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572b tube

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CQCQCQ

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Apr 11, 2013, 1:36:42 PM4/11/13
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Anyone got a 572 b tube they dont need, I need one to try somthing
out, and dont wish to purchase a pair, until i rectify the fault. Was
sitting listening the other night when i heard a hissing sound and and
smoke just before the valve popped, any helpful information would be
of a great help stripped it down last night and nothing apparent to
the cause of the valve popping.

FranK Turner-Smith G3VKI

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Apr 11, 2013, 5:49:45 PM4/11/13
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"CQCQCQ" <liste...@googlemail.com> wrote in message
news:2f7173ec-75ae-40a4...@r4g2000vbf.googlegroups.com...
Check or replace any capacitor connected to the control grid (pin 3). A
positive voltage here would cause the tube to saturate and probably fail in
the manner you describe.
--
;-)
.
73 de Frank Turner-Smith G3VKI - mine's a pint.
.
http://turner-smith.co.uk

BIG BOOMER.

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Apr 11, 2013, 6:10:31 PM4/11/13
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nice one Frank.

A. Non Eyemouse

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Apr 11, 2013, 6:40:28 PM4/11/13
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FranK Turner-Smith G3VKI <g3...@turner-smith.co.uk> wrote:
> "CQCQCQ" <liste...@googlemail.com> wrote in message
> news:2f7173ec-75ae-40a4...@r4g2000vbf.googlegroups.com...
>> Anyone got a 572 b tube they dont need, I need one to try somthing
>> out, and dont wish to purchase a pair, until i rectify the fault. Was
>> sitting listening the other night when i heard a hissing sound and and
>> smoke just before the valve popped, any helpful information would be
>> of a great help stripped it down last night and nothing apparent to
>> the cause of the valve popping.
>>
>>
> Check or replace any capacitor connected to the control grid (pin 3). A
> positive voltage here would cause the tube to saturate and probably fail in
> the manner you describe.

Aren't 572B's normally run in grounded-grid configuration in CB
amplifiers such as Yeasu FL2100Z's?

--
Mouse.
Where morse meets house.

G4KFK

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Apr 12, 2013, 3:55:42 AM4/12/13
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On 11/04/2013 22:49, FranK Turner-Smith G3VKI wrote:
> "CQCQCQ" <liste...@googlemail.com> wrote in message
> news:2f7173ec-75ae-40a4...@r4g2000vbf.googlegroups.com...
>> Anyone got a 572 b tube they dont need, I need one to try somthing
>> out, and dont wish to purchase a pair, until i rectify the fault. Was
>> sitting listening the other night when i heard a hissing sound and and
>> smoke just before the valve popped, any helpful information would be
>> of a great help stripped it down last night and nothing apparent to
>> the cause of the valve popping.
>>
>>
> Check or replace any capacitor connected to the control grid (pin 3). A
> positive voltage here would cause the tube to saturate and probably fail
> in the manner you describe.

572Bs are also prone to grid/Kathode shorts, which causes them to get
demoted to diodes. I had a brand new 572B (one of an alleged matched
pair) arrive in that state from an ebay seller in China.


CQCQCQ

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Apr 12, 2013, 4:05:41 AM4/12/13
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On Apr 11, 10:49 pm, "FranK Turner-Smith G3VKI" <g3...@turner-
smith.co.uK> wrote:
> "CQCQCQ" <listener...@googlemail.com> wrote in message
I read somthing about that Frank, and cannot find it,

FranK Turner-Smith G3VKI

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Apr 12, 2013, 9:44:53 AM4/12/13
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"A. Non Eyemouse" <some...@work.invalid> wrote in message
news:G9adnQC2FddBpvrM...@giganews.com...
Eh? Is this a wind-up? There is no cathode so in grounded-grid you would
have to drive the tube by modulating the filament volts. Would that work?

Ian Jackson

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Apr 12, 2013, 10:02:22 AM4/12/13
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In message <CdU9t.153$YK...@fx25.fr7>, FranK Turner-Smith G3VKI
<g3...@turner-smith.co.uK> writes
You feed the AC to each end of the heater through RF chokes, and you
feed the RF to each end of the heater through capacitors.
--
Ian

A. Non Eyemouse

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Apr 12, 2013, 10:25:10 AM4/12/13
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IIRC directly-heated (as opposed to indirectly-heated).

