Posted by Steve L.

June 13, 2021 - 06:54 am

I'm posting here a PDF file containing an interesting email exchange I just had with reader Michael S., with his kind permission. It concerns his experience with substituting transistors into the Cortina 3070. Enjoy: http://www.tronola.com/misc/Michael S. thread on restoring another Cortina 3070 with DS.pdf

Posted by Steve L.

November 09, 2020 - 07:37 am

Hi Fred, It's kind of you to post. Will be happy to help if you have any questions. Let us know how it goes. Best wishes for your restoration!

Posted by Fred

November 08, 2020 - 10:57 pm

Thanks for posing this information. It gives me the confidence to begin restoring my 3070.

Posted by Steve L.

October 14, 2020 - 06:08 pm

Hi Jake, Yes, that fuse will be fine and yes, I'll send you an email. At this point, it probably makes sense to take it off the public comments anyway, in case we get into the minutia of debugging.

Posted by Jacob B

October 14, 2020 - 09:29 am

Hi Steve. I checked the fuses and they are indeed blown so yea looks like I shorted things with those transistors. Glad that I can get the insulators still. Is this the right fuse? I measured the fuse and this appears to be correct. Mouser part# 576-0312002.MXP Thanks for your help. Can you email me at j b r i t s c h @ gmail.com? Jake

Posted by Steve L.

November 09, 2020 - 07:13 am

Hi Jake, That sounds like an excellent background. Yes, not having the mica insulators would mean that the collectors were shorted to ground. Take heart though, the good news is that it should have blown only one or more fuses. It's likely that the output transistors would not be damaged. More good news is that TO-66 mica insulators still exist and are available at low cost from Mouser. (Just search "TO-66 mica insulator" on their website.) When installing, I usually coat the bottom of the transistor, apply the insulator to it (it will be held by the grease) and then coat the bottom of the insulator. When you replace the DC fuses, I recommend 2A instead of the original 1A. Also, it would be good to check the collector to emitter resistance of each power transistor. The main failure mode is a C-E short of typically less than 10 ohms. A value of 1Kohm or more would usually exonerate that failure mode. Let me know how it goes. We can get this!