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 Post subject: Majestic 90 Radio w/ 90-B chassis restoration from rats nest
PostPosted: Jan Thu 11, 2018 9:28 am 
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I hope someone else here can give me some pointers and ideally a *clear* schematic and/or manual to restore a Grigsby Grunow Majestic 90 Radio (with the 90B radio chassis within ). I found some schematics online but I can't see the values of half the resistors and capacitors and voltages, etc. Information about the can condenser configuration would be nice. I've already cleaned and greased the tuning capacitor as well as cleaned all of its contacts with de-oxit on pieces of cardstock (great trick I learned here). I've swapped out the paper caps, one 8MF electrolytic and the two .001MF caps, but I haven't yet dealt with the can capacitor which is an old can condenser which has a ground wire plus 4 colored wires BUT one wire (a red one) is cut off at the base. Was this done at the factory? Perhaps they never used this red wire? Or did someone cut it years back for some reason? I hope someone else has an idea. The entire chassis as you can see was a real rats nest, but after removing many layers of rat waste I found the chassis. Look forward to some feedback. Will post pictures with my progress, as it seems like no one has really documented the restoration of one of these *heavy* beauties. - Scott


Attachments:
File comment: majestic 90-B chassis before restoration
chassis90b.jpg
chassis90b.jpg [ 106.16 KiB | Viewed 1028 times ]
File comment: After taking off a couple layers using 409 with a wire brush and then WD40 with a brush. A screwdriver pulled of the big ugly pieces.
chassis90blayer1.jpg
chassis90blayer1.jpg [ 77.71 KiB | Viewed 1028 times ]
File comment: The inside was in very nice shape but I can't tell if one of the can condenser wires (a red one) is supposed to be cut off at its base or not.
chassisbottom.jpg
chassisbottom.jpg [ 97.51 KiB | Viewed 1028 times ]
File comment: Any comments on this item (resistor?) would be appreciated. It looks like cardboard with some wire wrapped around it. Is it a resistor? Advice?
resistor.jpg
resistor.jpg [ 51.3 KiB | Viewed 1028 times ]
File comment: Grigsby Grunow Majestic 90 Radio - currently waiting for its innards to be serviced and returned. Then we'll clean up the cabinet and install fresh vintage speaker cloth.
grigsby-grunow90.jpg
grigsby-grunow90.jpg [ 99.73 KiB | Viewed 1028 times ]

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Fri 12, 2018 1:14 am 
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Location: Mountains of Mourne. Ireland.
Schematic 90B: http://a4.pbase.com/o10/56/215056/1/166 ... titled.png

Additional info here http://radio.codegods.ca/node/6519
click on schematic twice... :)
homepage: http://radio.codegods.ca/

Greg.


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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Fri 12, 2018 5:55 am 
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Greg, thank you for the links. I was able to discern all of my "unknown" values on my printout. Thank you.

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Fri 12, 2018 6:55 am 
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Question: does anyone know if there is a good reason to retain the flat-former wire wound resistor? Below is a page describing them (new to me), and they are labeled in the schematic as a "1.6 ohm non-inductive center tap resistor". The readings of each leg are .78 ohm. Here is a link about such old resistors: http://www.resistorguide.com/wirewound-resistor/

The photo which I posted earlier is relisted.

By the way, yes, I plan to replace the red and black rubber jacketed wires that are cracking and splitting.


Attachments:
resistor.jpg
resistor.jpg [ 51.3 KiB | Viewed 963 times ]

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Fri 12, 2018 9:02 am 
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Can anyone verify if this paper capacitor (the blue one in the photo) is from about 1929? I'm thinking it was added at a later date to fix a dead capacitor lead from the can condenser unit. It is actually an 8MFD at 450v and it is also a polarized electrolytic (but I believe the condenser caps are not polarized electrolytic)... Is that right? Any thoughts are appreciated.


Attachments:
oddcapacitor.jpg
oddcapacitor.jpg [ 86.96 KiB | Viewed 959 times ]

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Fri 12, 2018 5:04 pm 
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I had one of those I got working back in the 80's. The push-pull 45 outputs give it a wonderful sound.

The blue electrolytic is not original.

I had a couple big problems with the set. The lesser problem was that the ballast was missing. Mine had a separate power supply. A thick umbilical ran between the power supply and the radio chassis. The power supply plug (which had canted prongs) plugged into an electrical box down by the speaker which had two outlets. A metal ballast plugged into the other outlet. The actual power cord ran out of the electrical box. I never really found a suitable substitute for the ballast.

