New Life for Dentron MLA2500s HELP
NI4L
(QST May 96 pg.45-48)
MLA2500b.zip MLA 2500A/4CX800A Conversion package including
builders' details, ARRL Lab test data for all nine HF bands and
several
photos of the author's modified amplifier. This is a "zipped" file
898K in size.
(Does not include actual article)
http://www.svetlana.com/docs/TechBulletins/TB.html
i need some help i tried to download this but it will not work can
someone else try or do you have it on file somewhere and could you email
it to me?
thanks chris NI4L
--
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Dick Carroll
the menu. Probably as good a conversion. I couldn't get the QST article
to download, either.
Dick W0EX
Gary - KJ6Q
That article, like every OTHER one I've read on the subject, involves LOTS of effort, money and
contortion - and leaves you with an amp that is a butchered monstrosity that will deliver about the
same output as a stock Heathkit SB-200 or Yaesu 2100B that can usually be bought for LESS than the
cost to modify the Dentron 2500...
According to the pointed to article, the BEST observed OUTPUT power AFTER modification, was 840
watts - MY Dentron 2500B will put out 2KW into my dummy load any time, any day! The swapping of tube
types proposed by such articles are HARDLY to be considered a valid "improvement", OR a reasonable
method to ressurrect a 2500B...
I *am* surprised that some enterprising soul hasn't tried swapping in the more easily obtained
572B's - they operate at the same voltages, current and drive levels as the 8875's, use the same
type and placement of cooling, and it LOOKS as though they would fit in the provided space. If and
when MY 8875's fail, I'd be inclined to try the 572B's - but NEVER tubes like that article
suggests...
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"NI4L" <ni...@charter.net> wrote in message news:3CB5BF91...@charter.net...
Duncan Clark
In message <3CB5BF91...@charter.net>, NI4L <ni...@charter.net>
writes
> i need some help i tried to download this but it will not work can
>someone else try or do you have it on file somewhere and could you
>it to me?
Easy but you have do a bit of abstract thinking and pray.
Take the file name, mla2500b.zip, and search for it using say Google,
http://www.google.com.
Results 1 - 7 of about 11. Search took 0.07 seconds
I could download it from:
http://www2.arrl.org/files/qst-binaries/
Duncan
G4ELJ
--
Support bacteria. They are the only culture some people have.
Duncan Clark
Kenneth D. Grimm, K4XL
> i need some help i tried to download this but it will not work can
>someone else try or do you have it on file somewhere and could you email
>it to me?
>thanks chris NI4L
The ftp site that Svetlana has listed (oak.oakland.edu) seems to be
down. Odd, too, since it has been operating since way before the web
was invented!
What you are looking for is a file called mla2500b.zip. I think you
will find it at the following address:
http://ring.omp.ad.jp/pub/misc/ham/funet/arrl/qst-binaries/ or at
http://ring.tains.tohoku.ac.jp/pub/misc/ham/funet/arrl/qst-binaries/
Good luck with your conversion.
73,
Ken K4XL - Replace "invalid" with "net" to reply.
*** BoatAnchor Manual Archive ***
On the web at http://bama.sbc.edu or
FTP site info: bama.sbc.edu login: anonymous p/w: youremailadr
NI4L
Has anyone tried this and if so what was the outcome. Anyone have any better
ideas?
chris NI4L
--
Gary - KJ6Q
suggested - and compare them with the 2 KW the STOCK Dentron's do -
THAT alone should convince you of the validity of the "conversion"...
There are FAR better ways to spend yer time and money than on a
"conversion" that leaves you with an amp the now only has about the
same OUTPUT as a stock SB-200 or similar amp that can be bought for
LESS than the cost of the conversion of the 2500B...
--
Gary - KJ6Q
= = = = = = = =
"NI4L" <ni...@charter.net> wrote in message
news:3CB5E884...@charter.net...
Dick Carroll
Gary - KJ6Q wrote:
>
> Just carefully check the claimed power output AFTER the mods
> suggested - and compare them with the 2 KW the STOCK Dentron's do -
> THAT alone should convince you of the validity of the "conversion"...
>
> There are FAR better ways to spend yer time and money than on a
> "conversion" that leaves you with an amp the now only has about the
> same OUTPUT as a stock SB-200 or similar amp that can be bought for
> LESS than the cost of the conversion of the 2500B...
>
Something isn't right. The 3cx400 is reported to be equal to the 8874
which is identical electrically to the 8875, the original tubes in the
MLA2500. What is it about the conversion that drops the power? It
shouldn't.
