• 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.

help on amp gain structure


Sin Bin
2004-10-06 12:20 pm
Anyone have link to learning how calculate the gain structure / input V ?

I'm building 10y or 26>10y>300b
10y amplification is 8 ,400v 25ma on IT to eml300bxls amplification is 3.9 ,the 26 is 8.3

now 8x8x3.9 near 250 how many V in the input ?

thanks Manu
my jfet phono is 9vrms but the new tubes 1,5v ....speakers 93db

It is easiest to calculate backwards.
The typical 300B needs around 55 VRMS at the grid for full power, maybe the super 300B type a bit more.
Your 10 driver tube with 1:1 interstage transformer will have a gain equal to mu, so that is 8.
55 divided by 8, OK we need another 7 VRMS when we look or an input sensitivity of 1 VRMS.
That will be nicely supplied by your 26 or 10Y first tube.
When your jet phono delivers a good 9 VRMS try also to skip the first tube (when a tube is not really necessary skip it, the less active stages the better).
Amplifier gain structure has nothing to do with speakers.
(working on your transormers).
7 VRMS related to 1,5 VRMS is a little over 13 dB.
I don't like the idea of using tvc's with step up ratios; for gain with a transformer you are very dependent on source and load impedances. My inductive volume control has no step up. They simply work best as step down (auto)transformers.
For necessary voltage amplification it is best to use active devices.