The bigger problem was that the main tuning capacitor was full of cheap pot metal that warped over the years, shorting out the plates. With some fairly major surgery I got it working, but the pot metal continued to warp so that in a couple years it shorted out again. If I had it to do over again I would have made a more permanent repair.

The only other advice I could give is for aligning. Because it is a TRF, I wound up making a special tool with a long handle and a knob on the end. That helped a lot. It has to be non-metallic.

Oh yes, I also had to change the power switch. I was fortunate to find an exact replacement toggle with a long neck.

I believe I got the schematic I had for it at the time out of an old radio book. It also had the alignment procedure, such as it is. I'll look around and see if I still have it some where.


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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Fri 12, 2018 6:42 pm 
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Sol, I've never aligned a TRF unit, so the alignment procedure would be a HUGE help. I'm not there yet but I'm moving at a good pace with the restoration. The tuning capacitor was nice and clean and the blades nice and true, so I'm hopeful. If I run into an issue with the switch after cleaning it I might be able to swap the antenna switch as I believe they are identical. I'll look again today.


Attachments:
powerswitch.jpg
powerswitch.jpg [ 43.35 KiB | Viewed 927 times ]

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Fri 12, 2018 8:51 pm 
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Location: Santa Clara, CA 95051
I have a 230A, very similar to your chassis.
I left that 1.6 ohm, center tapped wire wound resistor alone. Like yours mine measured within tolerance and I noted that you cannot get more basic than open wire on a wafer. It's on the filament string. Works great.
You have checked your tuning capacitor so that would have been my first recommendation.
Next, rotted rubber wire. It's sneaky, looks perfectly OK until you touch it. The cloth covered wire is all good in mine. My speaker cable was dead shorted even as it looked great. Is your speaker field good? Mine was open but I was able to fix it.
There are resistors and fixed capacitors out of tolerance buried in the bottom of the IF cans. I looked into replacing them but determined not to do that given the amount of work it would have taken to get to them. Radio works fine like that.
Somebody added that blue tubular electrolytic to yours. I agree, they then clipped the wire from the multi-capacitor can. All of the electrolytic capacitors are polarized. There is a common ground in that can which is one of the five wires coming out. The other 4 are the electrolytic capacitors labeled on the print as A-B-C and D.
I clipped all the wires from mine and just life the can for show. I built my new power supply right on the power terminal strip plus a small added terminal strip adjacent. I found all the contact points I needed right there. I also found a couple of those wire wound resistors out of tolerance. Two are buried under that strip, hard to get to.
You need both of those switches, the remote distance switch is important to the radio functioning right. Those simple toggles are around and if you can't find one PM me and I'll look through my junque. I don't own any junk, mine is all very high quality junque. The important part is you have both the bezels. They polish up really nice.
There is a manual here that covers your chassis. It has alignment information in it that I used to align mine. Was a piece of cake by the way. I had to build my own hex head alignment tool. This manual was the only source I could find that had an accurate schematic for mine. Mine has the turntable on top and the switch configuration is different than what is shown in the Bietman service manuals. https://www.google.com/url?sa=t&rct=j&q ... AoU9iN6XjI
Weird looking link but it works for me. Let me know if you can't make it work and I'll send you copy. PM me with an email address.

It was a fun restoration and the radio sounds good. I'm going to have to give mine up because I simply don't have room for it. I have a link here that speaks to some of my ongoing questions I had. It also has pictures of the underside of my chassis and the resistors I spoke of above. Ask me if you have questions. I'll do my best to answer. viewtopic.php?f=1&t=317872
If I don't respond right away send me a PM, perfectly OK.


Link here for cabinet work. http://antiqueradios.com/forums/viewtop ... 1&t=314144
Yes, your right, the chassis weighs almost as much as a 1964 Pontiac. In all seriousness does anyone know what one of those complete units weighed? It is very difficult to weigh mine, cabinet, chassis, et. al.


Tomie


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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Sat 13, 2018 8:31 am 
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Tomie, thank you for the info. I am adding to my knowledge base as I go and I'm hoping to document and photo as much of my work as possible for the forum. I like that you only have "junque" aka French junk. :D I'll check out the switch and let you know if I need a replacement. Thank you.

So I removed the two red and two black rubber wires tonight and replaced them with new cloth red and brown pairs. Notice in the photo that I even fed them through a wrap around wiring setup that I imagine was done originally. I know there's a reason for doing that but I can't remember why. All went smoothly except for the mess of dried out rubber that littered the interior of the chassis. (see photo)

So I looked underneath the power strip and didn't find any more wired board resistors but I did find a massive wound resistor, about 7 inches long. (see photo) Didn't even know it was hiding under there. I'll be triple checking everything before we try power in the near future.

