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C3m linestage

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I am thinking about making a parafeed C3m linestage.
However I have not been able to find typical values for this tube when triode strapped.

I am especially looking for the plate resistance (Rp) value in triode mode.

Several people have used the Lundahl 1676 transformer for prafeed linestages.
Any comments regarding this transformer in combination with the C3m?
 
I made an RC coupled triode-connected (whew!) C3m linestage - it sounds very neutral.

a warning about the C3m - I've had two C3ms die because I moved them while they were warm. Not hot - just warm after 3-5 minutes of use while I was doing some troubleshooting. So make sure you let the tubes cool down before you unplug 'em or turn over your preamp. Also - every C3m I've ever used (I have 5 pairs of different brands) have been very microphonic.
 
(I have 5 pairs of different brands)

Siemens, Lorenz, TFK, Valvo....

So far I've seen (dismantling Siemens and TFK) two varieties of internal constructions; Siemens with mesh and TFK solid (think it's the second screen).... Also read somewhere that Siemens is the only manufacturer of C3m, so both could be Siemens variations over time... Dunno what's true.

Simon
 
Cool tube!
Have a look at the guts of a Siemens C3m. A small mesh pentode/triode inside!



DSCF0004.jpg
 
I have Philips, Haltron, Valvo, Siemens and Lorenz C3ms... I would say that the majority of them look to be Siemens made... vintage varied with the Haltron looking the oldest to me. Didn't know that the TFK was had a solid-mesh - interesting. Some of the older EF40s used a solid-mesh and it's also used with some EF86 tubes.

I used b+ 350V
15k plate
430 ohm cathode with bypass

it's DC coupled to a 5687 white cathode follower...

off the top of my head - bias was ~6V

I used DC on the filaments... it was easier for me run a 7820 regulator with transformer I had on hand then buy a 20V unit.
 

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kstagger said:
I have Philips, Haltron, Valvo, Siemens and Lorenz C3ms...

The C3m was made by Philips (Valvo), TFK, Siemens and Lorenz; Haltron is only a rebrander


kstagger said:
... TFK was had a solid-mesh - interesting. Some of the older EF40s used a solid-mesh and it's also used with some EF86 tubes....

This mesh in the C3m, EF40, EF86, EF806 is the sreen, the anod is solid (analoque 6C6).

Regards Andreas
 
bequerel said:
Great looking preamp, kstagger! :)

Nice to see projects where the constructors have made an effort to make their projects look good, too.

thanks - I made that preamp to be used for a long long time so I could concentrate on other parts of my stereo. So far I've been very pleased with the sound - but I may be going back to a triode connected EF86 for my next linestage project.
 
kstagger, if you are still with us on this thread:

Did you "lift" the heaters up by means of a voltage divider, let them float or did you ground them?

The anode voltage is relatively high, so I would suppose that you exceed the maximum cathode to filament voltage differential if you did not "lift" the heater supply?

:scratch1:
 
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