Pre amp

[richt]

hi folks !!!!

i recently modified my preamp using 6922 tubes & cathode s tied
to ground (from factory)

originally the manufacturer was pushing 55 volts to the plate making the preamp to sounds like transistorizied (harshy).

i lowered it to 35 volts obtaining a better sounding but still frustrared with the hi hats (little harshy)

the i decided to lower the voltage to 25 volts !!! obtaining what i want,

there is a better way to calibrate with an miliampmeter ?
thanks
richt

 

[tsz]

There are obviously people with different philosophies; low bias and high bias.
I might try to increase the bias when I've built the case but for now I will run it with 4 mA bias(B+ 150 V).

>>dice45
Is a National Electronics tube a "Junk tube"?
I bought their cheap model ($14) since I didn't want to pay a fortune until I knew it worked. Anybody tried National Gold Line? Is it worth the money (here it's $55)?

>>John S.
I'm using CircuitMaker 2000, what additional features does TubeCAD provides?

 

[HarryHaller]

Cathode followers

Yep, I have owned tubes before..... The White cathode follower is also an interesting circuit. Current source bias is a good idea for any follower. Also using the plate supply for ground reference is a neat idea. Have used that aproach in AC coupled Fet follower circuits before.

http://www.glass-ware.com/tubecircuits/Easy_Cathode_Followers.html

http://www.tubecad.com/

H.H.

 

[dice45]

Originally posted by tsz

[>>dice45


Is a National Electronics tube a "Junk tube"?


I bought their cheap model ($14) since I didn't want to pay a fortune until I knew it worked. Anybody tried National Gold Line? Is it worth the money (here it's $55)?

Cannot tell; i do not know the brand. I know the NOS stuff from Valvo, Telefunken, Philips, Siemens works terribly well, TME General Electrics is reliable and well-sounding, and so is Sylvania.

Old RCA NOS is often tricky, µphonic but sounds terrific.



For checking if your circuit works any tube brand will do provided the particular sample you use is ok.

With tube brand changing, you get small sonic changes, with changing your circuit you big ones.
By using a NOS Telefunken, you never will manage to turn a crappy sounding circuit into a good sounding one.
My advice: get your circuit working 1st, then after all is ok, you still can start tweaking by changing tubes.

 

[John S.]

TubeCAD has several types of circuits in the program that can be tweaked and adjusted to your hearts content.You pick the circuit, the tube/tubes,voltages,current,etc and it will show results. It has all the building blocks to create either a front end for a power amp or a preamp.Very useful and easy to use. I have noticed that some of the plate curves don't quite match with what's in the tube manuals,but it's still worth the money.I just use the curves in the manuals,although they seem to vary a bit between manufacturers.