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Old 20th March 2009, 08:48 AM   #1
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Default Push-Pull 6CL5's

Just wondering if anyone has played with the 6CL5 sweep tube much?
Data on them is scarce.
I was thinking of using a pair with a 3.5Kohm (plate-to-plate) output transformer,B+ maybe around 400Volts,will probably keep the screens ~175V or so.

Does 3.5K seem like a reasonable impedance for these guys?
Any other thoughts?
Thanks!
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Old 20th March 2009, 09:31 AM   #2
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Gah! No plate curves for those anywhere, eh?

What I do in a situation like that is run them to *just* visible distortion on the scope and make a note on the power output.

By adjusting the load resistance, make notes for 2K to 8K in 500 ohm increments (a good OPT is needed for this with lots of primary inductance.... I use a Pioneer OPT that's 8K:8R for tests).

There will be an impedance that gives maximum output.


If you want to get picky, you can repeat the steps only at 1 watt instead of maximum out and make a note of the Z that gives lowest THD and place the operating impedance in between the two

I'm lazy, so I do step 1 for max output and just add 20% and call it a day

Cheers!
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Old 20th March 2009, 10:21 AM   #3
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Quote:
Originally posted by Geek
Gah! No plate curves for those anywhere, eh?

What I do in a situation like that is run them to *just* visible distortion on the scope and make a note on the power output.

By adjusting the load resistance, make notes for 2K to 8K in 500 ohm increments (a good OPT is needed for this with lots of primary inductance.... I use a Pioneer OPT that's 8K:8R for tests).

There will be an impedance that gives maximum output.


If you want to get picky, you can repeat the steps only at 1 watt instead of maximum out and make a note of the Z that gives lowest THD and place the operating impedance in between the two

I'm lazy, so I do step 1 for max output and just add 20% and call it a day

Cheers!

hey Geek,
Your last step, adding 20% to the load with pentodes is perhaps going the wrong direction. I'd go to max power and subtract 20%( numerically) to make the load line steeper. For Triodes, you've got a reasonable method...
cheers,
Douglas
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Old 20th March 2009, 10:24 AM   #4
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hey-Hey!!!,
Given the 'preferred substitutes' lists the 6CB5, and comparing the short list of publilshed specs( gm, dissipation, and heater current), I'd design around the 6CB5 and be confident of being *VERY* close.
cheers,
Douglas
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Old 20th March 2009, 11:34 AM   #5
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Hi,

Quote:
Originally posted by Bandersnatch



hey Geek,
Your last step, adding 20% to the load with pentodes is perhaps going the wrong direction. I'd go to max power and subtract 20%( numerically) to make the load line steeper. For Triodes, you've got a reasonable method...
cheers,
Douglas
I'll keep that in mind, thanks!

I was dealing with trioded pentodes when I developed that actually

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Old 20th March 2009, 10:53 PM   #6
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6CB5 huh? Cool,Thanks Douglas!
I'll poke around and see what I can come up with.
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Old 21st March 2009, 12:25 AM   #7
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hey-Hey!!!,
For your 3k a-a plate load, try a 300V B+ and 80 mA plate current. Put g2 at about 125 V. It'll run to about 50 or so Watts.
cheers,
Douglas
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