AirTight ATM-1 Schematic

[DK1327]

That is a 0.2 higher than rated. A 3% deviation from specs. Tube are made from a time where 10% tolerant is the norm, I don't get how it could negatively damage the amp in long term operation?

 

[genome]

Hi Francois,
I don't understand the reasons behind my instructions.

The "Copper tab" was a bare wire link between taps on the output transformer.
Perhaps centre tap...? Looking at photos on here, think its between terminals 3 and 4 on the left side of the left output x-former from beneath.

It looks ATM-1 uses TAMURA PP OPT. Does anyone know which TAMURA OPT model is used?

 

[igs]

Does anyone know what the source impedance of the output transformers is (Ra) and the % UL taps?

 

[genome]

No spec is available for the OPTs of ATM-1. Though it is interesting to dig out a couple fun facts of ATM-1:
1. Air Tight founder was a veteran of Luxman during the vacuum tube era. When Luxman turned its focus to transistors, the ATM founder decided to started ATM to continue his tube zeal.
2. ATM-1 old version (with 5AR4 tube rectifiers) uses TAMURA PWR and OPT.
3. ATM-1 new version (with diode rectifiers) uses Luxman PWR and OPT.

 

[igs]

UTM offers this kind of transformer.
https://utmindustry.com/utm7250/

 

[pred]

Does anyone have an idea who makes the yellow coupling capacitors marked .22K600V NCC?

 

[directdriver]

The easiest way to measure bias is still having four 10-ohm matching resistors, one for each cathode installed by the owner or a qualified technician. In each cathode, disconnect the jumper wire between pin-8 to pin-1 and add 10-ohm resistor. Make sure all ground connections go to pin-1. Pin-8 should not have other parts or wires connected to it other than one end of 10-ohm resistor. The resistors also act as fuses for protecting the output transformers. If you worry about resale value, just remove the 4 resistors and solder back the jumper wire before selling.