Regarding the electrodynamic field coil, it looks like its in good shape cosmetically, but I've never dealt with such a thing before. Any testing tips are much appreciated. I have to replace the multi-conductor cable because it stunk like rat pee. Luckily found some similar gauge 4-conductor cable at my local thrift store with a cool-looking yellow jacket. The cable looks like those fancy yellow spark plug cables you find on muscle cars.

Had to order some 2.2uf/450v and 4.7uf/450v electrolytics to replace the can condenser wires which tested at 2.4mfd (green), 2.3mfd (blue), 1.2mfd (yellow) and unknown/fluctuating on the red wire (which someone cut off in the past and replaced it with a blue 8mfd capacitor - in earlier photo). I own some 10mfd caps at 450v but I felt like jumping up to 10mfd was too much.


Attachments:
File comment: Notice that I fed the replacement wires through a loop of wire that was wound around the original wires. I know this is done for a reason but can't remember why.
rubberwirereplace.jpg
rubberwirereplace.jpg [ 112.93 KiB | Viewed 888 times ]
File comment: Found this big resistor, about 7 inches long, hidden underneath the power strip.
bigresistor.jpg
bigresistor.jpg [ 60.79 KiB | Viewed 888 times ]
File comment: This is massive tuning capacitor, about a foot long. This is a photo before I regreased it, cleaned the contacts and the end potentiometer.
90btuningcapacitor.jpg
90btuningcapacitor.jpg [ 91.93 KiB | Viewed 888 times ]

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Sat 13, 2018 5:37 pm 
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This thread brings back a lot of memories for me.

I remember I was moving the speaker one day and it fell against the wall, actually punching a big hole in the wall! Everything on these radios is very heavy. The cabinet on mine was constructed entirely of 1" hardwood plywood. Mine was missing the escutcheon. :(

Scott's picture reminded me of the trouble I had with the tuning cap. It was the center part where all the rotor plates come out of the casting around the center shaft. I don't know why, perhaps QC on the castings wasn't that great, but some of these suffer from a chronic deterioration where the casting just splits apart, spreading the plates until they short against the stator plates. Mine was really bad. Scott's looks really good.


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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Sat 13, 2018 6:05 pm 
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Location: Santa Clara, CA 95051
Scott, I use DC resistance measurement to establish continuity through the field coil. You also have a choke in that radio, so two coils to check for continuity. My memory is fuzzy but I recall that I was able to trace the wires to that long terminal strip and I isolated them there at that point. Isolate the coils and measure the continuity. Don't worry so much about the reading, if you have continuity the coil is probably good. In addition to creating magnetic flux lines so the speaker can work, those large coils of wire help to take away the AC ripple in the B+.

If possible, before I get very deep into a radio, I do a basic, no tubes in, slow power up for the main transformer and then continuity check for the field coil and any high voltage chokes. Those are the really tough parts to find to replace and can make or break a restoration for me.

My recollection is I used 4.7 MFD electrolytic capacitors. The A-B capacitors have the potential to increase the B+ when bigger like that, but mine did not spike much as I recall.

SOL, my speaker was ripped to bits. Everything was there but the cone had been torn out. I have a contact who does really good speaker work, but it cost me $100 to get that speaker coned. $50 to cone the speaker, $25 each way to ship it.

Tomie


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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Sat 13, 2018 7:12 pm 
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Sol and Tomie, thank you both for your help. Although I've done some simple recaps and simple restorations of some 1950ish tabletops, I'm really just a newbie. The setup and parts in this Majestic, a real tank, are new to me. For example, the .001mfd and .004mfd capacitors look like poop (see photo), but when I tested them they were still within range. I swapped them out anyway just to make me feel better. Next week I'll dig into the field coil. I'll continue to follow your tips to ensure this is done right. I'm not there yet, but I'm a little nervous about aligning this because, like I said, I'm a newbie to this. I have to admit, when I started this I wasn't as excited as I am now. The more layers I scrape off and clean, and the more sweat I invest the more I'm falling in love with this beauty. The journey of restoration is truly wonderful.


