..HOW TO BRING UP VOLTAGE,SLOWLY ?

[ve6pg]

..a friend is getting an old tx and rcvr...he does not have a vari-ac....question...how might he bring the line voltage up slowly to see if these old pieces are any good?..
..i've read some guys use light dimmers, light bulbs in series, etc....
..what are your thoughts?...

..sk..

[KF1Z]

I've heard a different Tim Smith say on many occasions, that there really isn't any need to "..bring it up slowly.   turn it on...if something is gonna go..it's gonna go."

[w4bfs]

You can blast old stuff ifn you have plenty of spare iron ... I don't so I usually ballast the power feed with a 100 W incad lamp AFTER pulling the rectifier tube .... this way lets you check tube fils and power xfmr soundness before worrying about leaky caps .... 73 ... John

p.s.  consider adding appropriate fuses on multiple power xfmrs ... I'll bet 32Vx owners will be interested ...beefus

[WQ9E]

Definitely NO to the light dimmer!  They put out a much modified waveform that your transformer definitely will not like!

You can use an incandescent bulb for current limiting but if your friend wants to bring the voltage up slowly (for forming filter caps, finding major faults before it goes Chernobyl, etc.) then a variable voltage transformer is what he needs.  If he does find/borrow a variac then the vacuum tube rectifier (s) should be temporarily replaced with SS plug in types because otherwise you will not get a gradual B+ voltage ramp-up, there will be little B+ up to the point that the rectifier begins emission at which point the voltage will jump quite a bit.  Although not touchy like MV rectifiers, even high vacuum ones don't like running for extended periods with a cold cathode and AC on the plates.

If he is trying to just determine whether the equipment is good for purposes of selling if he isn't careful it is easy to turn potentially working gear into non-working gear far too easily.  At the very least check to make sure that an oversized fuse has not been installed, look for obviously burned components and crumbling insulation, make sure the chassis is connected to a good earth ground for his safety (assuming it is a transformer operated set), be ready to pull the plug quickly if any odd smells or sounds occur, and have a fire extinguisher somewhere nearby.   If it is a receiver make sure that there is a proper load connected to the audio output jack to avoid a flashover and short in the output transformer, for a transmitter it should have a proper load connected to the output.  If it has been stored anywhere but a perfectly dry location it would be a good idea to "bake" the power transformers and any chokes to be sure the moisture is driven out either using a controlled voltage source or an external heat source.

Good luck!
Rodger WQ9E

[WU2D]

All good advice!

For stuff that you want to keep or restore and use on the air you should assume that the electrolytics are toast, but bringing things up slowly may reform them enough to tell if the unit "works". As soon as you know what you need in terms of electrolytics (yes even the cathode electrolytics) go ahead and order them!

Before lighting anything up - pull and clean the tubes and panel lamps and spray the sockets with deoxit, along with any switches, pots, relay contacts, and jacks cleaning and inspecting as you go. Testing the tubes is somewhat useful. Lube the shafts of all controls. Clean the chassis as best as possible. LOOK FOR ZORCHES.

Now install a proper fuse and replace the AC cord with a fresh grounded one (it is toast usually anyway) and replace the tubes into the sockets. Work all of the controls and put them in the proper setting according to the manual...

Some people check all of the hardware like screws and nuts loosening and re-tightening, especially around ground points and lugs. Another tip is to check the values of all power resistors (resistors all age but the ones that see heat age faster) and replace those that are higher than 20% of original value. A 22K resistor feeding a driver stage can go so high in value that the stage is starved!

Now you are ready to bring the unit up.

Or don't bother with the above and just unload the radio crack a beer and do the Timmy method - after all it is just a boatanchor!

Mijke WU2D

[KM1H]

All good suggestions.

A variac is the best choice of course and they are cheap on Epay for the smaller sizes. I use a Variac with ampmeter to watch for problems as I slowly bring the voltage up with rectifier tube removed or SS diode leads lifted. Then I do it over again with B+ and attempt to reform the caps so I can at least check the unit to some degree before doing the usual refurb.

An alternative is a 24V 2A secondary xfmr wired as a bucking transformer which will at least limit the input to 100V for starters. Even two in series parallel and switched for a sort of stepper setup.

If he intends to keep the radios its better to simply replace the filter caps from the git go. Old, used, reformed caps are usually much lower capacity than when new.

I run all my operating tube radios with 12.6V filament xfmrs in bucking mode, they run much cooler. One suitably rated xfmr feeds the outlet strip for each bench. Some equipment brands are notorious for transformers operating on the edge of or in partial saturation at 122-125V.

Carl
KM1H

[W1EUJ]

The time for reforming caps has passed. They should all go, as a rule. All old electrolytics and paper caps have no business in a working radio. Spending time checking ceramic/mica caps,  resistors and coils is always a good investment, you can trust them afterwards and not worry as much about component failure. All it takes is a couple minutes to check a tube on a simple emmision tester and eliminate the really-bad ones.

Troubleshooting becomes far easier when you can rely on the components being the values on the schematic and performing as expected. There is a far lower chance of working through a 'constellation of failures'.

[N3DRB The Derb]

The time for reforming caps has passed. They should all go, as a rule. All old electrolytics and paper caps have no business in a working radio.

Everyone read this 3 times, like a mantra. One other thing, just because your radio is not humming or buzzin does not mean the original filter caps are good. The load they place on your set's power transformer from the leakage will kill it in short order, and many times it wont make noise.