CC Source in a Spud?

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Dave the bass
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#1 CC Source in a Spud?

Post by Dave the bass »

Imagine a Spud amp. One gain stage. Its to be used on a pair of Saburo (fairly large and efficient) speakers in a fairly small room (my workshop/guest bedroom). Source with be a SB Touch via an AK4396 DAC so 'line level'.

6C45, I've got a couple spare, that'd be an ideal candidate (IMO).

Now then, (I think I've got this right) using a 6C45 as the single gain stage ...if I were to put a CC Source in the Anode of that spud amp that should enable that stage to achieve maximum gain as it'll be swinging into a very high Z. So, is there anything that should stop me para-feeding off that node between CCS tail and anode via a quality cap and small inductor?

6C45 is a proper little grunt of a valve I believe, its got fairly low ra and thus lends itself to this application in that it doesn't require a high ratio step down op TX which may rob the stage of what little power its got already yeah?

LED cathode bias to prevent any local feedback/'degeneration' in the stage too perhaps?

Nobel prize for clever thinking or Knobhead Prize for being errr....a knobhead.
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pre65
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#2 Re: CC Source in a Spud?

Post by pre65 »

Nice to see a valve project being talked about. :D
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#3 Re: CC Source in a Spud?

Post by Dave the bass »

Ta, I've been 'somewhat involved in other crud' for so long its nice to be able to start thinking about ideas and projects again.
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#4 Re: CC Source in a Spud?

Post by Nick »

Just remember that the valve will see the CCS in parallel with whatever load impedance you are hanging off it, so there is no free lunch.
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#5 Re: CC Source in a Spud?

Post by Dave the bass »

Meh, thats what I'd forgotten, I'm very rusty here.
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#6 Re: CC Source in a Spud?

Post by pre65 »

Something like an ECL82 (with a triode and pentode) may be more versatile ?

http://tdsl.duncanamps.com/show.php?des=ECL82

There may be other similar types in that old box of tv valves you once had ?
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#7 Re: CC Source in a Spud?

Post by Dave the bass »

Yeah I know Phil but I've been there and done that before on BOBA.

I really fancy a true spud (its nearly lunch time, arf) and after reading up a bit on CCS and Diode biasing again in Merlins latest Tome I'm beginning to get the itch to try Silicone around a valve.
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#8 Re: CC Source in a Spud?

Post by Nick »

There is no reason why what you want to do wont work. Andrew uses a 6c45p as a spud amp and it works well. Just dont forget the load when working out the loadlines. Also remember that unlike a inductor a CCS wont swing above B+
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#9 Re: CC Source in a Spud?

Post by pre65 »

Fairy nuff.

What about using the CCS in the cathode ? EDIT-- forget that suggestion. :oops:
Last edited by pre65 on Tue Jul 11, 2017 11:35 am, edited 1 time in total.
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#10 Re: CC Source in a Spud?

Post by Dave the bass »

Nick wrote: Tue Jul 11, 2017 11:14 am Also remember that unlike a inductor a CCS wont swing above B+
Thats another thing I'd forgotten, kerrikey, I'm more rusty(ier) than I thought. OK, so in brief, a CCS will allow the Valve to swing into a massive AC impedance and in Merlins book he also mentions excellent PSRR and low distortion only limited by the 'linearity of mu' amongst other things whereas with an Inductor in the Anode, less so.

Yeah, I remember many years ago AndrewL saying he used 6C45 in a Spud and at the time was using huge Schicko (sp?) cabs to to make the most of it.
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#11 Re: CC Source in a Spud?

Post by Nick »

Yep, a CCS is a easy way to get a large anode load and good PSRR with the proviso of the driven load setting the actual load the valve sees. The downside is you need a higher B+ to allow the headroom the CCS needs, which will increase the dissipation in the CCS. A choke load will do all the above, increase PSRR at AC, just not a DC, High load (again at AC) and makes the most of B+, so has little problem with dissipation. The downside of the choke is size and cost. In both cases, the quality matters as well and you can hear a bad CCS as well as you can hear a bad choke.
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#12 Re: CC Source in a Spud?

Post by andrew Ivimey »

Um mm in a spud amp the output transformer is the choke too, isn't it?

Was BOBA that bad? Nope. Could it be worth experimenting with, bigger chokes, better output tx ?
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#13 Re: CC Source in a Spud?

Post by Nick »

andrew Ivimey wrote: Tue Jul 11, 2017 2:33 pm Um mm in a spud amp the output transformer is the choke too, isn't it?

Was BOBA that bad? Nope. Could it be worth experimenting with, bigger chokes, better output tx ?
Yes, the output transformer is doing the job of the choke. I think Dave wants to do stuff to learn stuff, not just to make a sound.
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#14 Re: CC Source in a Spud?

Post by andrew Ivimey »

Yes I realise that. BOBA has many more variables to learn from. I well member AndrewL's 6c45 spud, at Owston. Imp ressive ++.

Did he use an input transformer as input?
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#15 Re: CC Source in a Spud?

Post by IslandPink »

Nick wrote: Tue Jul 11, 2017 2:38 pm I think Dave wants to do stuff to learn stuff, not just to make a sound.
Ooh, like designing loudspeakers then ?
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