PCL86 SE Ultralinear Monos

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Cressy Snr
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PCL86 SE Ultralinear Monos

Post by Cressy Snr » Thu Aug 09, 2018 1:15 pm

So, finally I'm getting around to building me a nice set of PCL86 monoblock amps.

The PCL86 variant of the ECL86 triode/pentode is such a great valve that it would be silly of me not to build
something that would do them justice and be of manageable size. The existing spud amp, cobbled out of the Pink SET, is so big considering what it is being asked to do, it borders on stupidity. In short, the existing amp is overkill on a massive scale. It sounds absolutely fantastic as a lash up, but hopefully (fingers crossed) that's not because of the overkill. If it is, I'm on the road to dissappointment. However, as they say, "nothing ventured..." etc

Racking my brains about a pair of chassis, I did a bit of lateral thinking and got a stainless steel door kick plate...
https://www.screwfix.com/p/eurospec-doo ... 50mm/5759p

Cut in half, and suitably punched and drilled, this will make for a nice pair of 6" x 14" quality top plates, for not much money.
It might even be fun to cover the top plates with the left over purple Rexine so that the amps match the speakers.

Surround will be 9mm plywood, veneered with the left-over walnut strips I saved from the Fane Fullranger project.

The circuit is based around the 1962, Mullard " Economical 3W Stereophonic amplifier" but with a lot less gain.
Happiness is not good for the economy Matt Haig.

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Mike H
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Fri Aug 10, 2018 3:24 pm

Image Watching.
 
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RhythMick
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Re: PCL86 SE Ultralinear Monos

Post by RhythMick » Fri Aug 10, 2018 9:38 pm

Me too. And I haven't heard the Pink SET....

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Mike H
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Sat Aug 11, 2018 7:50 pm

Cressy Snr wrote:
Thu Aug 09, 2018 1:15 pm
The circuit is based around the 1962, Mullard " Economical 3W Stereophonic amplifier" but with a lot less gain.
Found that on't 'net, nice simple little circuit. Prolly dump the tone controls. I notice R6 (1st triode's anode resistor) is 220k, I'm thinking if drop it down to 100k, that will go a ways to reducing the gain. I'm frequently somewhat amused when I see old circuits like this with huge value anode resistors for triodes, 'cause beyond a certain value you don't get much more out of it. :D
 
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Mike H
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Sat Aug 11, 2018 7:53 pm

PS: found the circuit on National Valve Museum site: http://www.r-type.org/articles/art-003g.htm
 
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Cressy Snr
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Re: PCL86 SE Ultralinear Monos

Post by Cressy Snr » Tue Aug 14, 2018 2:00 pm

Mike H wrote:
Sat Aug 11, 2018 7:53 pm
PS: found the circuit on National Valve Museum site: http://www.r-type.org/articles/art-003g.htm
Yep, that's where I found it.
The current amp uses 100K on the triode section, with no cathode bypass. No tone controls of course :)

It was only when I'd built the spud amp in the pink SET chassis, that I found the Mullard 3W SE amp and saw the similarities.
Nothing new under the sun as they say. :)
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Nick
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Re: PCL86 SE Ultralinear Monos

Post by Nick » Tue Aug 14, 2018 2:56 pm

I'm frequently somewhat amused when I see old circuits like this with huge value anode resistors for triodes
Yep, but with a 1.2ma max current for the triode and a ra of 62k. 220k doesn't seem excessive.
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Mike H
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Tue Aug 14, 2018 5:13 pm

Not as much as 470k! Which I have seen... :D
 
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Tue Aug 14, 2018 5:16 pm

Cressy Snr wrote:
Tue Aug 14, 2018 2:00 pm
Mike H wrote:
Sat Aug 11, 2018 7:53 pm
PS: found the circuit on National Valve Museum site: http://www.r-type.org/articles/art-003g.htm
Yep, that's where I found it.
The current amp uses 100K on the triode section, with no cathode bypass. No tone controls of course :)
Quool. Image

It was only when I'd built the spud amp in the pink SET chassis, that I found the Mullard 3W SE amp and saw the similarities.
Nothing new under the sun as they say. :)
Natch.

Have now got hold of a couple of Tungsram PCL86 so may be able to have a tinker in due course
 
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IslandPink
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Re: PCL86 SE Ultralinear Monos

Post by IslandPink » Tue Aug 14, 2018 6:19 pm

Mike H wrote:
Tue Aug 14, 2018 5:13 pm
Not as much as 470k! Which I have seen... :D
You still seem uncomfortable with this Mike. Surely 470k or even 680k would be entirely sensible as a load on an ECC83 at 1 or 1.5ma, for instance, given the Ra. If it has much voltage swing, then anything much below these values will increase distortion and give a muddy toneless sound, in the same way loading-down a cartridge too much causes similar.
I use 20k on a D3a in my phono. Ra there is about 2.5k at 12 or 13ma. So that's a loading of 8x the Ra.
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Re: PCL86 SE Ultralinear Monos

Post by RhythMick » Tue Aug 14, 2018 6:44 pm

Maybe consider an anode choke? Lundahl 1667-05mA would give 800H ish!

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Nick
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Re: PCL86 SE Ultralinear Monos

Post by Nick » Tue Aug 14, 2018 8:45 pm

800H and 65k would have a -3dB of 13Hz which would be marginal IMHO.
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Re: PCL86 SE Ultralinear Monos

Post by IslandPink » Tue Aug 14, 2018 9:05 pm

Ha ! - I did that calc earlier with the same conclusion !
What's the problem we're trying to avoid here ?
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Re: PCL86 SE Ultralinear Monos

Post by RhythMick » Tue Aug 14, 2018 10:52 pm

Ok fair point

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Mike H
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Wed Aug 15, 2018 4:23 pm

Gain of a triode does not increase significantly with large increases of anode resistor value. Ergo I don't see much point (IMHO).

HTH
 
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