Hi everyone, I just bought a variac and had guestion about its use. I have been reading some items on the internet that says using a variac on the AA-5 tube radios can be harmful on the tubes(rectifier tube in general) by bring the AC voltage up in steps. The heaters on the tubes can be damaged. Before I use this can any one out there tell me the correct procedure for bring up the power on a 5 tube radio?
I am very greatful for all your help!!! Have a great day.
Daniel

Before you even put any AC to the radio, inspect the circutry first. bad wires, open or cut connections, burnt parts, Ect. If the set has a dial lamp. Check the wires and lamp socket for shorts. An open heater tap on the rectifier tube too. You can use a variac after all that. Bring it up about 10 volts at a time. Monitor the B+ as you do.

I have never heard of a variac damaging tubes.

Typically, when I obtain a radio that has not obviously been electrically restored, I disconnect all critical capacitors and test them for leakage, and of course check for obvious electrical faults. Some simply replace all capacitors. Sometimes, if the radio is in good condition, I like to see if I can make use of the original capacitors, though I usually add a fuse of some sort to the power supply. A good one is a #44 or 47 bulb, depending on the current, in series with the B+. This will burn out easily if a short occurs.

Though it is nice to slowly power up a radio after all obvious faults have been removed, I do not believe that it is a good practice to power up a radio in which none of the capacitors have been tested, as sometimes a shorted capacitor can cause damage before it is obvious.

T.

:I have never heard of a variac damaging tubes.
:
:Typically, when I obtain a radio that has not obviously been electrically restored, I disconnect all critical capacitors and test them for leakage, and of course check for obvious electrical faults. Some simply replace all capacitors. Sometimes, if the radio is in good condition, I like to see if I can make use of the original capacitors, though I usually add a fuse of some sort to the power supply. A good one is a #44 or 47 bulb, depending on the current, in series with the B+. This will burn out easily if a short occurs.
:
:Though it is nice to slowly power up a radio after all obvious faults have been removed, I do not believe that it is a good practice to power up a radio in which none of the capacitors have been tested, as sometimes a shorted capacitor can cause damage before it is obvious.
:
:T.
:
Ideally, all the tubes should be removed and the power gradually brought up. In a transformer set, then put the rectifier in and do the same. In an AC/DC of course, all of the tubes need to be in to complete the filament string. If possible, try and have the set situated so that you can easily look at the top and bottom. Look for smoke from the transformer, capacitors or resistors.
Terry

::I have never heard of a variac damaging tubes.
::
::Typically, when I obtain a radio that has not obviously been electrically restored, I disconnect all critical capacitors and test them for leakage, and of course check for obvious electrical faults. Some simply replace all capacitors. Sometimes, if the radio is in good condition, I like to see if I can make use of the original capacitors, though I usually add a fuse of some sort to the power supply. A good one is a #44 or 47 bulb, depending on the current, in series with the B+. This will burn out easily if a short occurs.
::
::Though it is nice to slowly power up a radio after all obvious faults have been removed, I do not believe that it is a good practice to power up a radio in which none of the capacitors have been tested, as sometimes a shorted capacitor can cause damage before it is obvious.
::
::T.
::
:
:One of the main reasons to use a Variac is so you DON'T damage tubes, especially the rectifier or output. A red glowing plate on either one indicates a short.
:Ideally, all the tubes should be removed and the power gradually brought up. In a transformer set, then put the rectifier in and do the same. In an AC/DC of course, all of the tubes need to be in to complete the filament string. If possible, try and have the set situated so that you can easily look at the top and bottom. Look for smoke from the transformer, capacitors or resistors.
:Terry
Dear Terry,
Thank you for the input. I have used the Variac for the first time on a radio the I have replaced the filter capacitors and I used 2 voltmeters, one on the AC input line and the other on the B+ output from the filter capacitor. Worked very well. Have a great day!!
:

:::I have never heard of a variac damaging tubes.

when I worked at AT&T, part of out equipment was the L-3 carrier system, the one on co-axial cable. We had a tube type repeater every four miles, and the ampliers and regluaters were connected in series and fed from Augusta, GA. Therefore, for a forty mile loop, there would be 20 stations, 10 in each direction, as it was a four wire system and each station had an amplifer and regulator for each direction. When a unit failed, it switched itself to the spare co-ax tube, and we sent a man out to fix it.
To change a unit, we used a BIG motor driven VARIAC (regulated AC power) to s-l-o-w-l-y lower the AC to zero. When the man was finished changing the unit, we would s-l-o-w-l-y raise the power to 1.41 Amps and switch to automatic. Otherwise, we would burn up a bunch of tubes associated with the power loop for that co-ax tube. God help the man that did that. He would be checking the S. G. of battery acid for a long, long time.
Lewis

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