Teaberry Model T, Gemtronics GTX-2300/5000, Robyn T-123/T240
Mar 15, 2022 21:27:26 GMT -5
tecnicoloco2000 likes this
Post by oldgeezer on Mar 15, 2022 21:27:26 GMT -5
Unlike many failing solid-state 1970s CBs, these CBs usually work, but are still a risk. All these radios have the same chassis and are Tube design. Three capacitors may fail and the value is .1uF @ 600 volts. These are oil capacitors and are responsible for guessing 90% of these radios failing to operate. I would replace all the electrolytic capacitors, but the Elna stock caps never failed on the four radios I owned. For the most part if the channel display works the radio will work unlike many 1970s solid-state CB radios. Very few have channel display issues.
These radios when in good condition produce 4 watts and swing to 14-16 watts. 16 watts is enough power to drive any linear to full power output. These CBs have nice sounding ultra clear receive audio with the larger 4 inch speaker and tube audio. The receive is sensitive enough using a RF amp 6LB8 pentode section with a high 6200 transconductance and fairly quiet receive. 40 channel models are preferred and sell on eBay. However the Robyn T-240D can be expensive. Except for ultra expensive Browning MKIV and Tram 201A the 40 channel models I mentioned are the only other tube type CBs I know of. Three variations exist. They can be identified a first model has two small IF cans in front of the power transformer. Second model has one large IF can in front of the power transformer. Third has a ceramic 6kHz IF filter below the chassis. This may be only installed on the Robyn CBs.
Note- none of the forementioned radios have a noise limiter switch, but noise limiter is active all the time. I would not buy a CB without a noise limiter.
The RCA 6BA6 have better receive vs the stock Matsushita 6BA6 in the Robyn, Gemtronics, Colt and Teaberry. The Matsushita 6BA6 draw too high a plate current and lower the receive. I used RCA 1950s square getter, but newer RCA 6BA6 will work well. These receivers are a little quieter on receive vs most SS CBs, but the Robyn and Colts Midnite Special have receive RF controls. Variable on Robyn, Hi-Low on the Colt.
The 6BQ5 transmit tube (left side) can be sensitive to the brand, the 6BQ5 audio tube (right side) is not. A Sylvania 6BQ5 works ok as the transmit tube in these CB radios with about 3.5 watts carrier and 14 watts peak vs 4 watts carrier and 16 watts peak using a Matsushita 6BQ5. For some reason some only have 12 watts peak. The Matsushita 6BQ5 is factory stock, but new is expensive. Good used are available on eBay. A potentiometer is next to 12AX7 tube. Turn up clockwise for highest transmit audio.
The GE short plate 7025 and JJ E83CC are the best 12AX7. Both produces slightly better (clear) receive audio and better transmit audio. It is a low hum spiral wound filament that is superior to the 12AX7 for the microphone amp and removes any AC hum. The 12AX7 is used for receiver audio and microphone amplification.
The Robyn T-240D sell for about $200 to $450 in good condition. It has an RF gain and Range Expand switch the others do have but the range expand always on other manufactures. The 40 channel Gemtronics and Teaberry sell for about $100 to $150 on eBay. Many of these radios have marks around the channel select dial due to fat fingers- a new 1.25 inch knob usually covers up the marks.
These radios when in good condition produce 4 watts and swing to 14-16 watts. 16 watts is enough power to drive any linear to full power output. These CBs have nice sounding ultra clear receive audio with the larger 4 inch speaker and tube audio. The receive is sensitive enough using a RF amp 6LB8 pentode section with a high 6200 transconductance and fairly quiet receive. 40 channel models are preferred and sell on eBay. However the Robyn T-240D can be expensive. Except for ultra expensive Browning MKIV and Tram 201A the 40 channel models I mentioned are the only other tube type CBs I know of. Three variations exist. They can be identified a first model has two small IF cans in front of the power transformer. Second model has one large IF can in front of the power transformer. Third has a ceramic 6kHz IF filter below the chassis. This may be only installed on the Robyn CBs.
Note- none of the forementioned radios have a noise limiter switch, but noise limiter is active all the time. I would not buy a CB without a noise limiter.
The RCA 6BA6 have better receive vs the stock Matsushita 6BA6 in the Robyn, Gemtronics, Colt and Teaberry. The Matsushita 6BA6 draw too high a plate current and lower the receive. I used RCA 1950s square getter, but newer RCA 6BA6 will work well. These receivers are a little quieter on receive vs most SS CBs, but the Robyn and Colts Midnite Special have receive RF controls. Variable on Robyn, Hi-Low on the Colt.
The 6BQ5 transmit tube (left side) can be sensitive to the brand, the 6BQ5 audio tube (right side) is not. A Sylvania 6BQ5 works ok as the transmit tube in these CB radios with about 3.5 watts carrier and 14 watts peak vs 4 watts carrier and 16 watts peak using a Matsushita 6BQ5. For some reason some only have 12 watts peak. The Matsushita 6BQ5 is factory stock, but new is expensive. Good used are available on eBay. A potentiometer is next to 12AX7 tube. Turn up clockwise for highest transmit audio.
The GE short plate 7025 and JJ E83CC are the best 12AX7. Both produces slightly better (clear) receive audio and better transmit audio. It is a low hum spiral wound filament that is superior to the 12AX7 for the microphone amp and removes any AC hum. The 12AX7 is used for receiver audio and microphone amplification.
The Robyn T-240D sell for about $200 to $450 in good condition. It has an RF gain and Range Expand switch the others do have but the range expand always on other manufactures. The 40 channel Gemtronics and Teaberry sell for about $100 to $150 on eBay. Many of these radios have marks around the channel select dial due to fat fingers- a new 1.25 inch knob usually covers up the marks.
