Paleo-Electronics Blog

The Songbird is the next project for me, after / along with the Real McTube.

The major goal of this project is to get me a Champ/GA-5 (Pre-Crestline) style amp for far less than the 500 or so for an original. I don’t like any of the re-issues, both the Gibson and Fender re-issues sound very thin to me. Also, I don’t think they use a tube rectifier, but I could be wrong there.

These are real Class A Single Ended amplifiers.   Three tubes, one knob and just fantastic sounding.   Although they are very similar, I am going to build off the Gibson GA-5 schematic.  The basic reason is that I like the Crestline GA-5 I have so I trust the Gibson.   Not that the Fender would sound bad, they are far too similar for that.   Thus the name “Songbird”.  I will be basing this on the original Gibson Skylark.

The primary motivation is to get that sound into my arsenal.

So thats the key motivator, but secondary considerations abound.  This is a simple amp,  5Y3 rectifier, 12AX7 pre-amp and 6v6GT power amp.  Maybe 30 parts in all.   If this was just a straight copy of the old amps, I’d be done already.   I have some ideas that I’d really like to try.  Most of the things I want to do different were design decisions in the original.

I point out that the original GA-5 was the lowest priced amp in the Gibson line.   It’s purpose was to get an amp that could be played at home or in the dorm room into the hands of as many kids as possible.  When you are building an amp the two basic ways to cut costs are to put fewer parts into it and pay less for the parts.   Gibson and Fender both did as much of the first as possible and then started trading off quality parts to keep the costs down.   Nothing wrong with that, but I am trying to capture the sound, not save money.   I am going to use high quality parts (although I won’t be buying 80 dollar capacitors, no matter how freaking good they are).

I want to improve the circuit that Gibson made by doing the things I think they would have done if cost were not an object (as can be seen in the more expensive amps).  I have a few ideas of my own too.   Some new options, and every damn thing I can think of to keep it noise free.

Power 

This amp was only designed to push about 5 watts.   You can still piss off your housemates with a 5 watt amp, but the neighbors might just resent you rather than develop outright hatred.  This became the genius of the amp when that overdriven sound got popular and people started realizing that big amps do not work well in the studio.

I want to keep the max power the same, but I am considering a Triode/Pentode switch.  In theory this would allow me to push the thing into overdrive at even lower volumes.   Probably with some changes to the tone, but who knows it might sound better.

Also, I am strongly considering separating the PT and rectifier circuit completely from the rest of the chassis.   Essentially, I would have two chassis’ :  one for audio and one for power.   I expect to run the power and heater lines to the bottom of the chassis and punch them in exactly where they are needed.

Heaters

I am almost certainly going to rectify / condition the heater voltages.   This will not be tube rectification, of course.

There is way more..  stay tuned.