"High Gain" DIY Tube Guitar Preamp Demo using 1Ж24Б (1J24B) Subminiature Rod Types



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Here is a demo of my DIY'ed tube guitar pre-amp using soviet subminiature rod-type radio tubes 1Ж24Б (1J24B). Those are made for battery operation and feature friendly filament current draw.

Anode voltage won't kill either as low power supplies are sufficient. The schematic is based on the Marshall jcm800, but I didn't achieve too similar sound or characteristics.

0:00 teaser
0:17 off, guitar noise reference
0:25 on, bubble, v2, gain 80, vol 70, bass 0, mid 100, treb 100, boost off
0:51 on, bubble, v2, gain 100
1:05 on, grzzle v2, vol 55
1:25 on, grzzle, v2cap, vol 47
1:59 on, bubble, v2cap, vol 55
2:24 on, bubble, gain 80, vol 40, effect of zero-boost, boost knob & v2cap with boost
2:48 on, bubble, gain80, vol 40, v2, boost 50
3:14 on, grzzle, gain 80, vol 40, v2, boost50
3:34 on, grzzle, gain 80, vol 40, v2cap, boost50
4:10 crank & demo boost knob
4:02 on, bubble, gain80, vol 40, v2cap, boost50

The controls:
- gain (tube drive)
- volume (tl072 output buffer drive)
- bass/mid/treb passive EQ - filament on/off Switch
- filament voltage/resistor switch ("grzzle" / "bubble")
- boost/bypass switch (TL072 inbuilt boost "pedal")
- boost pot (active only if switch is on)
- V2 / cap switch (V2 cathode bypass capacitor)

Trickiest things were the biasing of directly heated cathodes, and also 'triodization' of the pentode tubes. Triodization schemes were varied vastly from tube to tube to bring forth the best of each one's ability to live up to their job.
Filament resistor changer switch (warm up "bubble" vs. all out "grzzle") is my favorite and most intresting feature.
Total development time was about 1,5years.It's a fun Rock'n'Roll amp, to be evaluated as a metal pedal platform.
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Audio
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