Anyone Driving An F4 With A 300B SET?

Oscar Heil was way ahead for his time. My dad bought the 1Ds in the mid 70s. It was a modern sounding loudspeaker in a console era.
 
Zen Mod said:
anyway, that's why I wrote that using higher values of shunt resistor at output of toob amp is possible: output toob itself is more than happy to see higher load, overall THD is lower, while you can have double swing with 16R or even quadruple swing with 32R, in place of usual 8R
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You can do that, but will end up limited by voltage clipping on the primary side of the transformer if running a lot higher than the matched Z load rating. You can only generate so much negative voltage swing on the primary. You won’t get undistorted 4 times the voltage but you will lighten the load on the tube and should get lower distortion for the linear output range. That may or may not sound better. The beauty of this setup is that you are free to experiment with all kinds of termination options on the tube side of things and also output impedance on the SS amp. A DIY feast for hungry boyz!
You could even put an attenuator on the output of the tube amp and feed it into a gain of 10 F5 if you already have that on hand.
Sounds like a plan to me. I’m putting it on the long list of DIY stuff to try.
 
Zen Mod said:
it'll give 4times at secondary if bloody thing is NFB-free, and most of nowadays sissy SE amps are, ya know, Kosher

:clown:
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Dear ZM- How can you get 4 times the swing on the negative transition. If you have a 300B with 400v on the plate and a primary load of 5k ohms terminated properly at 8 ohms on the secondary side. You would have maybe 300v negative swing before the tube is saturated. That would mean a current change of 300v/5k = 60ma. If you increase the secondary load to 32 ohms the primary now reflects a 20k load. You will get slightly more negative swing due to the lower change in current required with the reflected 20k load. So if the tube now saturated at 50volts you would have 350volts of swing, an increase of 17%. The current swing would be reduced to 350/20k=17.5ma. However on the positive going side the current could swing the full standing plate current value of say 80ma. If the tube was driven to cutoff it could deliver a maximum + swing of .08x20k=1600volts. Obviously this would be a grossly distorted waveform since you cannot get more swing from the negative side than the B+ voltage - the tube saturation voltage and transformer resistance loss. This is the case regardless of feedback.
 
you know, it's always possible that I'm in brainfart situation, I mean as semi-temporary state

at least I hope it is semi-temporary

in this moment I can't even start thinking of it, playing doggie-chasing-tail routine with some other things ......

so , let's presume that 16R instead of 8R will give double swing , and that's already enough

🙂
 
Hello !
I´m driving my F4 with a singelend 300B, the Edison Triod 300B mk2 with Lundahloutput-
transformers and my DIY F4 is connected to my old Snell type C.
I think it works very well, much of 300B-sound with the power from F4, I have 10 ohm/10W resistorload at the 300B amp but after reading this i will try higher values and see what difference it will be.
 
well, after some more coffee, I'm certain that I ooked some ratios there ( no double voltage and no quadruple, due to losses, which Bfpca pointed out) but I'm also certain that you'll have significant higher swing without any ill effects , if you go with quadruple load... as long you are using ears while operating volume knob
 
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My output transformers are only tapped for 8R. I can certainly get 8R & 16R 10w and see which I like better.

So, just put them across the transformer secondaries, then out to the F4?
 
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