If MLA2500 owners would use them a bit more carefully they wouldn't eat
tubes. Of course it would help if the manual had instructed users to
keep the grid current down to a VERY LOW value. Instead they allowed 100
mils, and that tube just won't handle it longterm. IIRC the specs for
the 8874/8875 series show 4 ma grid current continuous. I have a
MLAS2500, and keep the meter switch on the 'grid' setting. If anything
changes that causes *any* observable grid current to flow I want to know
about it-normal tuning is for zero grid current here. I've had this
MLA2500 for over 15 years and the original tubes are still virtually as
good as new. I like it because it is very compact for the power output
and it covers all bands 160 through 10 meters, since it was built before
the 10 meter amplifier ban.
Dick W0EX
Gary - KJ6Q
AFTER switching to the 400's - how much power can YOU get outta YOUR stock 2500B?
*I* can get 2 kw outta MINE - so I agree, something IS seriously WRONG with those 2500B
conversions - so why MAKE the conversion for so POOR a return in efficiency - as clearly indicated
right in the conversion articles themselves?
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"Dick Carroll" <di...@townsqr.com> wrote in message news:a95alu$j4l$0...@208.206.142.99...
Dick Carroll
Gary - KJ6Q wrote:
>
> SO, a quick and simple question - the "conversion article" claims a MAXIMUM power out of 840 watts
> AFTER switching to the 400's - how much power can YOU get outta YOUR stock 2500B?
Mine is not a B model, but it never did output 2KW, more like 1.5,
which is the legal limit anyway. And I've tried a brand new set of Eimac
tubes in it with the output nearly the exact same 1.5KW. I used a
separate wattmeter and dummy load for the test. Internal wattmeters seem
to rarely be very accurate.
>
> *I* can get 2 kw outta MINE - so I agree, something IS seriously WRONG with those 2500B
> conversions - so why MAKE the conversion for so POOR a return in efficiency - as clearly indicated
> right in the conversion articles themselves?
Certainly no argument from me, but if I was faced with buying a pair of
finals for it I might view it differently.
I still think the answer is to run the amp right in the first place and
not fry the final tube grids. This won't help after the fact, of course.
tongaloa
some research into the 2500B specifications:
2500B power transformer is good for 750 W CCS. With 2 x 4cx400
the 840 W reported is single tone PEP translates to 595 W RMS
In consideration of the typical 50% over CCS that one can usually get out of
a transformer in ICAS (1120 W) this translates to about 52% efficiency, and
agrees with most CW specs for ham amps.
The GI7B conversion is reported to yield 1200 W out (two tone)
or 600 W RMS. Same power!
I bet the 2 KW output reported, corresponds to voice peaks and
not the single tone it is compared to. Voice has a higher peak to average
ratio than two tone so 2 KW peak seems pretty reasonable.
-bob
WB4MNF
"Gary - KJ6Q" <davi...@gte.net> wrote in message
news:0Mjt8.745$I64...@nwrddc02.gnilink.net...
Gary - KJ6Q
first is the class of operation they appear to be operating in - which seems to be AB1/AB2 - both
down in efficiency compared to the more common class B operation for linear amplifier operation...
SECOND, is the likelihood that the final tank circuit needs significant tweaking to comphensate for
the different plate impedance of the substituted finals.
2 OTHER inherant, potential issue with those conversions, is the unsatisfactory adaption of cooling
system from the 8875's to the vastly differing system needed for tubes like the 400's and 800's -
the 8875's survive quite nicely with low-pressure, high-volume airflow, while the others desperately
need both high flow rates AND decent flow PRESSURE for adequate cooling under power levels the MLA
2500 was designed to operate - but which the specified muffin fans are NOT capable of! NEXT on the
list is the specified need, common in grid-driven amps, for LOW-LEVEL drive in those conversions,
which while possible in most late model transceivers, is VERY likely to lead to unwanted impurities
in output as various audio/electronic impurities are NOW being brought up much nearer to the level
of the DESIRED signal for amplification - much like a hifi driver with low output, when the
following audio amp is turned up to comphensate, bringing an increased hum and distortion level WITH
it... At the very LEAST, a power deviding T pad SHOULD be used in these cases, rather than merely
relying upon turning down driver output as the only solution.
