This Week on the Breadboard: the Subdecay Variac - highly modified
- Thread starter Chuck D. Bones
- Start date
Chuck D. Bones
Circuit Wizard
If we're interested in the DC bias, then it's R3. If we're interested in the gain, then it's everything between the source terminal and ground.
Back when I was in college, I walked out onto the quad and saw five PhD candidates standing on each others' shoulders next to a flagpole with a long tape measure. I asked them what they were doing and the guy on the bottom told me "We're measuring this flagpole."
Then I asked, "Wouldn't it be easier to lay the flagpole down down on the ground and measure it that way?"
The guy on the top shouted down "that would work if we wanted to know the length, but we want to know the height."
Back when I was in college, I walked out onto the quad and saw five PhD candidates standing on each others' shoulders next to a flagpole with a long tape measure. I asked them what they were doing and the guy on the bottom told me "We're measuring this flagpole."
Then I asked, "Wouldn't it be easier to lay the flagpole down down on the ground and measure it that way?"
The guy on the top shouted down "that would work if we wanted to know the length, but we want to know the height."
Chuck D. Bones
Circuit Wizard
Your drain and source voltage measurements don't add up. You're using 9V for power, right?
fig
Village Idiot
On this build, yes sir. Hang on... I think one rail lost continuity. I added another wafer so I could include the Volume pot.
I'm not certain how many people as ignorant as I come through here asking you questions they should go read about for themselves, but I am not going to take advantage of your patience nor good nature. I will return when it is working. Thanks so much!
I'm not certain how many people as ignorant as I come through here asking you questions they should go read about for themselves, but I am not going to take advantage of your patience nor good nature. I will return when it is working. Thanks so much!
Chuck D. Bones
Circuit Wizard
's all good, Man.
Chuck D. Bones
Circuit Wizard
I just rechecked my Maniac breadboard. Using a 2N5457 with Vp = -0.86V, Vcc = 8.99V, R3 = 22K and R5 = 100K, Vd = 7.51V, which is way too high. When I reduced R3 to 6K, Vd was 4.9V. Since R3 is in parallel with R13 from an AC perspective, lowering R3 that much increases the low freq gain to the point that we might as well delete R13 & C9. Which is exactly what Temol did and why he did it.
fig
Village Idiot
It's working....power to the people (and components). The configuration above biased fine Vcc = 9.03V 2N5457s R4 = 220KΩ / R8 = 56KΩ. Q1 Vp = 4.485V, Q2 Vp = 4.190V.
I've got a new scope I'm itching to try out (don't tell FF). This and the auto-bias circuit should be good break-ins.
I've got a new scope I'm itching to try out (don't tell FF). This and the auto-bias circuit should be good break-ins.
Chuck D. Bones
Circuit Wizard
Have you unpacked that scope yet?
fig
Village Idiot
Nope.
I was putting together that new micro-protoboard. I need to send @temol one for pincushioning on the go. It's pocket-sized.
Edit: I actually bought two scopes by accident. I had them both in the cart to compare. One is 2 channel, the other 4. The 4-channel offers a digital channel as well, so I'm likely to keep that one (which was my original intention). I've been playing with these fruit computers and shield boards a bit.
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Chuck D. Bones
Circuit Wizard
Well... before you unpack those scopes, we should talk. Standby for an invitation to a conversation.
