Topband: 8877 Tube

[John Harden]

The Alpha 77-SX is a great amplifier with plenty of reserve. The plate 
voltage runs just under 4KV on the Hi-Power position. If you go to the 
larger transformers you are asking for trouble. The filter capacitor has 
to be changed to one with a 5 KV rating. When you do this you will push 
circuit components to their HV limit. There have been too many problems 
out there with those who have done this...

73,

John, W4NU

On 11/14/2012 9:56 PM, ZR wrote:
> The only problem with pushing an 8877 or the 3CPX to or over the 4KV 
> limit is that it enhances the chance of instability.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "Paul Christensen" <w9ac at arrl.net>
> To: <topband at contesting.com>
> Sent: Wednesday, November 14, 2012 7:23 PM
> Subject: Re: Topband: 8877 Tube
>
>
>> Bob,
>>
>> A non-issue.  Many of us have been running 8877s with Ep of 4KV.  For 
>> example, the typical no-load Ep of an Alpha 77Dx/Sx amp is right at 
>> the specified limit of 4KV.
>>
>> Some owners have been converting their 8877 amps over to the 
>> 3CPX1500A7 which has a much higher rated Ep since it was designed for 
>> pulsed service. Unless someone has access to a supply of pulse-rated 
>> tubes, I think it's waste of time unless the plate supply voltage is 
>> also increased.
>>
>> Paul, W9AC
>>
>>
>> ----- Original Message ----- From: "Chortek, Robert L" 
>> <Robert.Chortek at berliner.com>
>> To: <topband at contesting.com>
>> Sent: Wednesday, November 14, 2012 6:56 PM
>> Subject: Topband: 8877 Tube
>>
>>
>>> Wonder if someone can help with a technical question with the amp I 
>>> use on 160 meters.
>>>
>>> The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate 
>>> Voltage of 4000 Volts" for the tube, and also says in "typical 
>>> operation" the plate voltage is between 2700 and 3500 volts. In my 
>>> amp (Ameritron AL-1500), the plate voltage is 3750.  My question is 
>>> - should I be concerned (it's clearly below the maximum" but above 
>>> the range that is considered "typical"?   I just want to be sure I'm 
>>> not adversely affecting the useful life of the tube.
>>>
>>> Any help would be appreciated.
>>>
>>> 73,
>>>
>>> Bob/AA6VB
>>>
>>> _______________________________________________
>>> Topband reflector - topband at contesting.com
>>
>> _______________________________________________
>> Topband reflector - topband at contesting.com
>>
>>
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