http://www.nostalgiaair.org/Resources/811/M0013811.htm
I’m working on a Philco 630 that has had some restoration work done prior which is confusing me. Both of the two original electrolytics were still hooked up. I replaced the 16 mfd one already.
The photo is the 8/8/10 electrolytic. I’m not sure how to safely wire the positive and negative connections. I’m assuming the blue circled wire is the common negative because it goes to the center tap but I don’t know how to tell from the three, red, black and silver connections which one is the 8, 8, and 10 connections. There isn’t anything marked on the cylinder to indicate which is which.
I realize that I should be able to find this out from the schematic but I’m new to radio restoration and I just don’t want to mess the polarity.
The yellow circled item at the bottom is a 20 mfd cap that I don’t know how it fits into the scheme. It goes from the speaker connection to Pin 1 of the 4989 Bakelite condenser. Not sure why it’s there. Do I just remove it after replacing the electrolytic I’m inquiring about?
Any and all advice is more then welcome.
Unless you can read the printing on the outside of the can on top of the chassis as to which color dot corresponds to which capacitor value, the only way to determine which is which is to trace the wires out using the schematic. It appears the common or "negative" of all three (#67 on the parts list) are tied together going to the center tap of the transformer, and that the 10 mfd is a positive ground. Meaning the positive side of that cap is going to chassis ground.
Regarding the 20mfd, you didn't tell us if the positive or negative is connected to the speaker connection. In any case you probably can remove it, it may be connected wrong. The bakelite block has a ground terminal and it's probably connected to that. BTW, you could replace the 8s with 10s but I wouldn't go any higher.
If you look at the schematic, one of the 8s is connected to the 80 tube, pin 1 or 4. It looks to me like that is the wire on the black terminal. The other 8 is connected to the output transformer primary and may be the red terminal. That leaves the 10 as the silver. You'll have to verify because the photo isn't clear as to which wire goes where.
As far as the 20 mfd cap, the + is to the speaker and the - to the bakelite block. That lug where the + is soldered is also where #1 in the photo attaches to the speaker connection.
#2 on the photo goes to the speaker connection and then continues on to Pin 1 of 80 tube. I’m assuming then that 1 and 2 are the 8/8 portion of the electrolytic.
#3 goes to Pin 4 of the 78 tube. That is also where the - connection for the 16 mfd electrolytic, Part 52, is currently attached. Is that the + ground connection for the 10 mfd that NostagiaRadioTime was referring too?
It is hard to tell from the photo, but the yellow cap is probably replacing one section of the filter cap or connected parallel to one section (not a good idea). To keep things simple, you can use three 10uf caps to replace the 8uf/8uf/10uf. All negatives go to the HV center tap, one positive will go to one side of the field coil, another positive will go to the other side of the field coil, the last positive will go to chassis ground.
Steve
Without seeing exactly how the 20 is connected it's hard to say what cap it is replacing and from the info you gave it looks like it is incorrect, so I would leave it out.
Pin 4 of the 78 is grid 3 which is grounded. So that is correct to have #3 go to that pin. It would be the 10mfd. (so many numbers).
Thanks very much gents. I appreciate all the help and input.
Thanks very much gents. I appreciate all the help and input.
I have the radio picking up stations now but I have two questions.
The wire in the red box is not connected to anything, nor does it appear that there ever was anything soldered to the middle portion of the variable condenser…so I don’t know what it’s purpose is. If I touch it or go near it with my hand, the reception/ volume goes up quite a bit. Why does the volume increase so much and is there other items that I should be checking that would account for the increase in volume. I’m still new to radio restoration.
The other question regards the volume control. I get ok volume but it doesn’t go up very much when I turn the control up. I did spray the volume control with Deoxit but was wondering where I could get a replacement volume control and how do you determine which volume control is needed for any certain radio.
The red unterminated wire may be what is referred to as a gimmick capacitor. The capacitance of the loose wire is sometimes used to neutralize the coupling between the oscillator and RF input of the converter tube, preventing interaction at the higher SW frequencies.
The lack of volume does not necessarily mean there is a problem with the volume control itself. Rather any number of problems in the various other circuits can cause loss of gain and resulting low volume. As long as the volume changes smoothly as you rotate the control, then its probably not the problem
What are you using for an antenna? The fact that the volume increases when you touch the tuning capacitor may indicate problems with the antenna coil or RF amp stage. There could also be a problem with alignment of the antenna, RF and IF stages.
Hallifcrafters used the gimmick cap in the models S38B-E sets for a BFO for single side band. Just moving the wire around can change things!
The antennae I’m using is what was there when I got the radio, photo enclosed.
How would I go about checking the antennae coil/ RF amp stage? Sorry for my ignorance on probably basic items but I’m not sure how to check those items.
If that's where you have the antenna wire connected, then it explains the problem.
You have the antenna wire connected to the ground terminal of the radio. Unroll and extend the wire and connect it to the similar looking clip at the back towards the center. That is the antenna terminal.
Thanks Mondial, I definitely have a lot to learn. My woodworking skills are very good, electronics…not so good.