Hi guys! Had a slow night at work tonight, I've done some guitar effects pedals and different things and decided I wanted to build a simple stereo tube amplifier. So I broke out a schematic and I decided I'd check out Eagle CAD and see if I could make heads or tails of it. Below is the schematic I made in Eagle and then the PCB that I made from the schematic. Where the circuit connects to the transformer I simply turned all of those connections into pads so I could place the transformer wherever I wanted in the case and simply wire it to the board. My question is does the eagle schematic look like the schematic I'm working from? Also I can't figure out what they want me to put in for the Bias Trim? I couldn't find any trim pots that didn't require 3 contacts and the wiring shows it as just being in line with the other resistor. Thanks for your time!
Also note: The caps are not polar so I didn't pay attention to the way the schematic has the symbols flipped in eagle.
TUBEBUILD - Imgur
Also note: The caps are not polar so I didn't pay attention to the way the schematic has the symbols flipped in eagle.
TUBEBUILD - Imgur
The trim pot will be a three terminal device with the wiper wired to one of the other terminals to change it from a pot divider into a variable series resistor.
I think the two 6V6 tubes are going to be too close together. Most glass types bulge significantly and with the two sockets that close together they would probably touch or might not even fit. Either way, they will generate a lot of heat and need to be much more widely spaced to allow for proper ventilation.
Cheers
Ian
I think the two 6V6 tubes are going to be too close together. Most glass types bulge significantly and with the two sockets that close together they would probably touch or might not even fit. Either way, they will generate a lot of heat and need to be much more widely spaced to allow for proper ventilation.
Cheers
Ian
Are you sure that Bias TP is supposed to be interpreted as Bias Trim Pot? It looks to me to be more likely intended to mean 'Bias Test Point', particularly since there is a negative supply and there is a volume control depicted a three terminal device.
I concur with the advice that the two output tubes are too close together. Also need to keep electrolytic capacitors away from heat, ie not next to tubes or on other side of board,
I concur with the advice that the two output tubes are too close together. Also need to keep electrolytic capacitors away from heat, ie not next to tubes or on other side of board,
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Yes, I was right...
You need to look at the separate schematic for the power supply to see where the bias pots are:
6V6 Amp Power Supply Circuit; Parts Expo
You need to look at the separate schematic for the power supply to see where the bias pots are:
6V6 Amp Power Supply Circuit; Parts Expo
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Maybe have the output tubes in chasis-mounted sockets and take wires from the tube sockets to the pcb (heater wires twisted and taken directly to the heater transformer). With the power tubes mounted off the pcb you can keep the design you have. That way you get to keep a small pcb, the ability to position the tubes away from the electrolytics. Best of both worlds ?
I did this and got serious stability issues. Had to redo the whole thing. Maybe the wires were too long. Either way, it was a huge hassle to deal with and I would not recommend it.
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Oscillations - solution depends on the cause. I would be surprised if there was an issue if the wiring was done right but I'd be interested to learn more from your experience of this one - did you follow the usual "Grid stoppers have to be at the tube socket and wiring has to be done properly to keep the input away from the output" ?
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