The AM Forum

I noticed someone on another board had drilled holes in the bells of a transformer to make it run cooler.  This sounds okay but I would like feedback from anyone who has tried
this.  Pros and cons

Drilled holes where? Would they allow any airflow?

Here.

And yes, they do run cooler.

Ive seen diode bridges, but rarely diode ladders.


KLC

Thanks Buddly. That's how you can thrash that Viking.  ;D

Look in the qso portion of the board, on the amp thread I started.  I have the exact same rectumfrier solid state.  Someone had put the plate caps on these, too!

Matter of fact, I'll throw these here, so his rectumfrier don't get lonely!

--Shane
KD6VXI

If the transformer is running hot, I doubt that any type of ventulation is going to solve the problem or even help. There are other factors involved here thats causing the transformer to over heat. First thing that comes to mind is high line voltage.
Regards,
TRS
Gary

I am running the primary of the plate transformer through a variac wired for 140% output which is why the temps went up.

When I did the PS mods I did take temp readings with thermo-couples UL style. After drilling the vent holes the windings ran 5 degrees C cooler and the core was 7 degrees C cooler.

The mods were done in 1974 and these are the original irons so any doubts about effectiveness would seem unfounded.

Hi Steve!

I was blowing the cobwebs out of the Viking the other day on 40M. Had the variac full scrote running 150 watt carrier. Gave you a call a couple times during the day.

She can still boogie!

BC

Likely the max cooling would take place if the holes were set on the top of the bell (assuming vertical mount)
and the bottom.  This produces the "chimney" effect which is actually more betterer than just random holes...

I have an R-388 power transformer of the "old" non-potted type that likely has internal leakage or a shorting turn
and runs WAY too hot. I ended up mounting a little 2" DC computer fan, slowed down to blow air across the iron
when the rig is on. It works.

Need a new power transformer for that R-388... yet to find one. :(

           _-_-

You're probably right on the chimney effect Bear. Maybe I'll tape up the holes on the faces and see what happens. But after 43 years I think it'll be ok!!

Good luck on the transformer hunt!
 

If it ain't broke, don't fix it!! :p

Buddly
      
      heard you and Robert VMC on 40 the other day, blasting in here, it works!!

deano

In some 200-300VA transformers in old TV sets a large heat sink was bolted to the outside of the transformer core. This was most common in old tube type TV sets which would be on all day long. The heat sinks were simple stamped and bent steel sheetmetal about .02" to 1/32" thick (did not measure), held in place like a clamp with a long bolt above, and one below, the core. IIRC Zenith did this on black and white sets that used a 3DG4 or 5U4 tube rectifier and that heat sink had about 140 square inches of area and only convection was used, so it works at moderate levels. They still ran hot to the touch, hate to think what they would have been like with no heatsinks. Showing my age having serviced 19-21" black and white console TV sets.

Holes in end bells like the picture - fine on non-potted units. A small fan or air directed to the holes in each bell will make a bigger difference because you are actually cooling most importantly the winding assy and secondarily some of the core. Less holes are needed if a fan is used and it will still work better, but I always preferred a small fan to lots of holes. I used to take end bells off if they had no terminals. They are only there to protect the windings and keep them clean. In paper/synthetic tape-insulated transformers the windings are insulated from the core not only electrically but thermally because the paper or material is not a good conductor of heat.

In many cases an airflow directed right at the transformer core also works very well. I have done this on several 100-300W RF amps I built in the 1980s. These had separate power supplies with only the amp sitting on the desk and ran 800-900VDC@300-600mA plus filaments, bias, etc.. The single 4" fan cooled the compact 10x10x10 power supply box. Hit the transformer from the side first and out the bottom on the other side. I have a decent amount of hobby experience with additional cooling to small transformers 200-500W. Only a few CFM does wonders.
 

I once used a Viking I that I had put an 813 in the final. Long story, but the stock plate tranny had a floating CT, and a FWB rectifier. Had a good 1500v this way. If you want to use a variac on that tranny input, use a FWB, and beef up the HV circuitry to take 2X the voltage. That means different caps, and get the HV wiring out of the harness, and replace with HV wire. Keep that variac under 75%, and you should be fine...till it arcs somewhere... ??? 20db effort to get 1-2DB increase in signal!

Jim
Wd5JKO

Jim,

That was my thought on deriving voltage needed for pwm on my V2, as well.  FWB the tranny.  I've used ones pulled from valiant before in FWB for scream supplies, so I know it will take it.

Just another thought.

--Shane
KD6VXI

I had/have a TV power transformer that had what looked like "extended" lams that made heatsink fins...
...no idea if they were lams or just steel they put in there for cooling.

It MIGHT be the one I used in my novice transmitter, in which case it is sitting "on display" downstairs from here.
But I recall it clearly. Think it is the only one I have ever seen.

Going back even further than the old Zenith TV xfmrs with fins, does anyone remember the TV xfmrs than had two 5U4s mounted right on the top endbell.  These xfmrs really ran hot.

I think I remember it but not what make or model it was. I definitely remember transformers with one tube on the bell.

Alas there was a time when those old TV chassis hung like beef in the back rooms or attics of TV shops to be used for parts, could have had many for a song. All those really nice transformers..

You may be right that only one 5U4 was mounted on the endbell.  Although I keep thinking I remember seeing two, must have been a big xfmr.  Burnt my forearm on one of those 5U4s reaching around it while the set was on.  The sets were probably RCAs.  We would throw out 25-40 sets at a time, lot of good parts went to the dump.

I still have some NOS RCA TV xfmrs from the 50s.

Fred

I thought I remembered seeing this, so looked through my old xfmr lists and found this:

UNK H-5038    H.V., 2 TOP 5U4 SKTS, 6.3 @8A & 2A & 1A,       4 1/2 X 4 1/4 X 3 3/4

Obviously don't know who made it,  but at least my memory is not entirely shot.  This list was somebody's sale list and not my stock, unfortunately.