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@earthlink.net>
To: "Discussion of Ten-Tec Equipment" <tentec@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@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@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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