[Moon] [Moon-Net] SSB Electronics LT-2s broke!

DW Harms (Dick) qtc at kpnmail.nl
Thu Jul 16 12:54:24 CEST 2020

Correction Peter/John,


The BD’s are low frequency transistors, used for the bias…. I need new glasses hi!

The typenumbers of  T1/T2 (driver/final) are not mentioned in the schematics… so, open it up Peter and exchenge them 😉


73, Dick PA2DW


Van: Moon-net <moon-net-bounces at mailman.pe1itr.com> Namens DW Harms (Dick) via Moon-net
Verzonden: donderdag 16 juli 2020 10:50
Aan: John at pa5ms.nl; 'Peter Shilton, VE7PS' <VE7PS at shaw.ca>
CC: moon at moonbounce.info; moon-net at mailman.pe1itr.com
Onderwerp: Re: [Moon-Net] SSB Electronics LT-2s broke!


Alas Peter/John, the PA is not fused like in most of DB6NT’s products.

It is therefore very likely that the final transistor (and maybe also the driver…) have gone to heaven. 

What John says could be very true, that the coax cable provides a very low impedance on its outer end. Deadly…


However the good news is, that the final transistors are very regular and not difficult to replace. Driver is a BD135, final is a BD675.


A down sight of the LT2S is the postmixer stage with BF982. I have seen two cases (one was of Gary, KB8RQ…) in which this stage oscillates and thus producing a lot of bad signals. Check that out! A simple cure is a 100 Ohm resistor across the draincoil, but it does not always help. In the cases I cured, I replaced the BF982 by a MMIC (MAV11 or alike). Works way better.


Good luck fixing Peter!


73, Dick PA2DW


Van: Moon-net <moon-net-bounces at mailman.pe1itr.com <mailto:moon-net-bounces at mailman.pe1itr.com> > Namens John--- via Moon-net
Verzonden: donderdag 16 juli 2020 9:25
Aan: Peter Shilton, VE7PS via Moon-net <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com> >; Peter Shilton, VE7PS <VE7PS at shaw.ca <mailto:VE7PS at shaw.ca> >
Onderwerp: Re: [Moon-Net] SSB Electronics LT-2s broke!


How long is your cable with the open end? An electrical quarter wave open-ended is a rf short-circuit... 


The LT2S has a transistor final. 


Is your meter on the LT2S still moving? If it's not it's quite obvious there's something wrong in your final. Don't tnow it it's fused or not. The final stage is in the tin plated box on the rear. 


73! F/PA5MS

Verzonden vanaf mijn Huawei-telefoon

-------- Oorspronkelijk bericht --------
Van: "Peter Shilton, VE7PS via Moon-net" <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com> >
Datum: di 14 jul. 2020 22:56
Aan: Moon Net <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com> >
Onderwerp: [Moon-Net] SSB Electronics LT-2s broke!

HI all:

Hope this is an OK request as I know there are many on here who have 
likely used, or are still using, these transverters.

Any repair experts out there who have dealt with these?

I have had the LT-6 through LT-70 for many many years, without issue, 
though none have been operational since 2007.

Yesterday I fired up the LT-2s and was pleased to see it working fine 
with adjustable output up to 20w, as it should.  I set it for 10 watts 
out as was looking to run an on-air test with a new local ham.

I then inserted a new-to-me wattmeter in line with the Bird 43 to check 
it out.  Odd that the Bird was reading 20 watts now......hmmmm...I 
didn't twig fast enough and suddenly lost all power output.  Turns out 
one of the connectors on the 2nd wattmeter was not screwed all the way 
in and was open - hence the high reading on the Bird.  And now there is 
zero output. My bad!

I do have low level 144 Mhz RF going into the PA, but nil coming out 
apparently.  I can see the strong signal at 144.200 on a nearby SDR rcvr 
and it gets much stronger with an antenna wire brought close to the PA 

I am really hoping the final transistors are not toast - seems odd that 
transistors supposedly rated at 50w would die within 5 seconds at 10w 
out into an open line!  I am hoping it is one of the other small parts 
in there that smoked instead.   Either way, I need to pull the PA board, 
which is not going to be a simple task from the looks of things.  
Looking for advice from anyone that has been there/done that.

Thanks and 73,

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