Lordgnome

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Apr 12, 2013, 10:39:35 AM4/12/13
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>>>> Aren't 572B's normally run in grounded-grid configuration in CB
>>>> amplifiers such as Yeasu FL2100Z's?
>>>>
Worth checking the grid stopper resistors if it is a FL2100Z - they are
favourite for going high and may account for the OP's fizz.

Les.

CQCQCQ

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Apr 12, 2013, 10:40:06 AM4/12/13
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On Apr 11, 10:49 pm, "FranK Turner-Smith G3VKI" <g3...@turner-
smith.co.uK> wrote:
> "CQCQCQ" <listener...@googlemail.com> wrote in message
it's a kw-1000, was usuing the tx ground from a yaesu ft 2000 to
switch on the linear, someone has suggested it could be the tx gnd
from the ft 2000, that has caused the problem.

John

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Apr 12, 2013, 10:57:46 AM4/12/13
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"CQCQCQ" <liste...@googlemail.com> wrote

>> Anyone got a 572 b tube they dont need, I need one to try somthing
>> out, and dont wish to purchase a pair, until i rectify the fault. Was
>> sitting listening the other night when i heard a hissing sound and and
>> smoke just before the valve popped, any helpful information would be
>> of a great help stripped it down last night and nothing apparent to
>> the cause of the valve popping.
>>
>>

Are you sure its the tube - it may well be something else. Given that
something smoked, have a look for any components looking the wrong shade of
brown or black.



BIG BOOMER.

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Apr 12, 2013, 11:33:41 AM4/12/13
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its definitely the tube lol.

CQCQCQ

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Apr 12, 2013, 12:07:27 PM4/12/13
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On Apr 12, 3:57 pm, "John" <J...@invalid.invalid> wrote:
>  "CQCQCQ" <listener...@googlemail.com> wrote
Done that john, everything in amp seems ok at a glance, and unless
tubes come with an air vent, yes it's certainly the tube, I am just
trying to determine what would be the cause of the tube over heating
and popping, while the amp was idiling, got another one coming for
test purposes. Hope to pick it up tomorrow or sunday, and put it on
the bench. Someone suggested it may be the tx ground from the ft 2000
that caused it, dont know yet till I get another valve and fire it
up.

Ian Jackson

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Apr 12, 2013, 3:44:34 PM4/12/13
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In message <kLSdnWykF_LbhPXM...@giganews.com>, A. Non
Eyemouse <some...@work.invalid> writes
Which is what Frank said (in as many words). If the heater = the
cathode, you have to do what I said. You can use two separate RF chokes,
or one bifilar wound.

Even if a valve is indirectly heated, because of the inherent
capacitance between the heater and the cathode, there might be some
advantage in feeding the heater supply via RF an RF choke (or chokes) -
even though the impedance looking into the cathode will be inherently
quite low.
--
Ian

FranK Turner-Smith G3VKI

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Apr 13, 2013, 4:14:53 AM4/13/13
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"Ian Jackson" <ianREMOVET...@g3ohx.demon.co.uk> wrote in message
news:qzSP35Zu...@g3ohx.demon.co.uk...
Would this not produce a large 50 or 100Hz AM component to the output?

Ian Jackson

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Apr 13, 2013, 4:42:17 AM4/13/13
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In message <ku8at.2178$YK....@fx25.fr7>, FranK Turner-Smith G3VKI
I think you use a floating (or bi-phase) AC power feed for the heater,
and feed the RF to both ends of the heater (using caps and RF choke(s)).
I've not done it myself, but I'm pretty sure it's done something like
that.
--
Ian

Brian Howie

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Apr 13, 2013, 5:01:43 AM4/13/13
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In message <ku8at.2178$YK....@fx25.fr7>, FranK Turner-Smith G3VKI
<g3...@turner-smith.co.uK> writes
>>
>Would this not produce a large 50 or 100Hz AM component to the output?

Thermal time constants are too long.

BTW - why do transformers hum ?

Gurl qba'g xabj gur jbeqf

I'll get my coat.

Brian
--
Brian Howie
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