[DKinYORKpa]

The negatives from the two 8uF electrolytics are the B- and they go over to that big wirewound resistor on the other side of the chassis. The other electrolytic can has its 3 negatives going to chassis ground, I believe.

[Pithicus999]

Well....I hope this isn't just a philco phourm hazing...I'll go switch the 10 ufd cap. If it works, (and I mean if that's the only problem with this radio) I'll post a vid.

Thanks for the help guys. This little mistake is increasing my interest in these radios and electronics overall.

[Pithicus999]

Well I switched the cap and i'm not dead so that's a good thing. I also switched 2 wires on the speaker...I can't find schematics about how to wire the speaker however so it's trial and error at this point unfortunatly.

[morzh]

Pithicus

We don't do hazings here....(should we?)

As for "all electrocytics go to heaven" (all minuses to GND), this should be "most" i/o "all".

The rule is:

ALL ELECTROLYTICS' MINUSES GO TO THE POINT THAT IS NEGATIVE RELATIVE TO WHERE THE PLUSSES GO.

So, if the Chassis is positive towards something else, the plus wil'l go to it.

In the 18, as in many Philcos and other radios, the most negative point of ANYTHING EVER (well, let's not go to complicated cases of non-radio related stuff and AC-coupled circuitry; let's talk power) inside a radio is its recifier's section winding's centertap (in case of the full-wave with centertap rectifier, such as based on 80 tube). It does not get any more negative than that in the power grid inside a radio.

But, to create some biases that are more negative than the chassis, the rectifier's negative is connected to the chassis via a low-ohm (few hundred ohm down to 30-70 Ohm) resistor, often a milty-tap. The voltage drop across it is decoupled with this very cap you are talking about (in code 124 it is the cap #59 and the resistor is #52). The #59 will have its plus to the Chassis, and its minus to the centertap.


As for the sound, yes check the speaker, but as there is no feedback from the secondary this is not Positive feedback at play.
As someone suggested, nay be bad decoupling capacitor.

Speaking of which, your electrolytics on top look untouched, but you said you replaced all caps, so that means you replaced the lytics also, correct?

Very similar sound was produced by my 80jr when the regenerative was out of whack: upon the warm up the same thing happened, only it took 2 seconds, and then the radio would play.
Could be some feedback.

Have you tried to do the test where you touch the grids with a screwdriver and try to hear the buzz? This would check the Audio section and detector.


IMPORTANT: Trial and error when wiring the speaker can result in smoke or damaging your transformer, your speaker and/or your 42 tubes.

[TA Forbes]

Something useful to make careful note of when replacing the "can" electrolytics is to note if the can has an insulator sleeve around it or a washer-insulator that it sits on. If so this means that the negative side of the cap does NOT go to chassis. In these cases there will be some kind of lead that is connected to the can's external body.

In the case of your model 18, C53, 54, and 55 all share a common (negative) side. Note that this is CT of the plate winding for the rectifier, which will have less potential than that of the filament winding, where the positive sides of C53 and 54 are connected. C55 has it's positive side to ground.

Frequently the negative side goes to a potential that is relatively negative to the potential on the positive side. Example: positive side goes to 100V, negative side goes to 50V. In this case the 50V is negative in respect to the 100V. BUT the negative side of the electrolytic must still be insulated from chassis.

Philco sets (and some others) often have an electrolytic with the positive side going to ground. As was well expained in a previous entry, this is usually to provide some form of negative bias.

