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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