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Vintage threads from the first ten years

Power Tubes for Ampeg V4B

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12/1/1999 6:02 AM
Dwight	Power Tubes for Ampeg V4B Does anyone know if there is a viable substitution for a 7027A in this amp?

12/1/1999 7:45 AM
Psycho Bass Guy	6550's will work, as will any GOOD 6l6. For more info, see http://www.triodeel.com/7027.htm Psycho Bass Guy (the real Psycho) >^}

12/1/1999 10:30 AM

Dwight
If I remember correctly, the 7027a tube is an industrial version 6l6. the article at triode electronics talks all the specifics. I recently retubed a v4b with svetlana 6l6's. I had to add an adjustable bias trim pot to get the proper idle current. I did this by replacing the 75k resistor in the bias supply with the 100k pot. this gave me -70 volts and the proper idle current. you can find a schematic for the v4b at,
http://www.servtech.com/~piazza/joepage/

12/1/1999 3:50 PM

Dwight,

Angela still had 7027s last time I looked. More expensive than the imports but considering the really long service life of these tubes as compared with current production a good buy if not a bargain. They also had 7581s which seemed to be essentially identical to the 7027 in latter production runs (check basing) and a bit cheaper. Why take a vintage amp that requires good tubes and retube with short lived current production? You probably pay the same dollars over the next ten years either way and you gain reliability.

GW

12/1/1999 4:19 PM
Bruce	I've used Svetlana 6L6Gcs and 7581As with a slight bias mod. Make sure the unused tube lugs are not used for something else as a tie point in the amp.

12/1/1999 11:03 PM
Doc	Luckily, these amps were already set up with tube sockets wired to accept standard 7AC based tubes, like the 6L6GC.

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