[Jordanbkc]

Chas - dv/dt.  This is what I had ordered for part 40 capacitor.

[Jordanbkc]

After y'all talked about the power transformer, I checked it out.  Primary on A side terminals 1-2 is 5.4 ohms.   3-4 and 8-9 are .1 ohms   5-6 is 138 ohms, 6-7 146 ohms (both a little low). 

I got around to soldering the power cable on, and the caps in the Bakelite box.

I sat awhile trying to figure out how I was going to replace the part 4 capacitor that's hidden under the wax antenna tubes.  One end you can clip and solder a wire, the other you can't get to where it's attached to the A switch.  Don't want to move the sub-chassis.  Finally figured out there's a green wire under the switch that connects A2 to A10. A10 is much easier to reach. Might be longer, but I'm connecting it to A10.

[Chas]

Kudos on that .03 cap selection...  

Here is some general tips, from the images you have posted. That AC cord is tied to a dual AC line bypass cap (Bakelite block) these are also paper and have been known to "explode" making a foil/paper mess.

Though the proper AC line rated caps may not fit the inside the block they can be tied externally to the block after disconnecting originals. These two caps "should" be "Y" type caps but can be "X" type (across the line) rated. This type of cap if/when it fails, is designed to fail open and not short which could be a issue as opposed to "rapid disassembly" of a paper cap. Keep the same MF value of these caps.

When working in and around the coil area, antenna or oscillator avoid disturbing or re-routing of any wires and make repairs in as much to keep same mechanical position and robustness. "Practically" any disturbance in this area will likely mean an alignment will be required to get dial markings to agree with the real signal and uniformly across the dial as well as overall sensitivity. Never turn the screw on any mica trimmers unless a RF generator is available.

Any caps that are of mica construction, although are lesser suspect, generally should not be "shotgun" replaced. Because mica caps are almost always in tuned circuits their actual value is critical as well as they may be of temperature compensating construction, "Temco" . Mica caps should not be rotated on the axis of their connecting wires, the twisting can dislodge the internal connection to the mica stack and break a seal at the wire entrance, use a dental mirror to see the identification. Mica caps that have split open casings are suspect but, again, should not be replaced until the radio is operated to evaluate. Obviously a shorted mica will have to be replaced, but care taken to properly identify.

Though I don't think that tubular ceramic "temco" caps are used in this radio they could be, often seen as appearing like a "dogbone" resistors, but marked with colored dots. Only the schematic or consultation can determine what such a cap is, if it is spoiled. Same rules, test before replace and replace as exact as possible. These ceramic caps are found in the RF area.

Be aware of wires without connect, wrapped around another wire or even lay adjacent. These are "gimmicks" and must not be disturbed unless the insulation is crumbling, then duplicate as much as possible. Gimmicks may or not be shown in the schematic and may or not appear as an adjustment on alignment instructions.

Final, note: The power transformer could be "live" tested. Remove or disconnect any power rectifier (unplug the tube). Other tubes can be left in place if confident there are no shorts in the filament or filament wiring, same applies to the pilot lamps. Pilot lamp sockets do short.

When all is well, power the radio, the lamps will light and the tubes will glow. If, in 5 minutes or often less a cracking is heard within the transformer or a bad burning smell, the transformer is already ruined. If not, carefully monitor for another 1/2 hour. if transformer is reasonably cool to touch and no other signs of a short, the transformer is good

When done with the refurbishing, many restorers do a "dim bulb" test, this test establishes if there is an overload from erroneous repair.

Alternately, before applying first power, use an old school VOM and connect the negative to B- (the chassis) and the positive to the filament circuit of the rectifier (highest B+), look for at least 5k ohms and resistance rising (as filter caps charge)to the value of any series of shunt resistors in the radio, usually 20K. If this "sanity check" is valid it is safe to power the radio.

I will admit that faults in the 6F6 circuit can cause a dramatic rise in "B" current working in that area of this radio you should be confident of the connections.

It is possible to make a "live" "B" current reading. Measure the value of the resistors from chassis ground to the center-tap HV of the power transformer. Record this value, then switch the meter to volts, place the positive of the meter on the chassis connection and the negative on the center-tap of the power transformer HV secondary.

