220V Transformer question

[jeffhigh]

Look like our AU nominal voltage is 230V +10%-6% (216V - 253V). So I'll try out the transformer before deciding on the buck transformer.

Our nominal voltage in Australia was changed to 230v a few years ago, but they did not change any of the existing Power distribution system. so mostly the voltage at the wall is still 240ish.
The 220v transformer will probably be alright, but you will only know by trying.

 

[cl1238]

Finally tested the 220V transformer. My GPO is around 240V and can go up to 250V.
The transformer seems to be able to handle the voltage, however the output of the windings varies quite a bit. When the GPO is 250V the output are:
300V-0-300V -> 350V-0-350V
6.3V -> 7.8V
5V -> 6V
Not sure is these voltage would affect 5z3p, 6n9p and el34 tube?

I managed to build a 240 to 220 stepdown transformer using buck auto transformer technique posted earlier (using 240 : 2 x 9V). Here is the result of the 220 transformer
GPO 250V, output of stepdown is 226V.
300-0-300 -> 317-0-317
6.3 -> 6.7
5 -> 5.5

I'll see how the buck transformer perform under load when I finish building the amp.

 

[TonyTecson]

i design and build my traffos to run on 240 volt primaries....like i said tube amp can run on a wide voltages within reason...

if that traffo is not overheating at 240 volts, chances are you can use it...

 

[TonyTecson]

Finally tested the 220V transformer. My GPO is around 240V and can go up to 250V.
The transformer seems to be able to handle the voltage, however the output of the windings varies quite a bit. When the GPO is 250V the output are:
300V-0-300V -> 350V-0-350V
6.3V -> 7.8V
5V -> 6V
Not sure is these voltage would affect 5z3p, 6n9p and el34 tube?

I managed to build a 240 to 220 stepdown transformer using buck auto transformer technique posted earlier (using 240 : 2 x 9V). Here is the result of the 220 transformer
GPO 250V, output of stepdown is 226V.
300-0-300 -> 317-0-317
6.3 -> 6.7
5 -> 5.5

I'll see how the buck transformer perform under load when I finish building the amp.

tube flament failure due to voltage is rare in tubes...
if those are unloaded, then those voltage will drop when delivering current, still if you find the voltage still high, then resistors of appropriate sizes can be used...

 

[costis_n]

Do not bother with the cost and complexity of buck transformers etc. Just design around the increased H.T. voltage (more voltage is usually better to design with. The only actual issue is the filament voltage being high. You can solve this very easily, by inserting one sub-ohm resistor per filament leg (will help with minimising the inrush "kick" when you turn on cold filaments, too) . Easy , The amount of required resistance has to be adjusted on test, under full load, of course.

 

[TonyTecson]

^i agree, it is easy to lose voltage, to me it is more difficult when you undervolt, it is like an itch you can not scratch.....

the atx psu ii gave rescued contains an ntc which i use in series with filaments when i wanted to lose a few mV or so...