I bought my first tape recorder when I was about 12 or 13 with my paper route money. It was a used 1957 Bell Sound Systems BT-205IB. It is a mono recorder but has a stereo half-track head with a separate preamp output to play prerecorded stereo tapes. It wasn't much but it got my interest going in audio. I eventually upgraded to a Sony TC-366 which I still have.
The biggest downfall of the BT-205 was there was no automatic shutoff. If I left my room and forgot I was playing a tape, I would come back and find 1" snippets all over the floor. Every time the reel spun around at full speed it would slice off a snippet on the tape head cover. I eventually added an external timer that would shut off the AC at the appropriate time.
There were two models of this recorder, a BT-205IB and a BT-205OB. The IB had a stacked stereo head and the OB had an offset or staggered head. I never did buy any stereo tapes to play on it.
RT-205 Monaural Tape Recorder
Years later I found a good condition RT-205 which is the same tape recorder without the stereo head and preamplifier. It still has the tag on the volume control but did not come with a manual.
I still have my original BT-205IB manual which I scanned and cleaned up. Since I couldn't find a RT-205 manual on-line I did some editing and created my own version for the RT-205. I don't know that it is anything like the original manual and I had to make some guesses on the parts list. What is interesting is the schematic says RT-205 but clearly shows the preamplifier for channel #2 which I removed in this document.
Bell Sound Systems recreated RT-205 Instruction Manual
BT-205IB Stereophonic Tape Recorder
Later I found a well used 205IB so I bought it with the intentions of swapping the preamp and head to the RT-205. Years later I finally got around to working on this tape recorder and decided to simply restore it. The supply reel platform was broken but glued together nicely. The AC cord was brittle and someone had done some poor repairs that I needed to back out. The biggest issue was it would not rewind. This has a complex push switch arrangement and the top of the phenolic which holds the rewind contact had snapped off. I made a new contact and used epoxy to glue it on to the phenolic as seen in this photo.
I reformed the capacitors by bringing it up slowly on a variac and it came back to life. The next issue was it was missing the record lock mechanism but I had one in the RT0205 for a pattern. It was made of brass with a leaf spring across the front. I made a new one from brass and chose to just use open cell foam for the spring. It looks identical and works great.
Here is the restored BT-205IB. Note the record lock looks identical.
I scanned the manual and did extensive cleanup. There is one digit missing from a part number and I had to guess at one digit on a voltage reading.
Bell Sound Systems BT-205IB Instruction Manual
There is very little information on Bell Sound Systems tape recorders on the internet. I found this ad for Bell Sound Systems which shows this tape recorder on a Bell Sound Systems amplifier/speaker cabinet.
The 1958 issue of Fawcett Hi-Fi Tape Recorder had these two references to the monaural model RT-204.