Majestic Model 90 Restored

This was a project! All came out well. These TRF receivers are a PITA to get to work right. I also had to replace the gain control (went with a smaller value pot). Also I thought the audio was a bit muffled, so I changed the detector plate cap to a .001mf which made a nice difference. The Bluetooth connection was tricky as I had to use a DPDT switch to switch the grid and cathode connections. The power supply came to me in pieces...but all came out well.

[@ethandickerman2715]

This video was very informative. I recently purchased the same radio, and I plan to restore it over the coming months. I am not crazy about the bulky power supply and ballasts. Can you tell me more about your conversion process? I am also curious to know more about the Bluetooth addition. Would you be able/willing to share schematical drawings or point me in a direction to learn the process?

[@pf_n1ps]

I replied to your email too. OK....on your 2 questions: 1. The ballast. I tied 2, 2 amp transformers together as an autotransformer to reduce the 120VAC down to 80 V. One was 24V and the other was 16V IIRC. I found this on the web...not my idea (the poster used a 24V and a 12V, which I found was not enough as the filament voltages (2.5V) were too high, thus the 16V. I did not want a toaster in a wood radio. Bad combo. I put the transformers on a metal chassis and added a fuse to it. The transformers run luke warm. 2. On BT, as a rule I take a stereo output from the BT and tie it to the pre-amp in a radio usually at the volume pot high side. I like to use 600 ohm resistors off each side of the stereo connection and tie them together into a coupling cap of about 2-5 uF I should have a schematic of this I can send to you. I then use a SPDT switch, to switch between the radio (detector output) and the BT output into the G1 grid of the radio (volume pot etc). In some cases, there isnt a pre-amp and I had to build a transistor amp to bring up the audio level for the speaker audio amp. In this case we had something different with the Majestic as the detector uses a triode power detector. The tube runs at cut-off, effectively creating a detector. My fix for this was to use a DPDT switch and switch in a much lower value cathode resistor (1.8K, I believe was what I used), which now makes the triode a class A amp when in BT mode.. I added the switch on top of the chassis near the 45s. I used mini coax for all connections, terminating the shields ONLY at the switch side to reduce any ground loops. In the radio I worked on, I replaced all caps except a few of the micas. Most of the resistors were also replaced as they were way off or open. Also, if you are lucky, the neutralizing caps are set OK. These triode TRF receivers are very touchy. I had to retune all of them in this case and it was a PITA to get them set right. Hope this helps. Peter