Attachments:
File comment: The dial cleaned up really nicely. Had to lightly sand the numbers with fine sandpaper to remove a layer of tarnish. Black sharpie pen took care of the black background that was dinged up.
dial.jpg
dial.jpg [ 99.63 KiB | Viewed 855 times ]
File comment: Just a reminder of the original mess.
chassisoriginal.jpg
chassisoriginal.jpg [ 99.46 KiB | Viewed 855 times ]
File comment: This capacitor ruined my image of what I thought a capacitor should look like.
004mfd.jpg
004mfd.jpg [ 93.51 KiB | Viewed 855 times ]

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Sun 14, 2018 7:45 pm 
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Hi Scott,

You did right I think. There are only about half a dozen of those caps total in the radio and you should replace them all.

Kudos on that dial plate. Mine needs attention too but I stopped because I became convinced I would do more damage than good. The writing is embossed into the plate on mine and back filled with a darker, not white, paint. To do it right it will have to be cleaned up painted and the writing repainted.
Your chassis was in far worse shape than mine, you've done an incredible job so far.

I'll edit this post with a PS: Regarding the alignment, I'm going to go out on a limb and say that if you put the B+ right, and the paper caps and the rotted wire, with workable tubes, and you have a sound power transformer and field/coil choke, that radio is going to play for you right out of the chute. I think you're going to find that the alignment isn't nearly as difficult as it appears and it will only make it better. I worried about that too.

Also, I didn't want that Majestic as such, by that I mean I didn't go looking for it. The restoration I inherited was torn completely apart. I felt the radio was sufficiently unique that if we are indeed in the business of restoring and preserving old radios, this one should be on the list. And I too must admit, the deeper into it I got the more I fell in love with it. It delivers a nice, mellow, rich sound. The 78 RPM turntable with that ancient horseshoe pickup delivers the most iconic sound. I was not disappointed. If I had another 1000sf in my house I would keep it along with a dozen others I would like to own/restore.

Tomie


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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Tue 16, 2018 4:52 am 
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I'm having trouble making some decisions on this restoration and I hope someone can offer some advice.

QUESTION 1 :
Regarding the tuning coils, (see photo) I took the covers off three of them and didn't find any capacitors or resistors within. Instead there were smaller coils. I've seen photos online of similar Majestic radios and they had recognizable capacitors and/or resistors within them. Any feedback regarding these coils within coils would be interesting.

QUESTION 2 :
Regarding a metal-encased 1mfd capacitor that goes between pin 4 (cathode) of the 27 tube and ground (see photos), I'm not sure if it is polarized, electrolytic or not. Because it looks similar to electrolytic polarized capacitors I've seen before, I'm assuming that's what it is, but I don't want to re-open this chassis once re-sealed. I'd appreciate any input to push me toward 1mfd polarized electrolytic or 1mfd mylar.

QUESTION 3 :
Regarding all wire wound resistors, they are within 5% but nearly 90 years old. Should I keep them or replace them?

QUESTION 4 :
The four original .5mfd wax paper caps in the unit were actually 0.25mfd, although the schematic calls for 0.5mfd. The 0.25mfd ones were definitely original, so I wonder if I should go with 0.22mfd or 0.47mfd. Feedback much appreciated.

Tomie, regarding the dial plate, mine is stamped with raised metal numbers but no white paint on them at all. I like the brass numbers on black look. The numbers actually shine. Regarding the replaceable capacitors, there are a total of only 11, including the new-found one listed above. I hope you are right about putting everything back to what it was originally and turning her on to find good reception. That day is coming soon, although I still haven't tested out the electro-dynamic field coil. Heck, I haven't even tested the transformer for shorts. At this point I'll buy whatever I need to make this thing work properly. I'll keep my fingers crossed it won't come to that. Definitely looking forward to that first power-up.


Attachments:
File comment: Hidden inside this metal box is a 1mfd capacitor. It runs parallel with a 36K ohm resistor.
11capacitor1.jpg
11capacitor1.jpg [ 93.14 KiB | Viewed 783 times ]
File comment: Opening the metal box to reveal the 1mfd capacitor.
11capacitor2.jpg
11capacitor2.jpg [ 52.74 KiB | Viewed 783 times ]
File comment: Ripped apart capacitor to determine a reading of 0.8mfd, but I'm not sure if it's polarized electrolytic or not. Advice appreciated.
11capacitor3.jpg
11capacitor3.jpg [ 78.75 KiB | Viewed 783 times ]
File comment: Shot of the tuning coil bank. The covers twist off counterclockwise.
11coil2.jpg
11coil2.jpg [ 54.2 KiB | Viewed 783 times ]
File comment: A look inside the coils revealed even smaller coils. I assume these are in good working order.
11coil.jpg
11coil.jpg [ 85.4 KiB | Viewed 783 times ]
File comment: Not sure if I should replace these wire wound resistors. After 85 years with 5% accuracy perhaps they'll go another 85 years.
11resistor.jpg
11resistor.jpg [ 107.42 KiB | Viewed 783 times ]

