Heat sink for these transistors - Videokarma.org TV - Video

TinCanAlley · #1 10-14-2013, 02:53 PM

I have updated NOS video output transistors that I want to use, but they are a different case than the currently installed. This was supposed to be an upgrade kit, but the only pieces included were the transistors. The heat sinks are gone, so now it's up to me to figure it out. I tried them and actually think the overall image is better (my brother and friend noticed it as well).

I'm attaching pics of the current and you can see in the right of the picture the TO-39. That is what's under each heat sink. The replacements are TO-202 style. I know that the current ones run about 98 - 100 degrees. I ran the new ones without heat sinks and they rant about 94 degrees, but that was only for 10 minutes. I don't know how hot they would get if left for long periods. I also don't know if the heat sinks are just a precaution.

Anyway, I was hoping there was some kind of aluminum heat sink designed to just attach to the metal tab. Something with fins to dissipate heat by way of air cooling (don't want to short it out by touching the chassis).

zeno · #2 10-14-2013, 04:01 PM

IIRC the heat sinks were on the 9-121 & 9-155 CRT modules.
maybe also on 9-89 but its been years.
BUT I dont think the fat leads will go into your sockets.
I would leave well enuf alone, they were quite reliable.

73 Zeno

TinCanAlley · #3 10-14-2013, 04:25 PM

Quote:

Originally Posted by zeno

IIRC the heat sinks were on the 9-121 & 9-155 CRT modules.
maybe also on 9-89 but its been years.
BUT I dont think the fat leads will go into your sockets.
I would leave well enuf alone, they were quite reliable.

73 Zeno

They fit perfectly and work (a little better if my eyes aren't fooling me). The leads are only slightly bigger than the TO-39s. I just don't want them to overheat. I don't think they will as the operating temp for them is up to 150C. Of course you never want to get them that hot. In my limited time running them, they never got over 94F.

I think I found what I need. It looks like the NTE406 is a slip-on heat sink.

Electronic M · #4 10-14-2013, 05:11 PM

Can also grab bolt on ones and heat sink compound at your local Radio Shack....

Reece · #5 10-15-2013, 01:46 PM

You can cut some aluminum sheet to the shape you want, drill a hole for bolt, use heat sink grease.

TinCanAlley · #6 10-15-2013, 04:56 PM

Quote:

Originally Posted by zeno

IIRC the heat sinks were on the 9-121 & 9-155 CRT modules.
maybe also on 9-89 but its been years.
BUT I dont think the fat leads will go into your sockets.
I would leave well enuf alone, they were quite reliable.

73 Zeno

You're right. I pulled the sinks off an old video driver board from my other CCII. That board also uses the 121-868 output transistors I'm trying in the Avanti, so they're the right clips and the same as sold at Radio Shack.

Now the specs say the max junction temp is 150C. I don't know what that means for external temp. I do know that with the clips they run between 105 and 130F, or 40 and 54C. That's about 20% hotter than the TO-39s with the stock heat sinks. I don't know if these naturally run hotter. I do know they have a composite or silicone type case and the old ones are metal. That might account for the heat difference. I imagine the metal dissipates heat better.

Findm-Keepm · #7 10-15-2013, 06:37 PM

Why the modification? The 121-868 is specified for the CCII chassis - is there something wrong with your originals? Mod kits are always 800-XXX part numbers, so if you got a kit (and not simply the 121-868's), the heat sinks would not be there, as they are already with the CCII's.

Is there something wrong with the original outputs? Zenith engineers specified the ones in your Avanti for a reason, and if they are running ok, why mess with them?

Zeno is right, it seems that with all of the other troubles, you are only inviting more.

Cheers,

TinCanAlley · #8 10-15-2013, 06:57 PM

Quote:

Originally Posted by Findm-Keepm

Why the modification? The 121-868 is specified for the CCII chassis - is there something wrong with your originals? Mod kits are always 800-XXX part numbers, so if you got a kit (and not simply the 121-868's), the heat sinks would not be there, as they are already with the CCII's.

Is there something wrong with the original outputs? Zenith engineers specified the ones in your Avanti for a reason, and if they are running ok, why mess with them?

Zeno is right, it seems that with all of the other troubles, you are only inviting more.

Cheers,

This is a CCII Avanti.

These are the upgrade transistors and were part of an upgrade kit. They came in a sealed packet of three and in an envelope with a different part number (I'll look for the envelope and find the number). Even Sams lists these as the outputs. When you search for the part number of the ones installed, it shows these as the ones to use. So Zenith at some point designated these as the correct ones for this chassis.

I put them in for testing. After seeing an overall improvement in image quality and color, I decided to keep them installed after going back and forth between them and the originals. The originals are put away if needed.