And finally, we entirely agree on proper loading and driving of the stock 2500 amps - I operate mine
on 220 volt mains, use 50-60 watts drive, and normally show 1250 watts out on an instant reading
peak wattmeter, and RARELY see the faintest trace of grid current - tho it WILL load MUCH higher if
I so desire. It IS a shame these amps don't use tubes more easily obtained - but SO FAR, the
suggested "conversions" leave MUCH to be desired to match the abilities of the stock MLA-2500's
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"Dick Carroll" <di...@townsqr.com> wrote in message news:a96fsi$gmp$0...@208.206.142.113...
Gary - KJ6Q
indicated level...
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"tongaloa" <tong...@alltel.net> wrote in message news:a9752t$oc5$1...@iac5.navix.net...
Gary - KJ6Q
2100B - as well as some issues to power supply capabilities - my response...
You're entitled to your opinion - but *I* have actually owned and operated the SB-200, a pair of
Yaesu 2100B's and a Dentron Clipperton L - BOTH amps using a PAIR of 572B's were capable of a best
key-down power out of over 800 watts into a dummy load - the Clipperton, with 4 572's was capable of
over 1600 watts out... NOW, THAT'S actual experience, NOT theory or assumption!
Power supply capabilities, or tube charts are NOT the issue here - the efficiency and ACTUAL
operation of a proposed MLA 2500 "conversion" IS! And I steadfastly maintain that the suggested
conversions are NOT getting the best/most out of the specified tubes, or the original capabilities
of the MLA-2500 - and THAT is what this thread is about!
Gary Schafer
carrier (or single tone) and
get 1000 watts output that is 1000 watts average power. Same power on
cw. It is also 1000
watts PEP. If you switch to SSB and drive the audio up to full power
out you are running 1000
watts PEP. Now the PEP may be slightly higher because the power supply
will not sag quite as
much on SSB as it does on CW. You may actually get another 150 or so
watts PEP out on
SSB because of the power supply. Your average power out with voice
will be in the area of
150 to 300 watts depending on voice characteristics.
With a two tone signal the same amplifier will still put out 1000
watts PEP. The average power
will be 1/2 that or 500 watts average.
The best way to compare outputs is with carrier (single tone). This
gives all the power out that
the amp can do. Less a little of course for power supply sag.
Be careful of watt meter readings when comparing amps. All watt meters
are not created equal.
I see some claims of 800 watts out of an SB200. If it would in fact
put out that much I would
think the 3rd order products would be pretty bad. You would have to
overdrive it to get that
much power out.
73
Gary K4FMX
On Fri, 12 Apr 2002 13:21:20 -0400, "tongaloa" <tong...@alltel.net>
wrote:
Peter Voelpel
Gary - KJ6Q schrieb in Nachricht <5ZEt8.62$93...@nwrddc04.gnilink.net>...
>I suspect 2 major issues create lower than hoped for output in the
conversions under discussion -
Make shure you use the same instrument to measure the power... into the same
dummy load...
>first is the class of operation they appear to be operating in - which
seems to be AB1/AB2 - both
>down in efficiency compared to the more common class B operation for linear
amplifier operation...
The MLA2500 is operating AB2 !! that is the common class of operating zero
bias tubes !!
>SECOND, is the likelihood that the final tank circuit needs significant
tweaking to comphensate for
>the different plate impedance of the substituted finals.
On same platevoltage and platecurrent there is no difference in impedance at
all !!
>
>2 OTHER inherant, potential issue with those conversions, is the
unsatisfactory adaption of cooling
>system from the 8875's to the vastly differing system needed for tubes like
the 400's and 800's -
provided adequate cooling, there is no reason for lower output, of course
the 4CXs need some pressure..
>it... At the very LEAST, a power deviding T pad SHOULD be used in these
cases, rather than merely
>relying upon turning down driver output as the only solution.
best is to let the driver work into a dummy load at the grid through an
attenuator
>> > AFTER switching to the 400's - how much power can YOU get outta YOUR
stock 2500B?
2 KW out means > 3KW in -----> plate dissipation > 1 KW, the 8875 is
limited to 300W by Eimac..
I suspect that also other parameters are exceeded:
max Plate Voltage is 2200V, maximum plate current 0,35 A , data for one tube
or, which is more likely, the measurement is wrong !!
>> > *I* can get 2 kw outta MINE - so I agree, something IS seriously WRONG
with those 2500B
would be interested to see it running in a rtty-contest with 2kw out :-)
>> > conversions - so why MAKE the conversion for so POOR a return in
efficiency - as clearly
>indicated
>> > right in the conversion articles themselves?
There will be nothing wrong with the conversion, the 8875 has the lower
plate dissipation,
so with the higher dissipation of the 400s there is some safety margin.
