Help! Does anyone have a photo or advertisement of this Grebe cabinet? I have searched everywhere but can only find references and poor photos of the "Deluxe" cabinet, which is different. I'm missing the doors and would like to see what they originally looked like in order to try and duplicate. If not, I'll have to try and copy from some other period cabinet.
Nearly every joint in this cabinet was loose enough to completely disassemble with just a little gentle persuasion. Almost all edges of the veneered boards needed gluing. Because the cabinet was in such poor shape, I decided to tackle it before the radio since if it turned out to be beyond repair, there was no use in working on the radio. This is the first time I tried such an extensive cabinet repair, but it turned out ok. Certainly not museum quality, but good enough for my satisfaction. I would like to make some doors, though.
Wow! That's awesome! That looks great!!! I've wanted a Synchrophase for 40+ years, but never have seen the deluxe cabinet before. Now I want one of those...
Thank you, but don't look to closely. My veneer repairs leave a bit to be desired! I left many of the little dings for "character" (actually, too many to fully repair - I'm not very good at filling and hiding.) The original color was very brown. The wood veneer is some form of mahogany, and was more red than brown after removing the original varnish or shellac or lacquer. The camera flash, though, really accentuated the red. Here is a bit closer representation of its color.
This is not the Deluxe cabinet that I've seen in my internet searches. I cannot find this cabinet anywhere. I want to know what the doors looked like - how ornate were they? What kind of hardware? What kind of veneer pattern? Maybe I'll just leave it this way! Now to start the radio.
(This post was last modified: 02-24-2018, 09:28 PM by rfeenstra.)
Work has begun on the Radio. I liked the speaker so I decided to start there. It is a self powered, Jensen electrodynamic speaker with an AC switch to turn it off for whatever reason. I suspect it came from Jensen that way and Grebe just left it in. The full wave rectifier is, I presume, a copper oxide unit (selenium rectifiers were invented a bit later according to my research). It consists of 2 parallel, 2-discs in series units, for each diode in the full wave rectifier. (That's probably clear as mud!) I have not yet powered up the power transformer so i'm not sure of the operating voltage, but it must be fairly low. There is no filtration for the field supply, just a hum bucking coil. Question: who knows about copper oxide rectifiers? Are they safe to power up or do they exhibit the same potential problems as selenium rectifiers? I've only tested it with the diode testing portion of my fluke meter. Forward reading is about 10 times lower than reverse reading. How much reverse leakage is to be expected with copper oxide diodes? I have not been able to find a good answer by googling it.
The cone is in good shape but very fragile. Obviously, the edge surround need to be replaced. not sure what to do with that but will do some research. Any suggestions? Thanks in advance for any help you can give!
I thought the brown, paper tube would be just a capacitor. It's across the primary of the output TR. Damage was done in removing the assembly from the tube as it was encased in very hard tar. It turned out to be a .02mfd cap (measured, but not sure of the accuracy) in series with 180 turns of 38 awg wire wrapped around the cap, in series with another inductor of 2500 turns of 34awg wire round an iron core. I unwound it all to figure out what it was. Now I've got to wind it all up again (with new wire)! Interesting project.
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(This post was last modified: 02-26-2018, 12:17 AM by rfeenstra.)
I powered up the supply TR with a variac. All's well with the TR. AC output is about 15 volts. I then hooked up the rectifier and the field coil and slowly powered it up. it works but the output DC voltage is about 6.7 volts DC with 15 volts AC in. Not very efficient! I think the speaker would certainly work, but not up to full potential. I suppose I should hide a silicone full wave rectifier in there somewhere. But then, that may over tax the TR. should I also put a resistor in series to more closely match the deficiency of the copper oxide rectifier? those of you with experience in these rectifiers, I need your input! Thank you.
Tried a full wave silicone rectifier. Dropped the TR output voltage to about 12.7 volts AC with a DC reading of 9.5 volts (unfiltered). Transformer remains absolutely cool so I guess I'll hide a rectifier inside the pedestal. I'll put wires on the copper oxide rectifier to make it look like it's in the circuit. Now to rewind the coils and fix the cone.
I think that you can actually service those copper oxide rectifiers, they are a series of washers held together with a bolt, so you could try tightening the bolt to see if that helps, I'm sure there is better info on them then I have. Selenium is different, they degrade with age, they are also for high voltage low current applications whereas copper oxide is the opposite, low(ish) voltage and high current applications. The original surround, or hinge, was probably made out of a leather or chamois material which has dried up and fallen apart, you can buy a chamois for cleaning cars and cut it up for a replacement. The cone looks fairly simple to replicate, but I wonder if the cone speaker specialist has any replacements, Mr Chidester I think is his name.
