Just a note:
Kenwood made a TS511 which was a 100 watt out model.
I owned both the TS511 and the TS511S. The "S" model being the 500 watt input model.

I have a TS 511S and like it very much.
They are good radio`s for driving a 4-1000 due to their higher power.
They seem to have a good receiver too.
I bought my first TS 511S back near 1980? I think.
I bought the one I own now this last year.
It wasn`t working when I got it, I bought it "as is not sure of condition", but I had it fixed the same day.
The 9 volt regulator was not working and I replaced it with one I had to get it back on the air.
I did a complete tune up on it the next day to make sure it was working the way it should.
It is sitting along side my simi old TS 850SAT.
I`ve never bought a "new" HF rig as long as I`ve been a ham.
That`s been 37 years now.

To AD5CZ:
I never said I was upset at anything.
I happen to have some info I thought I would share with others.
It`s funny, to me, that some people think they know what other people are thinking without asking them first.
As I said before, I don`t want another one of those amps.
If I want another amplifier, I will build it.
I enjoy building amplifiers. It is very rewarding. I know the design and every part in them.
By the way, I do like Dentron equipment. I owned a DTR 2000L. I never had a problem with that one.
The MLA 2500 does have lots of problems, though.

To AD5ZC:
No, I don`t want another one of those amps.
I build my own amps.

When I talked with a engineer at Eimac he told me the story of Denny and Dentron.
We didn`t go into a lot of details but Vhf parasitics can be caused from where the RF leaves the tubes and travels through the tank circut. It`s in the design. All leads need to be as short as possible along with good plate choke design and the right parasitic suppressor design.
Check out AG6K`s web page.
Some people don`t believe that there are parasitics in amplifiers but the MLA 2500 was a good example of just that.
By the way, When I talked to the engineer at Eimac, this was many years ago, I called him to get his opinion on switching out the 8875 tubes for a single CX 800. His answer was" WOW ! that looks like it would work good". I had bought a MLA 2500 and was going to put the 800 tube in place of the 8875`s. I had done some reading on the tube specs vs the 8875`s and thought, myself, that it would work well so I called Eimac to see what they thought.
I don`t believe anyone, back then, had done the mod. yet.

When Dentron came out with the MLA 2500 amplifiers I bought one.
I later learned the story behind these amps. It`s not a good one.
After Dentron designed the amplifier they gave a copy of the design to Eimac to get their ok since they would be making and and giving a warranty on the tubes.
Eimac told Denny that the design needed to be improved, that there would be vhf parasitics if he went ahead and used that design.
Denny ignored Eimac and went ahead and used his design.
To make a long story short, when the amplifier came out on the market, the tubes started going bad left and right. I had one go bad in my amp. within 2 months.
Eimac, at that time, was replacing them as they came back.
After about a year Eimac stopped replacing the tubes. They told Denny that he didn`t change his design as told to by Eimac, and the warranty on the tubes was now going to stop.
From what I understand this was the down-fall of Dentron.
It wasn`t long before Dentron went out of business.
Dentron made some outstanding equipment and amplifiers for their time but the MLA 2500 was a lemon.
So why, you ask, am I bringing this subject up now?
I see these amplifiers listed on ham ads where people are asking $600.00 to $700.00 or more and I just shake my head.
These amplifiers arn`t worth more that $250.00 as far as I`m concerned.
You can`t buy new tubes for them unless someone happens to have some from way back when. Eimac stopped making them years ago.
There are some mods on the internet for replacing the two tubes with a single CX800 but that will take a little work to do.
When looking for a used or new amplifier, do your homework it sometimes pays off.

Please don`t put one of those things on the Amateur bands.
They are built bad and are dirty when on the air.
They are made for CB and are not type accepted by the FCC.

I got the biggest one I could find. I think that is the way to go. Mine is rated at 5 kw rms. See my web site for a pic. of it. It is a dry dummy load and will handle more power than I have.

Also. Check the swr on the input of the amp. Maybe it some how changed?

One of the tubes may have become gassy also. I take it the high voltage is where it should be?
By the way, I have never liked the 3-500 tubes. I have had so many problems with them in ALL of the amps. I have owned using them.

Do what I do. Just give it a try. I believe it will work fine. I like to try stuff that may or may not work. That`s how I`ve learned some things. It gets you thinking. Don`t be afraid to try new things.

As was said, they have done that for a long time now. But you are right. Ham gear should have no place on C.B.
  What gets me is that allot of these people who run C.B. have Ham licenses and they bring their bad operating habits along with the C.B. jargon to the Ham bands.
  I wish they would decide which side of the fence they are on. Choose a side and stay there.

I forgot, Check the fan/blower that cools the bottom of the tubes. That HAS to work or bad things happen.

I would first pull out the dark tube and check it with a VOM to see if the fil. is good. If it is, then go into the Amplifier and work your way back from the tube socket to the fil. transformer. On the way, check the fil. choke to see if it is ok also.

I bought some off of Ebay. They were out of a multi KW broadcast transmitter. They work great in my Home Brew 4-1000 amp.