Power the radio, as the radio warms the voltage will rise if there is no other obvious fault, the apply the meter volts to ohms law, the value of the resistance measured. that will be the total "B" current for the radio. Looking for a calculated value of at least 50ma but more likely 70 or so ma. Each radio stage will be around 5 to 10ma but the 6F6 will be as much as all other stages combined..

The current monitoring is just a tell tale, actual values could be closely calculated from schematic notes. Values in the schematic are made with a certain meter type, if a meter with a different load resistance is used, readings may not agree and could lead to errors in fault finding.

The most often cause of failure of a refurbishing is "shotgunning" without interim testing, so any error becomes lost. Wire snips, miss-connected wires, shorts, solder blobs at terminals and sockets are problems too.

All of what I have stated for this Philco radio are, essentially, applicable to any brand of radio.

There are, some nuances that I have likely missed, often when I restore these are so routine as to become oblivious.

Here is one: Do not "trust" riveted electrical connections to the chassis. Even though your best meter says the connection is "O.K." it cannot determine it the connection is sensitive to any RF. Re-solder as a routine and if there is too much chassis heat sinking, drill out the rivet and replace with hardware. Most chassis soldering will require an iron with a large copper bit, often 125 watts or more. The chassis can be pre-heated to accomplish this with a heat gun. Fifty years or more, the solder at the metal interfaces is subject to inter-grannular corrosion.

GL

Chas

[MrFixr55]

Varistors are useful on units with solid state rectifiers and high value caps to limit inrush current. Common to add these to such units like the Fisher 400, 500 and 800 series Hi-Fis from the late 1950s to early 1960s.

Only issue that I have with using a matching transformer as opposed to a standard audio output transformer is that the 70V matching transformers are not designed for a DC component. If you really try to use one, use a 70V primary. I don't think that you are gonna get the turns ratio and current capacity needed from a 25V Unit, but I defer to Ron Ramirez as he has actually done it.

[Ron Ramirez]

Regarding use of the 25 or 70 volt line transformers as replacements for single ended audio output transformers -

Is it an ideal solution? No.

Do they work as replacements? You betcha.

And for the cost-conscious folks like me, why pay $70 or more for a transformer which will not 100% match the 7K plate impedance to a 1 ohm voice coil anyway, for use in a radio which will likely only be used occasionally (not daily, for several hours each day) when a $10 line transformer will do the job?

The only vintage radio I use on a daily basis, for a few hours each morning, is the RCA C15-3 console in my home office. I've only been using it daily since I put a Part 15 AM transmitter back on the air here; otherwise I would have no reason to listen to AM radio where I live as there is nothing good to listen to around here. There is only one local AM station, 10 miles away, and it runs an all-Spanish format. Other AM stations which may be received where I live are mostly lost in the noise which permeates the AM band here. I don't listen to the radio at night anymore - that is our TV time.

The RCA is still running on all original transformers (knocking wood). If its audio output transformer failed, then yes, I would likely look for a better replacement than a line transformer since I use the set daily.

A word or three on Philco voice coil impedance, Yes, Philco factory specs give a voice coil impedance of 0.7 ohms for the very early electrodynamic speakers such as used in models 70, 90, and 112. Starting in 1932, they bumped their voice coil impedance a bit, to 1.25 ohms for most K series speakers, and 1 ohm for most S series speakers. (FWIW, the speaker used in the OP's 37-60 is an S-7, the same speaker as used in all Philco 60 sets, and it has a 1 ohm voice coil.) Here it remained until 1939, for the most part. Higher end Philco consoles such as the 14, 16, and 17 consoles and chairsides had 2.28 ohm voice coils. Philco came out with a speaker with a 3.9 ohm voice coil for models 200 & 201, later 116X and 680X, still later 37-675, 37-116, 37-690, 38-116, 38-690, 38-1.

I think all Philco speakers made from 1939 on had 4 ohm voice coils.

8 ohm impedance voice coils are actually a more recent development. I think they began to come out in the 1950s. For many years, 4 ohm voice coils were the standard on many speakers, and have become so again more recently for subwoofers and some car radio speakers.

