After over 10 years with my Shoog EL34 triode / antitriode amp on 300W toroids and a lot of travelling around, time to use my bigger bottles (813s) that I have had for more than 20 years as SE with parafeed Toroids before I pop my clogs, especially as I have the bases, top caps and PSU Iron.
I want to use mosfets as the valve loads but am not into sand. HT around 1.2KV. Any ideas for these loads, I remember seeing something using about 600V HT a few years back maybe modifiable to higher voltages with more advanced components today. Not looking for lots of power 10W of "Good" sound would be fine. This will be for a winter project, Covid permitting.
I want to use mosfets as the valve loads but am not into sand. HT around 1.2KV. Any ideas for these loads, I remember seeing something using about 600V HT a few years back maybe modifiable to higher voltages with more advanced components today. Not looking for lots of power 10W of "Good" sound would be fine. This will be for a winter project, Covid permitting.
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If I remember correctly when I looked at this before Ia was around 100mA but I was thinking of running with about 600V (my Mains transformer is 435-0-435 at 250mA) I still think it is the best way to go with the 813 triode connected. Bias requirements are easier too. The mosfets and wire specs are also much easier than going for 1KV or more along with PSU components etc, I have quite a lot of 450VW Caps too. I definitely will not go for the higher voltage, so 600 it will be!
Chassis metal here in Spain is hard to come by so when I go to Italy next month I will pick up what I need.
Chassis metal here in Spain is hard to come by so when I go to Italy next month I will pick up what I need.
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450V caps in series, OK . . . as long as you use some resistive dividers to keep the voltages across each cap at 1/2 of the 600V.
And those resistors also serve as bleeder resistors.
An 813 in Pentode mode is somewhat of a current source. But now you need 1200V B+, and you need more filament supplies (isolated), and + voltage for the screen.
As a current source, the total affair will have whatever the rp of an 813 in pentode mode is.
But, it does require 2X B+, and becomes a real space heater.
The advantage is, there is no saturation and no limited inductance there.
But even so, it is probably better to use a plate choke there, so much simpler.
And those resistors also serve as bleeder resistors.
An 813 in Pentode mode is somewhat of a current source. But now you need 1200V B+, and you need more filament supplies (isolated), and + voltage for the screen.
As a current source, the total affair will have whatever the rp of an 813 in pentode mode is.
But, it does require 2X B+, and becomes a real space heater.
The advantage is, there is no saturation and no limited inductance there.
But even so, it is probably better to use a plate choke there, so much simpler.
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