If you are using the SK-640 sockets, which lack integral screen bypass
capacitors,
what kind of other screen bypass do you use?
Be advised that attempting linear operation of the 4X150 on 50 MHz using
conventional screen bypassing
is a disaster waiting to happen. There is very little control over the
self-resonant frequency of the screen circuit under these circumstances, and a
"cold screen grid" is essential for stable operation.
The previous suggestion of operating the amplifier in "grounded grid" will only
work if the proper voltages and bypassing are present on both grids.
Just tying both grids together and to ground will easily damage the control
grid, as the 4X150 family is not suitable for operation as an "high-mu" triode.
73/
Karl-Arne
SM0AOM
SM0AOM
----Ursprungligt meddelande----
Från : ai7rogerroger@gmail.com
Datum : 2015-07-27 - 20:17 (V)
Till : donroden@hiwaay.net, amps@contesting.com
Ämne : Re: [Amps] Follow-up...re: Time to ask for help.
Sockets in use are Eimac SK-640.
73, Roger
AI7RR
On Mon, Jul 27, 2015 at 10:49 AM, <donroden@hiwaay.net> wrote:
> I woke up and the thing on my mind was .....
>
> Are you using Eimac SK-630 sockets ?
>
> I think those sockets may have been the reason my amp was so stable on six.
>
>
> Don R.
>
>
>
> Quoting Roger <ai7rogerroger@gmail.com>:
>
> Don,
>> Thank you for the information. I've been studying other circuits and
>> combined with the info you just mentioned regarding screen loading, I have
>> a change to make. Both my grid and screen supplies are very stiff with
>> capability of supporting reverse current. My screens however are shunted
>> with very high resistance at the terminals just to hold them at ground
>> during rx.
>>
>> I've gone through many different wiring configurations with this amp and
>> have even had output once or twice, but every time I try to improve it, I
>> screw something up. This time finding the error hasn't been so easy.
>>
>>
>> 73, Roger
>> AI7RR
>>
>> On Sun, Jul 26, 2015 at 8:17 PM, <donroden@hiwaay.net> wrote:
>>
>> No problem... Just think of the 250Bs as a big variable DC load on the
>>> plate power supply. You should be able to change the grid voltage and
>>> see
>>> a smooth
>>> increase in plate current from zero to near 1000ma ( very briefly !!! )
>>>
>>> I would suggest zero to 500ma as a minimum range to check.
>>> No more than that until absolutely sure everything is stable
>>>
>>>
>>> THEN hook up the grid circuit and see if you can do the same thing..
>>> something may be breaking down in the grid circuit and killing the bias
>>> voltage and
>>> then ...... BOOM ... Plate current runs away.
>>>
>>>
>>>
>>>
>>>
>>> Quoting Roger <ai7rogerroger@gmail.com>:
>>>
>>> "I'm confident my DC is stable."
>>>
>>>>
>>>> Scratch that. I misunderstood the statement:
>>>>
>>>> "He has to make the amp DC stable before hooking up the input and output
>>>> RF
>>>> networks."
>>>>
>>>>
>>>>
>>>>
>>>> 73, Roger
>>>> AI7RR
>>>>
>>>> On Sun, Jul 26, 2015 at 5:50 PM, Roger <ai7rogerroger@gmail.com> wrote:
>>>>
>>>> Sorry, I thought it was clear what I was trying to do. I have four
>>>> 4x150a
>>>>
>>>>> tetrodes in parallel, attempting to make them operate on 50mhz. I'm
>>>>> confident my DC is stable. Additional information includes, a Pi tuned
>>>>> input and output. Input and output terminations are quality 50 ohm
>>>>> devices.
>>>>> Power supply and rf deck are in separate boxes. My problem appears to
>>>>> be
>>>>> related to instability possibly caused by insufficient or incorrect
>>>>> neutralization.
>>>>>
>>>>> It was mentioned that the neutralizing cap needed to be by-passed and
>>>>> that's something I have not even considered. By-passing anything in the
>>>>> grid circuit seems contradictory to me.
>>>>>
>>>>>
>>>>> 73, Roger
>>>>> AI7RR
>>>>>
>>>>> On Sun, Jul 26, 2015 at 3:56 PM, <donroden@hiwaay.net> wrote:
>>>>>
>>>>> Quoting Ron Youvan <ka4inm@gmail.com>:
>>>>>
>>>>>>
>>>>>>
>>>>>> I am trying to find out what you are trying to do.
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> Me Too Ron,
>>>>>>>
>>>>>>
>>>>>> He has to make the amp DC stable before hooking up the input and
>>>>>> output
>>>>>> RF networks. We don't know if that's the case yet.
>>>>>>
>>>>>> Don W4DNR
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> Amps mailing list
>>>>>> Amps@contesting.com
>>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>
>
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