| ::::::::::::::::::::::::I have a Majestic radio model 70B with 7P6 power supply. The voltages are present for the 5Vpower, 1 1/2 V A.F, 2 1/2 det and 1 1/2 RF, but no +50, +96 or +260. All of the tubes light up and the radio is in very good shape (the old wiring has been replaced). :::::::::::::::::::::::: ::::::::::::::::::::::::I suspect the transformers that generate these voltages or a "common" feed to these transformers. :::::::::::::::::::::::: ::::::::::::::::::::::::I would appreictae any information that anyone can share. I have .pdf files of the chassis showing graphics as well as a schematic. :::::::::::::::::::::::: ::::::::::::::::::::::::Grigsby-Grunow Co. ::::::::::::::::::::::::Model: 70B ::::::::::::::::::::::::Power: ::::::::::::::::::::::::Chassis: ::::::::::::::::::::::::Circuit: ::::::::::::::::::::::::Year: Pre 1932 ::::::::::::::::::::::::IF: ::::::::::::::::::::::::Tubes: ::::::::::::::::::::::::Bands: ::::::::::::::::::::::::Resources ::::::::::::::::::::::::Riders Volume 1 - MAJESTIC 1-5 ::::::::::::::::::::::::Riders Volume 1 - MAJESTIC 1-10 ::::::::::::::::::::::::Riders Volume 1 - MAJESTIC 1-24 ::::::::::::::::::::::::Courtesy Nostalgia Air ::::::::::::::::::::::::Courtesy Nostalgia Air ::::::::::::::::::::::::Courtesy Nostalgia Air ::::::::::::::::::::::::Courtesy Nostalgia Air :::::::::::::::::::::::: ::::::::::::::::::::::::I am persistent and not ready to give up on bringing this radio back to life. :::::::::::::::::::::::: ::::::::::::::::::::::::Thanks in advance for all of your help. :::::::::::::::::::::::: ::::::::::::::::::::::::Terry ::::::::::::::::::::::: :::::::::::::::::::::::Hi Terry, ::::::::::::::::::::::: :::::::::::::::::::::::One of the first things I would check would be continuity of the speaker field winding. If it is open you will not get any +B voltages. ::::::::::::::::::::::: :::::::::::::::::::::::Radiodoc ::::::::::::::::::::::: ::::::::::::::::::::::Radiodoc, ::::::::::::::::::::::I have continuity from the LARGE pins on the 80 tube rectifier to the speaker and have continuity of the speaker. :::::::::::::::::::::: ::::::::::::::::::::::When I measure the AC voltage at the large pins of the 80 tube I get 3.8V and 356V at the small pins. Is this 400 ohm resistor in the bottom part of the power supply? :::::::::::::::::::::: ::::::::::::::::::::::Any help woul be appreciated. :::::::::::::::::::::: ::::::::::::::::::::::TF ::::::::::::::::::::: :::::::::::::::::::::Hi Terry, ::::::::::::::::::::: :::::::::::::::::::::The AC voltage on the large (filament) pins of the 80 should be 5 volts. You said you had continuity from the large pins to the speaker (this goes through the filter choke). Was it around 400 ohms as the PS schematic shows? Have you changed the filter capacitors A,B,C & D? If the filters are original they are probably bad, shorted even. With the power off check for continuity between the small pins of the 80 tube and the black (ground) wire from the power supply. Measure for plus voltage between one of the big pins of the 80 to the black (ground) lead to see if you have voltage. ::::::::::::::::::::: :::::::::::::::::::::Radiodoc :::::::::::::::::::: ::::::::::::::::::::Radiodoc, :::::::::::::::::::: ::::::::::::::::::::I have 378 ohms from the speaker to the large pins of the 80 rect. No, I have not replaced the caps, but I ordered them today. I have continuity from the small pins to the ground ( I assume it is the top connection of the 'condensor bank" as shown on the 7P6 power supply (I traced the "neg" connection on the terminal strip back to this connection as reference. If this is not correct, please let me know. :::::::::::::::::::: ::::::::::::::::::::I do not have any voltage from the big pins of the 80 to the negative (ground) lead. :::::::::::::::::::: ::::::::::::::::::::I hope this helps you. :::::::::::::::::::: ::::::::::::::::::::TF ::::::::::::::::::::: ::::::::::::::::::: :::::::::::::::::::Terry, ::::::::::::::::::: :::::::::::::::::::With filament voltage on the 80 filament pins and high AC on the 80 plates there should be a plus voltage on one of the big pins to ground. It is possible, since you have not changed them, A or B capacitor or both are shorted and possibly damaged the 80. Just for the heck of it you may want to check the resistance between either of the big pins to ground (black wire). The resistance should be fairly high. May want to do the same from the red wire to the black wire. If you can locate the wires from the A and B capacitors, may want to disconnect these and see if you have plus voltage on the big pins of the 80. ::::::::::::::::::: :::::::::::::::::::Radiodoc ::::::::::::::::::: :::::::::::::::::::Radiodoc, :::::::::::::::::: ::::::::::::::::::No + voltage from the big pins of the 80 to ground. The 80 has continuity on the big pins. The small pin voltage is now 715V AC (I didn't do anything either) just remeasured the voltage on the small pins. The big pin voltage is now dropped to <1.0 volt. :::::::::::::::::: ::::::::::::::::::The resistance of the big pins to ground is 230 ohms. I disconnected the A and B capacitors