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Old 4th February 2012, 10:29 PM   #1
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Join Date: Feb 2012
Smile HELP! new to working on tube amps and need help with project im going to take on

help! i just recently acquired an old tube amp with 1x 6bq5 power tube and 1x 6x4 rectifier and 1x 6av6 preamp tube. it is all hand wired and i dont know where to start! i plugged it in when i first brought it home and there was sound, but it was very quiet (my hollow body electric was a little louder) and i was wondering if anyone here could help me with this. thanks in advance

-Austin
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Old 4th February 2012, 11:01 PM   #2
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Join Date: May 2007
Greetings from FixitLand!

And welcome to the fun world of tube amplifiers!

What you have could be the beginning of a nice little amp for guitar, but as it is, it does not have enough amplification (that's why it was very quiet). The 6AV6 "preamp tube" is a voltage amplifier and the 6BQ5 power tube (class A single-ended) drives the speaker. Straightforward. But a guitar produces a very low-level signal (much like a microphone). Your amp was probably intended to work with a ceramic- or crystal-cartridge phono cartridge, or perhaps a tape player, all of which provide a higher-level signal. To make this rig a guitar amp, you'll need at least one more stage of amplification. The 6AV6 single-triode (plus two unused diodes) can be changed out for a 12AX7 twin triode which would give you that extra stage. That would require replacing the 7-pin 6AV6 socket with a 9-pin socket to accommodate the 12AX7. I would suggest looking for basic guitar-amplifier schematics (I'm a hi-fi guy, not a guitarist). You'll also need to gain some basic electronic skills such as reading schematics, soldering, learning about tubes, resistors, capacitors and other components, etc. Doesn't need a college degree, but you don't want to just go in and cut wires without knowing what you're doing.

Please keep us informed as you proceed with this project!

Take care,
--
J. E. Knox "The Victor Freak"
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Old 4th February 2012, 11:23 PM   #3
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Join Date: Feb 2012
Quote:
Originally Posted by rojoknox View Post
Greetings from FixitLand!

And welcome to the fun world of tube amplifiers!

What you have could be the beginning of a nice little amp for guitar, but as it is, it does not have enough amplification (that's why it was very quiet). The 6AV6 "preamp tube" is a voltage amplifier and the 6BQ5 power tube (class A single-ended) drives the speaker. Straightforward. But a guitar produces a very low-level signal (much like a microphone). Your amp was probably intended to work with a ceramic- or crystal-cartridge phono cartridge, or perhaps a tape player, all of which provide a higher-level signal. To make this rig a guitar amp, you'll need at least one more stage of amplification. The 6AV6 single-triode (plus two unused diodes) can be changed out for a 12AX7 twin triode which would give you that extra stage. That would require replacing the 7-pin 6AV6 socket with a 9-pin socket to accommodate the 12AX7. I would suggest looking for basic guitar-amplifier schematics (I'm a hi-fi guy, not a guitarist). You'll also need to gain some basic electronic skills such as reading schematics, soldering, learning about tubes, resistors, capacitors and other components, etc. Doesn't need a college degree, but you don't want to just go in and cut wires without knowing what you're doing.

Please keep us informed as you proceed with this project!

Take care,
--
J. E. Knox "The Victor Freak"


thanks for putting the time into helping me with this so i could hook my older transistor phonograph to this amplifier and get that classic warm tube tone? it has two prongs on top which i had soldered to a 1/4 inch jack, would i be able to unsolder the jack and hook up wire from those pegs to the two screws on the back of the phonograph and use the tube amp to amplify it? also i bought this amp to work on my electronics skills like soldering and recapping etc. etc.


-Austin
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