[SBE] Freeland Products -- a user's experience

[Mike Langner]

I've used Freeland for many years.

I've never gotten a bad tube from them.


Here's one interesting example of how Freeland works with their customers,
and what Freeland staffers know.


I was putting a new (rebuilt, that is) 4CX10,000D into an (ugh!) Wilkinson
10 kW FM transmitter.

Neutralizing Wilkinson FM transmitters of this power class can be tricky,
and this one didn't "feel right."

I called Freeland the next morning, and related the experience to them.

When they asked what kind of transmitter I was putting their tube into, I
told them.

"Ok," the fellow on the phone said.  "That explains it.  Send the one we
sent to you back to us -- meanwhile we're sending you another by air today."
The fellow on the phone went on to explain "4CX10,000D architecture comes in
two versions of the anode internal cavity, and only one of them works well
in the Wilkinson." (Note -- I never did ask what the two architectures are,
but suspect they're Eimac and RCA, but I could be 100% wrong -- could be
Eimac and Amperex, for example!  Maybe someone can fill me in on this one!)

The replacement tube arrived the next day, at no cost.  I installed it, and
everything fell into place perfectly.  I returned the first tube, grateful
for the education.

All subsequent 4CX10,000D tubes worked perfectly, as did replacements I
ordered for all the other Citadel Albuquerque tube-type transmitters over
the years that followed.

Tube life was excellent.


On one phone call while I was ordering a rebuilt tube, I asked why their
tubes appeared to last longer.

The fellow on the phone explained to me that when rebuilt tubes are finished
out, they can have "hot" or "cold" filaments -- tube rebuilder jargon. "Hot"
filaments, it was explained to me, emit more at the beginning of life, but
do not last as long.  "Cold" filaments, he went on to say, are not as
high-current emissive but last longer before going "flat" or "soft."  Since
my application did not require extreme emissivity at any point in the tube's
life, they were finishing out for me "cold" filaments -- plenty of emission
for my applications, and longer tube life!


As I'm sure anyone reading this knows, most of the tubes we use these days
(you're still using tubes?) reach end of life not because of a lack of total
emissivity, but because as the tubes age, the uniformity of emission from
the filament coating (thoriated tungsten in most high power transmitting
tubes) becomes uneven -- the filament coating (cathode) emits more in some
spots, and less in others.

As a result, there is a smaller cross-section of grid wires intercepting and
controlling the now-more-concentrated electron stream flow within the tube
(electrons given off from the "hot spots,") causing a reduction in the
effectiveness of the grid's control, and a falling-off in the grid's
effectiveness in varying the flow of electrons from the cathode (filament
coating) to the plate.  If this were not the case, we could just keep
jacking up the filament voltage (hotter filament, more emission) until the
filament eventually burned completely out.  We would get full output and
full efficiency over the entire life of the tube.  But, of course, with
filament surface (cathode) "hot spots" the emission becomes quite
non-uniform.

By the way, varying the number of grid-wires through which the tube's
electron stream flows is the underlying principle of the "variable-u" tubes,
such as the receiving type 6SK7.  Varying the bias changes the electron flow
from "more grid wires per square centimeter" to a region of "fewer grid
wires per square centimeter."

Side note -- pure tungsten tubes emit far, far fewer electrons under the
same conditions as do thoriated tungsten (used in transmitting tubes) or
barium oxide (used in receiving tubes) cathode sleeves or coated filaments.
Early transmitting tubes like the 892 and its air-cooled cousin, the 892-R
required very high plate voltages and had a lower (by today's tube
standards) plate current flow.  But pure tungsten tubes do indeed maintain
full gain over their entire life -- there's no thoriated tungsten or barium
oxide coating to degrade.  They either work, or they don't!

But I digress.

My experience with Freeland was 100% positive.  I recommend them very highly
!!

Mike Langner, CPBE
Albuquerque, NM
__________________________________




-----Original Message-----
From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org]On Behalf Of Bob
Reite
Sent: Monday, June 23, 2008 2:05 PM
To: sbe member discussion mail list
Subject: [SBE] Freeland Products.


Does anyone on the list have experience with Freeland Products?  I've
always used Econco for rebuilt power grid tubes, but with todays fuel
surcharges shipping things from the West Coast seems silly when Freeland
Products is closer.
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