12-22-2023, 04:01 PM
Lately I've been getting some older projects fixed up a 21B chassis, a 70B early model chassis, and a 90 2nd version. The 70 went well just need a few resistors and the speaker overhaul (along with the all the caps, cloth cord, and such). The 90 was a little bit a a different animal. Someone had been in it before and did some iffy work. They did add a fuse and series resistor in the ac line circuit. Also replaced the line bypass caps but use .03 mf which is kinda big. Solder in a couple 10 mf filter caps. All the other caps were original. No I didn't try it to see if it would play.
Started restuffing the blocks and measuring the resistor. Found that there was more bad ones than good. Not a problem I got a lot of resistor. It's kinda fun taking out the bad and put in the good. Know that you've got a good chance that it's good to work when you get done. I get over the the block that is in parallel with filter choke. Check the resistance of the choke and Surprise! It's open. That's what happens when you don't replace the caps in the blocks and you keep playing the set! Fortunately I had a 370 parts chassis that yielded a proper choke. The line bypass block was broken so I needed to find a replacement. This one terminals face differently from most of the ones I had. I was able to take one spin one of the terminals around to match the original.
Next comes the speaker. Opt and fc check ok so it's just a matter of a good clean, recone, and a cord. On the early K speaker I haven't seen cones that were worth trying to save. either the paper the very fragile it just falls apart. Or it's wrinkled which can pull the vc off center ymmv. Soldered on a new cloth cover cord and ready to power it up.
Powered it up and nothing exciting happened. Went around and checked for hv on screen grids and plates of the tube. Found that there was no plate voltage on the rf amp. Rewound primary and secondary. If you are curious the the grid winding is 162t of probably 30g and is 296mH on my cheap meter and 7 ohms. The plate winding was open so I can't tell much about it. It's 96t and probably is about 38g but it's cotton covered. I used 40g cause I had it on hand. It worked fine but it's no picnic to wind on a form, shadow meter no problem. After rewinding this coil the set was working but the audio was low.
After double checking my work several times I found the 47 that I thought I had tested was weak. Found another 47 and that restored the audio level to what it should be.
I did change a couple of things in the circuit. The tone control seemed awful large in capacitance. By adding all cap together it would make the audio pretty muffled. Even by the 2nd position adding a .015 muffles a fair amount. I chose to use three .005mfd cap. This give the audio a nice bright clean sound till you get to the last position.
The other thing I did was put the filter caps inside #24 (metal tin). Just had to add three wires. No tie strips or caps hang off of the divider resistor. Easy peazy! Actually I did it on all of these set I just worked on.
After the alignment it's a fine playing set w/good selectivity and sensitivity. Am looking forward to putting some hours in listening to it. And this up coming Spring I'll be working on the cabinets of the above and two 16B's.
Started restuffing the blocks and measuring the resistor. Found that there was more bad ones than good. Not a problem I got a lot of resistor. It's kinda fun taking out the bad and put in the good. Know that you've got a good chance that it's good to work when you get done. I get over the the block that is in parallel with filter choke. Check the resistance of the choke and Surprise! It's open. That's what happens when you don't replace the caps in the blocks and you keep playing the set! Fortunately I had a 370 parts chassis that yielded a proper choke. The line bypass block was broken so I needed to find a replacement. This one terminals face differently from most of the ones I had. I was able to take one spin one of the terminals around to match the original.
Next comes the speaker. Opt and fc check ok so it's just a matter of a good clean, recone, and a cord. On the early K speaker I haven't seen cones that were worth trying to save. either the paper the very fragile it just falls apart. Or it's wrinkled which can pull the vc off center ymmv. Soldered on a new cloth cover cord and ready to power it up.
Powered it up and nothing exciting happened. Went around and checked for hv on screen grids and plates of the tube. Found that there was no plate voltage on the rf amp. Rewound primary and secondary. If you are curious the the grid winding is 162t of probably 30g and is 296mH on my cheap meter and 7 ohms. The plate winding was open so I can't tell much about it. It's 96t and probably is about 38g but it's cotton covered. I used 40g cause I had it on hand. It worked fine but it's no picnic to wind on a form, shadow meter no problem. After rewinding this coil the set was working but the audio was low.
After double checking my work several times I found the 47 that I thought I had tested was weak. Found another 47 and that restored the audio level to what it should be.
I did change a couple of things in the circuit. The tone control seemed awful large in capacitance. By adding all cap together it would make the audio pretty muffled. Even by the 2nd position adding a .015 muffles a fair amount. I chose to use three .005mfd cap. This give the audio a nice bright clean sound till you get to the last position.
The other thing I did was put the filter caps inside #24 (metal tin). Just had to add three wires. No tie strips or caps hang off of the divider resistor. Easy peazy! Actually I did it on all of these set I just worked on.
After the alignment it's a fine playing set w/good selectivity and sensitivity. Am looking forward to putting some hours in listening to it. And this up coming Spring I'll be working on the cabinets of the above and two 16B's.