3c24

[ACPEN]

Hello
Any unwanted 3c24's or equiv. anyone?
If so, please - how many, how much?
Rgds
David.

[nic]

I have some Heintz and Kaufman 3C24 going spare . NOS but boxes have disintegrated . You do know the caveats of using these valves ?

cheers

Nic

[ACPEN]

Hi Nic
Thanks for your email - I am aware of certain necessary procedures regarding first use after long storage, and have despite this had a few filament failures - interested in hearing your advice please...
Regards
David

[nic]

It's not just the filament , although the filaments are fragile with spiral filament thoriated tungsten valves like 3C24 . Running fils only at first use can help condition a valve , some valves do get hopelessly gassy and can't be recovered . You need to operate the valves with some colour in the anode for correct operation as these valves are self-gettered . If using as a driver I find running a minimum of 6mA gets some colour on the anode , keep the grid leak as low as possible , say 50k or use a grid choke . If running as a A2 power stage , you will need heat dissipators for both the anode and grid pins . These are uninsulated so will need some shrouding around the valve . I would advise running conservatively , far too many designs out there running these things ragged . I'll dig a few out and test

[Nick]

I remember having to play the same games with 100tl's

I ran them on filament only for a bit then with the grid and filament connected ran them with a bench HT supply to get the anode red. I have some of the finned grid and anode connectors somewhere to get heat out of the valve.

[nic]

100TL is a lucky find

[ACPEN]

Thank you Nic for your observations on using the 3C24 - pleased to say I was aware of modt of its foibles, but good to have them confirmed. Look forward to hearing the results of your tests.
And thank you Nik for your thoughts too. You
may vaguely remember that some years ago I posted several notes on building class A2 amps usjng 811A's, 812A's and TZ40 and Da42's. I have modified one to run 3C24's in A2 hence the enquiry for any stock. They produce a nice sound but I've found them to be rather unreliable beasts due to filament failure and the effects of gassing etc - still I persevere as I like the sound and running red anodes are quite unusual.
Thank you both for your input.
Rgds
David

[Paul Barker]

I used one to shunt regulate a 6em7 amp. Broke one at least memory fails me may have broke a few. Glass much too thin and fragile fir pinouts through glass. I now regretI never tried them as audio output, but the amps sounded great with these the last thing between the power supply and the output valve. One of those amps you wish youd never broken down for parts.