EL36/6CM5/PL36/25E5 triode strapped data
Tom Schlangen
some sort of "Oz special", since those folks down under have
tons of them, being used in TV deflection circuits ... but
these tubes are plenty and cheap in Europe, too.
Here you can find plate curves for triode strapped
EL36/6CM5/PL36/25E5:
http://www.tubes.mynetcologne.de/roehren/daten/el36pentode_as_triode.pdf
3 NOS samples (Philips EL36, RFT and Siemens PL36) were measured
and the data was averaged.
This time I have left out details on mu, gm and rp, since they
depend very much on the op point chosen. But it is easy to derive
them from the plate curves at the op point you consider yourself.
There is a site about EL36 audio usage (including several circuits
and further data) on the web:
http://www.alphalink.com.au/~cambie/EL36.htm
And Patrick Turner shows a trioded 6CM5 PP amp on his web site,
maybe Patrick could add a few hints on trioded PP output stage
op points?
Tom
--
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Gregg
Y'know, IIRC, a 60's CB used them as finals. Was it a Tram?
I know they amplify SSB *very* cleanly ;-)
--
Gregg t3h g33k
"Ratings are for transistors....tubes have guidelines"
http://geek.scorpiorising.ca
Patrick Turner
Tom Schlangen wrote:
> Gentlemen,
>
> some sort of "Oz special", since those folks down under have
> tons of them, being used in TV deflection circuits ... but
> these tubes are plenty and cheap in Europe, too.
>
> Here you can find plate curves for triode strapped
> EL36/6CM5/PL36/25E5:
>
> http://www.tubes.mynetcologne.de/roehren/daten/el36pentode_as_triode.pdf
>
> 3 NOS samples (Philips EL36, RFT and Siemens PL36) were measured
> and the data was averaged.
>
> This time I have left out details on mu, gm and rp, since they
> depend very much on the op point chosen. But it is easy to derive
> them from the plate curves at the op point you consider yourself.
>
> There is a site about EL36 audio usage (including several circuits
> and further data) on the web:
>
> http://www.alphalink.com.au/~cambie/EL36.htm
>
> And Patrick Turner shows a trioded 6CM5 PP amp on his web site,
> maybe Patrick could add a few hints on trioded PP output stage
> op points?
First a warning.
These tubes have top anode top caps, so well insulated connections are needed,
and with a cage over the tubes.
I use a pair of these per channel with Ea = +375V, Ia = 50 mA,
Idiss at idle = 18.75 watts, which is over rating, but OK for class A triode,
since the rating was for TV use.
RL = 7k to 20k a-a.
po max is about 28 watts, I am happy with about 23 class AB1.
I have fixed bias at about -60V, so you need a driver capable of
40 vrms, so 6SN7/6CG7/6H30 etc are the ones.
Triode u = about 5, so gain = about 4.
Patrick Turner.
Tom Schlangen
thank you for the additional information given!
At the moment, there are grid voltages only up to -84V covered by
my plate curve sheet. Considering your highish B+ and -Vg1 op point,
quite some additional work would be needed to cover that range.
Problem is scaling: compressing the B+ axis further to include
higher B+ will render the graph almost illegible. Maybe for -Vg1
I should go up from 2 volt steps to 4 volt steps.
Regarding the high Pd (at iddle) you set with your amp, I can
only say that during my test series - at up to 15 watts total
Pd plate and screen - my tube samples showed no stress signs
whatsoever. Using 100 ohms between plate and screen, screen Pd
stayed easily within specs, but max. allowed screen voltage
is _grossly_ exceeded of course ...
Tom
--
Patrick Turner
Tom Schlangen wrote:
> Hi Patrick,
>
> thank you for the additional information given!
>
> At the moment, there are grid voltages only up to -84V covered by
> my plate curve sheet. Considering your highish B+ and -Vg1 op point,
> quite some additional work would be needed to cover that range.
IMHO, I would not bother to draft the plate curves of a tube unless I
had a
up to a thousand volts avaialable, and some means of driving the grid
positive to
be able to include the positive grid plate resistance lines.
However, your work in presenting the curves of all these favourite old
tubes is invaluable
as a guide to many folks who may be wanting to design something.
>
>
> Problem is scaling: compressing the B+ axis further to include
> higher B+ will render the graph almost illegible. Maybe for -Vg1
> I should go up from 2 volt steps to 4 volt steps.
True, even 5 volt steps would do, but ppl can interpolate with 4v steps
easiest.
>
>
> Regarding the high Pd (at iddle) you set with your amp, I can
> only say that during my test series - at up to 15 watts total
> Pd plate and screen - my tube samples showed no stress signs
> whatsoever.
The 6CM5 don't glow red until about 25+ watts.
> Using 100 ohms between plate and screen, screen Pd
> stayed easily within specs, but max. allowed screen voltage
> is _grossly_ exceeded of course ...
The allowed screen voltage only applies to beam tetrode use, with the
screen voltage fixed.
But with triode there is a limit for Ea.
If you go beyond 375v, the bias required to "hold the current down"
becomes excessive, and the tubes tend to take off....
I have run my amp for 6 years no worries, only once adjusted the fixed
bias of the
4 ex TV second hand tubes.
Oh, and it sounds quite well, despite horrible OPTs, meant for 6GW8
in UL. I bought them from an old dude who never got around to building
a tube amp in 1965.
I am using about the same bias current as permitted for 6GW8, but 25%
more anode voltage,
and that is not a worry, since I still only use a an average of a less
than a watt.....
Patrick Turner.
> Tom
>
> --