DIY vacuum tube guitar amp building
Weber amp kit 6A14HP
- Top
- Research
- Equipments
- Cabinet
- Chassis
- Faceplate
- Mods
- Reverb
- Ground scheme
- Assembling
- Bias adjustment
- Done!
- Whoops!
- Cooling fan
CAUTION The voltages in your amplifier can be dangerous. Please use common sense and always think safety first. The author of this website takes no responsibility for any harm that may come to anyone or anything.
Weber amp kit 6A14HP building
DIY vacuum tube guitar amp
Introduction
This is my very first DIY guitar amp building. I'd like to share my experience with anyone who find it helpful.
Research
As I said, It's my first try to build a tube guitar amplifier, I'd like to start something small but useful.Here’s a few from some companies sell small amp kits.
Probably the most well known amp kit seller.They are reasonable but it seems that quality of the components they use are not very good.
It looks their kit components are better than Weber ,such as Orange drop capasitors.Bit pricey though.
Afer long research,I dicided to go for Weber 6A14HP.It'a Fender Princeton Reverb clone with 6L6GC power tubes instead of 6V6. Slight more power 30~35W.
Before start working on your amp, I suggest to read through Weber Forum.There're tons of useful infomation. I added some mods to my amp which recomend on the forum.
Also, this website "Building an amp" made by a Coutry music player in the Netherlands is worth reading.He's made a 6A20.Equipments
First,I built equipments I need.
- Current limiter also known as Lightbulb limiter. It prevents damage from short circuits.
- Dummy load lets you run an amp without an actual speaker.I used 8Ω 50W resistor.
- Discharging resister, a 10kΩ25W resistor with clips on both end to discharge filter caps.
Cabinet
I also made the cabinet by myself. Plan is here. Dimentions are taken from Fender Princeton Reverb cabinet. It's bit small to fit a 12inch speaker.
When I checked layout, I discoverd the output transformer hit the speaker so I moved it off centre.
Chassis
The chassis is pretty good quality. It's about 3mm thick, hard to drill halls without a proper drill press.Because I live in Japan, I chose a W025130INT PT.This transformer has wires exiting from both sides.You need 025130su endbells to convert to a stand up type.I had to drill extra holes to mount it & for wires.
Reverb
6A14HP kit include a Belton BL3AB3C1B reverb tank. It's a longest decay model, almost too much.
This thread helps to solve the problem.
Also It's good to read this thread about reducing reverb noise.
Ground scheme
I used Bus bar method, witch placed behind pots and only one side is grounded to near the input, as far away from PT. All grounds from the eyelet board and pots go here.AC ground goes to one of the PT mounting bolt or a welded bolt.The CE capcan automaticaly grounded when It's mounted. I didn't solder it for future replace. Isolated RCA jacks and reverb grounded V1 socket bolt.
Done!
It's gooooood!
Few things I changed after playing for a while.Repalced first 12AX7 from Electro-Harmonix to Tung-sol after reading Anticue Electronic Supply comparison chart.
Replaced 12AT7 to 12AU7 to get better reverb control.
Replaced first cathode bypass capacitor from 25uF to 10uF to tighten up bass. I think Split-Load PI can't handle bass well.
Whoops!
Few days after it's completed,smoke came out. The pilot lamp holder just touched to the chassi and 6.3VAC line shorted.I burnt PT up.
We learn from mistakes,I isolated it with a bakelite board.
For the new PT, I decided to order Mercury Magnetics FDP-20/100-120. I asked Mr.Patrick at MM about datasheet, He sent it to me right away.I think they are very professional people.
It arrived 2weeks after I orderd.B+ was a bit lower than W025130INT.Plate voltage became 420V.The sound didn't change much but less hum noise.
No more trouble please!
Cooling fan
A small AC fan installed for cooling.Airflow direction is to get hot air out from the cabinet.It keeps the amp just warm,never gets too hot and makes lifetime of some components longer.
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