Underheating on 6072 tube

[dukasound]

We saw many tubes in microphones have lower voltage for heating.
What about 6072 in my Ela m (still in progres :? , silicon holder for capsule not finished but all voltages are OK and I got sound :grin: )?
Thanks
Duka

 

[Guest]

[quote author="dukasound"]We saw many tubes in microphones have lower voltage for heating.
[/quote]
Decend underheating of (condenser) mic tube can solve problems
with input grid current and noise problems implied them.

Also it makes live of tube longer live decrease with
some higher power of voltage , t_live~1/V**4 ?
it is in each bulb design textbook.

Some producers (Hammond) uses this second benefit in their
equipment (organs, amps). Underheated tube have diferent
characteristics and i.e. Hammond used special type number for
normal tubes underheated in his schematics.

xvlk

 

[dukasound]

Thanks xvlk!
Does anyone know what voltage!
EF 86 and 6AU6 works good with 5,7V.
Duka

 

[Guest]

[quote author="dukasound"]Does anyone know what voltage!
EF 86 and 6AU6 works good with 5,7V.
Duka[/quote]
Simply uses for you tube the some percents lower.
6,4 to 5,7. it is 10 % lower.
Get 10 % low for your tube.
Think, that this 10 % real value, where benefits of
underheating are not yet stopped by emission loss
and that caused low plate current, transconductancy and so on.

xvlk

 

[Guest]

Under heating is not always good. Some tubes wont do well under heated (VF14?). Also, there is not a fixed amount of under heating that works. The best way to find out is really to try out some values. First, run it for a few hours at normal voltage as Gus suggested (from Steve Bench experiments), then try several underheated values and see what works best.

 

[Tim Campbell]

To quote Bernhard Vollmer from a thread at Klaus Heyne's forum:

Underheating of tubes has one main reason. These tubes do not have a sufficiently high impedanced input and normally would not be suited for a microphone design. But if you underheat them (and accept the disadvantages that comes along with that procedure) their input impedance will raise and may reach acceptable values for a condenser microphone capsule.

Note: Not all tubes accept underheating and those who accept it will show different behavior. Some will simply fail as their cathode changes chemically with a too low temperature at its surface. This may last some hundred hours but it will occur (for example with an AC701 with 3V heating instead of 4V)


--------------------------------------------------------------------------------
Bernhard Vollmer, SCHOEPS GmbH
http://www.schoeps.de
http://www.schoepsclassics.com

 

[dukasound]

[quote author="Tim Campbell"]To quote Bernhard Vollmer from a thread at Klaus Heyne's forum:

Underheating of tubes has one main reason. These tubes do not have a sufficiently high impedanced input and normally would not be suited for a microphone design. But if you underheat them (and accept the disadvantages that comes along with that procedure) their input impedance will raise and may reach acceptable values for a condenser microphone capsule.

Note: Not all tubes accept underheating and those who accept it will show different behavior. Some will simply fail as their cathode changes chemically with a too low temperature at its surface. This may last some hundred hours but it will occur (for example with an AC701 with 3V heating instead of 4V)


--------------------------------------------------------------------------------
Bernhard Vollmer, SCHOEPS GmbH
http://www.schoeps.de
http://www.schoepsclassics.com

[/quote]

Thanks Tim.
For other: Klaus recomended 6,1V-6,2V on tube.
Best
Duka

 

[Guest]

[quote author="Tim Campbell"]To quote Bernhard Vollmer from a thread at Klaus Heyne's forum:

Underheating of tubes has one main reason. These tubes do not have a sufficiently high impedanced input and normally would not be suited for a microphone design. But if you underheat them (and accept the disadvantages that comes along with that procedure) their input impedance will raise and may reach acceptable values for a condenser microphone capsule.

[/quote]

Yes, it is "impedance" caused by grid current.
If we underheat tube, we have lower grid current and
then greater input (current noise) resistance.
and then smaller input current noise.
But parameters of tube as (voltage) noise resistance are worse(r).


But we have differend (and worse) tube (electrical) characteristics.
And tube with different characteristics must be differently typed.
for EF86 at 4,5 V heating
type BV1 (Bernard Volmer tube No 1)
typing EF86 in schematics complicated reading.
Follow mr. Hammond.


And what is it?
[/quote]

Note: Not all tubes accept underheating and those who accept it will show different behavior. Some will simply fail as their cathode changes chemically with a too low temperature at its surface. This may last some hundred hours but it will occur (for example with an AC701 with 3V heating instead of 4V) [/quote]
Is this "fail" equivallent to rise of 1/f noise corner?





xvlk

 

[Tim Campbell]

xvlk,
you should ask Bernhard what he meant though from his explanation I'm sure he means perfomance in general deteriorates to the point where the mic becomes unusable.