Building EL34 based 10W Single Ended Guitar Amp

moses781202

TDPRI Member
Joined
Mar 26, 2022
Posts
34
Location
Japan
Continuing This thread, I finally built and made it work.

Setup
PT: Used National ETP-96A3A (former Panasonic by Matsushita Electric Industrial)
OT: Hammond 125DSE
Rectifier Tube: NOS Toshiba 5Y3GT
Power Tube: NOS RCA EL34 or New Shuguang EL34B (fat bottle)
Preamp Tube: Shuguang 12AX7B
Choke: General Trans. (a Japanese tube amp transformer manufacturer)
Chassis: Okuzawa BS-250

Power Tube
I was plugging 6P3S (Russian's 6L6) but plate voltage was too high, it's around 420V, and it's blown up after testing for days. Was adjusting it to have Pd around 23W. The sounds it produced was very weird, maybe caused by improper voltage(?).
Fortunately I got a RCA 6CA7/EL34 from vintage tube store in Akihabara's Radio Department Store for less than 20USD. It's a true pentode, not early beam tetrode like Sylvania Big Bottle 6CA7. RCA's EL34 was very microphonic that the vibration of the old transformer makes it sing out the "criccky-criccky" noise. It solved after pressing the tube from top so that it won't vibrate due to loosen socket. I bought Shuguang's EL34B and tested it. The difference of freq. response and volume is quite noticeable.
- RCA EL34: Flat spectrum (as reference), clear mid, fine grained when overdriven, breakup earlier.
- Shuguang EL34B: Mid scooped, stronger bass, audibly louder in same setting, coarse grained when overdriven, more headroom.

Preamp Tube
It's a Chinese 12AX7B, taken from Vox amp, no comment...

Thoughts
It's my first tube power amp for guitar. From selecting topology to choosing components. From making hole on chassis to wiring. Biasing the tubes, troubleshooting hum noise...etc. I've done all of them. It was a great experience! Although my schedule was full during Japanese Golden Week (a one-week-vacation on early of May), I still could find a day for assembly. There are many old Japanese tubes and transformer available here. Some are noisy, some not, but all in good quality. Was planning to make a beam tetrode American sounded amp, but 6P3S was blown up and I ended up with RCA's EL34. Expecting roaring sound but it makes fine grained, sandy sound which is kind of pleasing sound to me. Switched to Shuguang's EL34B, which is a TRUE beam tetrode and the roaring sound didn't make me upset. Seeing the tube glowing blue and watching it every time before sleep. Although my life did not go as planned, but this little DIY project makes me happy. It works as designed, and it did not fail me, nor betray me. DIY project costs a lot compared to factory made products, but the fun, the happiness is priceless.


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Front face.

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My setup.

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The blue glowing RCA EL34.

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Inside the chassis.

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Bottom cover.

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Glow in the night.

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NOS Toshiba 5Y3GT. (通信用 means for tele-communication)

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Old National (Matsushita Electric Industrial) PT.
 
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