PCL86 SE Ultralinear Monos

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Mike H
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Wed Aug 15, 2018 4:46 pm

PS: wish I'd never mentioned it :D
 
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Re: PCL86 SE Ultralinear Monos

Post by Nick » Wed Aug 15, 2018 5:48 pm

Mike H wrote:
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
Agreed, but the distortion will reduce so that can make it worthwhile.
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Wed Aug 15, 2018 8:06 pm

OK fairy nuff, I grant you that :D
 
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Re: PCL86 SE Ultralinear Monos

Post by rowuk » Fri Sep 14, 2018 9:05 pm

Did this project ever get off of the ground? I am looking for a dedicated single ended pentode tweeter amplifier with only a watt or two.
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Re: PCL86 SE Ultralinear Monos

Post by Cressy Snr » Sat Sep 15, 2018 12:04 pm

rowuk wrote:
Fri Sep 14, 2018 9:05 pm
Did this project ever get off of the ground? I am looking for a dedicated single ended pentode tweeter amplifier with only a watt or two.
I've got it as a stereo amp, but it is as big as a house compared to the size of the valve. Sounds great though.
Layout is critical and ceramic sockets are a must, or the buggers will oscillate at the HF end of the audio band if you so much as look at them the wrong way.
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Re: PCL86 SE Ultralinear Monos

Post by jack » Sat Sep 15, 2018 6:43 pm

Would a ferrite bead on the grid not help?

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Re: PCL86 SE Ultralinear Monos

Post by Cressy Snr » Sat Sep 15, 2018 10:30 pm

jack wrote:
Sat Sep 15, 2018 6:43 pm
Would a ferrite bead on the grid not help?
Not sure a ferrite would achieve much as the thing oscillates in the audio band at around 10-15KHz if there is any stray capacitance between the triode section plate and the pentode section control grid, both of which are on adjacent pins (8 and 9 respectively)
I discovered stray capacitance between the aforementioned adjacent socket pins on the valve that was squealing. Changing to ceramic sockets killed the problem completely.
The "Assembly of 3W Amplifier" section of the economical stereo amplifier, single ended pentode Mullard circuit write-up, warns of this problem with the ECL86 and suggests nylon loaded, skirted valve sockets, and putting the circuit components on a PCB if possible. http://www.r-type.org/articles/art-003g.htm
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Sat Sep 15, 2018 11:25 pm

rowuk wrote:
Fri Sep 14, 2018 9:05 pm
Did this project ever get off of the ground?
We're working on it! Cressy's got his, I'm "collating parts" ...
 
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Sat Sep 15, 2018 11:45 pm

Cressy Snr wrote:
Sat Sep 15, 2018 10:30 pm
Not sure a ferrite would achieve much as the thing oscillates in the audio band at around 10-15KHz if there is any stray capacitance between the triode section plate and the pentode section control grid, both of which are on adjacent pins (8 and 9 respectively)
Actually it's the other way round -

"In particular every precaution is taken to minimise stray capacitive coupling between the grid circuit of the triode section and the anode circuit of the pentode section of the ECL86. The valve-holders for the ECL86 should be nylon-loaded and skirted."

So triode grid pin 1, pentode anode pin 6, and are diametrically opposite on the socket. But yes I expect it would. Easy to get capacitive and even RF coupling between adjacent wires. First thing that occurs to me is that the triode grid wires must be screened.

HTH
 
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Re: PCL86 SE Ultralinear Monos

Post by Nick » Sun Sep 16, 2018 10:53 am

Actually it's the other way round -
Agreed, but if you are using feedback, the two descriptions can become the same. Just thinking out loud.
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Sun Sep 16, 2018 1:54 pm

Certainly, I'm trying to keep it simple. Phase-shift in NFB is certainly another can of worms.

-
 
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Re: PCL86 SE Ultralinear Monos

Post by Nick » Sun Sep 16, 2018 11:42 pm

Mike H wrote:
Sun Sep 16, 2018 1:54 pm
Certainly, I'm trying to keep it simple. Phase-shift in NFB is certainly another can of worms.
Yep, but as Steve had it osculating in the high audio range, I can't help thinking its going to need some reactance somewhere tp get that low.
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Re: PCL86 SE Ultralinear Monos

Post by Cressy Snr » Mon Sep 17, 2018 1:01 pm

Mike H wrote:
Sat Sep 15, 2018 11:45 pm
Cressy Snr wrote:
Sat Sep 15, 2018 10:30 pm
Not sure a ferrite would achieve much as the thing oscillates in the audio band at around 10-15KHz if there is any stray capacitance between the triode section plate and the pentode section control grid, both of which are on adjacent pins (8 and 9 respectively)
Actually it's the other way round -

"In particular every precaution is taken to minimise stray capacitive coupling between the grid circuit of the triode section and the anode circuit of the pentode section of the ECL86. The valve-holders for the ECL86 should be nylon-loaded and skirted."

So triode grid pin 1, pentode anode pin 6, and are diametrically opposite on the socket. But yes I expect it would. Easy to get capacitive and even RF coupling between adjacent wires. First thing that occurs to me is that the triode grid wires must be screened.

HTH
Hi Mike,
I had coupling between pins 8 and 9 with no valve in the socket on one channel. There was a clear voltage being set up from the triode plate to the pentode g1. So it's possible that I had that problem plus the known problem, that the Mullard book highlights. Yes, I know I got it wrong with the description :)

Either way, with the ECL86, I think it's fair to say that you have to be aware of strays, proper layout, in-band oscillation and the importance of using adequate valve sockets.
It is a superb sounding valve if you watch what you're doing.
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Mon Sep 17, 2018 1:39 pm

Hi Steve, yes not disbelieving you just thinking less likely. But always possible. 'Course I'm guessing at the mo as not got near the stage of turning mine on yet. (Long way to go yet.)

:D

I think prudent to use the socket with the central cylindrical screen, and ground it. Also I should have some screened sockets somewhere.
 
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Re: PCL86 SE Ultralinear Monos

Post by Mike H » Mon Sep 17, 2018 1:49 pm

At the mo so far I've actually executed a splurge on eBay and so got on order a case, (was thinking of hacking up and bending some alu sheets but couldn't be asked in the end); a Cosmos Tocos stereo pot, and some perforated alu sheet. Which I plan to use as top and bottom panels for ventilation. Already got 2 Tungsram PCL82's, and a spare.
 
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