TRIODE PA_060-S power tranny in 50W build ?

[pula58]

Im working a friends amp. It is 50W HRM build. Most of the build was done before I received it, I am on clean-up and problem fixing.

The power tranny the owner chose was the Triode Electronics PA-060-S power tranny. I am seeing 530V plate voltages with all the tubes installed and properly biased (output tubes biased at 66% (of max 30W) power dissipation).

So, what do you folks think about running 530V on 6L6GC's ? Also, what about running 530V on a 500V 20uF F+T electrolytic (the cap on the downhill/lower voltage end of the choke)?

I would hate to bring the bad news to the owner, that the power supply tranny is the wrong choice for this amp.

[ToneMerc]

With the screens only a few volts lower than the plate I wouldn't and definitely not on the caps. That PT seems to be high, your loaded B+ should in the 480-485V area. It seems to be 800V instead of 720V as 400V will have you around 530.

TM

[ToneMerc]

You could put a 100 ohm 25 or 50 watt alum cased resistor on the HT centertap to knock it down slightly.

TM

[pula58]

I have my own 50W build (4 preamp tubes and two 6L6GC's) that uses a Hammond Blackface Fender Bassman power tranny. it puts-out 330V at 275mA. I am seeing about 460V on the plates. So, I would think a 660V CT tranny would be about the right choise for this amp.

Any other opinions would be most welcome!

[ToneMerc]

My my D'lite 50W I has custom Heyboer that IIRC is 355@300mA and it hits the plates at around 465V as i like slightly higher voltage in that one. So yes 330-335 should be ideal.

TM

[pula58]

My my D'lite 50W I has custom Heyboer that IIRC is 355@300mA and it hits the plates at around 465V as i like slightly higher voltage in that one. So yes 330-335 should be ideal.

TM

Thanks,
Did you mean 335V or 355V ?

[Firestorm]

Convince your friend to let you add power scaling to the amp. Then you can preset the mosfet so the B+ never gets above 500V.

[ToneMerc]

My my D'lite 50W I has custom Heyboer that IIRC is 355@300mA and it hits the plates at around 465V as i like slightly higher voltage in that one. So yes 330-335 should be ideal.

TM

Thanks,
Did you mean 335V or 355V ?

In the range of 330-335V if you like the normal voltages.

TM

[triode3]

The PA-060 is for a Dynaco ST-70 stereo 35WPC Amp using four EL34s with a tube rectifier.


"...the power supply tranny is the wrong choice for this amp."


Most likely. It is designed to give about 520V DC on four EL34s biased pretty hot. Your choices are move to a bigger tube (KT88/EL34/etc) as the heaters are rated for plenty of current (unless you say you have 12 preamp tubes in there), or voltage scaling in some form.

No, I would also not put 530 or so volts DC on a 500V cap continuously, even considering the manufacturers margin for error. I would think 40 years ago caps had a nice margin of error, but in this day of "build everything as cheap as possible and maximize profit", I bet those margins for error have fallen down some.

I use the PA060 all the time, but in 70W to 100W amps using EL34/KT88/6550s in various configurations. I think 530V is a bit hot for screens on 6L6s. (RCA and GE claim max of 450VDC screens and 500VDC on the plates... would 530V on the plate kill it, probably not, but I would lower the screen voltage and crank the current down a bit to keep it within its max dissipation, or close to it).

[pula58]

[quote="triode3"]
"...the power supply tranny is the wrong choice for this amp."


[quote]

Yeah, that's what I think too.
I suppose we could add some resistance (power resistors) in series with the each diode branche in the rectifier circuit to drop some voltage, at least to bring it down to 500V or so perhaps. If it were my amp I would put in a lower voltage tranny.

Any recommendations for a Power tranny? It is a Ceriatone HRM kit, 50W. It needs a 6.3V (CT) heater output at ~ 4amps, 330-335V @ 250-300mA main output, and, an additional 6V, or 6,3V output, for the (regulated) relay power supply. And, it must fit i nthe Ceriatone chassis power supply tranny opening.

It would be great if I could recommened another tranny to my friiend so that he has all the choices avaialable to him.

[John_P_WI]

Convince your friend to let you add power scaling to the amp. Then you can preset the mosfet so the B+ never gets above 500V.

+1

Or even simpler, see the powered zener "voltage reducer" at the bottom of the page:

http://www.geofex.com/Article_Folders/m ... tfolly.htm

[Structo]

Does Magnetic Components make those Dynaco transformers?