CC Source in a Spud?

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Paul Barker
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#31 Re: CC Source in a Spud?

Post by Paul Barker »

I've often thought of parafeeding this way but always fallen at the hurdle of doubling B+ supply, whereas a choke load only needs the dc headroom of the drop across the choke. People have often reported the better sound of a CC load when passed through a choke. That may be so, but once you involve the CC you still need the headroom for performance at higher amplitude, or amp will simply switch into choke only mode. I'd go with the choke.
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#32 Re: CC Source in a Spud?

Post by Dave the bass »

I've started experimenting again. Even as just a regular SET Spud amp I like it. It doesn't get much simpler does it?

Heater LT from a regulated bench supply, HT from a regulated HT bench supply. Yellow LED cathode bias ~2.1V and Anode voltage of 150V equates to about 13mA it seems.

As its just one stage between source and speaker its really fun to listen to the effect changing HT has, the effects range from nowt to in yer face :) Luckily we pass through a comfort zone in the middle of those 2 extremes.

I'll 'build another channel in a bit.
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#33 Re: CC Source in a Spud?

Post by Andrew »

Be interesting to hear which you prefer CCS or choke, both have their advocates, advantages and compromises.

The great thing about a Spud, for me, is it's so easy to try different stuff and see what floats yer boat.

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#34 Re: CC Source in a Spud?

Post by Dave the bass »

After initial power up and about 5 mins settling down....Monitoring anode current, does a steady rise over (say) a further 20 mins from 8.8mA to 15mA ish indicate some sort of oscillation or thermal runaway? I've just noticed it with one particular 6C45. It was one I've thrashed in the past I confess.
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#35 Re: CC Source in a Spud?

Post by Nick »

Possibly, check the size of the resistor to ground.
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#36 Re: CC Source in a Spud?

Post by Dave the bass »

Erks,good point, HT is being supplied by a floating/unreferenced bench supply at the moment.

I've spent the entire afternoon 'building' the 2nd channel and generally trying stuff out and found some 6c45's climb in anode current and others don't.
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#37 Re: CC Source in a Spud?

Post by Nick »

I meant the resistor from the grid to ground, if the valve is a bit gassy it may start to pass grid current and if the path to ground is too large in resistance it will build up a +ve voltage on the grid.
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#38 Re: CC Source in a Spud?

Post by Dave the bass »

Aaah!

100K.
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#39 Re: CC Source in a Spud?

Post by Nick »

Try 10k and see if its any more controlled.
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#40 Re: CC Source in a Spud?

Post by Dave the bass »

2nd channel lashed up.

10K, Will do.
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#41 Re: CC Source in a Spud?

Post by Mike H »

The excitement never ends! :D
 
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#42 Re: CC Source in a Spud?

Post by Dave the bass »

Mike H wrote: Sun Jul 23, 2017 8:45 pm The excitement never ends! :D
S'true!

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#43 Re: CC Source in a Spud?

Post by Dave the bass »

Before going to 10K I've fettled in a pair of Silk (brand) Grid Chokes out of interest, very low DCR @ 1K2 Ohm. Thats quelled even the slightest wander on a pair of well behaved 6C45's. I think the source maybe be struggling drive this load a bit as I'm running the volume pot flat out almost all the time but tonally its a lovely balance IMO. Complex music with many layers like Tom Waits 'Swordfishtrombones' is very easy to listen to and 'follow', nothing distracts. Like.

In the back of my mind though I'm aware that any grid current will do the ungapped chokes no favours at all in the inductance stakes.

If I could up the gain of the stage it'd be a very nice long term listen in this setting only probably, ie- small room with reasonably efficient big speakers and no other distractions!
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#44 Re: CC Source in a Spud?

Post by Nick »

Yep, grid current will do no good to the choke, but the grid current may have been in the order of nA, remember 1ma across the 100k you had there before would have created a 1v offset, that would have caused a much bigger change in the current than you were seeing.

In theory, the choke should be no harder a load for the source than a 100k resistor.
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#45 Re: CC Source in a Spud?

Post by Dave the bass »

Nick wrote: Mon Jul 24, 2017 11:58 am
In theory, the choke should be no harder a load for the source than a 100k resistor.
But in practise?
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