[TenTec] Hercules 444 amp

[Bob McGraw - K4TAX]

I've found that glass bottle triodes do benifit, largely due to circuit 
designs, thus having matched tubes to be a plus in tube longivity.

And I agree that using a resistor, a fuse or RF choke between the grid 
terminals (3 of them) to ground for a grounded grid amp does leave a 
noticeable amount of room for VHF oscillations to exist.  The better and 
more stable amplifier design will take all three of the grid pins of the 
3-500Z to chassis ground at each grid pin using a 1/4" wide copper strap 
which has a length of less than 2" overall.

73
Bob, K4TAX




----- Original Message ----- 
From: "Mike Schatzberg" <cherokeehillfarm at earthlink.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Wednesday, August 13, 2014 12:22 PM
Subject: Re: [TenTec] Hercules 444 amp


> The whole world seems to buy matched pairs or quads.
>
> There doesn't seem to be a need for this when buying ceramic triodes, 
> although some users at VHF and UHF still try to buy matched pairs.
>
> I see that Richard Measures advocates the use of grid fuses to protect the 
> glass triodes, but I found that his theory does not work in practice for 
> me. A good control board will work, a resister of low wattage doesn't do 
> the job.
>
> 73,
>
> Mike
> W2AJI
>
> Sent from my iPhone
>
>> On Aug 13, 2014, at 11:03 AM, "Rick - DJ0IP / NJ0IP" <Rick at DJ0IP.de> 
>> wrote:
>>
>> That may be a little too optimistic, Mike.
>> Purchasing matched pairs does not assure they are going to draw equal
>> current throughout their life, but it does improve the chances.
>>
>> I have a hunch if you would pull several matched pairs after a couple
>> hundred hours and check them again, some may not be matched anymore.
>>
>> On the other hand, there doesn't seem to be any other choice.  Seems 
>> being
>> able to monitor and adjust the bias individually just requires too much
>> extra hardware.
>>
>> We don't really have that problem here in DL because we're only allowed
>> 750w.
>> The single 3-500z handles that just fine.
>>
>> 73 - Rick, DJ0IP
>> (Nr. Frankfurt am Main)
>>
>>
>> -----Original Message-----
>> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Mike
>> Schatzberg
>> Sent: Wednesday, August 13, 2014 3:01 PM
>> To: Discussion of Ten-Tec Equipment
>> Subject: Re: [TenTec] Hercules 444 amp
>>
>> The matching of the tubes when purchased assures they will draw
>> approximately the same grid current in the amp.
>>
>> Proper biasing will help assure the cleanest signal for the selected 
>> class
>> of service. The 3-500 is a zero bias triode, but needs to be properly 
>> biased
>> for good linearity for the desired class of service. Greater bias voltage
>> will increase the needed drive to reach full output.
>>
>> 73,
>>
>> Mike W2AJI
>>
>> Sent from my iPhone
>>
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