Tube tester transformer saturates at 50 Hz - tips?

[Skogsgurra]

I have a Precision Model 10-12 tube tester. It works in every respect, but I have a problem when I try to calibrate it to show 100% instead of the close to 95% that I can run it without popping the fuse*.

I have found a way around that problem. It is not exactly what I wanted, but it works. It involves standard passive components, but is bulky.

I think that my "solution" is quite interesting but I am interested in hearing what other ideas there may be.



*You calibrate it by adjusting a series resistor in the primary of the transformer (yes, crude - it was like 60 or 70 years ago) and then the 50 Hz/20 ms saturates the transformer core while the 60 Hz/16.7 ms does not.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[OperaHouse]

I would use a small filiment/buck transformer to drop the voltage 15-20V. Remember those older units were designed to work with lower line voltage of 100-110V anyway. You have been lucky so far likely because the transformer had more iron core than they would use today. That series resistance to cal works because the filiment is the major draw and it is constant. Since you are at 100% to start you still have the ability to drop more.

My first experience with 50HZ was at a power plant being constructed in Japan. Yup one of those hit by a big wave. I was just a kid when it was being constructed. Even then I was telling people that this was a disaster waiting to happen. This had an alarm panel filled with 50 transformers all in saturation. Plant hadn't even gone to startup and half the units had failed. Strangly the IC's failed, not the transformers and the units were labeled to work on 50HZ. Dropping the voltage solved that.

 

[OperaHouse]

If you are not familiar with this site they have manuals for a lot of old equipment. I found the data book for tubes and a schematic for similar model

http://bama.edebris.com/manuals/paco/dat10_12/

 

[Skogsgurra]

Update:
The reason that the transformer core saturates is that the volt-seconds (the area under the sine) are higher when the frequency gets lower.
That, in combination with the "Grid Adjust" function that was used to calibrate the unit so that it delivers the right results even if the grid voltage is off, makes the use of a buck transformer impossible since you will still get back to the same V/turn ratio when the adjustment is made.

What you need to do is to reduce period time, which seems to be impossible without adjusting frequency.

It isn't. I put a triac with a fixed firing delay in series with the primary so that the voltseconds are reduced without lowering the peak voltage. Works wonderfully.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

I forgot. My first "solution" was to create a 100 Hz supply by rectifying the 230 V, 50 Hz and feed the resulting 100 Hz ripple to the transformer via a capacitor. I also had to adjust voltage using a transformer and run the tube tester at its lowest input voltage setting.
The Triac alternative is much neater and not bulky at all.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[OperaHouse]

Nice solution. I bought some of these a while ago thinking they would find a use some day. A relatively small SIP package that is basically a 500V power 555. Wouldn't take too many parts.
IR51H420 - SELF-OSCILLATING HALF-BRIDGE