Tiny takt Three-Tube:
Cute Little 1960s TEISCO-Made Class-A Lunchbox Amp

(click on pics to zoom)

Many moons ago, my brother found this neat-o baby amp at a church bazaar; he paid a buck and charged me two. It looked almost perfect but was completely missing the power tube and the corresponding socket was badly burned and ruined. A bummer and blessing both, since I'll bet that's the reason this amp was in such nice shape; it was probably put away and untouched for 30 years or more.

There was nothing online then regarding Takt amps, other than a few other posts asking if anybody had heard of them. There still isn't much now, so I hereby present mine for posterity.

Given the simplicity of the circuit, I was quickly able to reverse-engineer it. Because it was a 7-pin socket, I had assumed it used a 6AQ5, which is a very common audio output pentode often found in small radios, TVs, and hi-fis. It is essentially equivalent to a 6V6, but in the "modern" miniature 7-pin glass base format. In a single-ended class-a circuit, it is good for about 3W output. However, with hindsight, I'll bet the original tube was actually a 6AR5, which was nearly identical in specs and often used in Japanese gear of the era, but is a much rarer tube today. Since I have a bin of good 6AQ5s and no spare 6AR5s, the original sub remains.

The other two tubes are both 6AV6, which is a 7-pin miniature containing a triode and two diodes, originally designed for use in small AM radios as the audio detector, AVC, and output driver stages. In this amp the diode sections are not used so functionally the two tubes are similar to a single 12AX7-style dual-triode.

Replacing the power tube socket was actually fairly challenging since it seemed as if everything in the whole amp connected to it. The replacement socket isn't the identical wafer style, but is also old (and of higher quality).

I have seen older relatives of this amp that use a rectifier tube, but this one uses two early silicon diodes instead.

My major clue that this is a TEISCO product is the power transformer, which looks identical to other TEISCO units I have experienced. I have never removed the outside cover bell because it is very awkward to access one of the the screw heads but I'll bet it even says TEISCO on the insulation opposite the terminals.

(It is fortunate that it even has a power transformer, for safety's sake. Some similar el-cheapo small amps, like many "All American 5"-class table radios, run directly off the power line, with one side of the line connected to the metal chassis - and by extension the guitar player - via a failure-prone "death cap". Such designs were barely acceptable in radios where at least the user was largely insulated from the chassis by wood and plastic, but this is simply a recipe for disaster in a guitar amp. Un-polarized power cords didn't help matters...)

The output transformer also looks very familiar.

The other side of the chassis is far more spacious.

Other than the repair, the amp is 100% unmodified and with the exception of the tube socket, it is 100% original. I was amazed when I tested all of the electrolytic and paper-in-oil capacitors and none were electrically leaky or otherwise defective. It has a little bit of 120Hz hum that is a natural result of the design, but that's it.

BTW, check out (bottom-right) the exposed-contact fuse holder on the outside of the chassis!

Despite the almost mythical status the paper-in-oil caps have among magical-thinking audiophiles and their guitar-playing brethren, I have found them to be incredibly unreliable when operated anywhere near their full rated voltages and they are almost always electrically leaky and need replacement. I figure these ones survived so well because the amp is only running about 250V B+ and the caps are rated for 400V. Even the funky dog bone resistors, which are not the most stable, were within 20% of their labeled values and not making frying noises.

This looks like it may be a sketch of the power supply part of the circuit, perhaps by someone attempting to repair it long ago, but I can't quite parse it.

Here you can see the 5" AlNiCo-magnet speaker's cone date code and model.

The two inputs are the same and it doesn't get a lot simpler than this. It gets a very raunchy, mid-rangey crunch tone at 1/2 volume with the tone wide-open and starts to sing at 3/4. As you would expect, it is not ear-splitting and would be good for recording, but it's still too loud for communal living situations. It doesn't sound half bad fed by effects at apartment practice volume, though, and it's hard to beat the cute factor.

I'll be posting a scan of my crudely drawn reverse-engineered schematic as soon as I find it... If anyone has the "official" circuit diagram, or even knows the story behind the Takt name or a TEISCO model number, please let me know.