Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Dentron MT-3000A Balun Question  (Read 2541 times)
AD6KA
Member

Posts: 2243




Ignore
« on: April 07, 2011, 11:59:53 AM »

Hi All:

Can someone please tell me the type of balun
used in my classic Dentron MT-3000A tuner?
4:1, 1:1, voltage, current? The manual I have doesn't say.

It is sealed in white PVC and is about 3-4" in diameter
and about 4 inches tall.

I just love this big ugly tuner, it's GREAT!  (14"W x 14"D x 5.5"H)
The only thing I would change is to add (or change
an existing) coax output to also handle "Thru" as
well as inline tune. Out of three coax outputs only
one has the "Thru" option. A definite "nit" of course, just my preference.

tnx es 73, Ken  AD6KA
Logged
WB6BYU
Member

Posts: 17271




Ignore
« Reply #1 on: April 07, 2011, 12:11:29 PM »

Virtually every tuner of that vintage used a 4 : 1 voltage balun.
Logged
AD6KA
Member

Posts: 2243




Ignore
« Reply #2 on: April 08, 2011, 12:39:42 AM »

Thanks Dale, I kinda thought that was the case but wanted to ask.

A couple of the SO-239 connector's threads are starting
to get stripped so I have to replace them too. Problem is the
tuner uses a panel mount SO-239 unlike any I have seen before.
Threaded on both sides of the panel, held in place both on sides
with thin nuts, and the insulation between the center pin receptacle and the shell
appears to be ceramic. Actually, I *have* seen *kinda* similar but they were
3-4" long, far too long for this application........Anyone familiar with these style SO-239
panel mount connectors with ceramic insulation instead of Bakelite or PTFE? Source?


I don't see any reason why I can't use the typical 4 screw mount panel mount SO-239's
if I solder carefully. The attachments on the rear center pins are long 1/8" aluminum
rods, not copper wire, and I hope I don’t melt the Teflon while heating that aluminum.
NO wire in this puppy except in the metering circuitry and balun.

73, Ken  AD6KA
Logged
K7GLM
Member

Posts: 51




Ignore
« Reply #3 on: April 08, 2011, 12:20:27 PM »

Is there a reason that you're anti-PTFE on this application? There are good sources for what (I believe) you need - a UHF bulkhead connector. It's essentially a PL-258 (barrel connector), except threaded the whole length and supplied with panel nuts. I know that they're readily available down to the 2" length.
Logged
AD6KA
Member

Posts: 2243




Ignore
« Reply #4 on: April 08, 2011, 12:56:47 PM »

Is there a reason that you're anti-PTFE on this application? There are good sources for what (I believe) you need - a UHF bulkhead connector. It's essentially a PL-258 (barrel connector), except threaded the whole length and supplied with panel nuts. I know that they're readily available down to the 2" length.

HI Greg:

Thanks for your reply. Looking back I was unclear in my post, sorry!  Grin
I am not "anti PTFE". All the interconnects between in this tuner
i.e. between variable caps, inductor taps to inductor switch, runs
to the back wafer switch and center of SO-239's and ceramic posts
etc are 1/8 inch thick aluminum rods, some 6-8 inches long, not copper wire.

Having never soldered 1/8 aluminum rods to SO-239's before, I was
wondering if there would be so much heat required that it MIGHT melt the PTFE
on a standard SO-239. (Yes, I know PTFE is quite rugged).
Maybe I am wrong and have nothing to worry about? I sure so!

Also, I am having a dickens of a time removing these old style SO-239's
as the very tin nuts they are held with just won't budge.
Locktite or age? Don't know, may have to cut'em off with a Dremel cutoff wheel.

There is also a concern because the "RF IN" SO-239 on this tuner is very
close to the PC board with the RF sense toroid transformer and associated circuitry.
This small PC board is held parallel to the back panel using 4 screws, one in each corner,
AND there are two long thin brass circuit adjusting screws coming off this board which must be
aligned with corresponding small grommet lined holes in the back panel.

SO,,,,,,it's a bit of a tight fit back there, even removing that PC board, and I
need to plan my work before I set upon it with a soldering gun.
I have seen the 2" SO-239 for "bulkhead use" you spoke of ..they are WAY too long.
But thanks for the tip regardless.

