450-0-450 transformer voltage reduction

[Masterwaiter]

So I don’t really voice myself on forums much, but I am trying to have some fun while waiting on a more appropriate power transformer to arrive.  I have a pretty friggin huge PT that came out of 60’s era Hammond or Lowrey organ.  It probably weighs at least 15 lbs and is measuring 450-0-450 in the high voltage secondary and is spitting out a b+ of 600v in a 5e3 inspired build with a couple capacitor and resistor tweaks.  It’s essentially finished, I just have to wire in a proper PT, which I plan to do, and it’s done.  In the meantime, for fun I want to try to wire in this 900 volt behemoth in a practical way that will reduce the secondary voltage by 100 to 350-0-350 and be legitimately functional.  My challenge is that I want to do this without the use of zener diodes or a variac.  My initial thought was to try to reduce the voltage on the secondary pre-rectification.  Is this possible?  Worthless to attempt?  Stupid?  Any thoughts or judgement of my character are welcome.  Thanks guys

[sluckey]

You could use a couple resistors between the secondary leads and the rectifier socket to reduce the voltage. But to reduce the voltage down to typical 5E3 levels is not practical with the resistors.

Another way to reduce the B+ would be to use a choke input filter rather than the more common cap input filter. This may just get you where you need to be. A 3H or 4H choke rated for 150mA would be sufficient for a 5E3.

[Masterwaiter]

Yeah, haha, I already experimentally tried a voltage divider circuit to drop 100 volts between the transformer and the rectifier using some power resistors I had on hand.  I had to cut the thing off pretty quick

[SnickSound]

Any form of voltage divider, zener or MOSFET regulation will generate a ridiculous amount of heat.

But... someone else here chime in if this is a bad idea... but why not just use half the transformer in a half-wave rectifier? From what you say, sounds like the transformer can take it (technically would reduce the current handling in half). With SS rectification you'd get just over 300VDC with no waste.

[Masterwaiter]

I hadn’t thought of trying a different style of rectifier.  I should have mentioned though that I’m gonna keep this build all tube. 

[DummyLoad]

IMO, you should wait for the correct part. doug sells the heyboer brand/model. good stuff.


--pete

[sluckey]

I hadn’t thought of trying a different style of rectifier.  I should have mentioned though that I’m gonna keep this build all tube.

You can try snicksound's idea with a tube. If 5Y3, just disconnect one transformer lead and tape up the end. If you like the results, then jumper pin 4 to pin 6 to double the current capacity of the 5Y3.

[Masterwaiter]

Oh my intention is definitely to finish the amp with the right kind of transformer, this was more for entertainment, education, and desire to try pulling off something in an unconventional way while attempting to achieve a positive result.  Also this enormous transformer needs to be used for something and has character

[Masterwaiter]

I hadn’t thought of trying a different style of rectifier.  I should have mentioned though that I’m gonna keep this build all tube.

You can try snicksound's idea with a tube. If 5Y3, just disconnect one transformer lead and tape up the end. If you like the results, then jumper pin 4 to pin 6 to double the current capacity of the 5Y3.

I am gonna give this a shot today and see what happens.  Why not, this thing has been a ridiculous adventure of salvaged parts and has been a lot of fun already.  The input jacks are trs jacks that I have cut the ends of the ring contact off of and contorted into touching the tip contact so that they could be used as a switching jack.

[Ed_Chambley]

Enormous transformers work as a nice power supply for a Tube Breadboard that is variac controlled.  This thing is unknown and if made in the early 60's your primaries may be based on 110 VAC, it is at least based on 117 VAC.  Meaning you will see more than 450.


Is there a number on the transformer?


But for science sake, if you gotta do it, head on! 

[PRR]

> why not just use half the transformer in a half-wave rectifier?

You get the same no-load voltage, and essentially similar loaded voltage; just a bit low because one side of the rectifier carries the full current.