Power Cascode!

[Austin]

Here is the schematic of how I modified my little magnavox amp. I have converted to solid state diodes and in the place of the 5y3gt added a 6080 tube. The heaters for the el84s and the 12ax7 run from a wall wart and the original heater output goes for the 6080 tube. The 5600 ohm cathode bias resistor is too big I think (and not bypassed) but it was the closest ballpark value I had.

Question: Can I still half wave rectify some negative volts of this for bias of the bottom tube?



Crazy? Ha! Maybe. The point is to be able to drive the el84 class a2 for more power.
My next project I have planned is going to be even further out in left field.



Tubeswell, I forgot the grid stopper resistor on the top tube again. I was in a hurry to see if it would work but I figured you would point this out so I beat ya to it.

[Austin]

Easy way to bias this?


SUPERS~1 by Dirtyrottenstinkingbiker, on Flickr

[Steve Conner]

Out of interest, where do you think the cathode current of the 6080 is going to go? The centre tap of the HT supply can only source current, not sink it.

[R.G.]

Hmmm. I think it can sink current. Look at what you have if you disconnect the (-) lead of the full wave bridge and remove the three lower caps and the 12AX7.

But other issues with the circuit bother me a lot. I haven't done the mental work to put my finger on it, but the 6080 driving the cathode of the EL84 and in turn being driven by the plate of a 12AX7 bother me.

[Steve Conner]

RG, you are right. I still think the circuit looks crazy, though. Sound clips or it didn't happen!

[Austin]

The bias for the 6080 can be from adjusted by changing the value of the 12ax7 plate resistor which I think is cool. The bias for the el84s could come from a bunch of nine volt batteries strung together off the center rail. I like how simple it is.

[Austin]

It works, I am still trying to get the bias right. Anybody got any suggestions? It has a nice sound, very clear. My power supply is getting a little warm tho.

[J M Fahey]

Well, primitive tube amplifiers got along with 3 batteries: "A", "B" and "C" .
Yet the full abecedary extends to "Z", so we can still add a lot of new batteries to our circuits and not get confused.

[Austin]

Well, primitive tube amplifiers got along with 3 batteries: "A", "B" and "C" .
Yet the full abecedary extends to "Z", so we can still add a lot of new batteries to our circuits and not get confused.

I had to look up "abecedary" and even now that I know the definition, I'm still not sure what you are trying to say with this comment. However I think batteries are a nice simple way to acomplish bias.

[J M Fahey]

Don't worry
Just forgot that in USA "Alphabet" is more commonly used
Only meant that more letters should be used to avoid confusion between all those batteries

PS: and, believe it or not, I have often played with lots of 9V batteries, stacking them up to hundreds of volts.
Live act customers often replace *all* wireless mic batteries at every important show, simply don't gamble with that, not worth it, and I get all the barely used ones iuf I wish.
Now if you have to *buy* them ... it's different.