[morzh]

Actually me growing up, the GND was positive. It was an era pf PNP transistors reigning supreme, and so the amps and other stuff I built had "+" to GND and "-" to the power. Took me a while to get accustomed to "-" to the GND.

[Pithicus999]

CodeFox – When you say ‘negative bias capacitor’ I hope you aren’t saying that one of my capacitors is in backwards? If so, there is only one (+/-) electrolytic capacitor in this set, and that is the one that (in earlier post # 6 which has a video) DKinYORKpa and Ron told me was in backwards so I switched it to make the (+) positive side hooked to the Chassis. I didn’t check any voltages though, I just switched it.

How do I tell if that (+/-) electrolytic cap is hooked up correctly? How do I measure the direction of flow (which is what B- is correct??) I would assume that it’s as simple as reversing where I hook up the black and red multimeter clips?

[morzh]

It is simple: you just take your DMM, make sure the black lead is plugged into the ""Common' socket and the read into "V/R" (or whatever it is called), set your DMM to "Volts", hook the black (common) lead to your chassis and your Red - to the other side of the cap, that is not connected to chassis.

if you see the value shown with the "minus" sign then your polarity is in backwards and the Plus voltage is on your black. If not then your plus is on your red.

[Pithicus999]

Thanks morzh.

This may take a week I'm sorry to say, I'm in the middle of moving and radio is packed up. Hope you fellas are still here when I get back!

Also, in my last post I said there was only one electrolytes cap, not true! There are a few in the aluminum cans (#53,54) but unly one is visible from under the chassis, and that is the one shown in post #6 of this thread.

[Pithicus999]

Ok, I'm all moved in, and ready to continue work on this radio.

As I said in a previous post, I blew out the 32K resistor which is part #61 (on the 121 model). I’m concerned that I may have hooked it up incorrectly? I was very careful to only remove one part at a time and then replace that part before moving on to the next part, however, there is a group (#40 on the 121 model) of electrolytic capacitors that I replaced and had to use the schematic as to where to place the connections, I think that’s where I made my mistake.

Thank God I took several before and after pictures, I just looked and I should be able to replace the #61 “Properly” and I’ll let you know how it goes.

Thanks!

[Pithicus999]

As morzh pointed out previously #40 on the schematic shows 3 caps (1,1,2ufd) in one can. The actual can has 4 leads coming off the front and is bolted or grounded to the chassis on the back.

Off the 'Green' tab are 2 of the 4 leads, 1 going to the wire wound resistor (#49) and the other to the speaker's field coil this is for one of the 1-ufd caps.

Off the 'Red' tab there is 1 lead going only to the plate load for tube 75.

The final lead is connected directly to the .1 Meg resistor #39.

Obviously I couldn't hook up the three caps this same way since the 2ufd is (according to the schematics) to be T-up with R61/R62 and none of these 4 leads went anywhere near R61/R62. I hate the idea of NOT hooking this thing up the way it was originally, especially since it makes it infinitely more difficult to trouble shoot, but when I tried doing it the same way as in my pictures, the 32K resister melted. So, I decided to trust the schematics (and also, since I didn't actually cut open the electrolytic cap to see the connections inside) and re-hooked up these three caps the way morzh suggested.

I left the radio on for about 4 hours, no smoke, no melted wires, no problems. However, I had my Ohm-meter hooked to the 32K resistor and it was reading 17K Ohms??? Is that normal? I thought the reason was because I didn't actually calculate what the Ohms going through the circuit should be, but the radio was turned off and also each lead was directly on either side of the resistor... so I don't know.

I just don't get how it could read 33K when it was OUT of the radio (I did measure it prior since the last one 'Chernobyl-ed' on me), but while IN the radio (with radio turned off) how could this resistor read anything other than 33K? I thought the multimeter sent the signal down one lead-through-the-resistor-and-back-to-the-other-lead completing the circuit? My only thought would be residual voltage from the capacitors leaking out power, but I thought that was a bit of a stretch.

Anyways, I think my Sig Generator is on the fritz or broken because nothing happened when I hooked it up. I'm going to check on that this week. There is a guy here in Ann Arbor who can help me, so I'll do that. That's all for now. Thanks again morzh, Jerry, and Ron and everyone else who's gotten me this far, couldn't have done it without you guys, thanks again.

[morzh]

Your 32K resistor probably melted due to incorrect wiring of the cap 2uFto Chassis.

I do not have 121 sch but on 124 those parts are Resistor #55 and cap #40 (part C of the multiple electrolytic). You probably shorted the resistor to GND when your cap went bust when probably wired backwards.

PS. That resistor has DC path to the chassis so it cannot be accurately measured in-circuit. The top part has a path to GND through the output transformer and Resistor 6.5 kOhm, and the bottom part has another resistor to GND. I cannot read the bottom resistor value.

So your resistance is (32K + Rtrans-prim + 6.5K) * Bottom Resistor / (32K + Rtrans-prim + 6.5K + Bottom Resistor).

If the bottom resistor is 50K then it will probably be on the order of 22K total.

[jerryhawthorne]

Deleted after reading your post in greater detail Pith.
Jerry

[Pithicus999]

Morzh – The bottom resistor on my schematic (by the way, I have a PDF, can I upload it somehow?) is #62 and that one IS a 50K resistor. I’ll check the Ohms when I get home, it might be 22K, that rings a bell, I was up late last night so everything is a blur. Looking at the schematic now I see what confused me, in real life (and I’m talking about looking at the actual radio and not the schematic) the GND end of the 32K resistor is soldered directly to part #20 (which is a 0.15ufd cap)—ie it’s not soldered to ground like I think it should be anyhow. However, if you look at the schematic, that #20 cap ALSO goes to ground but there are no lines on the schematic that connect #20 to the 32K resistor! I think I spent about ½ hour trying to find a path on the schematic that linked up the #20 cap to the 32K resistor! HA! Those tricky b@stards, I guess it is hooked up correctly since both the #20 cap to the 32K resistor go to ground, right?

