Replacing 2SC3067 with a pair of MPSA18 in SS CA 3.0 amp?

[JLH]

Now that I have my Sounstream 6.0 up and running, I've turned my attention to the two 3.0 amps that need repaired. I believe the first one has had its inputs over driven because the 2SC3067 are bad in both channels. I got some new ones from Jamie on E-bay. First attempt was a joke, I over heated it during soldering and cracked it. The second one resulted in 184mV of off set on the speaker outputs. Must have damaged this one too. The third one works as it should. I started to replace the other one on the second channel and managed screw it up too. These things are so freaking small and hard to work with.

So, to my question. What would happen if I just soldered in two MPSA18 transistors in the 2SC3067's place? It sure would be a lot easier.

Rgs, JLH

[Perry Babin]

It wouldn't be the same. The two transistors inside of the differential transistor have essentially identical electrical parameters (closer than you can get from individual transistors unless they come from the same silicon wafer). This is important for the differential stage of an amplifier if you want low DC offset.

To reduce heating, you could install the transistor a bit off of the board (longer leads) or use a soldering iron with an adjustable temperature. If you're going to do this type of work, you should invest in a good soldering iron. A WES51 with an assortment of tips (ETA, ETB and ETC) is a good choice and can do most anything you will need to do.
Amazon.com: Weller WES51 Analog Soldering Station, Power Unit, Soldering Pencil, Stand and Sponge: Home Improvement

[JLH]

Thanks Perry. Out of curiosity I searched to see if anybody ever made a DP6A package socket. The answer to that appears to be NO. I looked at the dimensions of the standard DIP-6 sockets and it appears to be too large to work. I'll try your suggestion of soldering the device up off the board more. I was thinking about buying one of those clip on heat sinks (looks like an alligator clip) but the DP6A package is just too small for this. I can vary the temperature of my soldering iron by plugging it into my variac.
Thanks again!

Rgs, JLH

[Dr Zeus]

Radio shack sells for $2 a Soldering Heat Sync Clip which will work great to keep the heat off components while soldering. Just attach it to a lead of the component on the cold-side of the PCB (Close to the silicon body of the piece) and then solder away. It should keep the part cool. You can also try some aligator clip-leads but this will work much better. I believe places like Digi/Mouser/Frys will sell one half the size of the RS piece for cheap.

RS Heat sync clip:
Soldering Heat Sink Clip Tool - RadioShack.com

Ya, those little 2SC3067s stay off the PCB about 1/4 inch.

If you are close to a Frys Electronics www.frys.com you can probably get the same soldering iron Perry posted for $65 after $20 MIR. Have them price-match to Amazon, and then mail in the rebate. http://www.frys.com/search?search_ty...er+WES51&cat=0

[JLH]

This might seem like taking the long way around things, but I’ll throw it out here anyway. What do you guys think about using something like the Analog Devices SSM2212 with a SSOP-8 to DIP-8 PCB adapter? Instead of using standard SIP pins I could use enameled wire coming off the PCB. I’ve had great success soldering surface mount ICs using solder paste.

Thanks for the pointer on the soldering station Dr Zeus!

Rgs, JLH

[zener_diode]

Originally Posted by JLH

This might seem like taking the long way around things, but I’ll throw it out here anyway. What do you guys think about using something like the Analog Devices SSM2212 with a SSOP-8 to DIP-8 PCB adapter? Instead of using standard SIP pins I could use enameled wire coming off the PCB. I’ve had great success soldering surface mount ICs using solder paste.

Thanks for the pointer on the soldering station Dr Zeus!

Rgs, JLH

That should work great. The SSM pair are matched way better than the 2SC pair.

You definitely should get a variable temp soldering iron!!! I have a couple of Hakko irons. Not expensive, but high quality.

By the way, B&D has many of the 2SC3067 parts in stock... http://www.bdent.com/2SC3067-p/2sc3067.htm

[Perry Babin]

I'd suggest getting it working perfectly with the original parts and 'then' trying the substitute parts. If the amp has some strange problem in the repaired channel you won't know if it's the subbed part or something else.

[JLH]

Originally Posted by Perry Babin

I'd suggest getting it working perfectly with the original parts and 'then' trying the substitute parts. If the amp has some strange problem in the repaired channel you won't know if it's the subbed part or something else.

Good point. I'll do that and repair it with the original parts first.

Rgs, JLH

[Dr Zeus]

Were you able to get the discount deal on that Weller iron from Frys? I'm thinking of getting on there myself if the deal worked.

[JLH]

Originally Posted by Dr Zeus

Were you able to get the discount deal on that Weller iron from Frys? I'm thinking of getting on there myself if the deal worked.

The nearset one is about 50 miles from me, so not yet. I'll see if I can find the time to get there. Thanks.

Rgs, JLH