60 MB restoration - Printable Version
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+--- Thread: 60 MB restoration (/showthread.php?tid=6431)
RE: 60 MB restoration - Art Hoch - 04-18-2013
You are one cool dude restorer!
RE: 60 MB restoration - Bob Andersen - 04-22-2013
I noticed the volume control doesn't quite work like I expected. There's a big volume increase for the first 1/4 travel then only a slight increase for them remaining 3/4. A quick check shows it to be about 2.5M while the schematic calls for 0.35M! I'll hunt around for something closer and see if it makes a difference.
RE: 60 MB restoration - Bob Andersen - 04-23-2013
I dug up a NOS 250K pot and wired it in. I have much better volume control now, but there's still faint audio when it's all the way down. I even grounded the center lug directly and still had audio. It must be creeping into the output tube elsewhere.
It's not a really a problem - I'm just curious where it's coming from.
[Image: http://farm9.staticflickr.com/8256/8675041313_a9ce4ce3e6_c.jpg]
RE: 60 MB restoration - w4rtc - 04-23-2013
Hi bob
I have a 37-620 that does that (vol all the way down an still get audio) I have not found why if you find out why, post it. Thanks. Joe
RE: 60 MB restoration - Arran - 04-23-2013
Does that junker 620 chassis still have a volume control? Maybe you could use that if it's the same value?
Regards
Arran
RE: 60 MB restoration - Bob Andersen - 04-23-2013
It too had been replaced long ago with a crummy looking 1Meg pot. Now that I think about it, probably half of my Philco collection has replacement volume + power controls.
RE: 60 MB restoration - Arran - 04-23-2013
It sounds like not only was the old pot too large but it also sounds like it had the wrong taper. A 350k (.35M) pot is somewhat of an odd size, 500K is more typical but a 1 meg one would also work.
Regards
Arran
RE: 60 MB restoration - Bob Andersen - 09-01-2013
I recently picked up this 60 chassis cheap. I figure I'll scavenge the electrolytic can caps, the volume control and whatever else I might need to finally finish off the 60MB.
Then I'm going to attempt my first recone on that trashed speaker.
[Image: http://farm6.staticflickr.com/5509/9362265962_43df9df3fe_b.jpg]
RE: 60 MB restoration - Radioroslyn - 09-01-2013
Just put a jumper between the center and "ground"
connections of the pot. If you still hear sound, the
"ground" really isn't ground or there is some leakage
in your 75 tube between the grid and diode. This
is common manufacture issue that has to do with
the placement of the internal parts. Won't show
on the tube tester as it's capacity coupled in side
the tube.
Terry
ps
As usual GREAT WORK from Bob! Keep it up!
RE: 60 MB restoration - Bob Andersen - 10-22-2013
I'm finally back to working on this set. Last night I salvaged parts from my donor chassis.
[Image: http://farm3.staticflickr.com/2855/10424544845_bdf69b1ccf_c.jpg]
The volume/power control is the exact Philco part number and the action is smooth. However, it measures about 1.7M while the schematic shows it as 0.35M
Could the resistive element change that much over time or is the schematic wrong ?[Image: http://farm8.staticflickr.com/7332/10424674953_d9053d53b7_c.jpg]
RE: 60 MB restoration - Ron Ramirez - 10-22-2013
The schematic is correct (350K).
RE: 60 MB restoration - Bob Andersen - 10-22-2013
I figured as much, but I installed this control anyway and it's working OK. I'm guessing that value isn't so critical.
RE: 60 MB restoration - Bob Andersen - 10-24-2013
I managed to glue the broken dial scale from the donor set back together. Not perfect, but good enough for me
[Image: http://farm6.staticflickr.com/5487/10452697665_acfa6533ce_c.jpg]
This 27-5000 scale is not quite the same as the original 27-5024, but pretty darn close. I'm planning on transplanting the tuning cap too since it's corrosion free and turns very nicely. Perhaps the difference is entirely in the tuning cap so it will line up OK once installed ?
[Image: http://farm6.staticflickr.com/5487/10452863083_1505288e2a_c.jpg]
One thing that really has me puzzled is the trimmer caps on the older tuning cap. How in the world are they supposed to be adjusted when they face down towards the chassis ?
[Image: http://farm6.staticflickr.com/5520/10452700955_15cc5f9f2f_c.jpg]
The newer cap has them facing up so they are easily adjusted with a nut driver.
[Image: http://farm4.staticflickr.com/3808/10452863953_b9fea1616a_c.jpg]
RE: 60 MB restoration - Bob Andersen - 10-28-2013
I just finished aligning it using an HP 3336A in sweep mode and a Tek 465 scope. Totally unnecessary but I wanted to give it a try. The marker works by modulating the brightness so it goes from dim to bright right at the desired frequency. I set it to 460 kHz and discovered the set was peaked close to 480.
[Image: http://farm3.staticflickr.com/2879/10531297443_d674ca3c23_c.jpg]
A little trimmer cap tweaking and I got it back where it should be. Radio is playing great now
[Image: http://farm4.staticflickr.com/3782/10531058125_02e1e148f2_z.jpg]
RE: 60 MB restoration - don'tdomelikethat - 10-29-2013
I hope you posted a Youtube video of your alignment using your 3336A. I purchased the same generator after seeing your video on it, and anxious to see how it works for alignments.