Exactly!!!!!
That's the reason that if the grid is open, or floating, the tube turns into a
diode and has no control of the electron flow. In effect, like you say, it
would run away and eventually burn up. Way back when I first got into this, I
said I never seen a problem with a grid fuse as long as the anode voltage was
killed as soon as the fuse blew. One would never want to continue broadcasting
after this condition happened. Since most amps monitor grid current, and plate
voltage / current, it would be quickly seen on the meters if it happened. A
trip could even be used to quash the B+ if this happened simply by watching the
anode current. If it got too high, just kill the B+.
I've not seen the Valvo article, but it would be a good read, and I'd
personally like to see it.
Thanks again,
Will
*********** REPLY SEPARATOR ***********
On 7/25/06 at 9:24 PM Peter Voelpel wrote:
>Hi Will,
>
>Yes, the grid must always keep its DC connection to ground not to turn into
>a runaway condition by a positive charged grid, it does not matter whether
>it is grounded grid or grounded cathode circuitry.
>For that reason VALVO suggested the 50KOhm safety resistor from grid to
>ground in their transmitting tube manual when the grid is not strapped to
>ground.
>
>73
>Peter
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>Behalf Of Will Matney
>Sent: Dienstag, 25. Juli 2006 20:52
>To: amps@contesting.com
>Subject: Re: [Amps] Fw: "Tubes 201" - How Vacuum Tubes Really Work
>
>Peter,
>
>Thanks! That is the very point I have been trying to get across all along!
>Remember, the original threads were asking about a 3-500Z with the grid
>resistor or fuse in G-G., or it was when I jumped in the mix There's been a
>lot of other tubes and circuits dragged into the discussion, but I've tried
>to center my comments around a 3-500Z G-G circuit. In grid driven circuits
>though as in receivers and transmitters, or some amps, the grid can be made
>to go positive for part of a cycle. This I think Rich means also. He can
>correct me if I'm wrong.
>
>Thanks,
>
>Will
>
>
>*********** REPLY SEPARATOR ***********
>
>On 7/25/06 at 8:40 PM Peter Voelpel wrote:
>
>>Hi Will,
>>
>>when the grid is kept grounded it can not become more positive then the
>>cathode if that is grounded and not negative biased as well, except by RF
>>drive on it above its choke.
>>
>>73
>>Peter
>>
>>-----Original Message-----
>>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>>Behalf Of Will Matney
>>
>>Peter,
>>
>>On that, I agree it's the only way to make one positive (for only part of
>a
>>cycle). Are there any other ways to make the grid positive and the grid be
>>at ground potential with the cathode at ground? A lot of amps cathodes are
>>at ground potential unless biased.
>>
>>Best,
>>
>>Will
>>
>>
>>
>>*********** REPLY SEPARATOR ***********
>>
>>On 7/25/06 at 8:04 PM Peter Voelpel wrote:
>>
>>>Nothing is easier then that if the cathode is going/driven negative with
>>>respect to ground.
>>>Grid voltage is always measured from grid to cathode, not to ground.
>>>
>>>73
>>>Peter
>>>
>>>
>>>-----Original Message-----
>>>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>>>Behalf Of Will Matney
>>>
>>>please explain how a grid becomes positive when tied to ground?
>>>
>>>
>>>
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>>
>>
>>
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>
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