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 Post subject: Re: Majestic 90 Radio w/ 90-B chassis restoration from rats
PostPosted: Jan Tue 16, 2018 8:16 pm 
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Hi Scott,

QUESTION 1 :
In my instance, model 230A, the schematic shows a 500 ohm and a .04 mF capacitor in the bottom of two of the tuned frequency cans. In your instance there is no such designation on the schematic. But there is a separate coil and sure enough if you look at your picture, “11coil.jpg,” you will see that coil. There may be fixed capacitors in those cans but there is no way to measure them because they are tied across the coil. I would not worry about them.

I do not believe there is any additional service work that needs to be done to any of these coils unless one turns out to be shorted or opened when you finally heat up the chassis. I don't anticipate that to be the case. I think you can put the covers back on those coils and forget about them. There are no trim adjustments to be made inside of those cans. The wire in those coils is very delicate with a delicate insulation, it's best to keep them protected by the covers.

All tuning or alignment takes place on the tuning capacitor. You will see the trim capacitors as those hex-head adjustment screws. There are four of them plus there is a trimmer for the antenna. On mine that is a black knob on the very end of the tuning capacitor. I can't see it on your picture, “90btuningcapacitor.jpg,” but I do see the four coil trim capacitors. You will need to make a tool out of something non metallic to adjust them when the time comes. I used a piece of nylon ridged tubing and I heated an Allen wrench in the vice and forced the tube over the wrench until I had a nylon socket of the right size. Minimal, just enough, heat. I know others have used a nylon screw that has a female Allen hex head. You can search and find references to that here on ARF.

On page # 21 of the manual I gave a link to above, is a discussion of how to align the radio. It's very easy.

The only other thing I did first was clean all of those trim capacitors. They are mica and mine were filthy, I can't imagine yours are any different. I carefully removed mine one at a time and cleaned them. I use those small lens wipes on the mica, and alcohol on the actual metal surface until they are clean. The mica breaks easy, be careful. If you find one is cracked in two you will need to find replacement mica. It's around.

After they are clean I then run them all the way in until they are gently tight and then back them out about half a turn. The radio will work like that and so that's my starting point when I began to align.

I used a signal generator but the instructions suggest tuning in a radio station as a signal source. I think that is only because signal generators were not a common field service tool in those days and I anticipate that these expensive receivers may have been trimmed in at the customers house...if necessary. Your chosen long wire antenna will need to be trimmed to the receiver once it's in place. Getting a new radio was a very big deal in those days.

QUESTION 2 :
I did not trust the can capacitor. I left the can in place but I disconnected it and ran a separate capacitor and resister apart from it. That capacitor is not electrolytic. The only electrolytic capacitors are designated by the letters, A,B,C, and D on the schematic near the power supply.

QUESTION 3 :
They are a single piece of wire, if they check you are good to go. A couple of mine had shorted internally, probably got too hot at some point, they checked way too high so I swapped them out.

QUESTION 4 :
I went back with the print values. I agree some of those capacitors may have been factory, but someone had been into mine and things were all swapped around when I got it. I could not trust the repairman. Those values in those instances are not that critical. But there is a long discussion about that very subject here on ARF.

Interesting about the dial face, yours looks all in the world like white letters against a black background. Mine shows up and is capable of being read but it is not nearly as nice as yours.

Good luck with your project, it's coming right along. Looks great so far.
Tomie


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 Post subject: Help - Accidentally discarded chokes - need value recommenda
PostPosted: Apr Tue 10, 2018 8:39 am 
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So I accidentally discarded two inductors/chokes from my ongoing Grigsby-Grunow Majestic 90 radio revival. They look like black mushrooms and the schematic does not give their values. (Please see the schematic and choke location images.) Since I no longer have them, is there any way to derive their values? Any help would be greatly appreciated. Perhaps an experienced guess would help me get to completion on this. Thank you in advance.


Attachments:
File comment: choke between 27 tube and 45 tubes. unknown value.
schem1.gif
schem1.gif [ 13.26 KiB | Viewed 451 times ]
File comment: choke at 1 end of tuning capacitor. unknown value.
schem2.gif
schem2.gif [ 21.47 KiB | Viewed 451 times ]
File comment: Overall schematic
90b.gif
90b.gif [ 56.2 KiB | Viewed 451 times ]
File comment: Location in chassis.
chassis.jpg
chassis.jpg [ 103.13 KiB | Viewed 451 times ]

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