You cannot expect to get more output then the amplifier was designed for.
The plate transformer and the plate output components are designed for
probably not more then 1KW keydown output
Repaired already a couple of MLA2500s from contesters, who fried
bandswitches and coils..
( output measures with bird equipment at 220 Volt never more then 1300
Watts )
73
Peter, DF3KV
Dick Carroll
tongaloa wrote:
>
> From the Svetlana 4cx400 conversion notes, and
> some research into the 2500B specifications:
>
> 2500B power transformer is good for 750 W CCS. With 2 x 4cx400
> the 840 W reported is single tone PEP translates to 595 W RMS
> In consideration of the typical 50% over CCS that one can usually get out of
> a transformer in ICAS (1120 W) this translates to about 52% efficiency, and
> agrees with most CW specs for ham amps.
>
> The GI7B conversion is reported to yield 1200 W out (two tone)
> or 600 W RMS. Same power!
>
> I bet the 2 KW output reported, corresponds to voice peaks and
> not the single tone it is compared to. Voice has a higher peak to average
> ratio than two tone so 2 KW peak seems pretty reasonable.
>
>
I expect you're right. My straight MLA2500 will do 1425 watts keydown
carrier into a dummy load operating on 240VAC. No way it'll do 2KW. But
I didn't check it at PEP.
Dick
Dick Carroll
a good bit under full carrier load was the 4-1000A I built myself using
a plate transformer from a Gates AM broadcast transmitter. Most will
drop a few hundred watts, which will be preserved pretty well on SSB
peaks on normal voice.
Dick W0EX
.Bill M.
>
> I expect you're right. My straight MLA2500 will do 1425 watts keydown
> carrier into a dummy load operating on 240VAC. No way it'll do 2KW. But
> I didn't check it at PEP.
>
> Dick
I've never owned the Dentron but I know two fellas who got them when
they first came out. They both easily did 2200 watts out keydown into a
dummy load, measured with a Bird wattmeter, one was using 110 vac. I
guess its only fair to mention that neither lasted very long :-)
-Bill WX4A
Gary - KJ6Q
what we recommend for normal, fulltime operation - but SOME like to fall back on extreme scenarios
as ridicule fodder, rather than recognize the INTENT of the measurement... NO, I not talking about
YOU or Dick...
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
".Bill M." <TheRea...@netscape.net> wrote in message news:3CB750FE...@netscape.net...
Gary - KJ6Q
mormally use...
"READ my lips - as stated in my last message to you I test with maximum key-down CARRIER in CW mode
on the exciter - SSB mode on the 2500B - when tuned for MAXIMUM carrier output from the amp, I get
the stated power levels. I *also* see the SAME or slightly BETTER output on voice peaks when
switched to SSB... On the SB-200 and FT-2100B, usually approached 1 KW peak outputs on SSB into a
peak-reading power meter - and while some might NEXT attack the accuracy of my meter, it HAS been
checked against other quality meters, and is HARDLY off by the 50-60% it would have to be to match
critics claims... As far as my MLA-2500B is concerned, at maximum output, I can easily see 2KW voice
peaks on SSB..."
I might mention that the SAME wattmeter indicates 100-110 watts out from my TS-570, and 100 watts
out from my IC-746 and IC- 706IIG - It indicates 1600 watts out on my Amp Supply LK500NTX - all
under the SAME test procedures - so it hardly seems my meter should be TOO suspect to other that the
extremely desperate...
I repeat - I'm SURE the 400 and 800 tubes referred to are EXCXELLENT power producers in circuits
DESIGNED to optimize their performance - but I maintain that the MLA 2500 conversion articles under
discussion here are NOT obtaining that capability!
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"Gary Schafer" <gasc...@attbi.com> wrote in message news:3cb72ce7...@netnews.attbi.com...
tongaloa
2 x GI7BT triodes, not expensive or complicated.
Tubes are $25/each, delivered, NOS ex Soviet military.
I machined some mounts and will sell for $32/each to anyone who
doesn't want to make their own. So there is $50 to $114 in parts.
Additional parts. Filament transformer (GI6B/7B/7BT is 12V)
2 x silicone rubber chimneys, a biscuit(tm) blower from Allied,
fits where the old blower went, about 2 sq. feet of 0.032 6061T6
Aluminum and some screws and pop rivets.
The clean, full output, SB200 will fetch $350+ on ebay.
Just what I'll have in the MLA2500B when the conversion is done.
3db and 160m on an even $ swap!
