On/Off cycling

[west_nm]

I try to respect the members of this forum by not asking too many stupid questions, so please bear with me.

Can lowering the incoming voltage via variac to an amplifier before shutting down help avoid any possible voltage spikes?
Someone suggested a thermistor, but that doesn't make sense to me for shut down. It does make sense for turn on AFAIK.


Steve

 

[DF96]

As you say, a thermistor may help limit current surges (not voltage surges) for switch-on.

For switch-off a suitable capacitor or snubber across the mains transformer primary will reduce clicks and lengthen the life of the switch.

A variac will not do anything useful. It could even shorten valve life by seriously under-running heaters.

 

[west_nm]

Thank you.

I only use the variac because I'm auditioning old gear that needs anywhere from 110-117 ACV.
I thought quickly turning down the power to about 80 volts followed by complete turn off might help.

When I settle on which gear to keep, I'll install a proper bucking transformer, thermistor and snubber if needed.


Steve

 

[DF96]

A variation from 110-117V should not do any harm. Typically, valves and valve-era components had 10-20% tolerance on parameters.

 

[cotdt]

You can use a computer system to raise B+ more slowly and automatically adjust the bias point. The computer can be used to keep a log to track the health of your tubes.

 

[west_nm]

A variation from 110-117V should not do any harm. Typically, valves and valve-era components had 10-20% tolerance on parameters.

These are stock units from the 50's and 60's.
I really shouldn't be running them until out of spec components are replaced, but I need to verify their present operating condition.


Steve