AIR TIGHT ATM-4

Commentary

A bulb-type stereo power amplifier using a beam tube 6L6-WGC.

The 6L6-GC has a long history. It was introduced as a military metal tube from its predecessor, RCA in 1936. Since then, there have been many variations such as 6L6-G and 6L6-GB, and it has been changed to 6L6-GC. The ATM-4 was developed when a very high-quality 6L6-GC was available from Russia.

UL connection is adopted, and the unique sound of 6L6 is drawn out by lowering internal impedance and operating without lowering power.
To obtain even higher power, a stereo / monaural switch is installed so that it can be used as a monaural power amplifier.

Gain is obtained by using 12AT7 with low internal resistance for high mu and high Gm for the first stage.
The NFB is set to a little less than 10 dB, and by minimizing for low distortion by minimizing the phase correction.

We use hand wiring that does not use any boards, and we use different wiring materials at important points for careful wiring.

Equipped with balance check circuit.
The balance of the output tube push-pull operation can be adjusted to the optimum condition by the center meter located in the center of the panel and the adjustment volume in the ceiling panel.

Highly reliable parts such as metal film resistance, detent type volume, large winding volume, etc. are carefully selected for use.

It is designed with attention to details such as large and thick aluminum panel, solid wood carving knob, and chassis paint that has been repeatedly painted.

Model Rating

Type	Stereo power amplifier
Effective power	Stereo : 24W + 24W (8 Ω) Mono : 48W (8 Ω)
Total harmonic distortion factor	0.1% or Less (1 kHz, 1W) 1.0% or Less (1 kHz, 24W)
Frequency characteristic	20 Hz ~ 20 kHz ± 1 dB (24W)
Input sensitivity	0.8V
Input impedance	100k Ω
Signal-to-noise ratio	100 dB (IHF input short)
Load impedance	4 Ω, 8 Ω
Accessory function	Input 2-system selector switch Stereo / monaural changeover switch
Vacuum tube used	6L6GC : 4 6FQ7 : 2 12AT7 : 1
Power consumption	Approx. 300W (Electrical Appliance and Material Control Law)
External dimensions	Width 380x Height 205x Depth 340 mm
Weight	Approx. 23 kg