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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Dentron MLA 2500B Help


Reviews Summary for Dentron MLA 2500B
Dentron MLA 2500B Reviews: 30 Average rating: 4.7/5 MSRP: $1200.00
Description: 2 KW PEP Amp 160 80 40 20 15 10 m
Product is not in production.
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VK3OT Rating: 5/5 Jul 29, 2011 22:19 Send this review to a friend
Oldie but a goodie  Time owned: more than 12 months
This is a short review about an old MLA2500.
It started life in Australia in 1979 at the CQWW VK2ATZ/Lord Howe Contest station after which I transported it to Xmas Island as VK9XT and ran it into a QUAD 1000 feet above sea level and worked 65000 contacts between 1980 and 1982.
If you have a light blue or dark blue VK9XT card then you worked this amplifier.
It never missed a beat and when it cme time to ship it back to VK, the post master would not accept it back the way it came so I was forced to carry it in my luggage in with my clothes. It was used at my home QTH to set a 5th word high score on 10 mtres in the ARRL and then by VK3AKK to set high score on 40M. Then in mid 1980s sold it to Jeff VK8GF who used it until he left VK8 in the lates 2000's, he sold it to Eddie VK4AN who sold it to Peter VK5PJ who just sold it back to me (VK3OT).
Its the original amp in original condition and is back here after 25 years. It still has the original tubes and I know that because when I hand carried it back through Singapore to VK3 the tube fell out and rattled around in the tank area and I had to use some straight nosed pliers to get the dents out and you can see the plier marks. I have jst pulled the tank circuit apaart and linished the silve rplating on the switch and lubricated the bearings and cleaned out all the red centre bull dust. I ran it into a load and get 1000 watts out for 65 watts of drive and it goes 800 mA key down at 100+. Original tubes, original caps, and the original well travelled case. Date codes on tubes are 1975. You can still see the engraving under the corrosion and rust spots. As someone said at $500-$600 good dollaars per watt. Pity about 9975's being obsolete, but then Im obsolete so what the heck. Just need to stop the power transformer humming and change the fan over to new 120mm 12V late design with modern blades to get the fan noise down at high speed. Need to find out if the Nulon shield has been left out of the power transformer mounting.
 
JUNKMAN Rating: 5/5 Feb 20, 2011 03:36 Send this review to a friend
Worth every penny  Time owned: more than 12 months
I've owned several of these amps over the past few years and I just acquired another one last week. This one is the MLA-2500 non B model and is in like new condition inside and out. Even the tubes still look new. 50 watts will produce about 1100 out and 80 watts will produce 1500 watts out. A full 100 watts in will get you 1800+ out! I just ordered the soft start kit from Harbach to make it easier on the tubes at start-up. Considering the ever increasing prices of the new amps these older amps are looking better and better. A simple upgrade to the power supply board with new caps and diodes is all that is needed to make these amps last for many more years of service. I know of no new amps that cost less than $600 and puts out 1500+ watts to the antenna. In my opinion these are a smart buy and worth every penny that they cost now.
 
N4EDX Rating: 5/5 Dec 30, 2009 19:03 Send this review to a friend
Great service  Time owned: more than 12 months
I bought one at the Asheville, NC (Waynesville NC)Hamfest from a private owner, it was a great buy. It has provided a couple years service with no problems. I know the tubes are original but its been a well cared for unit. 1800 out on 80 meters down to 1200 on 10 meters. Best purchase I've made at a hamfest!
73's
Ed (N4EDX)
 
KG8DP Rating: 5/5 Feb 13, 2009 07:29 Send this review to a friend
Great Amp.  Time owned: more than 12 months
For a number of reasons I made swing from Commander amps back to the Dentron. I now within 2 months own 2 of them plus a WP-1 watt meter and MT-3000A. match a 2500 and a 3000a and load up the box spring in your mattress just dont lay on it. LOL. To top it off, i have found 2 people that work on the stuff locally. One of the dentrons I purchased I sold to a guy back in the arly 90's and he did not use it anymore. thats why I marked it longer than 12 months. they are on e-bay all the time. good amp and good buy beats paying thousands for the 1.5 kw amps. Mark
 
