On/Off switching for preamp tubes

[Kai]

Hi guys,

I just posted another thread concerning power tubes. In this thread I would like to raise a similar problem.

I built all LP preamps during the last years. I have a standard layout with one PSU-PRE and two LP preamp boards in one rack unit. For example there is my "British preamp" rack unit with M-PRE and V-PRE. With a simple SPDT I switch between outputs of M-PRE and V-PRE. The SPDT is connected to the main preamp output jack. 

Most of the time I only use either Marshall or Vox sounds while I'm playing. This means, one preamp board including heat dissipating preamp tubes is permanently turned on but not used.

Is there any mechanical switching that would turn off the B+ plate supply and the heater feed at a time between PSU-PRE and for ex. M-PRE respectively V-PRE? Maybe anything better?

Unfortunately, most DPDT switches can only handle DC voltage up to 250V. B+ plate supply usually is much higher. The heater feed can easily be broken. It is 12 V AC from the power supply.

Can anybody help me?

Best wishes 
Kai

Kai I'm not certain that what you want is necessary.  Running a pre-amp tube at idle will have negatable wear. I think that's less trouble  than  the expense and hassle designing and implementing a switching system to turn it off .  Pretty much any multi-channel or amp with effects amp has tubes that are not in use some of the time.  For example the tremolo is rarely used in many amps but no designers have found it important to turn the tube off when not in use.  I hope that helps!