Here is the tube:
http://www.nd2x.net/gi7b.html
73,
Bob
wb4mnf
Gary - KJ6Q
pulsed operation - the plate dissipation looks good, as does the price and general design of the
tube in comparison to the 8875's. Sure would like to see a HF power chart, and the claimed 650 hours
tube life seems short, but that is probably at full frequency and power levels - dunno how that
would compare at HF with the 8875's - disregard my Email question concerning the Russian tubes -
this post has answered my questions..
Thanks.
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"tongaloa" <tong...@alltel.net> wrote in message news:a97p8n$l5b$1...@iac5.navix.net...
Dick Carroll
I imagine they spread some fairly trashy signals, too. Once the amp is
driven past the linear portion of the grid curve average output may go
up some but it sure ain't linear any longer!
Another aside- I always consider the difference between average power
and PEP on most ham amps to be the difference in power supply droop at
keydown vs voice signal input which is often a few hundred to several
hundred volts. The droop usually doesn't show up with voice signal
input. If no droop, no difference.
Dick
Gary - KJ6Q
"Dick Carroll" <di...@townsqr.com> wrote in message news:a97sni$6fg$0...@208.206.142.69...
>
> > >
> > >> I imagine they spread some fairly trashy signals, too. Once the amp is
> driven past the linear portion of the grid curve average output may go
> up some but it sure ain't linear any longer!
>
> Dick
Probably true to a degree - but all things being equal which would YOU *honestly* choose - an amp
easily showing 2 KW OUT, key down, or one showing only 1200 watts out, under the same test
conditions... No fancy footwork now, just a quick honest answer! <grin>
After all, MOST amps that will put out 2 KW at full grunt, will likely put out 1.5 KW pretty easily
and cleanly, all day long...
Gary Schafer
wrote:
. On the SB-200 and FT-2100B, usually approached 1 KW peak outputs on
SSB into a
>peak-reading power meter -
That wouldn't happen to be a swan watt meter that you use ?
73
Gary K4FMX
Gary - KJ6Q
ridiculing or questioning my power meter quality... Or MINE for that matter... Also read about OTHER
typical power readings from other pieces of gear, and past comparisons with other meters of
respected quality before falling back on cheap shots as a desperate debate tool...
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"Gary Schafer" <gasc...@attbi.com> wrote in message news:3cb78e84...@netnews.attbi.com...
Gary Schafer
at you or your
meters. By the tone of your post's it would seem that you wish to make
your point more by
assertion than by fact and are quick to try and belittle others that
may even question your
findings.
Rather than rant about how good the watt meters are that you are using
maybe you would like
to share with us what you actually used to measure the power with?
Please keep in mind that most good watt meters can have at least a 10%
error of full scale
reading. Using a watt meter with 2500 watts full scale at 1000 watts
could be in error by 250
watts. Some meters are not that good.
Most SB200's that I have seen do not put more than 600 watts. Maybe
mine and others watt
meters are in error.
73
Gary K4FMX
On Sat, 13 Apr 2002 02:35:09 GMT, "Gary - KJ6Q" <davi...@gte.net>
Gary - KJ6Q
"Gary Schafer" <gasc...@attbi.com> wrote in message news:3cb85883...@netnews.attbi.com...
> Much to your disappointment the question was not meant as a cheap shot
> at you or your
> meters.
SORRY Charlie - I know a cheap shot when one is fired my way - why not just be a man, and admit your
intent, instead of falling back into a tap-dancing routine as a coverup...
> Most SB200's that I have seen do not put more than 600 watts. Maybe
> mine and others watt
> meters are in error.
You know better than *I* do about the quality and accuracy of your own test equipment - so unlike
YOU, I won't profess to judge it unseen, and from a distance... Besides, why automatically assume my
meter - or those of others are reading HIGH? FACT is, the checks I have done with mine against
Waters and Bird wattmeters have indicated MINE read slightly LOW in the areas where there IS a
difference - but usually pretty much dead on on most ranges and readings...
And, I don't mind debate or criticism when it is applied in a constructive and courteous manner -
it's the mindless, juvenile taunts and childish insults that annoy me - sorta like YOURS...
AT this point, it's obvious that constructive communication between us is unlikely - sooooo...
*Kerplunk!*
MEANWHILE, feel completely free to continue to play to the crowd with witty response...
Frank Dinger
"Gary - KJ6Q" <davi...@gte.net> wrote in message
news:xPMt8.4370$8W5...@nwrddc02.gnilink.net...
