updated March 18, 2015

L'il Maggie

This is the third of my small box amps. The circuit is a Magnatone M2 which is the smallest, least expensive amp of the Custom Series, AKA the suitcase amps. You can read more about the M2 and the complete line of Magnatone amps at Magnatoneamps.com.

Remember my little PeeWee Hammond AO-44 conversion? Well PeeWee became the donor for L'il Maggie. The power amp was almost identical to the Magnatone M2. I scrapped PeeWee and put the iron in a 12.5" x 6.5" x 2.5" chassis from Watts Audio.

The circuit is true to the M2 schematic with a few minor improvements. I added a 1MΩ resistor to the input jack. I also added 2.2uF cathode bypass caps to the first two preamp stages to improve bass response. I reduced the value of one resistor in the vibrato circuit to increase the vibrato strength slightly. I reduced the value of the node D dropping resistor to provide a higher B+. And I increased the value of the node D filter cap from 0.1uF to 40uF to prevent motorboating at higher volume levels. (The Magnatone engineers missed that one big time! I know it's an entry level amp but what were they even thinking?)

Oh yeah! I added a Modulation Selector switch to provide true FM Vibrato modulation or bias vary tremolo modulation. I borrowed this idea from the Magnatone model 421. It works very well with the 6GW8 output tubes.

The amp sounds like a typical entry level amp when paired with an 8" speaker. But it sounds more like a big amp with a proper speaker cab. The tone is clean and surprisingly loud for the little 6GW8s. I would have liked a little more control of the tone, maybe some mid scooped sound, but the simple one knob tone control is sufficient for a small amp. The FM Vibrato effect sounds good, but it is not as lush as the more expensive amps with two sets of varistors and a dual modulator. The tremolo sounds very smooth also, and unlike the AC-15, the tremolo and vibrato effects are equal in strength.

This amp would work in a small venue if using a decent speaker cab. I had fun with this project and consider it a success. Now I have three small box amps that cover four completely different sounds. I may just add one more to this series! Here are a few pics. Hope y'all enjoy... Steve

The turret board is more complicated than most small amps due to the high parts count. Notice three underboard jumpers.

The chassis is drilled and all parts dry fit. The board is undrilled at this time.

Dry fit again with turrets and jumpers installed on the board.

PT mains and filament string wiring is complete and first power-on tests are done at this time. Also installed two RG-316 shielded cables and ground busses. I used two busses on the control panel because I wanted to keep the vibrato oscillator on the power buss ground since it gets it's B+ from the same node as the output tube screens.

Wiring is complete except for OT secondary and one off board grid stopper resistor. I decided to try Hoffman's method of loading the board last. I agree that it makes wiring the board easier.

All done. OT secondary phased properly and permanently connected. The odd looking brown components in the center of the board are the varistors. (click pic for closeup view)

Slightly different angle showing control panel.

Front view

Top view

Rear view

Update 02/22/2016... L'il Maggie finally gets a cab.

Here's the documentation... Magnatone_M2.pdf (568KB)

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