Radio Overhaul - Repair page 11

It's been a while since I've updated this. I have had the chance to finish the radio and acquire some more of the parts for the complete sound system planned for this '68 XL.

Without further ado.

The output transistors needed to be replaced because the left channel would still quit working and it was the transistor, if you pressed on it, it would start working again.

You can see the left channel mounted above the volume/tone control. It's in the shape of a TO-3 package, but it's not. I have two TO-3 package transistors next to it as an example.

This is a first, even for me, this is some weird TO-3 prototype that made it into production or is the prototype that was installed. It wouldn't be the first time a prototype escaped and I ended up with it. The actual transistor crystal is the blur disc and it's bonded to the plate, but the bonding is cracked, hence the intermittent contact.

Now the astute will notice a spot where rationally the right side output transistor would go. However, for whatever reason it's not there and installed in the back panel of the radio. After doing the testing on this radio I have a good idea why. This is a direct drive class A amplifier and they get warm. I think it was deemed too much heat to have in the front of the radio, so they put the other channel on the back to better dissipate the total heat of the output amplifier in the radio case.

This is one of my spare '68 AM-FM stereo radios and it has a TO-220 transistor in a TO-3 mounting plate.

New output transistors through Mouser, so there's a high probability these are high quality genuine parts and not cheap knock-offs.

Removing the old TO-220 off the TO-3 mount in the spare radio and installing the new NPN transistor for this radio I am working on.

This is the right side channel transistor mounted in the back plate. This of course was changed to a new TO-220.

Just to summarize, these are all the parts that were replaced in this radio to make it work for the long future.

Even the radio seemingly works, I want to do a full electrical alignment on the AM, FM and FM stereo decoder to see how sensitive and selective the radio is. So this involves injecting signals and looking at signals at different points in the radio.

I had some pretty interesting results.