> No, it was not, and read my OTHER post concerning my prediction of critics
falling back on
> ridiculing or questioning my power meter quality... Or MINE for that
matter... Also read about OTHER
> typical power readings from other pieces of gear, and past comparisons
with other meters of
> respected quality before falling back on cheap shots as a desperate debate
tool...
As mentioned earlier in this tread ,perhaps the arguments about watt meter
accuracy can be curbed by comparing the reading with that of a suitable
(calibrated ) oscilliscope using a known dummy load.
Frank gm0csz...@ntlworld.com
Peter Voelpel
Gary Schafer schrieb in Nachricht <3cb72ce7...@netnews.attbi.com>...
>I see a little confusion on PEP and average power.
Hi Gary ,
Your explanation could not be done any better
Peter, DF3KV
Dick Carroll
Gary - KJ6Q wrote:
>
> "Dick Carroll" <di...@townsqr.com> wrote in message news:a97sni$6fg$0...@208.206.142.69...
> >
> > > >
> > > >> I imagine they spread some fairly trashy signals, too. Once the amp is
> > driven past the linear portion of the grid curve average output may go
> > up some but it sure ain't linear any longer!
> >
> > Dick
>
> Probably true to a degree - but all things being equal which would YOU *honestly* choose - an amp
> easily showing 2 KW OUT, key down, or one showing only 1200 watts out, under the same test
> conditions... No fancy footwork now, just a quick honest answer! <grin>
>
> After all, MOST amps that will put out 2 KW at full grunt, will likely put out 1.5 KW pretty easily
> and cleanly, all day long...
Oh, I agree! But driving (or ovderdriving) such an amp sure offers
little benefit vs. the costs (a new set of tubes) involved.
I never knew that a MLA2500 *could* output 2kw since I never saw it
from mine, even with new tubes. Of course mine is unmodified.
Gary - KJ6Q
"Dick Carroll" <di...@townsqr.com> wrote in message news:a9an95$r1f$0...@208.207.71.144...
You mighta missed THIS post from Bill M back up the thread:
"I've never owned the Dentron but I know two fellas who got them when
they first came out. They both easily did 2200 watts out keydown into a
dummy load, measured with a Bird wattmeter, one was using 110 vac. "
Apparently I am not the ONLY one seeing 2KW or better from these rigs - of course, SOME critics here
will assert the Bird wattmeter used for the above measurement was probably out of calibration... Or
the tester too stupid to know how to use it properly...
And yeah, it's possibly true that the output at that power might not be as clean as at lower
levels - but with as much "headroom" as 2KW or better provides, such an amp can CERTAINLY run cool
and clean down at 1.5KW - while one that has to strain at 1200 watts will be operating well into ITS
distortion/nonlinear stage LONG before even reaching the legal limit - so *I* would take the higher
powered option ANY time!
Remember - that's what this thread is ABOUT - the rationale of converting from tubes in an amp that
originally delivered 2KW or better output, to tubes only putting out 800-1200 watts (depending on
whose test methods you prefer) - at a cost in excess of $400...
.Bill :-)
>
>
> You mighta missed THIS post from Bill M back up the thread:
>
> "I've never owned the Dentron but I know two fellas who got them when
> they first came out. They both easily did 2200 watts out keydown into a
> dummy load, measured with a Bird wattmeter, one was using 110 vac. "
>
> Apparently I am not the ONLY one seeing 2KW or better from these rigs - of course, SOME critics here
> will assert the Bird wattmeter used for the above measurement was probably out of calibration... Or
> the tester too stupid to know how to use it properly...
>
> And yeah, it's possibly true that the output at that power might not be as clean as at lower
> levels - but with as much "headroom" as 2KW or better provides, such an amp can CERTAINLY run cool
> and clean down at 1.5KW - while one that has to strain at 1200 watts will be operating well into ITS
> distortion/nonlinear stage LONG before even reaching the legal limit - so *I* would take the higher
> powered option ANY time!
>
> Remember - that's what this thread is ABOUT - the rationale of converting from tubes in an amp that
> originally delivered 2KW or better output, to tubes only putting out 800-1200 watts (depending on
> whose test methods you prefer) - at a cost in excess of $400...
>
> --
> Gary - KJ6Q
Geez, I feel stoopid now. In the late 70s when guys were gobbling up
the Dentrons I never heard of one putting out less than 2kw key down.
Both my friends who had them were very active DXers and the tubes were
cooked in less than two years. One guy sprang for retubing, the other
bought another amp. They knew they were abusing the amp...at the time
nobody knew how long they would (or would not) last.
