Brusque

Have you tried the "listen" test to a virgin tube? As I recall, most
tubes would have elements that would vibrate when shaken. Mostly the
various grids etc although the whole structure can also vibrate/rattle
a bit.

Is it causing a problem? Are you getting excessive microphony / feed back e=
tc?

Since the grids etc. are sitting in a vacuum they will not be subject
to speaker vibration directly, can you mount the valves using a
damping material or clamp them to something solid?

I don''t thing any external magnetic field from a speaker would be
enough to cause a problem. (I have seen how a magnetic field from a
power transformer can effect a CRT tube however - took a while to
figure out why part of the trace was running "backwards").

RP

2009/5/12 Edson Brusque <brusque.listas@citronics.com.br>:
> Hello,
>
> =A0 =A0 I have a question that maybe some of the tube guys on the list can
> answer.
>
> =A0 =A0 Can a speaker's magnetic field interfere with tubes/valves and
> damage it?
>
> =A0 =A0 Let me try to explain the situation. I've made some combo guitar
> amps. They are just prototypes I'm making while studying tube circuits.
> They uses a pair of 6L6 in the power section and gives close to 40W
> maximum output power.
>
> =A0 =A0 Almost all the 6L6s (3 pairs) I've been using have developed tuble
> rattle. I still have to make a simple single ended power amp to
> individually test the tubes and discover wich ones are really
> compromised but it seens all 6 have different levels of rattle. Tapping
> the tubes with a finger while holding it near the ear, I can hear
> something vibrating inside the tubes. The frequency/volume of the
> vibrations changes from tube to tube and also depending on where I tap.
>
> =A0 =A0 This is really intrigging me. The power section works at about 45=
0V
> on the tubes plates. Plate current is about 45mA (each tube). Screen
> grid voltage is about 420V and current is bellow 2mA. The power
> dissipation seens to be well bellow the maximum allowed. I don't have
> any fan blowing air to keep the tubes cool, but there's some airflow by
> convection.
>
> =A0 =A0 Now, one the power tubes are very near one of the speakers (it's
> two 10 inches). The physical layout, side-looking, is something like:
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 .
> =A0 =A0+--+ =A0+--+ =A0 =A0 =A0/|
> =A0 =A0|V1| =A0|V2| =A0 =A0 / |
> =A0 =A0| =A0| =A0| =A0| .--| =A0|
> =A0 =A0'--' =A0'--' | =A0| =A0|
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 '--| =A0|
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 \ |
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0\|
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 '
>
> =A0 =A0 I've been looking for a mail group about audio tubes/valves
> circuits but haven't found anything interesting. Maybe there's a
> "tubelist" somewhere?
>
> =A0 =A0 Best regards,
>
> =A0 =A0 Brusque
>
>
>
> --
> ---------------------------------------------------------------------
> Edson Brusque =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Stagetronics Eletro =
Eletr=F4nicos Ltda
> Research and Development =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Blumenau =A0=
- =A0SC =A0- =A0Brazil
> http://www.ryan.com.br/netiqueta.htm =A0 =A0 =A0 =A0 =A0 =A0 www.citronic=
s.com.br
> ---------------------------------------------------------------------
> --
> ---------------------------------------------------------------------
> Edson Brusque =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Stagetronics Eletro =
Eletr=F4nicos Ltda
> Research and Development =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Blumenau =A0=
- =A0SC =A0- =A0Brazil
> http://www.ryan.com.br/netiqueta.htm =A0 =A0 =A0 =A0 =A0 =A0 www.citronic=
s.com.br
> ---------------------------------------------------------------------
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