Stalker st9f dx no am audio

[tony2803]

Stalker st9f dx got audio fm.usb.lsb mid and high bands but no audio going out on am mode.
Legal fm works fine as well.
But when on mid or high I have no audio transmitting out on just am mode.
Does anyone have a possible solution to this fault.
Thanks in advance.

[MrJackson]

Replace Tr 48 2SA1012 at the back of the radio.

[MrJackson]

Just in case you haven't already tried adjusting the Am modulation vr, It's vr5 to increase the modulation on AM. I should have pointed that out before you replace tr 48.

[tony2803]

2sa1012 that's the regulator at the back by the power plug. Would that not affect fm and ssb audio as well.

[bigal68]

No, the 2SA1012 is the AM regulator. This feeds volts to the PA stages of the radio

AM audio is fed into this transistor, and it is biased to control the AM/FM carrier level.

FM audio is created by feeding some mike amp audio into the VCO/VCO mixer at a low level.

SSB is done elsewhere in the radio, and the 2SA1012 is driven flat out when on SSB which contributes to the higher output power.

If the transistor goes short (most common...... and very common on the PC-893 Stalker IX (Export)/ST9f-DX/President McKinley (Export) radios.....
due to poor heat-sinking), you will get a lot of output power on AM and FM..... but no TX audio on AM.

As MrJackson said, check the carrier level with the correct VR (have a look on CB Tricks for the circuit diagram), and if this has little or no effect, try changing the transistor.

[tony2803]

No, the 2SA1012 is the AM regulator. This feeds volts to the PA stages of the radio

AM audio is fed into this transistor, and it is biased to control the AM/FM carrier level.

FM audio is created by feeding some mike amp audio into the VCO/VCO mixer at a low level.

SSB is done elsewhere in the radio, and the 2SA1012 is driven flat out when on SSB which contributes to the higher output power.

If the transistor goes short (most common...... and very common on the PC-893 Stalker IX (Export)/ST9f-DX/President McKinley (Export) radios.....
due to poor heat-sinking), you will get a lot of output power on AM and FM..... but no TX audio on AM.

As MrJackson said, check the carrier level with the correct VR (have a look on CB Tricks for the circuit diagram), and if this has little or no effect, try changing the transistor.

Thanks for the in depth explanation. I can honestly say after reading your reply i fully understand what is wrong and will order the new part for the stalker.
Is there a better part to replace the original part to try and put not so much strain on the part that is odviously under a lot of strain.

[Mudslinger]

I had the same problem on a President Jack.

It had no Audio on AM, but the FM and AM deadkey power output was 20 watts.

[MrJackson]

You can use a TIP42C from Maplin's, which will work just as well.

[tony2803]

Replaced Tr48 with one from a president Ar144 back working again.
Great big thanks for everyone's advice.
Thanks All.

[robo70]

can anyone please confirm is this a PNP tranny ?
cheers rob

[zephyr]

Yes it is a PNP transistor.

[robo70]

Yes it is a PNP transistor.

thanks

[robo70]

You can use a TIP42C from Maplin's, which will work just as well.

thanks for the tip pal, i got one from maplins ( great western rd ) works ok, but kinda huge lol

[ghost123uk]

Surely a TIP42C is the same package as the 2SA1012 = "TO220" ?

[robo70]

Surely a TIP42C is the same package as the 2SA1012 = "TO220" ?

no..i got the TIP2955 Standard Bipolar PNP Power Transistor TO218 Case
its about 3 times the size it still works though
TIP42C seller on ebay let me down.. got tired of waiting

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