Opening my vault

Here's an experiment I did a few years ago. Sounded nice but a little noisey

analag said:

Sounded nice but a little noisey

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So, what's the point?

the point is that we were willing to grow along audio circuits, 

6DJ8 hangin' off 230V/10KOhms is not a long-term-stable idea, I think...

gyraf said:

6DJ8 hangin' off 230V/10KOhms is not a long-term-stable idea, I think...

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The common grid tubes? Why not? If I'm reading the curves right power seems to be around about a watt (assuming a generous 10 mA from the degenerated K170Bs) in each tube, well within the 1.5 W rated for. I mean it sounds like a room heater of an input stage, but wouldn't it be fine long term?

I'm genuinely asking here, I have never built a tube amp just staring at curves here..

Edit:
Just noticed the current source connected to -50V... Thought that was ground. What's the current supposed to be?

FET-tube cascode, I think (or rather guess) Manley Reference Silver microphone uses similar topology except single-ended.

https://www.tubecad.com/2007/09/blog0119.htm
https://www.manley.com/pro/mrag/ (interesting way to adjust the polar pattern, that's a single diaphragm capsule)
https://groupdiy.com/index.php?topic=67316.0

Why don't we close this thread?
Nothing interesting comes out of it, even the OP doesn't seem to care...

abbey road d enfer said:

Why don't we close this thread?
Nothing interesting comes out of it, even the OP doesn't seem to care...

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Who are you asking?  ;D

IMO Just let it be, unless it contains possible harmful advice.

JR

That was purely rhetorical, hoping someone would open the dictionary and check vacuity and vanity. 8)

Looks interesting for the use of  fet current sources - I would imagine it might have very low THD throughout.

I like the cross-coupled nfb from finals to first stage - interesting the way it is sourced from the finals' cascode.

The 5687 is an interesting 9pin tube with a lot of positive attributes except for heater power consumption.

I guess this is a moderately powered all-differential line amp with a 20K -ish load.

Some 6V6 in triode would be my personal choice - very linear, approaching the 5687 perhaps  ...  a pair of them is the same heater as a 5687 (dual triode) but can do more power.

I don't see any real problem with 230V as a plate supply voltage ... could be a little less I suppose.

Otherwise - interesting. Current sources and active loads  is the way forward to lower THD after all the obvious things are done.

I have one of analag's earlier takes on this kind of thing ...  a bit simpler than this one, but similar. 

If one can get some reasonable  'ccs modules'  then well worth trying I think  ...  clearly a job for a little pcb with some good heatsinking  ....

Pete Millet does this kind of thing alot.

Anyway - all good to take a squiz at and arm-chair comment!

Back in the day  when we experimented with FET/BJT current sources, we ended up going another route because it always ended up "sounding" much more like (pressed) solid-state than tube

Have you actually built and heard this unit, or is it sim-game only?

Jakob E.

I have to say I’m intrigued at the concept here and I’m also curious if you built it

gyraf said:

Back in the day

Jakob E.

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JR get out of this body !!!
;D

Best
Zam

abbey road d enfer said:

Why don't we close this thread?
Nothing interesting comes out of it, even the OP doesn't seem to care...

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C'mon old fella...whatsamatter.  I'm not done yet. I did fix it but do you care to know?