• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Questions about this line stage

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E

eapavant

Member
Joined 2005
So I am ready to try my first tube project. I found this schematic on the web. I have a few questions. Keep in mind that I have very limited knowledge of tubes, I have been reading some but it is not sinking in very fast. The 6h30 is a dual triode? Here each half is forming a differential pair? Or am I way off? Suggestion for a ps for the B+? I am going to change the front end a little but I don't think that will matter much here. Thanks for any and all help
schematic

One other question, I have not been able to find out what this is. I got it from a site in China.
 
L

lndm

Member
Joined 2006
The 6H30 is a dual triode. This appears to be a balanced stage. The 6H30's appear to be connected as buffers (with no gain), separately buffering each phase of the balanced signal.

Guessing based on the fets, it may be a mic pre. Are you still looking at designs?
 
E

eapavant

Member
Joined 2005
Well I could build something else. I chose this based on the fact that I have most of the parts and because it is balanced. Balanced tube preamps seem to be in short supply and I don't know enough to desing one myself. I also have been building some simple preamps with jfets. So this seemed to fit in with what I have been working around.
 
G

gingertube

Member
Joined 2004
The J-Fets are running as a diff pair with a J-Fet Current Source in the tail for good balance . The 6H30 are running as cathode follower buffers to give low output impedance. I doubt that it will impart much "tube-e-ness" to the sound but why not give it a go and see for yourself.
If you are doing this as an "experiment" and a "learning experience" rather than as a final "work of art product" then allow plenty of chassis space and a big enough power supply that you can expand your experiment to something like this if you want.
http://www.vacuumstate.com/schematics/rtp3c_s.gif
The link is to a full balanced phono stage plus line stage
Cheers,
Ian

P.S.
For learning:
Morgan Jones "Valve Amplifiers"
Allan Wright "Tube Preamp Cookbook" (the link shows one of the designs from that cookbook)
 
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