IDEALLY I would LOVE to replace these ceramic insulated, oddly shaped
SO-239's with identical ones, but I shan't search over hill and dale searching
for them.

Thanks again for the tip.
73, Ken  AD6K
Logged
WB6BYU
Member

Posts: 17271




Ignore
« Reply #5 on: April 08, 2011, 01:06:09 PM »

Quote from: AD6KA

I have seen the 2" SO-239 for "bulkhead use" you spoke of ..they are WAY too long.


How long (or short) do you need?  I've seen them in what appears to be the same
length as a SO-239 on each side of the panel.

You might have one where what appears to be the nut is fixed on one side and only
unscrews from the other side.


How were the aluminum rods connected originally?  You might be better off with some
sort of crimp fitting rather than trying to solder them.
Logged
AD6KA
Member

Posts: 2243




Ignore
« Reply #6 on: April 08, 2011, 02:20:30 PM »

Quote
You might have one where what appears to be the nut is fixed on one side and only unscrews from the other side.

Bingo! That is almost what I have. Overall length is one inch.
There is a not very wide keeper flange on the inside panel side of the connector,
The connector threads & body go through the panel, and a not very large nut secures the
whole thing in place from the outside of the panel. The body of the part appears to be silver plated,
and the inside of panel part has a ground solder tab off to the side, not used here.

I got carried away when I said the RF connections in the tuner were 1/8" AL.
They are smaller than that, but still beefy and very, very carefully
and skillfully left out. I think I will be OK with PTFE SO-239s, though my first choice
is to replace these SO-239's with identical parts. But oh well.....
I will paste the Dentron tunre wiring photos online somewhere for the
MFJ Antenna Tuner Assembly Department to take notes and emulate.
This tuner is built like a bric ****House!

The center for the pin appears to be brass, with only one "slit" in it
versus the 4 "slits" we often see in "gold plated" (HAH!) panel mount SO-239's these days.
All in all a very sturdy part and would love to get my hands on some
of these SO-239 panel mounts for future projects.

I took some photos but don't presently have time to run down one of those
free media posting sites. Wish we could post pics here.....come on mods,
what year is it?
Logged
WB6BYU
Member

Posts: 17271




Ignore
« Reply #7 on: April 08, 2011, 03:51:00 PM »

OK, so just a single-hole mount SO-239.  I have some of those in the junkbox,
but no idea what the insulation type is.  They can be a bother when the nut
loosens and they start to rotate when you are trying to unscrew the connector -
something with a couple screws through a flange is more reliable in that regard.
Logged
AD6KA
Member

Posts: 2243




Ignore
« Reply #8 on: April 08, 2011, 06:22:10 PM »

OK, so just a single-hole mount SO-239.  I have some of those in the junkbox,
but no idea what the insulation type is.  They can be a bother when the nut
loosens and they start to rotate when you are trying to unscrew the connector
-
something with a couple screws through a flange is more reliable in that regard.

Somebody already thought of that when they were designing this tuner!
Those odd (old) SO-239's do not rotate with removal of that nut,
because they have a 3/8" flat surface on the each side of the thread
that protrudes from the back of the panel, with the panel cutout to match.

So rounding those chassis holes with a small rat tail file and using
"standard" 4 hole flange SO-239's will be an upgrade.

Now I have to replace the Transmitter Loading knob, a  non stock quite
small one which some brilliant previous owner GLUED to the shaft.
The best way to do that I see of is to cut it apart with a Dremel
tool and cut off wheels. I've priced MFJ AL80B tuning knobs
and the look ideal.

There's always someting to be don around the shack...(sigh....)
Ken  AD6KA
Then what I'd REALLY like to modify this excellent tuner is to
make it so that there is at least ONE more coax antenna connector that has
a "THRU" option. Currently only one out of three coax antenna ports
have a "THRU" (no tuner) option. May have to get rid of the 200w
useless dummy load so I can use that switch position. Looks easy on the
schematic, but in real life a little more complex..I've no experience taking apart
hard to find high power wafer switches....I'll take a pass......fer now! Smiley
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!