Also, what is ‘Rtrans-prim’? The resistance of the ‘output transformer’? And if so, can I find the resistance of it by just using the two tabs on the bottom of the chassis? Or does that resistance change while in the ‘system’ as well?
Thanks.

Jerry – Lucky for both of us I copied your post before you deleted it! I printed up the 118 Philco schematic. Looks like you have 4 caps, and mine only has 3. You may have trouble reading the schematic for the model 18, so here is the breakdown with comparison to your model 118. I do have a question at the bottom that I hope you can answer for me.

• #46 (A) Is a 1.0 ufd cap that T-connects to #45 & #47 the 50K/0.1MEG [#40 (A) and #41 & #39 on my model] – This model 118 schematic corresponds exactly with mine.
• #46 (B) Is a 1.0 ufd cap that is parallel with #60 the 6.5 Wirewound [#40 (B) and #49 on my model] – This model 118 schematic corresponds exactly with mine.
• #46 © Is a 2.0 ufd cap that T-connects to #67 & #68 the 32K/50K [#40 © and #61 & #62 on my model] – My model 18 schematic is a bit different.
• #46 (D) T-connects to #67 & #68 (the 32K/50K) –I’m having trouble finding this one on your 118 schematic, but I hope you know where it is! That thing is hard to read!

Ok, now for my question. Our ‘A’ & ‘B’ are the same and I have those hooked correctly. I don’t have a ‘D’ so we are only talking about your #46 © the 2.0 ufd cap connection or rather #40 © and #61(32K) & #62(50K) on my model.

For #46 ©, if you look at your 118 schematic, you see there is a wire connection from the (+) end of the 2.0 ufd cap going to the 6A7 tube? Ok, I have almost the exact same thing on mine except the connection is going to the #78 tube not the 6A7 tube.

My question is, on your 118 model, can YOU make a 4-way (‘CROSS’) wire connection with the #6A7 tube wire, the 2.0 ufd cap, the #67(32K) & #68(50K) resistors? Because, now that my 3 caps are out of the tube, that’s the only way I could think to hook this up. My current connection for #40 © is this 4 way connection of the #78 tube wire, the 2.0 ufd cap, the #61(32K) & #62(50K) resistors.

And if not, do you have another suggestion? This isn’t a trick question by the way, it looks like there shouldn’t be an issue, I only question it because it didn’t look like that’s how this set was originally made, and I don’t want anything to blow up.
Thanks.

[jerryhawthorne]

Pith, I see what you mean, if there were a dot on the crossing on the two lines (connection) which is not shown on my 118 schematic it would appear very similar to yours. It would connect the 2mfd cap to the 78 RF amp g2, the 6A7 det/osc on G3 and the 78 IF on G2. I would personally wire it per your schematic. Friday I will do a little resistance check and see if indeed the 118 is wired as your 18 schematic shows. It wouldn't be the first time I found a connection dot missing on a schematic. Anyone following this chip in.
As a question related to Pith's problem, resistor 67 is a 32K on his schematic and mine. It is a large dogbone Philco P/N 33-1026 can anyone tell me the wattage on it? I get a little lost on these. Edit: Discovered the answer on Chucks fantastic web site. Lots of good info there.

Hang in the Pith, I deleted my message when I re read your original post and realized you had four wires on the can, not four terminals.
Always something to add, on the 118 schematic the 2mfd is located next to the left dial lamp shown.
Jerry

[morzh]

Pithicus

The Rtrans-prim is the Resistance of the Transformer's Primary, and it can be measured directly across it with an ohmmeter while still in the circuit, because it is about 2 orders of magnitude lower than the rest of the resistors that are in this arrangement can be considered in series with it.
I theorised it would be on the order of 1-1.5kOhm. Even if it is Zero it would not change much for the same reason - it is small compared to the rest of the resistors.

[jerryhawthorne]

Pith, looking at a little of the thread history I noticed you having problems with the 32K resistor. Mine is reading high and needs replacing. I'm certain your aware that this is a 2 watt resistor.
Jerry

[morzh]

Jerry, Pith

This resistor will dissipate exactly 0.3W. Choose your wattage the way you see fit

The Voltage at the top of the divider is about 250V.
The 32K resistor will drop 97.5V.
The dissipated wattage is U-square / R = (97.5*97.5)/32,000=0.29 W

[Mondial]

The 32K resistor probably dissipates closer to 1 Watt. Although there is a voltage divider formed by the 32K in series with the 50K, there is also screen grid current of the RF and IF tubes being drawn through the 32K. The voltage chart shows the screen voltage at 80V, which is also the voltage at the center of the divider. 250V supply minus the 80V at the center leaves 170V across the 32K.

(170 x 170)/32000 = .903 W, so a 2 Watt resistor would be a good choice, leaving a generous safety factor.

[jerryhawthorne]

Thank you, it is certainly an original dogbone and is rated for 2 watts. At this point there is some discreapancy and possible error on the 118 schematic in a missing "dot". The 18 schematic does involve both the RF and IF tubes in the total draw, the 118 does not. I will check the circuit to confirm.
Jerry