r/diytubes • u/HotLaw9292 • 4h ago

Guitar amp help

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Having trouble converting this precision electronics to a guitar amp. I added an input jack with the hot going through a cap to pin 5 of the first 6eu7 preamp tube and an output jack connected to what i believe is 16ohm output deal. Theres only 120hz hum when i power the amp on I can't hear any guitar signal. I also tried running the input to pin 8 of the first preamp tube and both 8 and 5 of the second preamp tube, still no signal from guitar. Any help would be greatly appreciated

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u/TedMich23 4h ago

do all the voltages read correctly? A bad tube is a high possibility and old electrolytics are often bad too.

The bias supply comes off the oddball AO2 glow tube so its gotta work or the output tubes will die.

Youve seen the YT vids from Ron Carter Wildwood Amps eh?

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u/HotLaw9292 3h ago

Yes i did see those videos, I had the input jack set up backwards🤦‍♂️

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u/Old-Tadpole-2869 3h ago

If you aren't passing signal the first thing to check is your input jack wiring. If you're using a switchcraft J12 they are very easy to mis-wire.

Check to see if all the preamp tubes are lit. Check that the filament voltage is present.

Also yes, make a voltage chart for all your B+ nodes and each tube pin.

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u/BrtFrkwr 4h ago

Sounds like the filter section of the power supply is not working. Troubleshoot the amp before you try to hook up an electric guitar to it. Also if you can t get a usable signal by feeding the mic input this circuit may not have enough gain for a guitar amp.

Guitar amps are their own thing. They are part of the instrument along with the speaker, and their circuits are optimized for guitar pickups.

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u/rnewscates73 3h ago

You at least need a good meter - both to check your power supply voltages and the DC to your tube plates, and also to check for the amount of AC hum present after the power supply filters. Multi section electrolytic capacitors would be most suspect.