I was fooling around in TubeCAD and was wondering about the following linestage. It has nice bandwidth and a comfortable gain of just under 3. What do you think?
An externally hosted image should be here but it was not working when we last tested it.
>curseword<load of feedback
that reminds me on AR line of preamps........ tons of feedback without actual need ;hehe-they sound exactly the same- sound without actual cause
12AT7 have mi in range of 70 ,academically speaking.....and wasting that to 10 db is blasphemy; at least for me.
Ra for first stage is too small
same for second stage
(this is explanation of Sy's post)
that reminds me on AR line of preamps........ tons of feedback without actual need ;hehe-they sound exactly the same- sound without actual cause
12AT7 have mi in range of 70 ,academically speaking.....and wasting that to 10 db is blasphemy; at least for me.
Ra for first stage is too small
same for second stage
(this is explanation of Sy's post)
Rule of thumb: when you decide what gain you want from the line stage, look for a tube with a mu 1.5-2 times higher.
One of the primary reasons to use a cathode bypass cap
is to keep the gain high if you arn`t after a lot of gain leave
the cap out. Eleminating this cap gives you a little local feed
backand removes the distortion from a cap. You also want your plate resistor to be a lot larger than your plate resistance. I seem to rember a good line stage using this tube (30 years ago so I might be wrong) using 47k for the plate resistor and about 20k for the cathode follower.
is to keep the gain high if you arn`t after a lot of gain leave
the cap out. Eleminating this cap gives you a little local feed
backand removes the distortion from a cap. You also want your plate resistor to be a lot larger than your plate resistance. I seem to rember a good line stage using this tube (30 years ago so I might be wrong) using 47k for the plate resistor and about 20k for the cathode follower.
well, here's another crack at a linestage, using the lower-gain 12BH7 tube. I've heard it's more linear than the 12AU7, which was my natural next recourse. I had the plate curves in front of me when fiddling with bias and stuff so hopefully this one turned out better.
An externally hosted image should be here but it was not working when we last tested it.
hmm. is it clipping? is there some kind of book or something that I should read in order to understand wth I'm doing? I'd kind of like to be able to make sensical designs but I'm just shooting into the dark at the moment...
I think the fundamental problem is that you've fallen in love with a topology (and not a good topology). That's bad because it prevents you from picking the pieces apart. Don't fall in love with topologies!😀
The phase is wrong (you want feedback to the grid, not the cathode), you haven't really worked out the impedances at the cathode, and you've tried doing tricks where none are necessary. It's easy to make a voltage amplifier stage that's superbly linear at line levels without feedback. And it's easy to direct-couple it to a proper cathode follower capable of flawlessly driving a reasonable load.
As for a book, you DO have "Valve Amplifiers, 3rd Ed" by Morgan Jones? If not run right out, etc. etc.
The phase is wrong (you want feedback to the grid, not the cathode), you haven't really worked out the impedances at the cathode, and you've tried doing tricks where none are necessary. It's easy to make a voltage amplifier stage that's superbly linear at line levels without feedback. And it's easy to direct-couple it to a proper cathode follower capable of flawlessly driving a reasonable load.
As for a book, you DO have "Valve Amplifiers, 3rd Ed" by Morgan Jones? If not run right out, etc. etc.
lol, i had kind of developed an irrational attachment to that topology, but i have pretty much an open mind, as long as it's simple enough. i guess i should pick up that book 
If you can find an old copy the RCA Receiving Tube Manual
has a real good basic introduction to tubes. This is in addition
to it`s primary use as a source for tube data. I have seen these
sell on ebay for ~$9. If you are going to fool with tubes I would
start with this.
has a real good basic introduction to tubes. This is in addition
to it`s primary use as a source for tube data. I have seen these
sell on ebay for ~$9. If you are going to fool with tubes I would
start with this.
you can look for Giaime's posts around ,and - in his sig-you'll find urrl to download RDH4
good enough for start
good enough for start
I might try doing this for fun... I have a bunch of these tubes from ripping apart old oscilloscopes. Hehe.
i should remove the pic links to not tempt people 
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