PP amp using 6p15P

[pwan]

Hi,

My friend having 6P15P, 6N1P, 12AX6 & transf 250-0-250 - 250ma) around. Could you advise the good PP schematic that make use of these parts?

Thanks!

 

[Eli Duttman]

6p15p = SV83 = EL84N. The thing to watch out for is the fragile screen grid.

Follow the general pattern of the Dyna ST35. 12AX7 voltage gain block DC coupled to 6n1p "concertina" phase splitter. Both small signal tubes would be shared between the 2 channels.

SS rectify the B+. A separate filament winding, with a CT, for the 6n1p is a good idea. The CT is used to bias the heater off B+, which ensures the heater to cathode potential limit is not exceeded..

Are there any filament windings on the 250-0-250 power trafo?

 

[maton00]

¿Can it be done the same like a elevated heater but at some 150 volts in order to keep the screen grid dissipation at a max of 1.5W? is it really
¿(10mA) at 150V Max?

 

[Eli Duttman]

Elevating the heater does nothing for screen grid fragility. Use full pentode mode "finals" and regulate g2 B+ with an 0A2.

The 6П15П (6p15p) data sheet is here. If you can source 6П15П-EB (6p15p-ev) stock, do so. The milspec tubes are better.

 

[maton00]

I do think a gas discharge regulator could be a little bit dangerous, because those things die very quickly, I'm afraid of getting 300volts in the screen in a catastrofic event
When i said "the same like a elevated heater" I was thinking of a voltage divider to supply the screen, but what about of the 10mA for a max of 1.5W of disipation, could it be better a string of zenners or a regulated mosfet supply?
What do you think could be better?

 

[Shoog]

I do think a gas discharge regulator could be a little bit dangerous, because those things die very quickly, I'm afraid of getting 300volts in the screen in a catastrofic event
When i said "the same like a elevated heater" I was thinking of a voltage divider to supply the screen, but what about of the 10mA for a max of 1.5W of disipation, could it be better a string of zenners or a regulated mosfet supply?
What do you think could be better?

This is not my experience. A salvaged VR150 has been doing stirling service in one of my amps for years. They are most likely to fail on power up and that should be obvious and a quick blast of higher voltage on the screens will do little harm.

However a MOSFET off as resistor divider reference string is easy to implement and should do excellent service.

Shoog