Please don't use used or pulls for a 2 tube amp. The way they're designed one
tube may be drawing 60 Ma grid current and the other 200 ma. Yet a total of 260
ma would be normal.
Grid to filament is the more common failure mode as the result of excessive
grid current.
Some one posted earlier about buying 2 used tubes and one failed after only a
few hours. It is reported to have taken out the bias ckt. Evidence of a grid
to filament short.
73
Bob K4TAX
Sent from my iPhone
> On Aug 10, 2014, at 6:08 PM, Brian Carling <bcarling@cfl.rr.com> wrote:
>
> Are there other sources for 3-500Z tubes? Such as NOS Eimacs? Or broadcast
> pulls?
>
> Best regards - Bry Carling
>
>
>
>> On Aug 10, 2014, at 2:08 PM, "Duane Calvin" <ac5aa1@gmail.com> wrote:
>>
>> This was certainly true of the EIMAC tubes, as long as you cared well for
>> them. I've not had as good a luck with the current Chinese-sourced tubes
>> (specifically, the 3-500ZG's from RF Parts, which the Centurion uses.)
>>
>> 73, Duane
>>
>> Duane Calvin, AC5AA
>> Austin, Texas
>> www.ac5aa.com
>>
>>
>>
>>
>> -----Original Message-----
>> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Wade Staggs
>> Sent: Sunday, August 10, 2014 12:54 PM
>> To: Discussion of Ten-Tec Equipment
>> Subject: Re: [TenTec] Hercules 444 amp
>>
>> *At least for now, even if we could afford one of the Big Gun Solid State
>> Amps. I would hope that we would have the good sense to stick with an Amp
>> which runs 1 or 2 of the 3-500ZG Triodes. They are as tough as Nails. How
>> can you argue with a system that with proper care, will run a lifetime. The
>> tubes in our SB-220 are Original. This means that they are approaching
>> their Fortieth Birthday. We recently replaced the Capacitors and Relay. The
>> Amp was still working Great when we did this Preventative Maintenance. And
>> Even a Cave Man with Knives and Bear Skins can repair the Amp if needed. *
>> * 73
>> from Wade/KJ4WS*
>>
>>
>>> On Sun, Aug 10, 2014 at 12:01 PM, Robert <rmcgraw@blomand.net> wrote:
>>>
>>> Many to most design parameters do change radically when converting from
>>> BIPOLAR to MOSFET devices.
>>>
>>> I seen to think MFJ does have their products in the reach of the average
>>> ham. I find typically they offer reasonable designs, reasonable quality
>> at
>>> reasonable prices. Maybe it's the hams average reach that needs adjusting.
>>> The days of the SB-200 and SB-220 KIT prices are long gone.
>>>
>>> Good quality amps, those that are clean and don't spew garbage across the
>>> bands, require good design and good quality parts. Then add a high duty
>>> cycle and it places more demand on the designs and the parts choices.
>>>
>>> 73
>>> Bob K4TAX
>>>
>>> Sent from my iPhone
>>>
>>>> On Aug 9, 2014, at 5:38 PM, Brian Carling <bcarling@cfl.rr.com> wrote:
>>>>
>>>> So maybe the Hercules can be converted to use MOSFETs. Seems like it
>>> should be possible.
>>>>
>>>> I also think MFJ needs some competition on MOSFET linear amplifiers to
>>> get the price point within reach of the average ham.
>>>>
>>>> There is just not a good reason why so many linear amplifiers should
>>> cost $3500 to $9500 when you look at the parts cost and manufacturing
>> cost.
>>>>
>>>> [/SOAPBOX]
>>>>
>>>> Best regards - Bry Carling
>>>>
>>>>
>>>>
>>>>> On Aug 9, 2014, at 5:24 PM, Douglas <sparks06524@yahoo.com> wrote:
>>>>>
>>>>>
>>>>> Date: Sat, 9 Aug 2014 10:12:45 -0400
>>>>> From: Brian Carling <bcarling@cfl.rr.com>
>>>>> To: "k9yc@arrl.net" <k9yc@arrl.net>,
>>>>> Discussion of Ten-Tec Equipment
>>>>> <tentec@contesting.com>
>>>>> Subject: Re: [TenTec] Hercules 444 amp
>>>>> Message-ID: <86F80EE5-1044-42AA-9641-D8859123467B@cfl.rr.com>
>>>>> Content-Type: text/plain;
>>>>> charset=us-ascii
>>>>>
>>>>> Seems like a lot of RF power transistors are similar, so it
>>>>> should not be too difficult to find a substitute.
>>>>>
>>>>> Best regards - Bry Carling
>>>>>
>>>>> ------------------------------------------------------------
>>>>>
>>>>> Ah - but it is hard to find a substitute. The Ten-Tec factory can't
>>> find one.
>>>>>
>>>>> There were only a few designs of 250 to 300 watt 50V bi-polar power
>>> transistors made. The remaining ones are hard to get and have an HFE that
>>> is too high. Several such transistors have been totally discontinued.
>>> Motorola for example is out of that business. M/AComm bought some of their
>>> designs but in general bi-polar RF transistors are considered passe. RF
>>> MOSFETS are now the name of the game.
>>>>>
>>>>> Per another poster: I've not had trouble with the power supply drifting
>>> upward with temperature rise. Perhaps they solved that with compensation.
>>>>>
>>>>> 73,
>>>>>
>>>>> Doug/WA1TUT
>>>> _______________________________________________
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