I find that interesting also. There appear to be three distinct camps:
1) Use no tuned input and use the radio output circuit (tuner on some
solid state rigs) to make the match, 2) Use a tuned input circuit
because you need the flywheel and reduce IMD, and 3) The rest of us that
are confused because such knowledgeable people have such diverse opinions.
I'm in group 3 but from what I read I am leaning toward being in group
2. I hope that we will get good discussion about this topic because it
goes beyond the simple "match it". I assume you've read the discussion
topics at Rich Measures' site and others.
73, Tony
W4ZT
Tomm Aldridge wrote:
>This is an interesting thread to me not because of the AL-811 vs
>MLA-2500 but because I am designing and building an amp. If I
>understand this correctly, using a TS570 transceiver to drive my amp
>implies I really don't need a tuned input circuit as I can just use the
>built-in tuner of my rig to achieve a good enough match to the input of
>the tubes. That saves me money and complexity.
>
>However, some on this list advise that the proximity of the output C of
>the tuned input to the cathode of the PA is very important for its
>"flywheel" or energy storage effect during the wide swings in impedance
>during a cycle of operation.
>
>My question is, which strategy should one employ and what are teh pros
>and cons? Assuming, of course, a built in AT such as in the TS570.
>
>Regards,
>
>KD7QAE
>Tomm
>
>Don Nesbitt wrote:
>
>
>>Hi Daniel - just my 2 cents follow. Each of these
>>amps has it's "warts" - some more serious than others
>>and they have been more than adequately covered both
>>here and on other reflectors. So I won't plow that
>>ground again. Instead, just my comments and, of
>>course, YMMV.
>>
>>I have a Dentron MLA-2500 - not the "B" model and have
>>had a number of Ameritron 811's and 811H's in the
>>shack over several years - both for my personal use
>>and as repairs for others. The Dentron is brute power
>>in a small quiet box. I easily get 1300 watts output
>>from it with about 90 watts of drive - even though it
>>does not have a tuned input!
>>
>>I don't know if the "B" has tuned input or not - you
>>likely do and that may be an important consideration.
>>
>>The Ameritron 811H is a very nice docile amplifier.
>>Reasonable power output (600 to 800 watts output
>>depending on band) with readily available (and
>>cheap)tubes and a tuned input. Most of the guys and
>>gals on the other end of your qso's won't see the
>>difference between this and the kw output from the
>>Dentron.
>>
>>While the tuned input is a compromise on the higher
>>frequencies in the 811H, it does a pretty good job.
>>The tuned input is important if you are using a solid
>>state rig and it does not have an antenna matcher
>>built in or if you don't have an external one that you
>>can put between the solid state exciter and the
>>amplifier. Some solid state rigs are very touchy
>>about what they look into!
>>
>>In addition, the Ameritron covers the WARC bands
>>easily. While the Dentron can be made to work on them
>>it's a bit sketchy and depending on the plate choke
>>used in your Dentron, it could go partially up in
>>smoke when you try to tune it up on the WARC bands.
>>
>>Ultimately, the amplifier has to meet your
>>requirements (cost, output, ease of tuning, quick band
>>change, physical size, availability of 220 vac, etc,
>>etc) and only you can make those decisions.
>>
>>For my part, it would depend on the price of the
>>MLA-2500B - and - it's condition - and - you say it
>>has good tubes so lets assume it does and that it is
>>in excellent physical condition. If it was really a
>>"great" deal (that depends on your definition of
>>"great" - mine would be $300 or less - and - btw: I
>>would not sell mine for less than $675 just as a point
>>of reference and it does have excellent tubes and is
>>pristine physicaly).
>>
>>Given all that, I would probably buy it - but - that's
>>just me!! Here is my reasoning
>>
>>- I have a number of rigs, each have built-in antenna
>>matchers so the lack of a tuned input is not an issue
>>for me. (The important part of this is the "for me!")
>>
>>- I don't "have" to run the Dentron at "full power" -
>>just let it loaf along at 750 to 800 watts output. At
>>that rate, the tubes should last a very long time!
>>But if I need to, I can always "crank it up!"
>>
>>- The WARC bands don't hold much fascination for me
>>and I can do what I want to do there barefoot.
>>
>>- I like the "low profile" look of the MLA-2500 series
>>as opposed to the somewhat higher and boxier look of
>>the Ameritrons.
>>
>>- If the deal is really that good, I could play with
>>it for a while and then perhaps sell it for more than
>>I payed for it!!! BTW: In over 45 years of hamming,
>>I've never been able to do that!! I always seem to
>>buy high and sell low!!
>>
>>- Ameritron is not likely to go out of business
>>anytime soon so the 811H's will be available for a
>>long time. The new price may go up but there is
>>always the used market.
>>
>>- If the tubes do go "south" in the Dentron, I could
>>offer the amp for sale without the tubes and could
>>possibly recoup some or all of my initial investment.
>>Then, go buy an Ameritron if I wanted to!
>>
>>- If the tubes do go "south" I could consider putting
>>3CX800's or 4CX800's in it an have a super amp! Of
>>course, this option depends on your technical skill
>>and willingness to work on it! (BTW: I'd also put
>>vacuum relays in it at the same time)
>>
>>Those are just a few of my ideas -
>>
>>Now, frankly, from your post, my advice to you would
>>be for you to buy the Ameritron 811H. You've already
>>had one so you know how to deal with it. It's a
>>"current" amplifier and really requires very little
>>technical expertise or hassle to make good use of it.
>>
>>BUT the real reason for my advice for you to pass the
>>deal on the Dentron and find an 811H is that you will
>>always feel bad about selling the 811H that you had
>>and not getting another one! That's pretty obvious
>>from your post - you had a love affair going on and
>>went to recapture it - or at least try to!
>>
>>Go with the Ameritron and have fun. 73 es gud dx --
>>Don N4HH
>>
>>
>>--- Daniel Hileman <n9wx@hotmail.com> wrote:
>>
>>
>>
>>>Hi Everyone,
>>>I have an opportunity to buy a Dentron MLA-2500B for
>>>a very resasonable
>>>price and it still does full output on most bands.
>>>over a kilowatt or near a
>>>kilowatt on all bands with only 50 watts drive. I
>>>can either buy this or an
>>>AL-811H for about the same price. I had an 811H
>>>before and loved it, I was
>>>stupid and sold it when I went to college, Now I
>>>want it back, but the
>>>greater power of the MLA-2500B is VERY tempting! Hi
>>>Hi.
>>>My question is, with the 8875 tubes VERY expensive
>>>or almost impossible to
>>>get, would the 811h be better perhaps for me,
>>>especially since I'm fairly
>>>new to amps? I know there is a conversion to other
>>>tubes, but not sure I
>>>have the expertise to do this, and probably couldn't
>>>afford to have it done
>>>unless some local "expert" ham helps.
>>>
>>>I need opinions of this amp, and this situation.
>>>
>>>Thanks,
>>>Daniel N9WX
>>>
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