[Ron Ramirez]

I just looked on Edcor's site, and they sell a single ended 5W transformer which will match a 7K load to a 4, 8, or 16 ohm secondary (you have to specify when ordering). And the price is reasonable ($38 and change compared to nearly double for the Hammond).

https://edcorusa.com/collections/tube-am...ransformer

Since Edcor custom builds transformers to order, and do not make these until you order them, it might be worth asking if they could wind one of these for you with a 1 ohm impedance secondary. They could get some business from us antique radio buffs if they would.

[Ron Ramirez]

One more thing.

The Speco line transformer I used on my Philco 90 speaker is a 70 volt transformer - for what that's worth.

[Jordanbkc]

Thanks all for the info.   On the power caps I used those on the attached picture. Also going to add an inline .5 to 1 Amp fuse.

On the antenna area, going to risk re-routing the part 4 cap, instead of trying to unhook the subchassis.

I remember about the bulb test. I found a ceramic light bulb socket & incandescent bulb I had bought for that.  

Don't nobody rag me    , but I just bought a parts 37-60 on Ebay for $133 (includes shipping).   Pig in a poke but if the dial, some tubes & speaker transformer are good might be worth it. I already have a bad volume control on mine that I haven't tried contact cleaner on yet.  

The Edcor site looks good. But looks like it's more difficult to ask for a custom T. 25 minimum.  Custom Transformers (edcorusa.com)

A lot of the issues people are mentioning with tubes or transformers burning out - didn't they have fuses back then? Even now, why can't fuses be used for critical parts? They have them in very small values to large values.

[Jordanbkc]

Replaced capacitor #4 hidden under the antenna coils.   Snipped the lead at the switch with a pair of scissors (only thing I had).  Same coming from tuning cap but somewhat looped the end and mashed a tight loop on it on the new capacitor. Hope I got a hot enough solder joint at the switch. Was afraid the glob on the other side would start dripping.

Reckon I'll catch a good ragging at the new routing, but only thing I could think of that would connect. 

Out to mow grass now.

Bryan

[Jordanbkc]

Dang, dang, dang - they lost the parts radio. Got a refund but was counting on it. My pig in a poke has run off.

[Jordanbkc]

Finding that the Bakelite 8318 or 8328 SU near part 42 & 44 is just a glorified terminal strip with a .03 uF 600V cap.

Think I'll just empty it out and add a ground terminal strip on the end, and a cap on top.

[Chas]

IMHO your fine with the re-location of the cap mentioned with an image of a wire with red dots. That wire is or looks to be the AVC bus. That is a negative voltage at very small current that is used to control the gain of the RF/IF tubes so stations are all at the same loudness level. The cap not only bypasses local RF but its value is part of a timing circuit so the AVC acts with reasonable timing.

It is important that the AVC circuit have no losses...

Placing caps on top of a block is O.K. especially when new caps are too large to fit inside.

BTW have you decided on a vendor and ordered your OPT?

Chas

[Jordanbkc]

Thanks a bunch.

On the OPT I had a 37-60 radio lined up from Ebay. Thought I would at least have some spare parts and possibly a speaker.

Either USPS lost the package or the vendor lost the radio and didn't know it. I got a refund but was going to see if it turned up again. There is a 37-62 on Ebay that has the same S-7 speaker, but the dial and power transformer don't match mine. $75 total is a little steep for just getting a speaker and a few tubes.

I've been studying tube theory and speakers on one or two web sites. http://www.radioremembered.org/edspeaker.htm
Trying to figure out the best solution. Would have liked to keep the speaker part somewhat original, since it is very visible, unlike the capacitors under the radio. If I can't I'll probably get that Edcor $38 OPT 7K to 4 ohm. I measured the existing OPT today. 2 3/8" spaced mounting screws, trans is 1 1/2" W and about 2" tall. Need to check possible new OPT.

[Chas]

What is wrong with this? It is NOT center tapped...

https://www.tubesandmore.com/products/tr...nder-champ

Specs:

https://www.tubesandmore.com/sites/defau...to-001.pdf

I would not cut the tap, the ultra-linear may be an option or not, try and listen...

Look at shipping, pad it out with other stuff if needed...

Chas

[Jordanbkc]

Even the mounting hole width is the same. 3/8 is .375.

I'll buy that and use the 8K connection. Thanks a bunch. Maybe even get tubes from them.

Bryan