band to the other. The LOAD control should be your main tuning control for power adjust. I ran a Varmint XL-150 daily for years over about 1.5 megacycles and re-tuned it maybe once a month. In 5 years I replaced the output tube once. |
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