This is my latest acquisition. I came across it by chance at a antique store accross the street from my office! I swore I would never buy any radio from a city antique store because of their over pricing, but this baby was $110 US! They gave me a discount too! So I wound up spending 100 bucks for a radio that needed an 80 rectifier tube and some dusting off!
It is a seven tube TRF AC radio from 1929. It has five stages of tuned RF amplifier circuitry utilizing a five ganged tuning capacitor. It uses type 27 tubes for RF amplification. Oddly enough, three places I looked at claimed that they are triodes. By this time tetrodes were available. According to the schematic, kindly provided to me by Nostalgia Air, the first three stages are connected to a potentiometer at the cathodes. This changes the bias on them to provide volume control. This consequently also makes for sensitivity control. Hence the need for it to be aligned and neutralized at full volume. Otherwise the full volume setting for weaker stations will cause it to oscillate. With five stages of TRF, this is not hard to do.
This unit has what looks like a ten inch "dynamic" speaker. I did not expect the high quality of sound that came through it, to come through it! It isn't HI-FI, but it is real good sounding and powerful. This can, I believe, be attributed to the push pull 45's in the output stage. The amplifier is transformer coupled. I take it that the transformers are of very high quality to be able to perform that well. I think that it perhaps puts out about three to five watts of power. It is quite clean sounding for what looks like it is a class B push pull. There is also no audible hum like I have with my other radios of the thirties with electrodynamic speakers. At any rate, I think it is my best piece.
Here are some pictures:
The original owner evidently replaced the grillecloth. I will of course purchase the correct cloth from www.grillecloth.com. I have seen four other peoples' Model 90's (three on the net and one in person) and they all agree that the one I am going to get is correct.
This is the speaker. There are plenty of plates identifying
this model and all are intact. There is even a paper tag on the right of
the chassis (from the back, on the inside wall of the cabinet) identifying
the cabinet as belonging to the models 90 through 103 (if memory serves).
The escutcheon. It is missing a nail on the bottom, but I found a place that sells them. I would like to polish this and leave some traces of the rust in the grooves. I did this to my RCA's dial plate and it has a very nice effect, sort of the way the name "Majestic" stands out of this one. As you can see, the cabinet seems to need very minor work to restore. On the lower right hand of the above picture you can see the scratch that there is on the front. That is the extent of the "damage".
More to come!
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