SE amp build Voltage drop

[cautious1]

Hi ,
In the process of building a SE amp using 6CA7 and 6U8 pentode / triode for input .

Power supply is giving 435 volts un loaded but when loaded drops to B+ of 277 . is this too big a drop ? And what could cause this ?

Transformer is 100 volts ac out to 3 times pump .
Cautious 1

 

[JonSnell Electronic]

100v AC times 3 will reduce the current available by a factor of at least 3.
Values of capacitors and current available would help to base a best guess.

 

[cautious1]

Current rating of Transformer unknown , its an old A&R transformer with yellow wires giving 100 volts, green giving 65 Also has brown center tap on 65 volt winding . Capacitors are 100uf , 400 volt .

 

[hpeter]

because it is related to peak voltages...
multipliers are not good, for hard supply you nned high capacitances which loads much the windings. trafo may get too hot from peak currents...
http://www.hammondmfg.com/pdf/5c007.pdf

 

[Alllensoncanon]

Power supply is giving 435 volts un loaded but when loaded drops to B+ of 277 . is this too big a drop ? And what could cause this ? Transformer is 100 volts ac out to 3 times pump .

With out a schematic, here is a guess. Assuming you are building a stereo system with each channel consuming 60mA. That is 120mA total. With a 3X voltage multiplication, the current load is also 3X or 360mA. Not knowing your power supply filter circuit, it is hard to tell if this amount of voltage drop are normal or not. It does seems excessive with ~20W being dissipated as heat . (120ma * 158V = 20W) Any smoke or sign of excessive heat ?

 

[cautious1]

Hi Allensoncanon .. The circuit is a simple SE one.. A 6AC7 output and a 6U8 pre amp stage . I hvae built PP amps before . I wanted a SE one and had a NOS 6AC7 And an old 6U8 . The power supply is just a 240 to 100 volt AC transformer into a 3 times charge pump which in theory as you know should give 425 roughly . The transformer is an old A&R one no indication of its VA ratings . My thoughts were that the voltage drop was much too great and wondered if anyone had thoughts ideas on the matter. I'm now suspecting the transformer is at fault .

 

[DF96]

Three possibilities:
1. the caps are not actually 100uF
2. the transformer has much lower VA than you need - have you weighed it or measured it? You probably need about 200-300VA minimum i.e. a transformer which would power a 50W per channel Class B amplifier.
3. you didn't build what you think you built

 

[cautious1]

ok changed transformer all is well now thanks .