My stepdaughter brought home a Majestic Model 70B and wants me to restore it for her. Problem is that it came with the wrong power supply (a 9P6). I'm pretty sure a Model 70B must use a 7BP6 power supply. Can someone confirm this for me? The chassis serial is 7B-552707.

Also, does anyone know of a source for a restorable 7BP6?

Thanks much,

Dave

:My stepdaughter brought home a Majestic Model 70B and wants me to restore it for her. Problem is that it came with the wrong power supply (a 9P6). I'm pretty sure a Model 70B must use a 7BP6 power supply. Can someone confirm this for me? The chassis serial is 7B-552707.
:
:Also, does anyone know of a source for a restorable 7BP6?

While I can't answer your question this very minute, a friend of mine just told me about the Majestic 70B he's about to get his hands on...it's in great shape, perhaps only needs a new power cord. I may be confusing it with a Crosley record cutter/player/radio (forgot to note the model).

Once he has it in hand (if he doesn't already have it), I should be able to find out what the power supply in it is. I recommend an email to me, as I may forget to return here in a reasonable timeframe.

The model 70 uses the 7BP6. The 9P6 has a higher B voltage, and different filament voltages.

You can occasionally find the 7BP6 on eBay. Search under Grigsby or Majestic Power, Majestic Tube, or Majestic Radio.

My model 180 originally took the 8P6, but it was missing when I got it. I built my own power supply for it. I was lucky in that I found an old transformer with a heavy duty primary winding. I then wound my own filament secondaries using 12 gauge stranded wire. If you wish you can make your own power supply, too. If you disassemble a transformer to make new voltages, removing the laminations will be a trick if they're varnished. Heating in a 150-200 degree oven can help. Be careful to not heat the transformer hotter. AES may have some 1.5 volt transformers, though I think that the lowest they go is 2.5 volts. If you wind your own transformer, wrap it with friction tape, which can be found at your hardware store. Friction tape is black cloth electrical tape. It is strong and durable.

Actually....AES does sell a power transformer with two 2.5 volt windings and a 5.0 volt winding. What you could do is use the 2.5 volt windings for most of the radio tubes, and use the 5.0 volt winding for the rectifier. Purchase a separate 5.0 volt center tapped winding for the output tubes. You need two separate 1.5 volt windings. For that, use one 2.5 volt winding to feed both the 2.5 volt tube and the 1.5 volt RF tubes. Omit one of the 20 ohm resistors you see across either the 2.5 volt filament leads or the 1.5 volt filament leads. Since the 2.5 volt tube and the 1.5 volt tubes are both going to the same winding, you only need one balancing resistor. The 2.5 volt tube actually has an isolated cathode, so the balancing resistor isn't really necessary for it, but it's there for extra hum balancing (nice radio). Use two resistors of equal value to reduce the 2.5 volts down to 1.5 volts for the 1.5 volt tubes. For the remaining 1.5 volt tube use the other 2.5 volt winding. Use two resistors of same value on each leg of the 2.5 volt winding so that you reduce the voltage down to 1.5 volts. ....And as I said before, use a separate 5.0 volt center tapped transformer to feed the output tubes.

This all sounds complicated, but it really isn't. You can build it in an attractive metal or wooden box, and then spray it with krinkle finish to make it look more original. Majestic type G-80 globe tubes are often available on eBay, too. If you want, build the power supply as a regular chassis, with no enclosure, and then you can marvel at the glow of the G-80 tube.

T.