OTL's and aircraft transformers

[vp36kv]

Hello all,
Anyone out there messed with the RCA OTL design? http://www.k-amps.8m.com/cgi-bin/i/P...uum/rcaotl.gif Looks pretty straightforward but something has to be done about that power supply altho having a tube amp without any iron is an interesting idea. maybe hide away an isolation transformer somewhere.
Speaking of transformers curious of others experiance repurposing 400 cycle transformers for 60 cycle use? Ive tried a couple for the heck of it 120V on the 130V tap. The idle current seems a bit high but not seeing any signs of core saturation or overheating at ~rated load.
Austin

[tubelab.com]

Speaking of transformers curious of others experiance repurposing 400 cycle transformers for 60 cycle use? Ive tried a couple for the heck of it 120V on the 130V tap. The idle current seems a bit high but not seeing any signs of core saturation or overheating at ~rated load.

A few zillion years ago when 400 Hz surplus transformers were common, I found a magazine article that said to use them on 400 Hz, wire the primaries and secondaries of two identical transformers in series. I tried it and it worked. Haven't tried this in years though.

I think that using a 400Hz transformer on 60Hz will invite the fire gods to dance on your project.

[sorenj07]

nah actually for best results, just switch the primaries for the secondaries to counteract the phase imbalance... fire gods, indeed

[vp36kv]

Parallel the secondaries out of phase
Its too bad about these things some would be really nice transformers if they were for 60 cycle. Ive been digging thru an old junkyard and coming up with neat stuff, getting ate up by mosquitos in the process. potted transformers arnt fun to burn up that smell lingers for days. Minus the power transformers these old avionics remotes still have some cool parts and are built like a brick dog house.

[Miles Prower]

Originally posted by vp36kv
Hello all,

Speaking of transformers curious of others experiance repurposing 400 cycle transformers for 60 cycle use? Ive tried a couple for the heck of it 120V on the 130V tap. The idle current seems a bit high but not seeing any signs of core saturation or overheating at ~rated load.
Austin

Don't do that.

At 60Hz, the 400Hz will have a volts/turn ratio that's way too high. The voltage has to come down at the lower frequency. If the winding is rated at 120Vac @ 400Hz, it'll have to be reduced to 18Vac @ 60Hz. If you try to run it at 120Vac @ 60Hz, it will poof.

Either that, or build a 400Hz inverter.

[refference]

Hi vp36kv ,

Miles Prower is correct . Don’t do that !!!

When you increase the working frequency of any
power tranny , the calculation shows up that you can
decrease the “ quantity of iron “ on the core .

So if you connect a power tranny at a lower frequency ( 60 Hz )
than the specified ( 400 Hz ) , the “ lack “ of iron core , will
increase the current a lot , then the tranny will overheat and ...
... ( probably ) burn out .

Regards ,

Carlos