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Hi all, I am new to the forum. I picked up a Model 20 Lowboy at a demolition sale for $20 a couple weeks ago and it will be my first restoration attempt. Three of the tubes were missing, so I bought (good tested) used ones. The other tubes were still in the chassis, and although everything was pretty dusty, it otherwise seems to be in good repair. It looks like it mostly just sat for decades. It has the original speaker which physically seems fine, all the caps, resistors and whatnot are all original. I have not plugged it in because I don't want to fry anything and I'm sure the caps and resistors are mostly no good.
I've found some schematics online, but to tell the truth I'm somewhat of a novice. I've done some of my own electrical projects, mostly turning vintage cameras into hi-intensity LED lamps, so I understand the basics, but tube stuff is new to me and I don't want to kill myself. Does anyone have a parts list with values for the various capacitors and resistors that I need for this? Does anyone have any suggestions or advice for how to go about this?
Thanks everyone!
Greg
"We are here to laugh at the odds and live our lives so well that Death will tremble to take us."
(This post was last modified: 02-23-2017, 06:07 PM by WallaceRoger.
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http://www.nostalgiaair.org/pagesbymodel...029582.pdf
This has both caps and resistors data.
If you want better quality sch you could buy one from Chuck Schwark at Philcorepairbench.com.
Welcome!
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Welcome to the Phorum. 
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Welcome to the Phorum!
All the caps will need replacing except micas and most resistors as well. There are a number of restoration threads in the phorum that would be worth a read to get a feel for what and how people approach restoration. Chech the technical section for tips. Clear schematics available from Chucks Philco Repair Bench for a few bucks. Take lots of pictures and notes as you go along.
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Thanks for the suggestions guys! I'm also planning on building a kit AM microbroadcaster so I can play a variety of music through it (and my Trav-Ler in the bedroom).
Greg
"We are here to laugh at the odds and live our lives so well that Death will tremble to take us."
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Hi and Welcome,
Just for grins unplug the spkr plug from the chassis and use your ohm meter to check the resistance from one pin (doesn't matter which) to the other three. If all is well you should see a fairly low resistance like less than 4,000 ohms
If you find something like 10,000 or a meg ohm this would indicate a problem.
Some common issues w/the 20 are: open(bad) field coil, output transformer primary, primary of the rf coils (easy to fix) and audio driver transformer.
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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Open sections in the bias vitreous resistor.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Hope I get this to load!!!!
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Hi guys, thanks for all the info. I ordered up a set of large schematics (very helpful). The caps seem pretty straightforward to me, but one thing I can't seem to find anywhere is what watt rating I should have for my resistors. The values are all there in the schematic, but I'm guessing 1/2 watt resistors probably wouldn't be sufficient for this, or at least for parts of it. I'm planning to just snip and replace the old, out-of-spec resistors with new (I'll save the old ones in case I want to try to cut and restuff them later to look more authentic).
Greg
"We are here to laugh at the odds and live our lives so well that Death will tremble to take us."
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The "dogbone" resistors in the 20 are all 1 watt.
You can't restuff old dogbone resistors, but you can make new ones. http://philcoradio.com/phorum/showthread.php?tid=5501
Steve
M R Radios C M Tubes
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1W was just a popular size: many of them dissipate very little.
Where the extra size is useful is that the span between connections is long sometimes and a smaller resistor simply cannot reach point to point.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Excellent, thanks again! Since they used 1w before I'll use that again, easy enough.
Greg
"We are here to laugh at the odds and live our lives so well that Death will tremble to take us."
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Check the value of the resistors first, they may have drifted upward, but maybe not if they were 1 Watters to begin with, no sense replacing and replicating unless you have to. As mentioned the big power resistors used as a voltage divider and for tube bias (part #25) are a common failure point as well, but you may get lucky As for anything else, the model 20 is a fairly common early 20s set (at least the Baby Grand versions) so lots of documentation and experience to be found with restoring one, some people like Mike (Morzh) have owned and overhauled several of them.
Regards
Arran
(This post was last modified: 03-24-2017, 12:16 AM by Arran.)
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In my experience with the 20s, every single dog-bone resistor in them drifted enough to warrant replacement.
Unfortunately. There might be exceptions, of course.
Same was the case with 70 and 90.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Yep, my research pretty much confirmed that, everyone seems to say they'll be out of spec and I figure it's cheap insurance to put in new ones anyway, even if a couple of them test ok. I picked up a load of resistors and stuff from a Radio Shack that was having a one-day store closing "everything must go" sale a few years ago, so I'm sure I have something here. If not I'll just run a couple half watts in parallel and double up to get back to the resistance I need. Learning and having fun as I go along!
Greg
"We are here to laugh at the odds and live our lives so well that Death will tremble to take us."
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