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Reviews For: Dentron Jr. Monitor

Category: Antenna Tuners/Matching Networks

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Review Summary For : Dentron Jr. Monitor
Reviews: 29MSRP: 79.00
Antenna tuner, mobile?
Product is not in production
More Info: http://
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
W9MT Rating: 2023-02-08
I haven't seen anyone mention the mystery banana jack... Time Owned: more than 12 months.
First of all, this is a great tuner for both balanced feeds, coaxial feeds, and single wire antennas. It will handle 100-300 Watt rigs with ease. I cannot say enough praise about its ability to match nearly anything while (as others have said) giving you a meter that tells you the maximum transfer out of the tuner into your combined feedline and antenna.

Here's some little known facts...

Over 8000 copies of this tuner were sold by Dentron. I own one that has a serial number just over #1500, and another that is #8130. Both work great.

The earlier units (like my s/n unit near #1500) have the word "Monitor" misspelled as "Moniter" on the metalized s/n tag. This is corrected on my #8130.

Around unit s/n #3000, a red banana jack was added to the rear of this tuner. It is unlabeled and is immediately under the pot used to set the sensitivity of the front panel relative power out meter. It's purpose is to make the 80-10m bands easier to tune or maybe the better term is "capable of BEING tuned".

This is due to the 2nd (smaller) toroid used to allow tuning to the bottom of the 160m band. Units under s/n #3000 often had trouble tuning all the way thru 10m because of "too much" inductance with this 2nd, smaller toroid being left in series with the larger one that the alphanumerically marked rotary inductor control will be used to increase or decrease inductance. The "mystery banana jack" simply connects a wire between the "hot end" (not the grounded end) of the smaller toroid and where the switched air inductor's "bottom" (closer to ground end) are connected together. The "bottom end" of this smaller toroid to "better enable" 160m band tuning is always grounded.

To more easily tune the 80-10m bands (including WARC) the "mystery banana jack" uses a bare wire to bypass (short out) all of the turns on this smaller toroid. This bare wire simply goes from the "mystery" red banana jack to the ground nut connection immediately to its left.

I have never found this "mystery banana jack" documented in any schematic or version of the Dentron Junior Monitor's user manual. I learned of the rationale in several on-line blogs only after a lot of extensive Google searches. But let it suffice to say that this "fix" was quietly implemented as a "running production change" just after unit s/n #3000. It was already on my #8130 when I bought it. I put the same update as a modification onto my #1500 series unit.

So leave the jumper wire out for your 160m band tuning use. Put it back in to short out the smaller toroid for ease of tuning on 80-10m.

Just in case you are wondering, the "larger toroid" is used to couple RF from the air inductor (and also the smaller 160m toroid) to the balanced feed banana jacks. Another bare wire jumper is called for and marked with a dashed line on the rear panel if it is desired to use a single wire antenna out of the other banana jack.

In the 50+ years I've been a ham, I've used a lot of different antenna tuners. These included a Johnson 275W Matchbox, several MFJ's, several LDG's, a Kenwood AT-250, and quite a few rigs and amp's with internal ATU's. My first tuner was an AirDux inductor on porcelain standoffs on a pine board, a couple of 100pF rotary caps, two SO-239's nailed to the side of the board, and alligator clip leads to interconnect the parts together. All can be made to work and did with varying amounts of efficiency. But they all got me on-the-air, when no-tuner would have "gotten me nowhere".

The Dentron Junior Monitor simply does this job very well for a manual tuner in a nice, compact package. Just don't put too much RF into it (stay less than 300W, just like with the low end MFJ's) and it will serve you very well for many years of happy operating. They are "keepers".
DH5AK Rating: 2023-01-24
Fine old tuner! Time Owned: more than 12 months.
These tuner bevome rare. I found one in good used condition. The dimensioning of the inner parts is fine for up to 100W, the typical radios these days have. The size of its box is not too small. This is a relevant factor as the stray field of the coil does not couple into the sheet Metall that much. Also the arrangement of the elements is done in an intelligent way. All this minimizes the loses and shows a fine design.
A second factor is the indicating meter. This Meter shows the relative output voltage or relative output power. This is really VERY helpful for any coupler with more than just two variable elements. This coupler has three variable elements as it consits of a highpass T circuit. Wirh all ouplers with more than just two variable elements there are indefinite setting combinations to match a certain imoedance - but there is just one with the best efficiency! A VSWR-meter shows you just the quality of the matching but this relative output meter shows you how much power comes out of the coupler and flows into the antenna. This meter allows you to find the point with highest output power. This meter makes rhis coupler a GREAT coupler!
WD5G Rating: 2019-04-24
Not everything new is better. Time Owned: more than 12 months.
I bought mine new in 1978 and it still works perfectly. It has seen a lot of Field Days and portable ops.
EI6DP Rating: 2019-04-23
Built like a tank. Time Owned: more than 12 months.
I bought one of these on eBay at a respectable price. When it arrived I had a look inside and found that the previous owner had modified it heavily :-(
I mentioned this to the seller and received an $25 refund :-).

