Galaxy-X4 popped a pill

[Cable Guy]

This amp, almost identical to a Palomar 400, just quit working mid-qso per owner (friend). I see a base bias resistor (10ohm) is smoked. Yes, it is clipped in the pic from troubleshooting. Schematic doesn't list it. I assume the pill shorted, sending 13.8v from collector to base. R13, 14, 19 and 20 look scorched too. C7, an alu electrolytic, has dome bulge. All else looks okay. Other than mentioned components, is there anything else I should scrutinize? Should all 4 pills be replaced with a matched set? All comments welcome.

 

[144inBama]

Ideally you'd replace all 4, at the very least I would put a matching pair in that section. A weak transistor will strain the new one pulling it down, so the weaker of the two sections of the 4 pill will pull down the stronger section reducing output and stressing the stronger section. If the other pill is weak, it's possible to blow it and damage the new one at the same time.

 

[nomadradio]

The four RF transistors need to share the load equally. Production date on those parts is Y2K. You won't find a supply of 23-year old transistors with that type number to choose from.

Replacing all four is the only way to be sure they will share the load equally.

73

 

[Cable Guy]

Thanks. I hoped I could get away with just replacing the pair but I know they are expensive and all 4 matched would be a little harder to find. I'll pass the suggestion on and see what he wants me to do.

 

[144inBama]

Thanks. I hoped I could get away with just replacing the pair but I know they are expensive and all 4 matched would be a little harder to find. I'll pass the suggestion on and see what he wants me to do.

Talk to Gate Keeper. I bought 4 1446s (Hgs) for 21 each.

 

[snippits75]

SD1446 STMicroelectronics Transistor Matched Quad (4) (NOS)

<p><span style="font-size: medium;"><strong>SD1446 ST Micro Transistors, 27-88 MHz, 0.380" Flange, Matched Quad (NOS)</strong></span></p> <p align="left"><span>The SD1446 is a 12.5 V Class C epitaxial silicon NPN planar transistor designed primarily for

www.rfparts.com

Matched set of four new old stock for $179.91.

 

[Cable Guy]

That's great. I'll look into that.

 

[lonestarbandit]

Rooster did this video "at" me, as I just had to re-pill my base amp due to a stupid failed cheap low pass filter shorting and taking a pill out.
I heeded his advice (and others here) and replaced all 4. (I also had hopes of one pill fix but was talked out of it.)

 

[9C1Driver]

Search results for: 'sd1446'

Default Description

www.rfparts.com

 

[Cable Guy]

I ordered a 4 pack from RF parts per snippets75's link. I will update when they get here. Gotta find the big iron while I wait.

 

[lonestarbandit]

For real. I never did find my big Weller.
I credit wifes occasional "reorganizing ".
I'm sure its in the garage somewhere but the where escaped me. Had to struggle through with a small iron. Not recommended lol.

 

[Cable Guy]

Yeah same here. I ordered another from Amazon. I think my wife throws my toys away while I'm gone. She says if you ain't used it in a month, you don't need it. Reorganizing the shop really means "toss your stuff out, make room for mine."

 

[lonestarbandit]

Ah. A fellow victim lol. Amazon has made untold 1000s from me for this self same reason. When I die, and they do an estate sale, someone is gonna find half of the man stuff is in triplicate which I never found while among the living.

 

[Cable Guy]

I got the old ones out, de-burred the screw holes, applied thermal compound and bolted the new ones in. Also replaced a domed capacitor and checked some other parts out. I still need to tighten some screws, replace the blown resistor (already removed) and solder the pills. Now,. .

I see some model amps have the pills strapped, could someone explain why and if I should do it too?

 

[Shadetree Mechanic]

View attachment 65918
I got the old ones out, de-burred the screw holes, applied thermal compound and bolted the new ones in. Also replaced a domed capacitor and checked some other parts out. I still need to tighten some screws, replace the blown resistor (already removed) and solder the pills. Now,. .

I see some model amps have the pills strapped, could someone explain why and if I should do it too?

I believe the strap across the pill body was for RF shielding. I don't know if it really makes a difference or if it was just good practice. I have also seen copper flashing about an inch wide ran vertically across all the pills to help shield the input from the output.