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Model 77 questions - Printable Version

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Model 77 questions - Guest - 06-24-2008

Hello, I've recently aquired a model 77 Lowboy radio. It does seem complete, however it has issues. (At 78 yrs old it's not surprising!). First, the veneer on the top and one side needs replacing. Does anyone know what type of wood was used?
As far as the innards go, the set will play (make noise) when it warms up, then the sound fades away after about 30 seconds. I noticed the voltage on the load side of the resistor @ point "G" on the schematic, drops consistantly with the fade. The resistor checks ok. I don't want to disturb too much in there, does anyone have any ideas? What is the normal voltage supposed to be at this point? Voltages are not listed on the schematic. Any help would be greatly appreciated. Thanks, Dan

- philco phan - 06-24-2008

voltages are here,it should help,phil
http://www.nostalgiaair.org/PagesByModel/838/M0013838.pdf
is c19 shorted?

- Ron Ramirez - 06-24-2008

Hi Dan

The original wood used was walnut veneer.

You will need to replace ALL paper capacitors in the radio in order for it to perform properly. To paraphrase a big home improvement store, "You can do it - we can help." Icon_smile

- Guest - 06-25-2008

Thank you for the quick replies! After reading up on the bakelite caps, I am going ahead and rebuilding them. This should be fun! I will tell my cabinet guy about the walnut veneer, that was a big help, as one side is still intact. (top and side damaged). I have another question: there are 3 flat metal containers screwed to the under side of the chassis, two cover up the IF stages, and one covers up the output stage. The two on the IF stage appear to have two wires coming out of one end, and the one at the OP seems to have only one wire. What the heck are these? Do they need attention as well? thank you in advance, Dan

- Ron Ramirez - 06-25-2008

Those are condensers as well, and yes, they also need to be replaced with new.

You can put new capacitors inside those old cans, as well.

Model 77 is a TRF set - it has no IF stages, only RF.

- Guest - 06-26-2008

Ok well, that explains the unusual schematic. Duh! I guess I need to brush up on my theory! Btw, is there a link as to what to do with these condensors? I don't want to ruin them in an attempt to fix them! Years ago when I was in my teens I was "restoring" old radios, but its been about 25 years since I've done this stuff. (I'm an electronic accessory tech in the auto industry now.) I have done some work with the "newer" old stuff recently; I've reconditioned and aligned a Dynaco FM 3, Pas 3, and ST70. And I've scratch built a single ended stereo amp using a 5U4, 12AX7, and 2 6BQ5's. But, I do not recall anything as peculiar and interesting as this '77! I would like to thank you again for all the help so far and will keep you informed of the progress on this project.

Cheers! Dan

- wonderwrench - 06-26-2008

frankenstein Wrote:Ok well, that explains the unusual schematic. Duh! I guess I need to brush up on my theory! Btw, is there a link as to what to do with these condensors? I don't want to ruin them in an attempt to fix them! Years ago when I was in my teens I was "restoring" old radios, but its been about 25 years since I've done this stuff. (I'm an electronic accessory tech in the auto industry now.) I have done some work with the "newer" old stuff recently; I've reconditioned and aligned a Dynaco FM 3, Pas 3, and ST70. And I've scratch built a single ended stereo amp using a 5U4, 12AX7, and 2 6BQ5's. But, I do not recall anything as peculiar and interesting as this '77! I would like to thank you again for all the help so far and will keep you informed of the progress on this project.

Cheers! Dan

Bakelite Block rebuilding http://www.philcorepairbench.com/capbuild.htm

Re-Capping Electrolytic Capacitors
http://www.philcorepairbench.com/tips/svctip46.htm
This may not be the exact type used in your radio but will give you a place to start. Many people just disconnect the cans electrically and mount new caps under the chassis. IMO a butch way to do it but it works OK. There are people that will rebuild your cans for you, I have no links at this time though. philcorepairbench.com has lots of good info so look around.

Hope this helps