IGS Audio One La 500

http://www.igsaudio.pl/en/product/500-modules/89-one-la-500
The IGS ONE LA is an opto-compressor built for the 500 series format. This is the first high voltage vacuum tube 500 series module that is offered by IGS.  It is powered with 250V DC from an on-board voltage converter, so it can be plugged into any 500 series rack equipped with a standard power supply.  
Every single ONE LA is hand made with high quality, matched components (1% metal film resistors, Wima caps). It is equipped with RFT NOS tubes and individually calibrated to give you the unique and unspoiled experience of one of the best opto-compressors in the history - the Teletronix '68 LA-2A. We have spent hundreds of hours designing the ONE LA, to make sure that it is as simple to use as it is versatile. Not only for harmonically rich vocals and strings, but also for huge and beefy drums and bass instruments. Three audio transformers (Sowter and Edcor in audio path and OEP in sidechain) have been used to provide excellent performance and with only two knobs and a single compressor/limiter switch, there is nothing that could go wrong.
Front panel:
VU Meter
Limiter/Compressor mode
Gain - Output level 
Peak Reduction
In/Bypass
Specification:
- 500-series double module, mono unit,
-+4dB operating level,
- Original Teletronix '68 audio path,
- tubes powered by 250V DC,
- JJ 12AX7 input and RFT NOS 12AU7 output tubes,
- Sowter input transformer,
- Edcor output transformer,
- OEP sidechain transformer,
- T4B replaceable photocell (for special order),
- Power consumption: max 180mA per slot,
- Input impedance: 10k Ohm,
- Maximum output: +21dBU,
- Amplification: 36dB,
- Gain reduction: 36dB,
- Frequency response: 20Hz - 20kHz, +/-0.1 dB,
- Potentiometer manipulators,
- Hard wire bypass,
- Compressor/Limiter mode,
- Large VU meter,
- 3 year warranty,
- Shipping weight: 3kg.
More about T4X:
 http://igsaudio.pl/en/product/others/70-photocell-t4bx