Regards
Arran
(This post was last modified: 02-26-2018, 11:50 PM by Arran.)
Thanks Arran. I just removed the metal parts that hold the surround in place and discovered that it was in fact leather. I used to repair payer pianos and it looks like what we called pouch leather. I actually have some, though it may be too old to use.
As far as the rectifier is concerned, I did disassemble it, cleaned the washers (the ones in contact with the copper oxide are lead so very easily distorted), and tightened up the assembly. It didn't really improve things. It very well may be that I'm expecting more out of it than it ever delivered. Regardless, I hid a silicone rectifier in the pedestal and hooked up fake wires to the copper oxide unit. Like I said, the transformer runs cool as can be and the magnet is quite powerful. It was ok with the copper oxide rectifier but there was noticeably more vibration in a screwdriver held close to the pole. I suspect there was a fair amount of reverse leakage in the old rectifier. What I've done should work just fine.
it was obvious that the speaker had been used with the voice coil rubbing. There was bare copper showing on the surface of the coil. I'm trusting that the insulation between windings is still there. Used some lacquer to seal up the bare wire. thanks for the tip on the "cone specialist". I found his name at "The Radio mad House".
I decided to work with the original cone, as fragile and warped as it was, and used a piece of leather that I had laying around from former player piano days to form a new surround. The project was quite a bit less successful than i had hoped visually, but given the condition of the cone, I was able to produce a working speaker. In fact, since it is self powered as far as the field is concerned, I hooked it up to my Scott 16A and it sounds remarkably good! There was tape on the cone that I had to remove and, of course, that took the top layer of paper away. To strengthen the fragile paper, I coated it with a layer of lacquer and tried to color in the tape damage. the leather surround fit poorly as the cone was so warped around the edges. Yet, all said and done, it works quite well. A silicone rectifier was hidden in the pedestal and the wires hooked to the copper oxide rectifier are for looks only. The screws around the surround hold down brackets will be replaced with rivets as in the original - or maybe not as this allows much easier repair. Haven't decided.
Next is the power supply. it consists of the power transformers (2 inside the box, the terminal block and rectifier tube, the filter choke and the capacitor can.
I think I have a lifetime supply of wax from the capacitor box!
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(This post was last modified: 03-05-2018, 12:51 AM by rfeenstra.)
Great job!!
Don't like the Philips screws, too new for the application. Would replace w/ slotted nickel platted brass or steel and paint to match.
These days it's hard to find good old slotted screw at the large hardware stores. Mostly they just have those ones that you can use
either driver on. https://web.archive.org/web/201107101035...illips.htm
Keep up the good work!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
I don't like the screws either. It's what I had at the time. They will definitely be changed to something else when all is said and done. Probably will stay with screws for now instead of rivets as I probably will work on a new cone for the speaker rather than the distorted one that's in there before I consider it finished. But for now...
The cones are not too hard to make. I use the heaviest paper I can get from the office store (42lb ??).
The pitch is different from later speakers so an off-the-shelf cone replacement will not work. If you remove the old one intact, you can use it to adjust the pitch of the replacement.
On this one I used felt, but the same cone can be used with a chamois surround, or pig skin, which is what I use.
Thanks Russ. I will experiment with making a new cone as I am not at all satisfied with the original. The original had been sprayed with some sort of coating, so I didn't think another layer of lacquer would hurt. But the edges where the leather was attached is so fragile and distorted that i was surprised to even be able to get where I did! As i said, it sounds great. But, a new cone is in order. Once finished, I may go back to rivets around the perimeter as in the original.
I'm not looking forward to working with the pot metal. In my player piano days, I did a lot of work with that stuff. Fabricating a few new parts as you did should not be a problem. Just work! I also need to try and find the tubes for this radio. would like to try and find the original #'s.
By the way, do you have any idea of the value of the grid leak resistors that are in the glass tubes mounted on the tuning caps? I find no indication in the schematics. No indication of the filter capacitor sizes either though I was able to measure most of them and they are fairly consistant. if my readings are remotely close to real capacity, this thing was fairly well filtered. I'm looking at 10 mfd before the choke, 20 after and another 6 after a series resistor. The bias supplies vary from 2 to 8.
The cap values seem a bit large for that vintage, But would be acceptable with an 80 rectifier. They should be replaced with 630V film/foil/whatever caps like the Solens available from AES.
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