Variac Variable Transformer

My personal preference is to bring the voltage up very slowly, over several days, or a week. Have seen guys in a hurry to hear their new (old) tube amps bring the voltage up to 120 and smoke the capacitors. IMO all of the internal components require small voltage increases to prevent malfunction.

If the amp uses a GZ34/5ar4 rectifier it will not do a slow start with a variac.

Think this may be true for other indirectly heated cathode rectifiers as well.

I substituted a directly heated 5Y3GT, for a GZ34, when slowly bringing up a Pilot 240 and it worked (someone @ AA made the suggestion).

A local tech used a DIY solid state plug-in GZ34 for the same reason when using a variac on my Pilot 232.

I agree with Commcat. I found rule of thumb on the internet to apply 5 min. plus 1 min for every month of storage. This would call for 41 min of reforming unit stored for three years. It seems too short and I would do this at least for many hours (if not days). Be patient.

Dekay - similar problem with SMPS power supplies. They will produce full output voltage (regulated) as soon as supply voltage crosses some threshold.

Hi guys. Thanks for this valuable information. I never thought my tube amp and preamp audio addiction would lead to these "other" issues. Oh well, It's still alot of fun even with this added to it. I found and bought a Variable Variac Transformer at Fry's Electronics of all places. It also has an analog meter. Will be using your suggestions. Thanks again...

What I do is start out at 10 volts (or 10 percent, depending on the scale of the variac) for about an hour and then increase by 10 volt increments for about a half hour at each increment. Takes a good six/seven hours.

I would clarify with QS about what they mean by "bring up the voltage slowly". What works for me doesn't mean it's correct for you.