Building a tube amp has been a dream of mine for a couple of years. Earlier this year, I was finally able to start my build which is now complete.
I was on a tight budget, and my main goal was to learn about tube/valve amp construction through this build, and not necessarily build the best possible amplifier. Thus I decided on the AX84 guitar amp circuit found online, more details are available here: http://ax84.rru.com/
Basically, it consists of two preamp stages using one 12AX7/ECC83 and a single-ended output stage using EL84. These being common valves made by BEL is another reason that I decided to go with this circuit. It is based on the vintage tube guitar amps of the '50 and '60s by Fender, Marshall, etc...
Here is the schematic:
![AX84 Circuit.jpg AX84 Circuit.jpg](https://www.hifivision.com/data/attachments/57/57887-a86dbd1649a1d6303e7496e523ad3c10.jpg)
And here are some of my notes on the various stages:
![283957630_386004446630826_4899227365092082727_n.jpg 283957630_386004446630826_4899227365092082727_n.jpg](https://www.hifivision.com/data/attachments/57/57889-ceb994ccca43bdb71f8a7c58e8f2ffdd.jpg)
![284032861_553052806346457_8986553316059213666_n.jpg 284032861_553052806346457_8986553316059213666_n.jpg](https://www.hifivision.com/data/attachments/57/57890-303f6441738585bf28004ecfd19e276f.jpg)
![284424745_733895357656641_288141563803276515_n.jpg 284424745_733895357656641_288141563803276515_n.jpg](https://www.hifivision.com/data/attachments/57/57891-0c11f88f2aad69ce571636e2efbc7d43.jpg)
![285646728_1875113106213064_6279557844555676189_n.jpg 285646728_1875113106213064_6279557844555676189_n.jpg](https://www.hifivision.com/data/attachments/57/57892-1ac7d48c2eec3403246e1d4d445c2e3e.jpg)
Started the build by fabricating the chassis from 18 gauge sheet-metal. Riveted on the tag strips for point-to-point wiring:
![Terminal Strips.jpg Terminal Strips.jpg](https://www.hifivision.com/data/attachments/57/57893-7eec0c6839d1b21fbd938d97e78c797b.jpg)
Here is the completed wiring:
![Completed Wiring.jpg Completed Wiring.jpg](https://www.hifivision.com/data/attachments/57/57894-b869651f542b690201daf50fdfcac3d3.jpg)
And the finished amp: Power and output transformers were salvaged from a junk valve radio chassis.
![Completed Amp.jpg Completed Amp.jpg](https://www.hifivision.com/data/attachments/57/57895-46e74b8dd80a1d65e94bd88e66ab0f3e.jpg)
I tested each stage as I built the circuit. More more details on each part of the build, please refer to my 4-part vlog videos on YouTube:
Part 1, chassis fabrication and planning, power supply:
Part 2, filament wiring and power supply updates:
Part 3, wiring the amp stages and some problems with biasing:
Part 4, some tweaks, checking gain and power output, final test:
More pictures of the build and circuit details are available on my Instagram page: instagram.com/_electroidiot
I was on a tight budget, and my main goal was to learn about tube/valve amp construction through this build, and not necessarily build the best possible amplifier. Thus I decided on the AX84 guitar amp circuit found online, more details are available here: http://ax84.rru.com/
Basically, it consists of two preamp stages using one 12AX7/ECC83 and a single-ended output stage using EL84. These being common valves made by BEL is another reason that I decided to go with this circuit. It is based on the vintage tube guitar amps of the '50 and '60s by Fender, Marshall, etc...
Here is the schematic:
![AX84 Circuit.jpg AX84 Circuit.jpg](https://www.hifivision.com/data/attachments/57/57887-a86dbd1649a1d6303e7496e523ad3c10.jpg)
And here are some of my notes on the various stages:
![283957630_386004446630826_4899227365092082727_n.jpg 283957630_386004446630826_4899227365092082727_n.jpg](https://www.hifivision.com/data/attachments/57/57889-ceb994ccca43bdb71f8a7c58e8f2ffdd.jpg)
![284032861_553052806346457_8986553316059213666_n.jpg 284032861_553052806346457_8986553316059213666_n.jpg](https://www.hifivision.com/data/attachments/57/57890-303f6441738585bf28004ecfd19e276f.jpg)
![284424745_733895357656641_288141563803276515_n.jpg 284424745_733895357656641_288141563803276515_n.jpg](https://www.hifivision.com/data/attachments/57/57891-0c11f88f2aad69ce571636e2efbc7d43.jpg)
![285646728_1875113106213064_6279557844555676189_n.jpg 285646728_1875113106213064_6279557844555676189_n.jpg](https://www.hifivision.com/data/attachments/57/57892-1ac7d48c2eec3403246e1d4d445c2e3e.jpg)
Started the build by fabricating the chassis from 18 gauge sheet-metal. Riveted on the tag strips for point-to-point wiring:
![Terminal Strips.jpg Terminal Strips.jpg](https://www.hifivision.com/data/attachments/57/57893-7eec0c6839d1b21fbd938d97e78c797b.jpg)
Here is the completed wiring:
![Completed Wiring.jpg Completed Wiring.jpg](https://www.hifivision.com/data/attachments/57/57894-b869651f542b690201daf50fdfcac3d3.jpg)
And the finished amp: Power and output transformers were salvaged from a junk valve radio chassis.
![Completed Amp.jpg Completed Amp.jpg](https://www.hifivision.com/data/attachments/57/57895-46e74b8dd80a1d65e94bd88e66ab0f3e.jpg)
I tested each stage as I built the circuit. More more details on each part of the build, please refer to my 4-part vlog videos on YouTube:
Part 1, chassis fabrication and planning, power supply:
Part 2, filament wiring and power supply updates:
Part 3, wiring the amp stages and some problems with biasing:
Part 4, some tweaks, checking gain and power output, final test:
More pictures of the build and circuit details are available on my Instagram page: instagram.com/_electroidiot