Not sure exactly where to put this since it is not quite chassis and not quite cabinet, so if this is the wrong location, can the moderators please move it?
I recently picked up a 38-5X console with the typical badly peeling veneer issues on the two pilasters. I can either repair this cabinet, or find a replacement cabinet. I may have found a replacement 38-5 tabletop cabinet in fair condition, but it does not have a speaker. The two use different speakers, the table top is smaller. I have no idea what size it might be. So my options right now are re-veneer the console (no experience with veneer, not much experience with spray paint, and none with spray lacquer) or find a replacement speaker for the tabletop version. I suspect the cost will be about the same either way, maybe slightly more for the tabletop since there will be some shipping. So I am looking for advice.
Thanks,
TerryMSU
Here's some speaker data that might be helpful to you...
LINK. You want the speakers.zip file. Its found in the download section of the Phorum.
It will tell you that you need a K39 speaker for the tabletop 38-5B cabinet while the console uses an H29 speaker. The K39 is an 8" speaker. The data for the output transformer, field coil etc. are in the spreadsheet.
looking on
oldradioparts.com (part# 4696-748 ) in the radio parts, speakers section it looks like he has a possible candidate but part of the description says "pp open,v" which might mean voice coil or the output transformer is open . Otherwise I "think" it might do the job as it appears to be a K34 which is probably close enough. (Terry, help me out here...
)
Put an Wanted Ad in the Phorum and you might get lucky with someone who has one sitting on their bench and you can keep an eye on ebay as various speakers come up from time to time or a junker chassis/speaker.
just something to ponder...
I think if it where mine and I was going to use the table top cabinet I would use a PM spkr and do away with FC. The main problem is that for the most part the K style spkrs are used lower tube count sets (table top set) There area few exceptions but the FC in a ten tube set is going to be able more current that a 6tuber with the same resistance. More current means more magnetism, conversely you could use a ten tube set's spkr in replacement on a six tube set but there may not be enough current flow to generate the full amount of magnetism to run the spkr properly.
The console's opt is usable with a PM spkr although not a perfect match. Most of the older Philco VC impedance is around 1 3/4 ohms, modern spkr are 3-4 ohms. Not too much to loose any sleep over.
Terry (Radioroslyn), I appreciate you...but I must disagree on using a PM speaker.
Using a PM speaker means that you must come up with a way to replace that 660 ohm field coil. Sure, a resistor can do the job...but it will also create lots of heat. The 38-5 uses eight tubes and that means a sizeable amount of current flowing through the speaker field (or resistor) which translates to plenty of heat dissipation if a resistor is used.
There are ways of getting around the need of a K-39. The same Excel spreadsheet also gives the specs of other 8 inch Philco speakers with 660 ohm field coils. There's the K-23 (19B, 144B) and K-34 (37-640B) as examples. Yes, you will have to replace the audio output transformer if you use a K-23, but if the transformer mounted on your current 10-1/2 inch speaker is good, you could remove it from the large speaker and mount it on the smaller one. A K-34's specs are close enough to a K-39 that it could serve as a direct replacement including output transformer.
You could even be really radical and remove the field and pot from your 10-1/2 inch speaker and mount it on the frame of a Philco K series speaker frame (not an S, but a K). But I would not recommend that to anyone but more advanced collectors with plenty of experience in repairing and restoring old radios.
I would only use a PM speaker and resistor as a last resort.
Ron, my personal inclination would have been to stick with a field coil design as you suggested for the exact reasons you suggest. Terry, the magnetic field is proportional to the product of turn count and . Double the turn count and you can use half the current. In any case, I am very appreciative of the input all three of you folks have provided. While I have the engineering knowledge and experience to know what might be possible, I am lacking in the practical wisdom that you all have provided. If the cabinet I am considering pans out and my current chassis is functional, I will definitely be looking for more advice. The idea of other Philco speakers in a similar size had not crossed my mind.
The cabinet (if I take it) will be coming from Alabama to Michigan. Any recommendations on how to ship it safely and cheaply?
Thanks so much,
TerryMSU
Insist on at least two inches of good packing material (peanuts) completely surrounding the cabinet. The inside of the cabinet should also be completely filled with peanuts or soft foam.
Insist on FedEx Ground/Home Delivery. Second choice would be UPS. If at all possible,
do not let the seller ship USPS.
Oh, and have him/her ship it face
down.
I think you're making a wise choice in switching to a 38-5B tombstone cabinet. Those are more desirable, and will take up much less room in your collection.
