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Philco model 18 (code 121) - HELP! - Printable Version

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RE: Philco model 18 (code 121) - HELP! - BrendaAnnD - 12-10-2013

Don't leave that beastie powered up for long... 467 volts is beyond the safety limit on the caps.

RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 12-16-2013

The filter choke, one of the 2 smaller transformers, is #51 on the schematic only has two connection points. Point (A) let’s say is connected to the big pin (filament) of the #80 tube the other connection coming out of the filter choke is point (B) and connects to #53 the 8 ufd cap.

With the set turned on and using DC voltage measurment (not sure if that is the right setting but figured I'd use it since I was using it for measuring from the #80 pin), I measured from the filament of #80 to point (A) on the filter choke just to make sure that I was using the multimeter properly and got 0.0 V which is what I was expecting since it’s essentially measuring from one end of a wire to the other end so there should be little or no load. Then I measured from that same point on the #80 (the filament of #80) to the far end of the filter choke, point (B). I expected to see a jump in voltage but it was fluctuating between 2 and 3 Volts.

So, 2 and 3 Volts is pretty close to zero. Doesn’t that mean that the choke is "open" because there was no load, no electrical potential difference? Shouldn’t there have been a noticeable voltage change? Or do I need to unhook the #51 filter choke and measure it separately because the other caps are also being measured here since they are part of the circuit?

RE: Philco model 18 (code 121) - HELP! - Bradley Rush - 12-17-2013

http://s1289.photobucket.com/user/TROG999/media/SNOW/MODEL_18_01037_zps96b0e588.jpg.html

SCHematcs in pic form trying to follow see what you guys are doing. Hope this helps

Bradley

RE: Philco model 18 (code 121) - HELP! - hsusmann - 12-17-2013

My only advice is to at least get a light bulb in series
with the line cord for initial power up. This will limit
the current if there is a problem.

I also have a variac which I ALWAYS use when working
on these radios. This is a variable auto transformer that
lets you ramp up the AC line voltage manually. I do so
very slowly at first power up!

I will always monitor one or more of the high voltage
points while ramping up the line voltage just to make
sure they are reading some reasonable value.

If I detect a voltage not doing what I expect or
taking a sudden nose dive then I hit the kill
switch right away!

Always always always treat tube devices with great
respect due to the potentially lethal DC voltages used!
One hand in the pocket, insulating shoes on, etc...

Herb, Ithaca NY

RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 12-17-2013

Thanks for the pic Brad, I have it as PDF so no html to load from. Thanks again.

RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 12-17-2013

Brenda/Morzh/Jerry,

My post #197 brings us back to earlier posts #161 - #167 about the filter choke.

A few months ago, I did try Brenda’s suggestion (from post #163) with hooking up a resistor but maybe I didn’t do it correctly? I’m thinking that may be the case. That is also when I found the resistance to be nearly infinity.

So, resistance at near infinity across the choke and voltage at nearly zero from the filament of the #80 tube to the return wire on the choke...

Brenda – if I go to AES and look for a replacement choke, what size/type do I need? All it says on the schematic is 166 ohms.
(Ron – if you’re following this, between work and other commitments I don’t have too much time unfortunately but I’ve decided I’ll be joining MARC thanks for the advice )

RE: Philco model 18 (code 121) - HELP! - morzh - 12-17-2013

1. Infinity across the choke means the choke is open and needs to be replaced.
2. This is the data on the 32-7115 choke from Philco 18.

http://philcorepairbench.com/choke.htm
5.25 H, 125 mA, 170 Ohm.

Now, you can go above 125mA, you should try to be reasonably close to 170 Ohm and you can go about 4-6H of inductance.

RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 12-17-2013

Thanks Morzh.

RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 12-18-2013

Ok, I think I found 2 that might work but I couldn’t find the exact specs. Ideally I want to use exactly what is needed (5.25 H, 125 mA, 170 Ohm) but I don’t think I have much of a choice here.

Can you please tell me which of the following chokes would be better and why? I’m thinking it’s better to have more inductance…?

• P-T158Q – but this one is 5H, 150 mA, with 105 Ohms (I think the resistance is too low and inductance a bit low on this one)
Can be found here: http://www.tubesandmore.com/products/P-T158Q

• P-T159Q – but this one is 7H, 150 mA, with 100 Ohms (I think the resistance is too low and inductance a bit too high on this one)
Can be found here: http://www.tubesandmore.com/products/P-T159Q

And if not…do you have any better ideas or websites I can check to buy this?

Thanks.

RE: Philco model 18 (code 121) - HELP! - morzh - 12-19-2013

Either one will work fine I think.

The resistance is, I suspect, may not be of a high importance as, although I cannot find the spec on the field coil, I suspect its resistance is at least 10 times higher than that of the choke, and so the choke DC resistance will not affect voltages that much.

The inductance is good, and the ampacity is good too.

I'd go with the first one.

RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 12-19-2013

Wow really?

That’s hard for a perfectionist to wrap his head around, but ok.

Thanks.

RE: Philco model 18 (code 121) - HELP! - Bradley Rush - 12-19-2013

Pithicus999

I went back and looked. But did not see you text what type of DVM are you using. Just I have had an issue with a a modern DVM

http://s1289.photobucket.com/user/TROG999/library/METERS

Here are some pics. I set up a 30 ohm coil and used my 87 Fluke RMs and a Chicom meter. On the Chicom only the 20K setting read .2 all the time. The other settings were random.

Not called AM for nothing. AM= American Magic

RE: Philco model 18 (code 121) - HELP! - morzh - 12-19-2013

Schematics are better off not designed by perfectionists. There is usually a good range across which a device like a tube or a transistor will work. There is a theoretical optimum but then it does not mean it works better overall at that point. In electronics every optimum is a compromise - you gain here, you lose there, you rob Peter, you pay Paul.

In this case you do not gain or lose - you prettyt much operate within acceptable range.

RE: Philco model 18 (code 121) - HELP! - Pithicus999 - 01-02-2014

I got the set up and running but I'm having an issue with the volume.

I think in a previous post Jerry suggested using a long wire for the antenna which I have but I'm wondering what else could be the problem with the volume. As you can see the volume increases when I put my finger on the 6A7 tube (I'm guessing that might be because the radio is using my body as an antenna)

Here's a video, please let me know if you have any suggestions.
Thanks.

https://www.youtube.com/watch?v=kYyhzg5YKjI&feature=youtu.be

(***If you have trouble playing the video, stop and restart in youtube. I had an issue for some reason)

RE: Philco model 18 (code 121) - HELP! - hsusmann - 01-02-2014

Hi,

I just watched your youtube video and have the following observation:

A 4 foot long wire antenna is not long. It should be at least
20 ft and 100 ft is better with some vertical height to it also.

If that does not help, you may have a problem with whatever
antenna transformer or antenna coil is used in that radio.
It is common for older fine wired coils or transformers to have
one or more of their windings "open" due to a break in the very
fine wire used.

I assume you have a schematic, if so you should be able to
locate the coil or transformer in question and check all the
windings with an ohm meter. Anything from a few ohms up
to several hundred ohms is probably OK.

Herb S.
Ithaca NY