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In Reply to: RE: now I am really puzzled ...... posted by vinnie2 on April 26, 2016 at 16:07:24
OK, you are making progress; well done.
Now you need to do what you should have done before you started your project: draw a full schematic (all you need is a pencil and a piece of paper). Drawing a schematic does several things for you. It gives you a reference to work from; it gives you a way to record voltages and changes; but most important it will be a learning aid giving you a visual means of understanding your circuit.
So, carefully draw out your circuit including every component, their value and their connections. Energize the circuit and record the voltages at each connection. Compare those voltages with the voltages you expect according to the calculations performed when designing the circuit. Use ohm's law to determine how the circuit is working by measuring voltages across resistors and computing the current.
Once you have drawn out the schematic and entered the voltages you will have a visual aid to help you understand how the circuit works and you will have a precise means of discussing your project with others.
Follow Ups:
Well I sort of did some of that a while back in the "hot time in the old town post" with this schem. Thought I needed a new thread, but maybe not a good idea. Anyway, I have not done all you suggested yet though as I have not filled in the voltages. I did not calculate the voltages when designing it as I used Drummer Willy's schem for his 26/26/45 amp and just modified it slightly here and there.
Ignore the operating point notes at the bottom of the page as they are not all correct. Still separate filament trannies for each tube though.
Is it best for me to fill in the voltages and post them in this thread, or should I start a new thread to give us a clean sheet of paper to work on?
Edits: 04/27/16 04/27/16 04/27/16
This schematic is inoperable!
1.)
If the second #26 grid voltage is 110V and cathode voltage is about 5V on 820R (target anode current is 6mA), the grid-catode voltage is +105V!!
The second #26 tube will destroy (grid-cathode diode will conduct several mA current).
2.)
The #45 cathode voltage is 1200R*0.034A=40.8V
If anode voltage is 223V and cathode about 41V, anode-cathode voltage is 182V.
Datasheet: 182V, 34mA -> grid-cathode voltage about -33V.
So grid will be at -8V potential.
IMHO the original schematic was AC coupled, capacitors between stages.
Grid to ground resistor shows this.
Impossible to build from well fuctioning AC coupled amplifier DC coupled ones without complete redesign.
There are coupling caps between the stages that aren't drawn in the schematic.
I'm puzzled about how the components on the 45 cathode work. Shouldn't they be the same layout as the 26?
Good catch. Boy did I ever screw up that schem. It is the same setup as the 26's, just different values. see my last post at the top of the thread for what comes next.
You need to show a full schematic of the power supplies also.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Can do. Do you think I should start a new thread with the new schems? This one is getting kind of long and rambling.......
That's probably a good ides.
With a complete (make it as complete as you can) schematic the people helping you have something concrete to go by and you will be able to make more sense of their suggestions.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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