ZL4TGH Rating: 5/5 Jan 5, 2009 00:52 Send this review to a friend
Bang for the bucks  Time owned: more than 12 months
15 years ago I swapped a TNC for the non-working amp. It came with 2 new valves and the originals also like new. A quick tweak on the voltage relay (about 5 minutes work) and in business. Put it in storage for 5 years and when I turned it on, bang! HT cap blew. Well tonight I replaced them all and with extra 0.01uF across them and 10 ohm on the HV B+ in case of arcing. Removed my GLA-1000B and put my sweetheart back in line. First contact with the repaired amp, over the south pole long path to Germany on 40! The guy was so excited it gave me a buzz also. Other ZL4's tried but he just could not hear them. My FT-2000D was only putting out 30w. What a great amp, before it's time.
 
KA9TZU Rating: 5/5 Nov 21, 2008 18:56 Send this review to a friend
Best amp I have owned  Time owned: more than 12 months
An extra class friend of mine bought this amp new in the mid 80's. I always thought is was great. When he moved he sold it to me for a song.

It sat on my shelf for over 5 years before I used it. Worked like a charm even though the caps arced now and then. The problem stopped on it's own, so I never replaced them. Put it away when I moved a year later and brought it back out 12 years later. Still worked great.

I have 2 sets of 8875 tubes I had bought back then in case I needed them. Not so far, originals are still at full power. I can easily get 1400 pep on 80 meters with a 40-50 watt drive. The swamping resistor is still in place. I have used this amp with numerous radios and it always has preformed for me. I am currently using it with an Yeasu 897D

I am converting a solid state medical research amp for amateur radio use. The amplifier uses 16 MRF150 MOS FETs in 8 push-pull output stages, which are driven by a push-pull stage using two additional MRF150s. Even when this amp is up and running, I will never part with my Dentron!!!!
 
W5VIN Rating: 5/5 Mar 11, 2008 10:48 Send this review to a friend
Retube  Time owned: more than 12 months
I just finished doing a retube on this great amplifier using the GI7B Russian triodes and W4ZT sockets. It will crank out well in excess of 1300 watts of power with less than 100 watts of drive power. To those that have this amplifier and it's tubes are going south this is a working modification that is not all that hard to do. It gives the MLA-2500 amplifier a new lease on life.
Charlie W5VIN
 
WA4RVB Rating: 4/5 Jan 28, 2008 07:50 Send this review to a friend
STILL GOING STRONG  Time owned: more than 12 months
THE AMP.STILL WORKS GREAT, OUPPUT AROUND 1400 WATTS. BOUGHT USED AT SHELBY ABT 20 YEARS AGO, THE ONLY THING I DON'T LIKE IS THE NOISY RELAY AND BLOWER FAN. THE 8875'S OR STILL PUTING OUT FULL POWER. A GREAT AMP FOR ITS TIME.....
 
AH6RR Rating: 5/5 Jun 9, 2007 20:02 Send this review to a friend
Rock Solid Amp  Time owned: more than 12 months
I bought my MLA-2500 at a local swapmeet for $85.00 it had 1 bad tube and the power supply had 2 bad filter caps and some blown diodes in the doubler. Well I could not find a 8875 that I could afford so I sold the good tube and bought 4 GI-7B tubes and all the parts I needed for the conversion plus a New Kenwood TM-271. So 2 months later and a little tweeking hear and there I now have an excellent amp with anywhere between 1300 and 1500 watts out with 2 of the GI-7B tubes. Great Amp.
 
W5VIN Rating: 5/5 May 19, 2007 18:42 Send this review to a friend
MLA-2500 Retube  Time owned: 0 to 3 months
I purchased a Dentron MLA-2500 with bad tubes. I replaced them with three 4CX-250B operating in modified grounded grid with screen and grid bias voltages. Both grids are at RF ground through coupling capacitors. I sort of followed the old QST article which used a Russian GU74-B. It was my initial choice but produced a less than stellar output. I redid the bias supplies using an LM431 and series zener for the negative bias. The screen bias uses an LR8N3-G high voltage regulator feeding a high voltage MOS transistor. For input matching I use an LDG 100Z Ultra externally between the antenna switching relay and the tube cathodes. It simplified impedance matching and is battery powered with memories. The amplifier will load to 1200 watts output and is quite comfortable at 1 KW out. There are several mistakes in the QST retube article article both in design and on the schematic.
Charlie W5VIN
 
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