Ron,
Everything you say makes sense except for face down. I will be surprised if Fedex or UPS will keep it in the same orientation. Am I missing something?
Also, would bubble pack work as well for packing and fill?
Thanks again,
TerryMSU
Well...
since it is an empty cabinet, its orientation really does not matter. If it were a complete cathedral or tombstone, face down is the way to go. Properly packed, a complete cathedral or tombstone can be successfully shipped
Proper packaging and padding, however, does matter. A lot.
If bubble wrap is used, I would combine it with peanuts. That cabinet needs to have, at a bare minimum, two inches of packing material completely surrounding the cabinet. Three is better.
I am actually considering asking him to double box it, one box inside the other, with suitable padding between the boxes. Is that overkill?
(10-29-2016, 07:35 PM)TerryMSU Wrote: [ -> ]Ron, my personal inclination would have been to stick with a field coil design as you suggested for the exact reasons you suggest. Terry, the magnetic field is proportional to the product of turn count and . Double the turn count and you can use half the current. In any case, I am very appreciative of the input all three of you folks have provided. While I have the engineering knowledge and experience to know what might be possible, I am lacking in the practical wisdom that you all have provided. If the cabinet I am considering pans out and my current chassis is functional, I will definitely be looking for more advice. The idea of other Philco speakers in a similar size had not crossed my mind.
The cabinet (if I take it) will be coming from Alabama to Michigan. Any recommendations on how to ship it safely and cheaply?
Thanks so much,
TerryMSU
> Double the turn count and you can use half the current.
This is true but you end up with a coil that is physically larger in less you shrink the size of the wire.
In terms of using and resistor I was thinking of cost also (it's cheap like me). A choke (or field coil) is much more efficient in reducing ac hum in comparison to a resistor. If the resistor was the same size FC I would think that the heat generated would be about to same as weather you are use either, both are dissipating the same amount of energy.
You can use a separate choke mounted on the basket of a pm spkr, mounted like the opt. Something like 5H @ 70ma should do the trick. You could go higher in inductance but size maybe an issue.
If you want to have a set that looks original by all means go with a Philco spkr but I'm thinking it may be a bit harder to find and may need reconing.
Just wanted to throw out the most options.
(10-29-2016, 08:45 PM)TerryMSU Wrote: [ -> ]I am actually considering asking him to double box it, one box inside the other, with suitable padding between the boxes. Is that overkill?
...nope...
(10-29-2016, 12:11 PM)Ron Ramirez Wrote: [ -> ]Using a PM speaker means that you must come up with a way to replace that 660 ohm field coil. Sure, a resistor can do the job...but it will also create lots of heat. The 38-5 uses eight tubes and that means a sizeable amount of current flowing through the speaker field (or resistor) which translates to plenty of heat dissipation if a resistor is used.
Ron
A little.... disagreement. The electrical truth is, the 660 Ohm choke (and this is a DC impedance) or field coil will dissipate exact same amount of heat as the 660 Ohm resistor that would replace it.
Sure the choke filters better as it is inductive and the resistance is a necessary evil.
Another thing is if one uses higher value resistor, that would filter better but dissipate more heat plus drop more voltage thus screwing B+ voltage value.
So, if I were to use a resistor, I would simply use the same DC resistance of 660 Ohm, but increase the output capacitor (after the resistor, not the one before) several times.
Yabbut...
...the field dissipates the heat more efficiently than does the resistor. I'm no expert on this as I am not an engineer, but I can tell you from practical experience that a speaker field seldom gets so hot that you can't touch it. This is not true for a resistor being used as a replacement for a field coil.
Since we've gone in an electronic restoration angle, I've moved this thread to Philco Electronic Restoration.
Unlike Ron, I am an electrical engineer. Here are my thoughts on the heat question. Resistors have a smaller surface area and typically do not have an inherent heat sink, but are rated at as high as 175C (347F) ambient. They will run hotter, but can tolerate the heat. Typical modern magnet wire is rated at 155C (311C), but this is the wire temperature. (Magnet wire from the late 1930s might be lower.) The surface of the field piece would run much cooler. The field coil and speaker frame provide a LOT more surface area so the field coil will run much cooler. On the other hand, it needs to run much cooler.
To get the same filtering from a resistor, you will need to have a higher capacitance on the load end of the field coil, but not on the rectifier end or you may get too high of a voltage on the rectifier end cap and damage the rectifier or capacitor.
TerryMSU
Perhaps the answer lies in the middle that is using a FC spkr with a resistor in parallel with the coil. This could limit the amount of current flow though the coil if it isn't rated at a high enough current.