Philco model 18 (code 121) - HELP! - Printable Version
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+--- Thread: Philco model 18 (code 121) - HELP! (/showthread.php?tid=5934)
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-19-2013
I replaced the 32K with a half watt resistor. I'll have to see if RadioShack has a 2 Watt, I'm pretty sure they don't. I'm kind of surprised that the schematic didn't say anything about watts? So besides the wattage problem, having my T-Connection meet the #75 tube connection in a 4-way is "OK" right?
RE: Philco model 18 (code 121) - HELP! - Mondial - 04-19-2013
Jerry. it definitely seems like there is a missing dot on the 118 schematic. Without the dot, there is no source of screen voltage for the RF and IF tubes. Their screen grids are simply connected together with nothing else hooked up and this obviously cannot work as shown.
Looks like no one checked the schematic for accuracy as that's not the only error. If you look at the 42 driver tube, there is also no connection from the screen grid to B+. only a bypass cap to ground.
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-19-2013
Mondial is correct, I just measured from the junction of the 32K and 50K resistor and indeed it is going to all three tubes grids for an increase in current! Another case of the missing dot. Mortz, you were no doubt correct in the current draw based on the schematic. Seems like about a year ago we "discovered" another missing dot Mortz on a members schematic. Pith, looks like you need to go per schematic and boost that 32K to 2 watts. I don't have one so will probably parallel a couple 1 watt resistors. Mine is reading over 50K. I corrected the 42 driver error per the 18 schematic, thanks Mondial.
Jerry
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-19-2013
It took me a minute to figure out what you were talking about with dog-bone. I just had an 'A-Ha' moment. That 'Dog-bone' was the biggest resistor I've ever seen, it's size must account for the wattage needed I'm thinking? Because the .1meg was half the size but 3 times the resistance, ok, I think I get it now.
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-19-2013
HOUSTON – I HAVE A PROBLEM
I need to stop the presses here a minute, I’m going to need someone to look at the model 18 schematic (code 121 NOT 124) and just verify that I’m not crazy. The one on nostalgia air is ONLY for the 124 I have both 121 and 124 schematics and they are NOT the same. I can e-mail you the PDF if want? Just private message me on this site.
The notes indicate that the dotted line is only for model 503…also, I checked the 124 schematics and the dotted line appears as a SOLID line. On my 121, it is a dotted line from #40-C 2.0 ufd cap to BOTH the T-connection of resistors and to the #75 Tube…and these are the only connections which would mean that it doesn’t hook into…ANYTHING??
Obviously that’s not correct. Looking more closely, another note says “Screen supply broken here on 503 model” and the ‘here’ is pointing to the dotted line connecting the cap to the screen plate of the #75 tube. This brings us back full circle to say that the 2.0 ufd cap IS connected to the #75 tube but NOT to the 2 resistors (#61/#62). Right?
Sorry for taking you boys in circles for the last few days. If what I have above is correct, that 2.0 ufd is connected to the #78 tube ONLY, then I believe this is how it was hooked up before I messed with it (because that is what my pictures show) and my problem was never with how it was hooked up, but that I needed a 2 Watt 32K resistor instead of the ½ watt that is in there now!
Sorry for being annoying, but hey, it helped me learn how to read a d@mn schematic a bit better, so that’s a good thing.
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-19-2013
Also, I plan on checking the voltages this weekend on everything BEFORE I turn the radio on again (and after I make the 2.0 ufd to #78 switch...and after someone confirms that switch of course.)
RE: Philco model 18 (code 121) - HELP! - jerryhawthorne - 04-19-2013
Pith, can you post your 121 schematic or a link to it? If not e-mail it to me.
Jerry
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-19-2013
I'll e-mail it. I don't have any website or anything.
RE: Philco model 18 (code 121) - HELP! - codefox1 - 04-19-2013
Lots of dots went missing, and lots of dots appeared over the decades. All those years ago drafting was done without many aids. If you doubt a diagram based on what else you have seen, it's probably incorrect. Best to stay with what looks original and discount whatever hacking has been done. After all, why did you end up with the set?
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-20-2013
Good point. I have another set 38-38 that I found is missing parts and wires, but won't be starting that one for a while. Hope the schematics are right!
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-20-2013
Getting back to my 1/2 Watt 32K resistor. If I can't hunt down a 2-Watt 32K can I just add 3 or 4 1/2-Watt 32K resistors in parallel to get a 1 and 1/2 or 2 watt resistor?
RE: Philco model 18 (code 121) - HELP! - Mondial - 04-20-2013
No, when you parallel equal value resistors, you divide their resistance by their number. For example, if you parallel two 32K 1/2 watt resistors, the result will be a 16K resistor of 1 watt rating.
If you have no other choice, you can try paralleling four 120 K 1/2 watt resistors which will result in a 30K combination. Four 130K resistors will give you 32.5K. The combination of the four should be able to dissipate close to two watts.
Strictly speaking, the wattage rating of each resistor is determined when it is in free air, not bundled close together with others, which may reduce the air flow and the cooling effect. But for practical purposes, it should work fine since the actual wattage dissipated by the circuit is actually less than a full two watts.
RE: Philco model 18 (code 121) - HELP! - codefox1 - 04-20-2013
Never trust a stressed part. Less than a dollar for sure to replace.
RE: Philco model 18 (code 121) - HELP! - BrendaAnnD - 04-20-2013
He could also take those four 32K half watt resistors and connect them series-parallel and have a 32K 2 watt. Still the cooling thing, but should work OK if you keep the resistors slightly apart from one another.
RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 04-20-2013
Found 33K 2 Watt at a Lil shop near me. Thanks for the advice.