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Just had to have one...Viking Thunderbolt
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by WA2MGB on October 22, 2002
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I recently made a purhcase of a "restored" Viking Thunderbolt... Always saw pictures of them... quite impressive for a 1957 amp. This one has all new electrolytics, caps, retubed...etc. It's in transit.
Question: Were they considered a "good amp" in their day? As it was built before I born... what sort of output should I expect from a pair of 4-400A tubes?
Nice looking, but did I just buy a 120 lb paperweight or nice, useable amp from the 50's?
Tnx
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RE: Just had to have one...Viking Thunderbolt
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by K0BG on October 22, 2002
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If everything is working up to snuff, 1,200 to 1,300 watts is about all you want to get from a pair of 4-400As. Personally, I won't drive it that hard. At 1,100 or so out, the amp will run nearly forever. Evidenced by the fact they are still around.
Alan, KØBG
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RE: Just had to have one...Viking Thunderbolt
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by WB2WIK on October 22, 2002
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Actually, the 4-400's in the T-bolt won't produce even that much power, ordinarily, because the plate voltage used was quite low.
I owned a T-bolt for several years. It's grid-driven, class AB1, with untuned input and only about 2200V on the plates. The amp was designed, built and marketed in a day when the amateur legal power limit was "1000W DC input power," so amplifiers didn't need to run more than 1 kW _input_, and typically produced about 600W output power.
If you modify the T-bolt, and this will take numerous changes, to place >3000V on the plates, it should run more than a kW output. But "stock," it will not.
The "stock" T-bolt used vapor rectifiers tubes and a choke in the power supply, and only a single, rather small filter capacitor mounted horizontally beneath the chassis, which wasn't a great idea because it was mounted close to many hot components -- and if I recall correctly, that capacitor was only rated 2000 or 2500VDC, a pretty low voltage for the application.
One neat thing about the T-bolt, other than the fact that it's so heavy it would be difficult for anyone to steal it, is that because it's grid-driven, it can be driven very easily, even by a 20W exciter, which is what it was designed to work with. But it does have a huge resistive padding network which can be switched into the grid circuit to allow for higher-powered exciters, up to about 100W PEP or so -- but be careful with the grid current.
73,
Steve, WB2WIK/6
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