F6 Amplifier

[Zen Mod]

Originally Posted by Antoinel

Unfortunately, diy F6 is unfinished business. I have a stash of 4 R100As and that is no consolation; R100A appear to be obsoleteium . DIY F6 has no spare parts;and there is not a clear solution for its new output stage.

well - if you have two pairs of Semisouths , it is finished business for you

and , if made properly - it will outlives you , for sure

[vitalstates]

I also have a stash of 4 x R100s, 2 of which were originally lined up to upgrade my F2, but that was a long time ago and the urge has passed. I'm not inclined to wade through the whole of this thread so could some kind soul let me know if they have to be matched for F6.......

Ed

[Zen Mod]

naah .......

now you can wade through thread just for fun

[vitalstates]

no, I said kind soul....chokies might not qualify

does the naah mean 'No, they don't have to be matched?
or
naah I'm not telling?

[Zen Mod]

Originally Posted by vitalstates

.....naah mean 'No, they don't have to be matched....

[vitalstates]

thanks....I'm on it....looks like I build all the even numbers

[Antoinel]

Originally Posted by lhquam

Has anyone built an F6 with "standard" MOSFETs? What is needed for temperature stability? Will source degeneration be enough or will active thermistor control of the bias be needed?

lhquam: I have part answers. Post #1317 showed MOSFETs in the output stage of the old classic. Also, pls search for the DIYer wimdehaan; he too had a schematic [c/o flg]in the early posts.

[flg]

Wim DeHaan's design I posted is a complementary output design. Still a nice idea I will attempt...

[lhquam]

I think I have the answer to that question and I am doing simulations right now.

Build the F6 using Nelson's "F6 with Variable 2ND Harmonic" schematic with "ordinary MOSFETs" and the lower (maybe upper too) source resistor with a higher value like 0R47. The FET degeneration will be determined by the Zen pots P3 and P4, not the source resistors. BUT the bias thermal stability will be improved by the DC drop across the source resistor(s). My guess is that this will work without thermistors in the same manner as the many F5s built without thermistors.

Originally Posted by lhquam

Has anyone built an F6 with "standard" MOSFETs? What is needed for temperature stability? Will source degeneration be enough or will active thermistor control of the bias be needed?

[Antoinel]

Originally Posted by Zen Mod

well - if you have two pairs of Semisouths , it is finished business for you

and , if made properly - it will outlives you , for sure

Zen Mod. You are logically correct. lhquam and buzzforb have them too. Fortunately, they are searching for solutions so DIYers [who will never have R100As] can appreciate diyF6. You too have a stake in diyF6. I hope that you augment their efforts so as to keep it alive.