I don't question at all that the MLA-2500 is (was) not beefy enough to
do this kind of power on any regular basis. Shoot, the pwr xfmr is
about the size of the one for my Galaxy 5 transceiver which is good for
about 200 w out with fresh tubes. And I remember both these guys
replacing other parts which had 'melted down'. Putting the Dentron in
the context of what I was used to seeing in that era, I thought at the
time that it was very cheaply built....certainly not up to par with MY
homebrew pair of 4-400As that only put out 600-800w.
That being said, jazzing it up with different tubes to run 2kw+ out
isn't such a good idea anyway but the headroom would be nice.
-Bill WX4A
Dick Carroll
Gary - KJ6Q wrote:
>
> "Dick Carroll" <di...@townsqr.com> wrote in message news:a9an95$r1f$0...@208.207.71.144.
> > Oh, I agree! But driving (or ovderdriving) such an amp sure offers
> > little benefit vs. the costs (a new set of tubes) involved.
> > I never knew that a MLA2500 *could* output 2kw since I never saw it
> > from mine, even with new tubes. Of course mine is unmodified.
>
> You mighta missed THIS post from Bill M back up the thread:
>
> "I've never owned the Dentron but I know two fellas who got them when
> they first came out. They both easily did 2200 watts out keydown into a
> dummy load, measured with a Bird wattmeter, one was using 110 vac. "
>
I also saw something about cutting out the grid swamping resistor to
make the amp output more than it was designed to do. Mine didn't get
that mod.
> Apparently I am not the ONLY one seeing 2KW or better from these rigs - of course, SOME critics here
> will assert the Bird wattmeter used for the above measurement was probably out of calibration... Or
> the tester too stupid to know how to use it properly...
>
> And yeah, it's possibly true that the output at that power might not be as clean as at lower
> levels - but with as much "headroom" as 2KW or better provides, such an amp can CERTAINLY run cool
> and clean down at 1.5KW - while one that has to strain at 1200 watts will be operating well into ITS
> distortion/nonlinear stage LONG before even reaching the legal limit - so *I* would take the higher
> powered option ANY time!
I'd want to do a linearity test to check that out. As for me, I've
always been able to do anything I wanted or needed with mine at the
lower power level, things such as work VK0IR on a nearly dead 20 meter
CW band where they couldn't copy me barefoot.
>
> Remember - that's what this thread is ABOUT - the rationale of converting from tubes in an amp that
> originally delivered 2KW or better output, to tubes only putting out 800-1200 watts (depending on
> whose test methods you prefer) - at a cost in excess of $400...
Somewhere it drifted off to the MLA's design capabilies.
Dick W0EX
.Bill :-)
> I also saw something about cutting out the grid swamping resistor to
> make the amp output more than it was designed to do. Mine didn't get
> that mod.
Bingo! I hate to keep jumping into this thread since I never owned one,
but that was the FIX of the era now that you remind me! That might
explain the disparity between the 2kw+ ones and the measly 1.4kw
examples.
-Bill WX4A
Peter Voelpel
Gary - KJ6Q schrieb in Nachricht ...
>Remember - that's what this thread is ABOUT - the rationale of converting
from tubes in an amp that
>originally delivered 2KW or better output, to tubes only putting out
800-1200 watts (depending on
>whose test methods you prefer) - at a cost in excess of $400...
Well, above is NOT what this thread is ABOUT-
originally NI4L was looking for the original qst-article (title),
when you jumped in to declare that this conversion make no sense...
Again, there is no reason the russian tubes do less output then the 8875s,
of course same mode used.
Anyhow there plate dissipation value is already bigger the 8875...
Under keydown condition ( steady carrier ) I do not have to worry about
distortion at all, so this test would be fine to find out how much power
is coming out of an original MLA2500 when measured with an oscilloscope
into 50 ohm dummyload.
To make shure everything has settled, measurement should start after 1
minute
keydown.
As mentioned in previous mails I repaired and modified a couple of
MLA2500s and also MLA1200s, so I am familiar with the Dentron
power-supplies and the capability of the 8875 tubes.
I never saw more then 700 Watts from one 8875 !!
This thread is about conversion of the MLA2500 to tubes available at
good prices.
Conversion will work fine with tubes like GU74b, Gi7b, 4CX800, 4CX400,
TBL2/500 .
Limiting factor is the ht transformer and the pi-circuit components.
73 de Peter, DF3KV
tongaloa
that 650 hour life is running full tilt pulse at almost 3000 Mcps.
Pulse is 9 kV and 7 A for 63 kW peak input.
