PCL86 Triode SE Spud Amp

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Cressy Snr
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#1 PCL86 Triode SE Spud Amp

Post by Cressy Snr »

Craziest spud amp?
Image

After having had the mains TX expire on my beloved Pink SET I was left a bit thermionically bereft. OK, so the NVA clone is a super amp but all the same, once you've used valves you find it hard not to have a working valve amp in the house.

I have half a dozen PCL86s, an Antrim Transformers, mains toroid bought long ago from Andew L, with a 12.6VCT heater, and 280V 600mA HT winding. The toroid had been fitted earlier to try to operate the 2A3s with PCL86s as input and driver stage but somehow it wasn't the same sound quality. Not enough volts to play the 2A3-40s at the 400 odd Volts I had been using, and at the same time too much for the small signal and drivers.

Anyway I stripped out the circuit and reconfigured it as a spud amp; a sort of cross between the Mullard 3-3 and the Decware Zen Triode.

Stupidly big OPTXs, stupidly powerful mains transformer, stupidly big power supply and stupidly large chassis for a spud amp and a stupidly long way from the plates of the pentode sections to the output transformers. It also sounds stupidly good; sweet, clean and dynamic. Hum is very low indeed.

A whole 2W and to get this power, the triode strapped, pentode sections of the PCL86s are being absolutely thrashed to within an inch of their lives. But as they are television audio section valves, they ought to be tough enough to withstand the onslaught.
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Cressy Snr
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#2 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

It's definitely worth building onto a new, small chassis.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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IslandPink
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#3 Re: PCL86 Triode SE Spud Amp

Post by IslandPink »

That didn't take you long !
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Cressy Snr
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#4 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

IslandPink wrote: Sat Jun 23, 2018 10:46 pm That didn't take you long !
It was a shame to leave the pink SET gathering dust and I was bored, so decided to break out the soldering iron. :)
Designed on the back of a fag packet.
It could do with a hybrid bridge valve rectifier to shave a bit off the HT.
Max diss for the pentode section is 9W and at the moment they are running at 10W. They seem OK at that diss; no red plates or any signs of distress, but I don't usually cut things that fine. OTOH the sound is great with the high efficiency Fane "12s" and I have another four of the valves as spares. PCL86 are cheap enough at the moment.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
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#5 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

Fitted a hybrid bridge rectifier this afternoon after the England match.
Valve part is a 5Y3G, which is heated by a Hammond 5V/3A filament transformer, bought off Phil a few months ago.
Now we have a classic 3 valve 1960s stereo record player amp with monster OPTs and monster power supply. :D

Image

That hybrid bridge rectifier has knocked 20V off the HT and brought the dissipation of the pentode section of the PCL86 down to 9.6W, which is within 10% of the max, so it'll do me. With the limited wattage available from this valve, with the pentode section strapped as a triode, it makes no sense to operate it at anything other than its max dissipation. I mean, it's not as if PCL86s are as rare or expensive as decent NOS 45s.

That's my excuse and I'm sticking to it. :)

I'll bring it to Owston as a curiosity.
In the absence of Thomas' 2W "Tower of Power" it'll be a good laugh.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
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#6 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

Stuck a Fivre 5R4GY rectifier in the back corner. Bass tightened up, became deeper and the music came pouring out.
This little big amp is a keeper; best 2W I've heard in ages. It's a match made in heaven with the Fane "12s" and if the Decware Zen Triode is this good, I can understand the excellent customer reviews.

The Zen Triode, which this amp most resembles, uses an ECC88 type to drive Russian EL84s whereas my amp, in effect, is using half an ECC83 to drive an EL84, all in the one bottle.

How it'll do, being of such low power at Owston is anyone's guess, but I'll stick my neck out and try it with the Fanes for my system dem. I can always switch to the NVA if the PCL86s start puffing and blowing. Hopefully I'll get to use the Fanes with Nick's 211 too.

The irony here that a back-of-a-fag-packet design betters my previous efforts is not lost on me. This is KISS taken to extremes with brute force PSU and output transformers, and it works a treat.
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IslandPink
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#7 Re: PCL86 Triode SE Spud Amp

Post by IslandPink »

It'll be fun to try it with the single FX120 on a 30L box that I'm bringing.
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Cressy Snr
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#8 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

IslandPink wrote: Tue Jun 26, 2018 11:56 am It'll be fun to try it with the single FX120 on a 30L box that I'm bringing.
Aye, that'd be interesting.
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#9 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

Been doing some research on this ECL86 type TV tube.

The received wisdom is that it is an ECC83 and an EL84 in the same bottle. I was not convinced to be honest. The pentode section biases up reasonably close to EL84, but it isn't one really. What I found out is that the pentode section actually biases up exactly the same as the earlier 8pin, rimlock based EL41.

The specs on the EL41 datasheet are exactly the same as those of the pentode section of the ECL86, and handily, there are triode curves for the EL41, which also match up exactly with what the ECL86 is doing in my circuit; bang on!

I think it is safe to conclude that the ECL86 is an ECC83 combined with an EL41.
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IslandPink
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#10 Re: PCL86 Triode SE Spud Amp

Post by IslandPink »

Nice work agent Cresswell :!:
"Once you find out ... the Circumstances ; then you can go out"
Cressy Snr
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#11 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

IslandPink wrote: Wed Jun 27, 2018 10:59 pm Nice work agent Cresswell :!:
More like, "What a sad bastard" :lol: :lol: :lol:

But...it keeps me out of mischief I suppose.
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simon
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#12 Re: PCL86 Triode SE Spud Amp

Post by simon »

So pleased you're enjoying them Steve.

P.S. does that mean I can keep the big JJs ;-)
Cressy Snr
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#13 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

simon wrote: Thu Jun 28, 2018 1:18 pm
...P.S. does that mean I can keep the big JJs ;-)
Aye, for a small fee. :)
We can talk about it at Owston.
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Cressy Snr
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#14 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

OK,
After a bit of unwanted fun with RF oscillation, we have a fine sounding little amp.
Lots of subtle musical detail coming from the amp, but it isn't up front and in your face, which is how I like things.
Suits the Fanes nicely and bodes well for the rebuild into Ed's donated metallic maroon painted chassis.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
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#15 Re: PCL86 Triode SE Spud Amp

Post by Cressy Snr »

Rectifier porn - Mazda UU10:
Image
I mean, isn't that lovely.
Art and engineering meet perfectly.
Only about as powerful as an EZ81, but I know which one I'd rather look at. :)
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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