[Amps] Best way to tune a Dentron ML2500 ?

R.Measures r at somis.org
Sun Jul 31 20:25:58 EDT 2005


On Jul 31, 2005, at 1:36 PM, Bob Maser wrote:

> More than 50ma

Eimac specs the 8875's grid diss. at 5W max., typical grid-cathode 
driving potential is c. 42v-pk, or c. 30V-rms.  I = P / E:  5W / 30V = 
0.1666A, so two 8875s should be able to withstand 333mA of grid-I 
without exceeding the grid-diss rating.

-  From my experiences, the greatest danger to the 8875's grid is from 
a UHF parasite and the possiblity of gold-sputtering therefrom.

> ----- Original Message ----- From: "R. Measures" <r at somis.org>
> To: "Bob Maser" <bmaser at tampabay.rr.com>
> Cc: "AMPS" <amps at contesting.com>
> Sent: Sunday, July 31, 2005 4:21 PM
> Subject: Re: [Amps] Best way to tune a Dentron ML2500 ?
>
>
>> On Jul 31, 2005, at 11:54 AM, Bob Maser wrote:
>>> I disagree with your note 5.  Tuning the tune and load controls for 
>>> maximum smoke will sometimes give you too much grid current.
>> Bob -- How much is too much?
>>> My Alpha 78 in the manual mode, for instance, requires a slight 
>>> clockwise tweak in order to bring the grid current down to 
>>> acceptable limits.  With the 8874's replacement cost, you can bet I 
>>> watch grid current like a mother hen.
>>>
>>> Bob  W6TR
>>> ----- Original Message ----- From: "R.Measures" <r at somis.org>
>>> To: <rees.a at btconnect.com>
>>> Cc: <amps at contesting.com>
>>> Sent: Sunday, July 31, 2005 2:43 PM
>>> Subject: Re: [Amps] Best way to tune a Dentron ML2500 ?
>>>
>>>
>>>>
>>>> On Jul 31, 2005, at 11:16 AM, Adrian Rees (M1LCR) wrote:
>>>>
>>>>> Whats the best way to tune a Dentron 2500 Linear, for max power and
>>>>> longest
>>>>> tube life ?
>>>>
>>>> For best tube life:
>>>> 1.  decrease the Q of the VHF suppressors in the anode leads.
>>>> 2.  decrease the VHF-Q of the lengthy lead that connects the Tune-C 
>>>> to
>>>> the anode HV RFC.
>>>> 3.  Tune the amplifier up for SSB with dits or a tuning pulsar.
>>>> 4.  do not drive the amplifier with more than c. 60w -- unless of
>>>> course you have more than a couple of dozen spare tubes.
>>>> 5.  tune for max out with c. 60w drive.  When the drive is right,
>>>> tuning for max RF out always produces safe grid-I.
>>>>   - note - For key down / RTTY / FM service the absolute max current
>>>> rating is 350mA per tube.  Exceeding this rating can strip the oxide
>>>> coating off of the cathode.  The SSB rating of the cathode is 500mA 
>>>> on
>>>> voice peaks.
>>>>>
>>>>> What should the Grid Current be at maximum power ?
>>>>
>>>> Tuning as above will insure that most of the electrons go into the
>>>> antenna and not into the grid.
>>>>>
>>>>> Thanks
>>>>>
>>>>> Adrian Rees
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>>
>>>>
>>>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>>>
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>>
>>>
>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>
>
>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org



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