and still do not have + voltage on the big pins to ground. :::::::::::::::::: ::::::::::::::::::Is the 80 the culprit? I am at a loss..... :::::::::::::::::: ::::::::::::::::::As always, any help is grealy appreciated. :::::::::::::::::: ::::::::::::::::::Terry ::::::::::::::::: :::::::::::::::::Hi Terry, ::::::::::::::::: :::::::::::::::::You may not have had a good connection with the meter probes. Between the black lead (center tap of the HV AC winding you should measure approximately half of the 715 volts or 357 VAC. The 80 could be bad. If you know someone who has a tester may check it. There is the possibility the socket is bad. Measure the voltage on the big pins of the 80 in the socket and measure the voltage on the socket wiring tabs. I have had radios with bad sockets sometimes. If the voltage is the same, try removing the 80 and measure the AC voltage on the big pins and see if it measures around 5 volts. I'm going to study the schematic for the power supply again. I am concerned about the 230 ohms from the big pins to ground as this is too low. Please be very careful testing as the voltages in tube type power supplies can be lethal! I use the one-hand-behind-my-back approach. ::::::::::::::::: :::::::::::::::::Radiodoc ::::::::::::::::: :::::::::::::::::Radiodoc, :::::::::::::::: ::::::::::::::::I discovered a loose wire from the large pins to the plate trans. It is now reconnected. :::::::::::::::: ::::::::::::::::I removed the 80 and measured the pins in the socket. 5V AC on the large pins - pin to pin and 716V AC on the small pins - pin to pin. :::::::::::::::: ::::::::::::::::At one point, the resistance from the large pins to ground was 412 ohms, but now it is back to the previous reading. The shock of my life was last night BFORE you sent me the warning. I am still here but wiser. :::::::::::::::: ::::::::::::::::As always, any help is greatly appreciated. :::::::::::::::: ::::::::::::::::Terry ::::::::::::::: :::::::::::::::Hi again Terry, ::::::::::::::: :::::::::::::::The 230 ohms from the big pins of the 80 to ground still bugs me. With the radio unpluged try disconnecting the terminal strip coming from the radio from the power supply and with the 80 out of its socket and caps A & B disconnected, measure the resistance from the big pins of the 80 to ground. The resistance should be high. This pretty much isolates everything from ground. ::::::::::::::: :::::::::::::::Radiodoc :::::::::::::: ::::::::::::::Radiodoc, :::::::::::::: ::::::::::::::Here is some news. After I checked the resistance as you suggested, I put the power strip back on. I powered up the radio and I got a distintive hum coming from the speaker. I attempted to tune in a station. Again, I got close but no cigar. :::::::::::::: ::::::::::::::I checked for loose wires and I think I have one from the terminal strip up to the chassis. I will check out the wires and will advise tomorrow. I am encouraged by the progress. :::::::::::::: ::::::::::::::Terry ::::::::::::::: ::::::::::::: :::::::::::::Terry, ::::::::::::: :::::::::::::Getting some hum from the radio is encouring. What I was attempting to do was isolate everything from the plus voltage path that could load it down.. I was going to suggest a 10K about 10 watt resistor from the red wire to the black wire for a load on the plus supply with the radio completely disconnected. Getting the power supply working right and then worry about the possible problems with the radio. ::::::::::::: :::::::::::::Radiodoc :::::::::::: ::::::::::::Radiodoc, :::::::::::: ::::::::::::I was only able to get 2-6.8K resistors +/- 10% at 15 watt. I have them soldered in series (13.7K ohms) and before I solder them to the red and black wire, I WANT TO BE SURE that I am looking at the same two locations on the power supply wiring diagram that you are. :::::::::::: ::::::::::::Since I rewired the device, I went from wire to wire location by location, so what you call a black may be a red to me. I wasn't worried about color as I should have been. Stupid move on my part. :::::::::::: ::::::::::::On the plate transformer, I interpret these wires to be the top two terminals on the left. Please advise if this is correct before I solder the resistor bank to the power supply. :::::::::::: ::::::::::::This may seem dumb, but .....I have to ask. You are considerably more knowledeable than I am. :::::::::::: ::::::::::::As always, your help (and patience) is greatly appreciated for helping me step through this problem. :::::::::::: ::::::::::::Terry ::::::::::::: ::::::::::: :::::::::::Hi Terry, ::::::::::: :::::::::::I hope I have not confused you too much. I had been looking at schematics for this power supply in two different books. It dawned on me you were probably using the schematic from this site so I decided to download it and print it out since is showed the physical wiring too. Might know it! My printer in the shop let me know the toner was out...the printout showed this. I will have to take the file home and print out. It also dawned on me that the wire colors may have faded out. The plus voltage point is the +220V and the ground is either the junction between the green (2170 Ohm) resistor and brown (1000 Ohm) resistor on the old wiring or the junction between the blue (4180 Ohm) resistor and the brown (1000 Ohm) resistor. I just wanted some sort of load on the +220 volt point while testing the power supply with the radio chassis disconnected. When I get a printout of the wiring diagram that I can read I will get back to you. ::::::::::: :::::::::::Radiodoc :::::::::: ::::::::::Radiodoc, :::::::::: ::::::::::The 4180 resistor measures only 348 ohms. I will try to get a functional replacement tomorrow and will advise. The 15000 ohm and the 1000 ohm resistors on the power supply top measure OK. :::::::::: ::::::::::Terry ::::::::::: ::::::::: :::::::::Hello Terry, ::::::::: :::::::::To get close to the 4180 you can use resistors in parallel or in series. In series the values of the resistors will add and in parallel the total will be somewhere less than the smallest value. Another reason for putting a load on the power supply when testing it disconnected from the radio chassis is that capacitors can retain a charge after the power is removed unless there is a load to drain the charge off them. You can get a nasty shock. Just be careful and most of all don't get discouraged. ::::::::: :::::::::Radiodoc :::::::: ::::::::Radiodoc, :::::::: ::::::::I decided to retrace my steps since I found a loose connection. :::::::: ::::::::From the big pin to ground is now 93VDC and the resistance from the big pin to ground is 390 ohms. :::::::: ::::::::Just for your information. :::::::: ::::::::Terry ::::::::: ::::::: :::::::Hi Terry, ::::::: :::::::Over the weekend is looked the schematic over and was trying to figure out where the 230 ohm or so could be coming from. Your latest post you stated you measured 390 ohms from the big pins to ground. This is almost the value of the choke coil. With the caps, receiver chassis disconnected and our 10K load resistor removed, measure the resistance at the 80 big pins to ground and the +220v position to ground and see what the resistance is. We may have a shorted winding in the choke to ground or a wire from the choke to the +220 volt point shorted to ground. ::::::: :::::::Radiodoc :::::: ::::::Radiodoc, :::::: ::::::From the big pins of the 80 to ground is 367 ohms. From the 220V position to ground is 2.1 ohms. :::::: ::::::Terry ::::::: ::::: :::::Terry, ::::: :::::I know the 2.1 Ohms is not right as is the 367 Ohms. If you can, disconnect the leads of the choke. This will isolate it from the circuit and then measure the resistance from either lead to ground. A low resistance reading will indicate the choke coil is shorted to the metal frame of the choke. If the reading is infinite on both choke wires, will have to look for a short in the +220 volt wiring from the choke. ::::: :::::Radiodoc :::: ::::Radiodoc, :::: ::::I disconnected both wires from the choke Each wire is infinite to ground. Choke wire to choke wire is 368 ohms. :::: ::::Terry ::: :::OK Terry, ::: :::I bet the resistance reading (I hope) from the 80 big pins to ground should be high now. I also bet there is a short in the wiring from the choke to the +220 point. That would result in our measuring 300 plus Ohms before. Could be a pinched or cut wire there or insulation off the wire letting it get against ground. ::: :::Radiodoc :: ::Radiodoc, :: ::If I remember, the resistance from the big pins to ground was infinite when I took the choke wires off to verify the resistance of the choke. I'll let you know tonight.The choke wires are still disconnected. Let me know if I need to solder them back in place. :: ::Terry ::: : :Hi Terry, : :If I remember correctly you said you measured 2.1 Ohms on the +220 volt point. The resistance there should be high. You can resolder the wire to the input to the choke. I would leave the wire from the choke to the +220 volts disconnected until what is causing the 2.1 Ohms reading is found. The best I can tell from the wiring diagram is a wire goes from the choke to a capacitor (you did disconnect this cap) in the capacitor bank and then a wire from there to the +220 volt contact where the radio cable connects. : :Radiodoc Radiodoc, I will reconnect the right hand tap of the choke to the condesnor bank tap (third from bottom) tonight. This will leave the center tap of the choke disconnected. I want to make sure that when I say ground (it is the top connection on the condensor bank.) This is where I measured the 2.1 ohms from the 220V pin to. I looked for pinched wires, contact with the outer case and wires last night. I couldn't find anything. Could a poor solder joint give me a resistance reading that was false? I am fishing here... Terry |
| Majestic Model 70B | |
 Terry | |
  Norm Leal | |
| Radiodoc | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Thomas Dermody | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Terry | |
| Radiodoc | |
| Thomas Dermody | |
| Terry | |
| Thomas Dermody | |
| Thomas Dermody | |
| Thomas Dermody | |
| Terry | |
| Thomas Dermody |
| < Previous Message | Index | Next Message > |