Lowering B+

[phsyconoodler]

One more question about lowering B+ .
I used a 25watt resistor between the PT center tap and ground. Its worked just fine when ive done it with no ill effects that ive noticed.
  Everyone says use zeners or a mosfet circuit.
   Im wondering why not use just a resistor and maybe a high voltage electrolytic in reverse?
 

[sluckey]

One more question about lowering B+ .
Im wondering why not use just a resistor and maybe a high voltage electrolytic in reverse?

That's so old fashioned.   

[HotBluePlates]

I used a 25watt resistor between the PT center tap and ground. Its worked just fine when ive done it with no ill effects that ive noticed.
  Everyone says use zeners or a mosfet circuit.
   Im wondering why not use just a resistor ...

(Deep) Class AB vs (mild) Class AB vs Class A

Played LOUD vs Played Soft.

Volts (Reduction) = Current (Increase) x Resistance (in-Series)

Sag vs No-Sag

Fast vs Slow


Guys that play mostly vintage-style amps, or that play low-volume relative to the amp's total power capability, or that like compression can forget how "stiff" or "fast" amps sound.  They can forget that not everyone wants the the softer, rounded-over sound.  They can forget that it can work fine at low volume, then collapse (or greatly restrict power output) at higher volume.

Some folks will recommend voltage-reduction strategies whose output does not vary so much with changing current.  Might be a zener, might be a voltage bucking transformer, might be a transformer replacement.

[jeff]

One more question about lowering B+ .
I used a 25watt resistor between the PT center tap and ground. Its worked just fine when ive done it with no ill effects that ive noticed.
  Everyone says use zeners or a mosfet circuit.
   Im wondering why not use just a resistor and maybe a high voltage electrolytic in reverse?
 

How many volts were you looking to reduce the B+ by?
What value(ohms) resistor did you wind up using?

[PRR]

....why not use just a resistor ...?

Is the current demand from idle to loud "constant" or varying?

If near constant, a resistor can work.

If it is a fix-bias deep-AB stage that rises from 17mA to 130mA (7189), then working B+ will vary all over the place, especially if you drop a lot.

[mresistor]

....why not use just a resistor ...?

Is the current demand from idle to loud "constant" or varying?
If near constant, a resistor can work.
If it is a fix-bias deep-AB stage that rises from 17mA to 130mA (7189), then working B+ will vary all over the place, especially if you drop a lot.

PRR - does this mean a cathode biased amp would be a better candidate?  I've seen the voltage dropping resistors on the hv leads to the rectifier drop B+, does the also have this effect? Note lowering B+ at the pt cventer tap also effects filament voltage in all amps and also bias voltage in fixed biased amps.

[sluckey]

Note lowering B+ at the pt cventer tap also effects filament voltage in all amps

Please explain???

[mresistor]

OOPs   sorry  not enough coffee yet this morning     of course it's not going to effect the filament winding    duh .

[jeff]

No one thinks you're a j---. I think you were quoted because that's the part he wanted explained, not to call you out, but to understand what you meant.
I've been away for a while but most people are here to help.
Sometimes it's better to say explain instead of "that's wrong!"(maybe you know something I don't know, maybe I know something you don't know, maybe simple mistake before you had your coffe)


I wouldn't worry about it.
Everyone makes mistakes and we're all here to catch each others mistakes, not point them out to make each other look bad.


Peace

[mresistor]

Sorry Sluckey      apologizies..     

[kagliostro]

May be you where thinking what happens when you feed a whole amp via a Variac

If you do that filaments voltage will be affected for sure

Franco

p.s.: I know lot of things, the problem is my brain very often apply an unwanted mix and not only before coffee 😭

[RadioComm]

Sorry Sluckey      apologizies..   

I don't know about everyone else... But Man... I've had my share of brain farts. Truly don't kick yourself in the butt for that, you're better than that, we all know it.