[Amps] EIMAC vs Amperex 3-500

[John Lyles]

Rob and all,

I apologize for the wierd WEtransfer link. On my desktop it works fine 
and is a simple storage location like Dropbox or Googledrive, for a 
temporary document or image file. On my Android tablet, however, I see 
the ads and question about my cookie preferences. I did answer them by 
making sure all the options were switched off and clicking save, but 
that still didn't get to the file. Here is OCR version of the text from 
the PDF document instead:

-----------------------

CONTINENTAL ELECTRONICS CORPORATION
314R-l/828C-l 3-500Z TUBE PROBLEM

Some brands of 3-500Z tubes will run very hot in the Modulator position 
but will operate
properly in the RF position. It is normal for the Modulator tube anode 
to appear red when
operating at full power without modulation and can be expected to be 
yellow with full
modulation. However it should never appear white hot with or without 
modulation.
The output pulse from the Switching Modulator Card has a fixed rise time 
going in the
positive direction. If this rlse time is too slow for the particular 
modulator tube used, there
will be excessive anode dissipation. If the rise time is too fast, you 
can not achieve 100%
modulation in the negative direction. It appears that somevof the tubes 
that are available now.
have different characteristics from those that were available when the 
transmitter was
designed and this rise time must be changed in order to use these tubes 
in the Modulator
position.

Continental has checked two commonly available brands of 3-500Z tubes in 
a 314R-l and
recommends the following changes to the Switching Modulator Card, A2, 
circuits:
1. Change R-12 to 2.7K, 2Walt Carbon Composition. Continental PIN 
745-5669-000
2. Change C-13 to 1200pf, SOOVolt, Plastic coated silver mica PIN 
CM06FD122J03
3. Verify value of R-I0. May be two parallel 1500 ohm, 2 Watt carbon 
composition.
4. Verify value of R-l1. Should be 3.9K if Q6 is IRF-330 or 1.5K if Q6 
is 2N6S7S.
NOTE: It is important that only non-Inductive, carbon composition 
resistors be used at R10, R11, and R12.
5. Add a Parasitic Suppressor in series with Modulator anode lead. 
Continental Part
Number 650-2969-001

Please contact Continental Field Service if you have comments or 
questions about these changes. We would appreciate any comments about 
your experience with any brand of tube that you may be using in this 
transmitter and your results. Since this transmitter is out of 
production. we must depend on your input to us to help provide useful 
information to all users.


> Message: 2
> Date: Sat, 22 Oct 2022 15:46:39 -0600
> From: John Lyles <jtml at losalamos.com>
>
> If you look closely at the Amperex tube, you may note that the anode
> (plate) shape is different than the CPI/Eimac 3-500Z.? Most of the
> Amperex/Covimag tubes have a wavy horizontal structure with a dull flat
> textured plate whereas the Eimac has vertical fins around the plate and
> is a more shiny thin metal. They are not precise clones of each other,
> and Amperex took some license from Eimac long ago to produce theirs, but
> there are differences. Noteworthy are some mechanical differences inside
> between grid/cathode/plate - possibly spacing as well as the pitch of
> the grid and design of the filament. This will change the mutual
> conductance which is related to the grid voltage needed for a particular
> plate current. A service note for the Collins 828C1 and Continental
> 314R1 1 kW broadcast transmitter indicates there is a difference in a
> critical application for the 3-500Z switch tube in that PDM rig. It can
> be viewed as a small PNG of the page on this link, good for one week.
>
> https://we.tl/t-lvcbHr0qyu
>
> I recommend NOT mixing an Amperex and Eimac triode in parallel in the
> same amplifier. One will run hotter and hog a share of the
> amplification. If you want to make them more alike, you would need to
> tweak the cathode bias diodes.
>
> I have some 3-400Z that are also from these two sources, and I am
> willing to pass them on with a very good deal. They are slightly
> different from 3-500Z, and require a shorter chimney to get same cooling
> performance. I have both types of chimneys if you need any.
>
> 73
>
> John
>
> K5PRO
>
>
> On Friday, October 21, 2022, 9:30 PM, john.keating at outlook.com
> <john.keating at outlook.com> wrote:
> Spec sheets for these tubes appear identical. Yet they behave
> differently in my dual 3-500 amp. I can drive the Amperex at 90w for
> near-legal limit out (power gain of about 16x) without exceeding 200mA
> grid current; Plate current is just about 800mA for the pair. With the
> Eimacs, I can't exceed 75W drive without exceeding 200mA grid current
> (running about 720mA plate), and they do give the same 16x power
> amplification at that drive. At 90W drive, the Eimacs exceed the
> recommended grid current limit. Wondering if the amp brain trust can
> enlighten me on the difference and cause.
> 73, John / AI6LY
>
> ------------------------------
>
> Message: 5
> Date: Sun, 23 Oct 2022 05:30:07 -0500
> From: Rob Atkinson <ranchorobbo at gmail.com>
> To: "amps at contesting.com" <amps at contesting.com>
> Subject: Re: [Amps] EIMAC vs Amperex 3-500
> Message-ID:
> 	<CALWD7Z7Q-G01Se54Cv6XvnbcFNXEz2HcahaJ0bUjnRMYL+7EQg at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Maybe the Amperex tubes have lower emission.  Maybe they've been used
> a lot more?
>
> The link to the Eimac switch tube note gave me some kind of crazy page
> wanting to install cookies or something.  No thanks.  No Eimac data
> there at all.
>