[Arran]

The other electrolytic can, the one under the chassis, can be replaced by three poly film caps if desired as they are small values. Whether they would fit inside the original can is another story but they are available and will survive much longer then replacement electrolytic caps. They can be purchased from Radio Daze and Mauser.
With regards to a positive side going to ground this is something to be careful with, there are some filter caps that have a common positive with two negative sides where a bias resistor network and speaker field coil will be connected in series with the negative side, the field coil acts as a filter choke and the resistors as a bias voltage divider.
Regards
Arran

[Pithicus999]

Ok, fixed cap and switched the wires to the speaker.
Here is a video, I think all that's left is to tune the I.F. according to schematics. Thoughts?
http://youtu.be/J1H18AGlBo0

Ha ha I was kidding about hazing

[Pithicus999]

Ok, still trying to digest all the advice, but I have a Q for Arran, I'm pretty sure (I will go double check) that I did replace all caps, but if you have the schematic, could you tell me what # cap you are referring to that can be replaced with the 3 smaller ones, because I'm not sure.
Thanks

[morzh]

I think Arran means #40, the triple electrolytics 1uf / 1uF / 2uF.

One 1uF is in parallel with the wirewound resistor 6.5K, which is in series with the speaker's field coil.
Another 1uF is T-filtering plate load for tube 75 (second detector).
And the 2uF is T-filtering with R61/R62 (right from the Filter choke rectifier's output).

All these can be plain non-electrolytic caps. With proper voltages of course.
Then you do not care about the polarity.

[jerryhawthorne]

Pith, at this point, from watching the videos you have posted, you certainly need to make certain you have the caps installed properly. Lots of great stuff supplied from an information standpoint. When you are certain they are in properly, some voltage measurements are in order. After you trying to adjust various trimmer, well don't expect to get any "music" from that radio. Never touch those without having the proper test equipment. Not much needed but a good meter, analog is probably the easiest and a signal generator. The radio is probably so out of alignment on the IF, Oscillator and Antenna depending on what you moved, that things are relatively hopeless for receiving a station.
You need to back up a bit and do some voltage measurements to be certain that you have the positive (B+) and the negative for bias voltages.
A quick touch to the center tap of the volume control with it turned up with a screw driver (no scary voltages on it ) should give a nice strong hum. If it does, you should have the B+ and negative voltage from the power supply. Good at that point, shows the speaker, and most of the power supply and amplifier works. It appears from some sound that I heard that at least the speaker is working and portions of the power supply.
Give it a test and report back.
Do you have a signal generator? Would be helpful for correcting the alignment of the radio's IF sections which appears you have moved?
Every one on the Phorum know more than me but sometimes it's easier for suggestions from a dummy. Your in deep do do right now with adjusting things before you get the rest of the radio sorted. Just my opinion.
Keep us informed.
Jerry

[Pithicus999]

Where is a good place to get a signal generator? They looked pretty expensive online from what I'm seeing.

[jerryhawthorne]

Pith, post on the Phorum in the want to buy for a basic signal generator with modulation. I believe I bought mine a few years ago for around $20 plus shipping. I have been happy with it. There are ways to adjust without one but if everything is out of wack (an electronic term) it could be very frustrating. Other option is to see if someone in your area can give you a hand. If you were close by I would be happy to help with alignment. You just have to sort if the power supply is working properly and the caps are in right. Try the good old touch the center tap and let us know.

Jerry

[morzh]

I got my sig. gen. and freq. counter on the eBay, and paid not too much - I believe about 75 bucks bought me both.

Certainly try "Wanted" section.
eBay, to me, is potentially faster as many more people sell there. May be a bit more expensive.
You can get a generator in fully working condition for anywhere from 30 bucks to 120 bucks.


Last thing: if this is your one and only project, for sentimental reasons - you may try to get by somehow without buying the proper equipment.

However if you plan to continue doing this, this is like keeping tightening the nuts and bolts with your fingers while working as an auto mechanic.
Get the equipment.
And read a book or two about popular electronics, the very basic one will suffice, and something about tubes, though the forum here will fill that void.

[Steve Davis]

Here you go. http://www.ebay.com/itm/Vintage-Heathkit...257a95aeba

Steve

[morzh]

Good link. It likely works, and if not, these are never more than two tube concoction.
If the bid goes over 30 bucks, ditch it.