Lafayetts Telstat 140 SSB now just low power

[Techno1]

Well i received brand new finals HG 1969 and 2sc2166.

I installed in radio and same low SSB power and little swing on AM.

Actually about 2 watts less on sideband 6 watts.

Am about 5 watts and peak to 6 watts.

Saying Ah on ssb i get about 3 watts and if i whistle i get about 8 watts max.

I guess i will have to give up for a while and work on something else.

 

[Techno1]

here is an update on this ssb 140 telsat.
I have run the radio on the 12v plug and all seems good 5 watt AM swings to about 10 watts and ssb about 13 watts.

When run on AC I get about 4 watts Am very little swing and ssb about 6-8 watts max.

I checked the Ac power supply and its dropping about 2 volts during transmit. I checked the power regulator and dropping there also.
So next the AC out of the transformer and loosing about 2 volts about 21v Ac to 19v AC which makes the dc voltage drop about 2-3 volts also
I think the transformer is bad I replaced the 2 filter caps and still same problem and the regulator seems to be working properly.

I checked the 4 diodes and all good replaced the 2 electro caps got same results 2v drop, go back to dc v in and all is ok.

I dont think i will be able to find a new transformer so is there a small power supply i can install in the radio plenty of room if transformer is removed.

 

[nomadradio]

It's almost never the transformer. That component tends to be a go/no-go proposition. A "partial" fault almost never happens. The unregulated voltage you measured sounds about right. The voltage regulator is failing to hold the output steady. Question is why? An oscilloscope is a handy tool for troubleshooting this kind of issue. The rectifier ripple can provide a hint about who to blame. Can't see that with just a meter.

How much current does the radio draw from the external supply? If the final bias is turned too high, this causes excess current drain in transmit, and shortens the life of the final transistor. If the radio draws no more than 3 Amps in transmit on the external supply, this is not the cause.

Back before we started replacing this type power supply with chinesium "brick" switchmode supplies the routine was to check both zener diodes and replace all the electrolytic capacitors in the supply. We can no longer justify the labor cost to fix the factory power supply when a switchmode replacement costs the customer less than fixing the old DC supply. Both zener diodes and all 3 transistors should pass a proper test just to be sure. Filter caps, the two zeners and three transistors are pretty much the whole lineup of possible culprits.

73


73

 

[Techno1]

It's almost never the transformer. That component tends to be a go/no-go proposition. A "partial" fault almost never happens. The unregulated voltage you measured sounds about right. The voltage regulator is failing to hold the output steady. Question is why? An oscilloscope is a handy tool for troubleshooting this kind of issue. The rectifier ripple can provide a hint about who to blame. Can't see that with just a meter.

How much current does the radio draw from the external supply? If the final bias is turned too high, this causes excess current drain in transmit, and shortens the life of the final transistor. If the radio draws no more than 3 Amps in transmit on the external supply, this is not the cause.

Back before we started replacing this type power supply with chinesium "brick" switchmode supplies the routine was to check both zener diodes and replace all the electrolytic capacitors in the supply. We can no longer justify the labor cost to fix the factory power supply when a switchmode replacement costs the customer less than fixing the old DC supply. Both zener diodes and all 3 transistors should pass a proper test just to be sure. Filter caps, the two zeners and three transistors are pretty much the whole lineup of possible culprits.

73


73

I replaced the 2 caps and still the same results. I will check the regulator again or replace and also the zener diode. Will also replace the D525 regulator

 

[Techno1]

Nomad you mentioned the chinese PS I was thinking of getting one to install plenty of room in the radio if i remove the transformer