>
>Rich said:
>
>"Any guesses at to what would happen if a 8660/4CX1500B were used in a DAF
>circuit. - with say 20mA of grid current instead of 0.06mA of grid current?"
>
>Rich:
>
>I have heard no one - except you - suggest using an 8660 in a DAF circuit.
>Your friend, Norm, used 4CX250 tubes in a mis-understood bastard adaptation
>of the original G2DAF circuit, which hung an electrolytic capacitor on the
>screen grid. It splattered badly.
Norm tried improving the original DAF circuit because it had a tad too
much splatter.
> It was not a G2DAF circuit. Yet, you
>use it as a basis to condemn any reasoning that is not consistent with the
>world as you view it.
I was there. I got splattered on by the wonderful orig. DAF. I got
splattered on by the modified DAF.
>
>Tubes do not have to be used as the tube manufacturer originally intended
>them to be used, and amateurs by their very nature are experimenters. I
>recently built an oscillator which used the screen as the plate. It works
>fine. Tubes were not intended to be used that way. It is called a Dynatron
>and was designed long before I was born (which is getting rare these days).
>Building any circuit - "good" or "bad" - is fine, so long as the builder
>makes sure he does not unreasonably splatter. Certain tube design
>parameters must be met for the long term health of the tube. Beyond that,
>the only other question is whether the output has undesireable
>characteristics such as splatter, harmonics or parasitics. And, it is up to
>the designer or builder to achieve those goals. It would be a boring world
>if all the amplifiers looked exactly the same and used exactly the same
>tube.
Running a tetrode to minimize splatter is a piece of cake. Select one
that can do AB1. (The 813 is not one of them). Use maximal regulated
screen potential and anode supply volts. Adjust the bias so that there
is no grid current with max. drive. Tweak the screen volts to set Zero
Signal Anode Current (ZSAC). Tune/load for the recommended screen
current. That's All, Folks.
>
>The other day, I raised the question of increasing the screen voltage on a
>grounded grid tetrode - from zero to something less than the "normal"
>voltage. Your response was "DAF circuits produce feculance".
Did I not also point out that the power out with your stated screen
potential was comparable to the power from the driver?.
>The
>"distortion" was in your response. I am sorry that Norm's splatter years
>ago affected your outlook on life so much.
The splatter from Norm's DAF amp was quite trival compared to W6CHR's.
The first time I heard CHR put his DAF on the air, I was talking with a
group at 3820KHz. We began hearing something that sounded sort of like
splatter. I tuned my aux. Receiver around to various signals while
listening for a match on 3820. I was surprised to find no matches within
25KHz . I had never heard such a thing before. Was I growing DAFt? The
splatter sounded more like it was coming from above than below, so I
tuned farther and farther up the band. I finally found the source on
3808. It was CHR He truly had a large signal. . Is this awesome or
what?
>
cheers, Colin
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|