Efficiency is only 10% but that's still a 6 kW pulse out.
A cathode that can handle 7A pulses should last a long time
running 50% duty cycle and 550 mA....
I'm about 1/2 done with a single in a SB200 for 50 Mcps.
I'll be surprised if I don't see 600W RMS out for ICAS operation.
Gain is a bit more than 2 X that of the 572B so an HF SB200
conversion should give full output when driven with the newer
50W max output transceivers.
-t
Duncan Clark
In message <Py5u8.8957$8W5....@nwrddc02.gnilink.net>, Gary - KJ6Q
<davi...@gte.net> writes
>so *I* would take the higher powered option ANY time!
But what you are talking about is low power :-)
http://i5uxj-2.cln.it/amp/hfamp.html
or for QRP
http://www.pollak.sulinet.hu/elektro/pa_rev/pa_rev.htm
Duncan
G4ELJ
--
Support bacteria. They are the only culture some people have.
Duncan Clark
R. Belcher
conversion seems to me to be capable of legal limit using 2 tubes... Should
I convert my amp?
rb
Gary - KJ6Q
There were several under discussion - the one using the Russian triodes certainly looked the most
promising and economical to me...
--
Gary - KJ6Q
**************
Two things we'll never see:
1. Perpetual motion...
2. A liberal Democrat complaining
about "Too much government"
"R. Belcher" <randy....@verizon.net> wrote in message
news:H5Dv8.6095$93....@nwrddc04.gnilink.net...
R. Belcher
same conversion you mention??
thanks!
Randy
http://www.svetlana.com/docs/TechBulletins/technoteNo14.html
If that isn't the proper one, could you please direct me to it.
thanks.
"Gary - KJ6Q" <davi...@gte.net> wrote in message
news:hiDv8.30820$bn2....@nwrddc01.gnilink.net...
w9gb
Svetlana Tech Bulletins
http://www.svetlana.com/docs/TechBulletins/TB.html
W6KT conversion
4CX400A Russian Tubes for the MLA-2500 Amplifier
http://www.svetlana.com/docs/TechBulletins/technoteNo14.html
The Easy MLA-2500 Conversion
http://www.svetlana.com/docs/TechBulletins/technoteNo44.html
New Life for Dentron MLA2500s - 4CX800A
(QST May 96 pg.45-48)
Zip file on Svetlana web site
Greg
w9gb
"Gary - KJ6Q" <davi...@gte.net> wrote in message
news:hWnt8.1863$I64...@nwrddc02.gnilink.net...
> Just carefully check the claimed power output AFTER the mods
> suggested - and compare them with the 2 KW the STOCK Dentron's do -
> THAT alone should convince you of the validity of the "conversion"...
>
> There are FAR better ways to spend yer time and money than on a
> "conversion" that leaves you with an amp the now only has about the
> same OUTPUT as a stock SB-200 or similar amp that can be bought for
> LESS than the cost of the conversion of the 2500B...
>
> --
> Gary - KJ6Q
> = = = = = = = =
>
>
> "NI4L" <ni...@charter.net> wrote in message
> news:3CB5E884...@charter.net...
> > hi i was able to download it from one of the new places listed thank
> you.
> > Has anyone tried this and if so what was the outcome. Anyone have
> any better
> > ideas?
> > chris NI4L
> >
> > "Kenneth D. Grimm, K4XL" wrote:
> >
> > > >http://www.svetlana.com/docs/TechBulletins/TB.html
> > > > i need some help i tried to download this but it will not work
> can
> > > >someone else try or do you have it on file somewhere and could
> you email
> > > >it to me?
> > > >thanks chris NI4L
> > >
> > > The ftp site that Svetlana has listed (oak.oakland.edu) seems to
> be
> > > down. Odd, too, since it has been operating since way before the
> web
> > > was invented!
> > > What you are looking for is a file called mla2500b.zip. I think
> you
> > > will find it at the following address:
> > > http://ring.omp.ad.jp/pub/misc/ham/funet/arrl/qst-binaries/ or at
> > >
> > >
> http://ring.tains.tohoku.ac.jp/pub/misc/ham/funet/arrl/qst-binaries/
> > >
> > > Good luck with your conversion.
> > >
> > > 73,
> > >
> > > Ken K4XL - Replace "invalid" with "net" to reply.
> > > *** BoatAnchor Manual Archive ***
> > > On the web at http://bama.sbc.edu or
> > > FTP site info: bama.sbc.edu login: anonymous p/w: youremailadr
> >
> > --
> >
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