[dreier3]

MAZ schrieb .. "Ich würde die Heizung an einer Seite auf ca. 85V über einen Spannungsteiler von der Anodenspannung legen."

so...bischen was gegoogelt:

quelle: http://www.valvewizard.co.uk/heater.html

"The other common method is to take the DC reference from a potential divider from the HT (useful if the amp has fixed biased power valves). Typical voltage references are around 20V to 90V, placing the heater supply well above the potential of most cathodes in the amp.
The potential divider should have a fairly high resistance so there is no significant current drawn from the HT (it can also serve as the bleeder path for the HT smoothing capacitors).
The lower resistor in the divider (R2) should not be excessively high or the maximum heater-to-cathode resistance may be exceeded. Many data sheets do not quote this so it is advisable not to make it greater than 100k. A fairly large value capacitor (C1) can also be added to ensure a smooth DC reference and to prevent the 50Hz heater hum reaching the HT supply. It's actual value is not critical, anything over 10uF should be fine."