Next Project - 37-116 - Printable Version

Next Project - 37-116 - Printable Version

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RE: Next Project - 37-116 - rfeenstra - 04-05-2020

Latest progress, the amp/power supply chassis. Interestingly, one of the wet E-caps was still full of liquid. Probably would have worked fine.

I kind of like this modular chassis design. It breaks the restoration of a semi-complex radio into smaller bites. Next I'll do the small audio chassis, then assemble that and the amp/PS. And finally the IF chassis.

RE: Next Project - 37-116 - rfeenstra - 04-06-2020

Partial reassembly. IF section next.

RE: Next Project - 37-116 - Jake Blake - 04-06-2020

I like these chassis that have the rectifier mounted on the transformer....That looks so cool! Icon_mrgreen

Good job!

RE: Next Project - 37-116 - rfeenstra - 04-07-2020

IF section complete. now to assemble and add all of the interconnecting wires. Two of the caps had been replaced previously so I couldn't re-stuff them. Hence, 2 Chinese yellows! I wish I had a stash of stuffables. I have a bunch of newer paper caps but I cannot get the ends to melt. Must be some sort of epoxy. by the way, the top side is painted, the bottom is not. They aren't too far from eachother.

RE: Next Project - 37-116 - rfeenstra - 04-08-2020

First power-up: mostly successful! Radio started playing at about 60 VAC. Stations all across the dial at 70 volts. Works good at full voltage. Magnetic tunig works though needs alignment. Two problems show up:

1. Looks like I was not lucky on my Police band oscillator coil rewind. Entire band dead except on the extreme high end. I get one station. I'll play with that a while before I try a rewind.

2. Audio hum that goes away only when the hum balance control is to one extreme. At that point I get smoke out of the WW balance pot. I'll have to check my wiring.

Better to work on individual problems rather than a completely dead unit!!

RE: Next Project - 37-116 - rfeenstra - 04-09-2020

1. Police band is working. I had to add a 1000pf cap across the compensator to get the low end in range. so now the high end and low end are close, but the center of the band is quite far off. The original coil was wound with 36 AWG. I didn't have any so I wound with 35 AWG. A question for you inductance guru's, how much difference would that make at these frequencies? If you think it would make the difference, I'll order some 36 AWG, disassemble the RF unit to get the oscillator coil out and rewind it again! However, one must wonder if the police band is worth the effort. I can now get the AM stations that are on the low end of the band, so... I have a similar tracking problem on the 4th band. Seems to me I've run into that before.

2. Problem solved. One of the WW controls was intermittently open, the other I smoked when trying to adjust the hum out. The reason it smoked is there was a short in that filament wiring to ground. So, when the pot reached that extreme, I was applying 6.3 volts through very low resistance. Two separate problems in the same 6B4 output tube filament circuits. The windings in the WW pots are copper, not nichrome, so I was able to bridge the breaks with solder. The pot is working and the hum is gone!

I have to redo the rubber coupler that connects the tuning cap to the tuning mechanism. and hook up the magnetic tuning lighting system. I'll also add my LED back light for the station dial. Then, tin plate the tube shields. The shields are missing from the RF unit since someone replaced the G tubes with metal tubes. I would like to replace those. See my ad in WTB.

RE: Next Project - 37-116 - 462ron - 04-10-2020

I had a similar experience with band #2 after rewinding the oscillator coil. I didn’t need to add any capacitance to the circuit as I was able to get the low and high ends of the band pretty close with the associated trimmers. I do have a definite loss of sensitivity in the middle of the range too. I chalked that up to not having the right inductance, thus the oscillator won’t track properly. It’s been a few years since I’ve done my 37-116 but if memory serves, I believe I used 38 gauge wire.

Ron

RE: Next Project - 37-116 - rfeenstra - 04-10-2020

Well, for now, I'm going to leave it. The radio is working great on the bench. I'll keep it going for a few days to shake out any problems. I also need to get some cloth covered AC cord rather than the 3 wire computer cord I'm using temporarily. I've finished the magnetic tuning back light system and added the additional LED lighting to help light the station tabs. Pat is sending me some tube shields - THANK YOU!. When I get those, I'll tin plate all of them as these are pretty bad looking. Madsowry is sending me some old paper caps so I can get rid of the 2 Chinese yellow ones. THANK YOU! Here a couple of photos, one with Magnetic tuning off and one on.

RE: Next Project - 37-116 - KCMike - 04-10-2020

Top of the line work Icon_thumbup

Great idea adding extra lighting to station tabs.

RE: Next Project - 37-116 - PhilcoJohn - 04-11-2020

Wow nice job I wish my 38-116 looked as good. Again good job bringing it back to live for another 70 years! Icon_clap

RE: Next Project - 37-116 - rfeenstra - 04-13-2020

I borrowed 3 tube shields from another restoration until I receive the 3 already shipped to me. I wanted to clear the bench so I put the chassis in its home cabinet. So here are the 37 and 38-116 siblings. They sound virtually identical.

RE: Next Project - 37-116 - madsowry - 04-13-2020

I only have one thing to say "WOW" !!!!!

RE: Next Project - 37-116 - Steve D - 04-14-2020

Lovely, those crystal clear 6B4G's make it pop.

Steve D