My circuit board is pretty empty (very basic circuit) so I should be able to manage keeping the power resistors in an airy spot.
Looking at my schematic, I decided to replace the 680pF cap with a 1500pF, which has a 3dB roll-off for the input stage at about 430Hz. Will this still be too low? I do have a 4700pF capacitor, and a more typical 22nF coupling cap as well. I guess I'll do some testing when I get it up and running.
Looking at my schematic, I decided to replace the 680pF cap with a 1500pF, which has a 3dB roll-off for the input stage at about 430Hz. Will this still be too low? I do have a 4700pF capacitor, and a more typical 22nF coupling cap as well. I guess I'll do some testing when I get it up and running.
So the new PT i got... the heater supply does not have a center tap. Can I make one with two 100-ohm resistors and then elevate that to 100v DC to reduce hum and keep the heater-cathode voltage within spec for the 12AX7 cathode follower?
So I'm finally soldering it together! 🙂
The power supply section and hookups are 100% complete!
I had to put it on hold due to school (just finished my last class ever)
I have a quick question. I ALWAYS put pots in backwards. Could someone look at the schematic (post 1) and perhaps label the pots pins for me? 😕
That would be greatly appreciated.
I have 4 1-meg audio taper pots. gain, treb, bass, master.
The power supply section and hookups are 100% complete!
I had to put it on hold due to school (just finished my last class ever)
I have a quick question. I ALWAYS put pots in backwards. Could someone look at the schematic (post 1) and perhaps label the pots pins for me? 😕
That would be greatly appreciated.
I have 4 1-meg audio taper pots. gain, treb, bass, master.
If I'm not mistaken, all the pots as drawn in the schematic have the "cold" (counterclockwise) position at the bottom.
Double-check the little drawings in Adam's Amplifiers: Tone Stacks , your tone stack looks like a combination of the brownface and the F/M/V. That would make VR2 the treble and VR3 the bass control.
Kenneth
Double-check the little drawings in Adam's Amplifiers: Tone Stacks , your tone stack looks like a combination of the brownface and the F/M/V. That would make VR2 the treble and VR3 the bass control.
Kenneth
well, i finished building it tonight... doesn't work! No sound comes out, and I followed the signal path... Hmm... I'm not discouraged, it'll be a fun problem to fix I suppose!
The light turns on at least!
Anyone have any basic checks I should do before I start pulling it apart?
The light turns on at least!
Anyone have any basic checks I should do before I start pulling it apart?
Probably just a single connection forgotten.
If you're comfortable using a multimeter, check that all tubes get their plate and heater supplies.
Or use a small speaker from a toy radio, with a 100nF/600V cap in series, to trace the signal. That way you can hopefully isolate the error.
If you're comfortable using a multimeter, check that all tubes get their plate and heater supplies.
Or use a small speaker from a toy radio, with a 100nF/600V cap in series, to trace the signal. That way you can hopefully isolate the error.
when i use my multimeter in "open / short" mode and i connect it to the two heater wires coming from the transformer, it says short...
This makes sense to me because there are so few windings, does this make sense to you as well? I think my heater circuit works fine.
This makes sense to me because there are so few windings, does this make sense to you as well? I think my heater circuit works fine.
Sure it makes sense, but it can't hurt to check for correct voltages also. Just be careful, read the safety thread in this forum. Connect your test leads before powering on the amp. After measuring, turn off amp, wait 10 minutes, only then remove the test leads.
Kenneth
Kenneth
Also, the first thing you should do now is connect a bleeder resistor across one of the big power supply caps. A 220K or 470K, 2W resistor would do.
I actually have a bleeder circuit built into the amp already, it goes from the first power supply cab to ground (eventually). Its 3 33k resistors, with the last in parallel with a 1uF capacitor. I use this to elevate my heater supply to ~100 volts, and the nice side effect is that it bleeds the voltage when the amp is unplugged and the power and standbys are on.
I'll get some alligator clips and see what I can figure out tonight. I'll check the tube voltages and then follow the signal path.
I'll get some alligator clips and see what I can figure out tonight. I'll check the tube voltages and then follow the signal path.
For the potentiometers... If i did happen to put them in backwards, could that make it silent? I figure if they are in backwards and i put them all to a center position, it should make sound if everything else is hooked up right.
What im trying to say is that if they are in backwards, they wont prevent the amp from working completely, it'll just have a funny knobs that operate backwards.. right?
What im trying to say is that if they are in backwards, they wont prevent the amp from working completely, it'll just have a funny knobs that operate backwards.. right?
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