[TenTec] centurion

[Bob McGraw K4TAX]

GREAT!!!!!  problem resolved.  Easy fix too.

73

Bob, K4TAX


On 8/9/2018 10:36 AM, Rodney wrote:
> I replaced the 2n3055  the plate is now 50 to 60 m  with no drive. the 
> 2n3055 corrected the 190m with no drive.
>
> -----Original Message----- From: Ken Brown
> Sent: Thursday, August 09, 2018 12:47 AM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] centurion
>
> There are about two possible reasons a good tube will draw excessive
> current when it has no drive. 1) The bias is wrong. 2) There is an
> oscillation. Even "Zero Bias" Triodes have circuitry that establishes the
> bias (however low it may be). Usually there are two bias modes, one when
> the amplifier is in standby, and one when it is keyed. The standby mode
> bias should be high enough to keep the current so low that there is no 
> gain
> possible and therefore no oscillation. The operating mode bias level is
> such that the tube can amplify and so there could be an oscillation when
> there is no drive.
>
> If the excessive current only occurs when the amplifier is "keyed" ready
> for drive, but not driven it could be that the bias is wrong, or if the
> bias is correct there is an oscillation. If it happens even when it is 
> not
> keyed, it almost has to be a failure to establish cutoff bias.
>
> Bias is often established by a zener diode. Most grounded grid zero bias
> triode circuits have the grids at ground potential both DC and RF. The
> cathode is held a bit positive by the zener diode, making the grid 
> negative
> relative to the cathode, and cutting off the plate current to a very low
> level during standby. When keyed the zener is shorted, or some other 
> method
> is used to bring the cathode DC potential closer to zero, allowing the
> proper idling current for class AB linear amplification.
>
> If the problem is incorrect bias, you need to look around the circuitry
> that establishes the bias.
>
> If the problem is an oscillation you need to look a the output network,
> plate voltage DC blocking capacitor pi or pi-L network and see if 
> there is
> a fault there which makes the tube not have a proper RF load impedance.
>
> Or it could be something else.
>
> DE N6KB
>
>
>
> On Wed, Aug 8, 2018 at 5:43 PM, Mcelmer1 <mcelmer1 at netecin.net> wrote:
>
>> Rodney,
>>
>> With no drive and cherry red, Houston, we have a problem. Short 
>> somewhere,
>> been there done that with the Centurion but mine was drawing about 50 
>> - 75
>> ma.
>>
>> Perhaps I a missing part of conversation. Is this 190ma with no drive??
>>
>> Other friends of mine have been thru this with the 3-500s: no drive but
>> tube(s) drawing current.
>>
>> Mike
>> W8TRN
>>
>> Mike
>> W8TRN
>> ----- Original Message ----- From: "Rodney" <w3krq at dejazzd.com>
>> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
>> Sent: Wednesday, August 08, 2018 19:28
>> Subject: Re: [TenTec] centurion
>>
>>
>> no it was 190 m with no drive and tubes got red
>>>
>>> -----Original Message----- From: Bob McGraw K4TAX
>>> Sent: Wednesday, August 08, 2018 8:53 PM
>>> To: tentec at contesting.com
>>> Subject: Re: [TenTec] centurion
>>>
>>> Is this idle current with no signal?   If so it is about correct.
>>>
>>> 73
>>>
>>> Bob, K4TAX
>>>
>>>
>>> On 8/8/2018 7:42 PM, Rodney wrote:
>>>
>>>> I was on my Centurion talking and looked at my plate current it was
>>>> resting at 190m but the amp was putting out 1200w so tubes I think 
>>>> are ok.
>>>>
>>>> ---
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>>>>
>>>
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