[AMPS] Dentron MLA2500B

[km1h @ juno.com]

On Tue, 2 Dec 1997 22:21:16 -0500 (EST) W2GR@aol.com writes:
>Hi guys, i've got some amp questions and this seems to be the right 
>place to
>ask them....Name here is Mike and I've got a line on a Dentron 
>MLA2500B for
>abt 500 bucks.

A great amp if the tubes are good; make absolutely sure of that first
since new ones are around $500 each.


 This will be my first amp and was wondering how this 
>amp
>stacks up.
>   It uses a pair of 8875's ..are they still available and how much 
>power can
>I expect out? Also$$$$$

The amp will do 1800W but for tube longevity keep it in the 1200-1300W
range. Make sure that the grid swamping resistor, R-1, is in the circuit.
Many MLA owners cut it out to get even more power!

>   I will be driving it with my 1000MP, will the TR be fast enough?

It seems to be since there are hundreds of MLA's in use and they do not
have relay induced or parasitic problems. The MLA relay is a clone of
most other open frame relays that are used in old and current production
amps. 

>   Does it have any protective circuits?

NO and the low speed fan is too slow. Add resistance in parallel on the
terminal strip to speed it up a bit. 

>   Can it be used for the WARC bands?

Many will smoke the plate choke on 12M. There appears to be a winding
difference or tolerance between some MLA's.  Try running it at 600W or so
on 12M then feel the lower end of the choke...AFTER discharging the caps,
pulling the plug, etc!!  If you feel a hot spot, remove 5 turns and try
again. The trick is to place the choke resonance up in the CB band. 

Check the PS. Early models had 6 filter caps; 3 in each leg. With almost
universal use of 240VAC +  in NA these days ( 220-230VAC was common in
the past) those 6 caps are at or over the DC limit. Dentron added 2 more
caps in later units; there are already cut-outs on the PC board. I'm not
sure if the B model was factory updated already.
While you are at it check the 100K equalizing resistors and replace any
that are out of tolerance. Better still replace with modern 3W metal
oxide. Next, measure the voltage cross each cap; they should be all
within a 5% tolerance range. If not,  you have to consider replacing the
caps or going to a lower value equalizing resistor across all caps to
force an equal distribution.

With a little bit of PM and TLC the MLA-2500 is a decent amp. 

GL   Carl   KM1H


>    Any other info will be greatly appreciated....Tnx in advance es 
>"73"
>
>                                   Mike Benjamin  W2GR
>
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