I'm doing an exercise for Steptoe, to help him with an amp design using some of his vast stock of ex military valves.
I / we decided upon 6L5G as a driver and 6Y6g as the power valve. Steptoe has a preference for PSE, but this prototype will be just one for simplicitys sake.
Now, I need a bit of help with the basics, I'm setting out the circuit diagram and not doing to badly.
1st question.
In using the calculator to work out the cathode bypass cap for the 6Y6g power valve, is the load resistor value the DCR of the output transformer primary ?
Or is it the impedance of the output transformer (5K in this instance) ?
The only thing necessary for the triumph of evil is for good men to do nothing.
As Steptoe may want to go PSE (if this experiment goes well) I have a potential current draw of 256ma for stereo, and that means I will have to dig out my dual mono PSU, as none of my other transformers could cope.
It will need the voltage reducing from 450v (ish) to around 180v but I have a box full of Arcol 50w resistors so should not be a problem.
Test 1 will be to use a 4.7K 50w and see how near I get to 180v. The circuit is now on revision 1.1, I'll redraw it after the next revision.
In the HT to the OPT I may need a small resistor (240R at the moment), I presume that is best decoupled ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Question from the fat kid at the back of the class Sir!
The 1st stage Anode load resistor, 20K Ohm, if you look at the Valve Data sheet the ra at Anode voltage of 135V is ~ 11K2.... which isn't far away from your OP of 100V @ 4mA.
Quite often (which doesn't make it a rule I know) you see a RL at least 3 x the ra. So, what about using a choke in the anode to increase RL and thus possibly increasing the voltage swing out of that stage? It'll still need decoupling above the choke still but will still enable you to more of the HT available to you but give the valve higher impedance to swing into rather than a purely resistive load?
Just an idea... and also just the sort of thing I fart about with at home when its raining
I found a piece of worktop in the woodshed, so now I can begin to screw down some of the hardware. There are six octal relay bases, so PSE can be attempted.
Question for the experts. With PSE, does the driver valve need adapting to drive two power valves, rather than one ?
The only thing necessary for the triumph of evil is for good men to do nothing.
pre65 wrote:
Question for the experts. With PSE, does the driver valve need adapting to drive two power valves, rather than one ?
You may need to raise the current through the driver stage, as you will be trying to charge and discharge twice the amount of Miller capacitance you would have had with only the one valve.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
I've been screwing everything onto the breadboard, and faffing around sorting out the wiring diagram and tagboard component layout.
Also the amp is going to be PSE straight away, as the output valves are in triode mode so a bit low powered. My big Hammond OPT should do 2.5K if I use the 16 ohm tap.
Might not get much done today as I hope to go out green lane riding on the KTM. Yippee.
The only thing necessary for the triumph of evil is for good men to do nothing.
