Hello,
There is no on / of Switch nor a Gainpoty but a Lamp at the Front. The Slider You mean is probably the Lever to lock the Unit into it s Dinrack. If You open the Lever You can move the Unit in or out , if it s closed the Unit is locked into the Rack.
There is a Poti You have access to at one side of the Unit where You can adjust Gain in a very small Range,just a few dB s for calibration. The Poti is in the Feedbackloop of the first Tubestage.
Inside You find a variable Capitor to adjust the high frequency Range and a Pot to adjust the Voltage of the Screen Grid of the Pentode for lowest Distortion , it s the Gainstage of the Amp. A Capitor is parallel to the Inductivity of the Inputtransformer and forms a 12 dB Highpassfilter at 40 Hz. The Outputtranny has multiple Windings . They can be wired seriell or parallel for a different Output Level (0,3 or 9 dB Gain or +6,+ 9 or + 15 dB Operation Level )
The Amp belongs to the v72a Family and was used as a no or low Gain Isolation and Splitter Amp. 5654 ( E 95F) as the Gainstage and E180F as the Cathodefollower Outputstage. Some Folks change the Voltagedivider in the Feedbackloop to generate more Gain ( less Feedback) but s it s for the Price of a higher Distortion. Some People change the Inputtranny (1:2 10k/ 40k Ohm) to a Micinputtranny 1:5 , 1:7 to use the Unit as a low Gain Micpre.
BtW. the Amp was build by TAB (Tonographie Apparatebau v. Willisen,) Wupperthal, Germany and not by Telefunken. Maybee some Units exist as a Telefunkenlabeld OEM, but I personaly didn t saw any.
Greatings
Lothar