I removed the modifications and other crappy bits (not much) and fitted 2 new SO239's and reconnected it as per circuit and gave it a good clean-up inside. The front of the Dentron was in pristine condition, so a coat of matt black paint to the cover.

WoW, It is one brilliant atu, very well built and put together. Tune for maximum smoke and away you go. 160m to 10m and very easy to tune.

For anyone who wants a very good atu, if you see one on eBay or your local Ham Sale - GRAB IT.

Delighted all-round :-)
N5XJT Rating: 2018-10-25
Grrreatt!! Time Owned: 0 to 3 months.
Picked up one at a Hamfest for a good price, took it home and gave it a bath, tightened a couple of knobs, re-solder one wire and gave it a try. Lemme tell ya - this thing will tune the proverbial wet string quickly and effortlessly. Could not believe how well this old tuner works. Faster and easier to tune than any manual tuner I have ever used. Find one - buy it!
K6RQR Rating: 2017-03-13
Wonderful small tuner Time Owned: 0 to 3 months.
I just received one today and have it hooked up to what used to be a 75 meter dipole fed with coax and a 1:1 current balun. The dipole is now a doublet connected to the Dentron with 450 ohm twinlead. I have used it on 75, 60, 40, and 20 meters and it tunes the antenna just fine. At first I was just tuning it using the RF output meter. That was fine but when I hooked up an SWR/Power meter I was able to fine tune the antenna even better. I'm getting SWR down to near 1:1 on many frequencies.
The Dentron is also small enough to use in my car if I should decide to operate mobile and I can see that it would also be a good tuner for portable operation.
As others have said it is a quality alternative to some MFJ tuner of a similar price. The construction is excellent. It is rated at 300 watts and I would not push that as another reviewer mentioned the damage that could happen to the meter sensing circuit.
The Dentron Junior is only about 5 1/2" wide, 3" high and 7" deep and it lives on top of my Kenwood TS-140S. Despite its small size it works very well and I am pleased with it. Recommended!
K2JF Rating: 2017-02-19
the good ol' days Time Owned: 0 to 3 months.
I just picked one up used for no other reason than to have a backup in case one of my autotuners conked out (MFJ did just that). My replacement was an LDG autotuner that was fine but when I opened the box and grabbed this tuner it reminded me of how cars in the 1950's were built - like tanks. this is one beauty and works so well I took my LDG autotuner out and plugged this in to work with my Icom 7300. I'm stuck with a 10-20 OCF dipole which the autotuner cannot tune on 40. But this Dentron handles it like a piece of cake. There are advantages in using an autotuner - they're faster. But this takes just a few seconds longer to lower the power, tune for noise level and then adjust the xmitter and antenna match. Takes seconds.
KC2WBK Rating: 2015-09-14
Works Well and as Designed Time Owned: 3 to 6 months.
For the same price as a new MFJ tuner, you can buy one of these used and get a much nicer piece of equipment. I run an 84 foot wire out the window that terminates to a banana plug that goes into the back of the tuner. Works fine, tunes all the bands I cut the wire for (80,40,20,15,10). I know it's working, I get great signal reports, especially considering the antenna.
N4DBM Rating: 2015-05-25
Great unit Time Owned: 6 to 12 months.
Perfect companion for field day or other times when a portable, lightweight design is needed. I had one years ago, now I can't find it. Hope I run across it soon.
WB2KWF Rating: 2014-05-03
AAA All the way! Time Owned: 6 to 12 months.
First time writing a review here...but this little tuner is just amazing. Running it mobile with my TS-480HX at 200W with hamsticks or bugcatcher antennas. Now I don't have to get out to QSY...just a short time tuning, and away I go! I can even hook it to my ladder line at home, and operate "mobile" with my full size antenna! HiHi!. I wouldn't be without it!