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RM HLA300 low power output.

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  #9  
Old 06-10-2012, 10:55 AM
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Im willing to bet that it got hot when driving it with 20 watts I agree and say pay close attention to the input section and when straightened out drive it with 10 i 12 watts input it will trun cooler stay cleaner and the power you would be lacking compared to the 20 watts in isnt even going to be noticable on the other end.

I know the SD-1446 transistors should easily handle 20 watts input but the rest of the resistors and parts used Im not sure about.RM Italy has come a long way and makes a great product but they do have to be run differently and to RM Italy specs.
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Old 06-11-2012, 01:44 AM
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Ok I found something
It looks as though someone has replaced R12 and R56 at some stage
These are part of the input network around the attenuator relay.

They are both supposed to be 68R according to the parts list but they have been replaced with 80R resistors.
Furthermore the resistors look suspiciously like wire wound ones to me which can't be right for RF input can it?

I'll get some 68R 5 watt carbons and replace them

Cheers

Stu

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  #11  
Old 06-11-2012, 12:44 PM
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post a pic.
wirewounds are a big no no with rf.
and if you can lift b and c on all 4 transistors to check them with a real tester like my sencore super cricket you may find one or more damaged.1446's are relatively high gain parts and do not need a lot of drive.probable damaged one or more.
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Originally Posted by Stuuk View Post
Ok I found something
It looks as though someone has replaced R12 and R56 at some stage
These are part of the input network around the attenuator relay.

They are both supposed to be 68R according to the parts list but they have been replaced with 80R resistors.
Furthermore the resistors look suspiciously like wire wound ones to me which can't be right for RF input can it?

I'll get some 68R 5 watt carbons and replace them

Cheers

Stu

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  #12  
Old 06-11-2012, 06:39 PM
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I replaced the wire wounds with carbon and there is a slight improvement but not much.

I've already lifted the base on each transistor and the b-c and b-e junctions pass the forward and reverse voltage test.

I dont have a tester that will check gain etc

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  #13  
Old 06-12-2012, 09:45 AM
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Default Power meter readings

Are you reading the power with a proper PEP meter?
If one set of transistors is running hotter than the others then something is possibly not right somewhere. Perhaps the transistors have been replaced at sometime and are not properly matched.
What frequency are you making the readings on?
I stopped importing these because they were too easy to abuse. Keep the input power down and they work very well but they are a little susceptible to swr and RF..but they do perform well when they work. Recently RM did make a few modifications to the board to improve stability and are now well past ver1.1

I assume you have the Hi/lo switch set on high?

rgds,
Dave

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  #14  
Old 06-12-2012, 01:11 PM
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Hi
Thanks for the response

Ok have found someting else

I did a cw keydown test about 7w in and 100 watts out
The sd1446's started getting warm to the touch but not hot
After about 10 seconds R37 was visibly getting very hot and started to smell

So need to work out why r37 is passing a lot of current

Schematic here if anyone cares to take a look
http://www.rmitaly.com/download/manu...al_rel_110.pdf

Stu

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  #15  
Old 06-12-2012, 01:41 PM
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So you tested those transistors that resistor is feeding?
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Last edited by Robb; 06-12-2012 at 03:13 PM.

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  #16  
Old 06-12-2012, 03:21 PM
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R37 is part of the base bias / feedback circuit for one of the sd1446 RF power transistors.
It connects via a capacitor from the collector to the base then another resistor connects from the base to ground.
I've checked all the components around the transistors and they all seem to check ok.

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