Subminiature tube/valve guitar amplifier

[Pedro Cardoso]

Hello,

After watching numerous videos on subminiature tube amplifiers(mostly from Thomas Hafemann), I have decided to build one.

Initially, I've watched videos from "Uncle Doug" who is an amazing Youtuber and teacher. He was the one who sparked my interest in valve amplifiers.
Thank you, Doug!

As a first project, I would like to start with lower voltages and small form factor amps. After looking on the web, I discovered the subminiature valves. :-)

This is what I have in mind. I am thinking of replicating either a Fender Champ or a Marshall JCM 800 amplifier (I came across schematics from Thomas on numerous amps including JCM 800s).

With zero experience in this subject, I thought of using the following components:

- 6N16B and 6N17B valves
- Monacor TR-1005 100V Line Transformer MONACOR: TR-1005
- 4'' woofer was taken from a Logitech pc sound system
- Laptop SMPS
- DC-DC boost converter for nixie tubes

I have several questions:
1 - Are the components above ok for these amps?
2 - The speaker that I have is rated 25W and 4 ohm. Will the tiny amp be able to deliver enough power to drive it? Usually, I see schematics with 8-ohm speakers, not 4-ohm ones.
3 - To have enough power to drive the speaker, would it suffice a two-stage pre-amp, or would I need more stages to increase the gain?

Thanks in advance.

Best regards,
Pedro

[Marcos - Munky]

1- yep. Well, can't say too much on the line transformer. But you indeed can use 6N17B's for the preamp and 6N16B for the power amp. Did two amps using them.
2- assuming your output transformer can drive an 4r speaker, then yes. You'll get a low power output, but it's enough to drive a 25W speaker. I test my amps using a 120W 4x12" cabinet.
3- a two stage preamp gives enough power for the power amp to drive the speaker. Maybe one stage can be enough. That assuming the power amp have enough juice for a reasonable output.

I'd just do this:
- take the power amp from Doug's Firefly, assuming your transformer can be used (the part after the 500K pot on this schematic https://firebottles.wordpress.com/guitar-amps/firefly-guitar-amp/)
- add the preamp you like in front of this power amp. And that's it.

Btw where are you from? Just out of curiosity.

[Pedro Cardoso]

Ola Marcos,
Eu sou português mas vivo em Inglaterra.
Muito obrigado pelas dicas. Eu acho que já vi o superfly, mas a sua ideia é muito boa.

Muito obrigado mesmo.
Pedro