[Jim Dutridge]

I have a model 27 that someone painted the cabinet brown. I've been trying to sell it for awhile but the cabinet paint makes it difficult. I did do a chassis restore on it and I must say that with even the shortest antenna it is a very sensitive radio.

[Eliot Ness]

Richard, Radiotrope was one of the many nameplates coming out of the Marion, Indiana U.S. Radio and Television Corp plant.
Gloritone was probably the better known brand coming from them.

[Arran]

Another make I have seen from U.S Radio and Television was Apex Electric, or U.S Apex, the badge on some of those had a pointed mountain top shaped logo, with A.P.E.X forming the crest with letters. The model 27 I have was built by Grimes-Phonola, likely under license, either that or they bought the chassis in knock down form, they made other U.S. R & T models too, though I don't own any, they also had a relationship will Wells Gardner, but they started as a Canadian affiliate of David Grimes, as the name reveals. Phonola owned their own furniture company so they could build whatever cabinet design they, or one of their private label contractees, wanted.
Regards
Arran

[radiorich]

Hello John,
Thanks for the information and Arran I have heard of Wells Gardner and I have heard of Apex but I did not know they had old radio mostly audio tape .

Sincerely Richard

[dconant]

Hello, The radio is playing now using the repaired antenna coil.

MrFixr55 you stated a while back I might need to add a resistor across the two end terminals of the volume pot. What would be the purpose of that?

Thanks,
Dan

[Arran]

Richard;
I believe that you are thinking of Ampex, they were magnetic audio tape, and tape machine people. I have some 8 tracks that were manufactured by them, they are the ones where the rubber on the pinch roller goes gummy or crumbles.
Regards
Arran

[MrFixr55]

Hi Dan, 

Sorry for the late reply.

I believe that you had a 2K pot for the volume control.  If we use the circuit where we vary the volume by varying the cathode bias of the RF Amp tube(s), that pot is part of a voltage divider.  the value of pot specified in that version of the schematic was 1K.  Putting a 2K pot in the "voltage divider" will change voltages at other "taps" in the divider.  Putting a 2K resistor in parallel with the pot will restore the correct voltages in the divider.  In addition, bridging with the 2k resistor will lessen the current passing through the pot and will extend its life IMHO.  I updated my previous post because I drew the suggested add-in resistor in the wrong spot. I updated the drawing and highlighted the circuit in question.  It is further reproduced here with further improvements:
   

The yellow highlighted area shows the circut path from the rectifier cathode back to the center tap of the transformer (the complete electron path.  Note that Chassis ground is not the endpoint of the circuit, the center tap is.  the center tap is actually at a more negative voltage than chassis ground.  This is to provide the "C-" or grid bias for the output tube.  This method was very common in the 1920s and 1930s.  Later radios used cathode bias resistors, as the "voltage dividers" tended to suffer open resistors which would stop operation or produce weak, greatly distorted sound.

Looking at the highlighted path, the current path is from the rectifier, through the filter, through the loudspeaker field coil, through the volume control and other resistors to the center tap of the transformer Rectifier plate winding.  Note the other series of resistors from ground to B+.  Changes in resistance along the highlighted path also changes voltages across "taps" in that voltage divider.  Since the circuit that we are reproducing is expecting 1K Ohm for the section of the divider that consists of the volume control pot, I suggest bridging the 2K Ohm volume control pot with a 2K Ohm 5 Watt resistor.

These "screen grid" TRF sets with biased detectors tended to be quite sensitive.  This is why the second version of this set added another 8KOhm section of the pot to shunt the antenna input.  In these sets, volume is lowered not only by increasing cathode bias but by also shunting the antenna inout progressively to ground as volume is lowered.

The advantage of TRF sets were:

• Simplicity
  
• Better bandwidth, greater fidelity
  
• Easier to align
  

The disadvantages included:

• Selectivity not as good as superheterodyne sets
  
• RF gain at higher frequencies.  By heterodyning and converting all signals to a lower "IF" frequency, gain and selectivity were superior in a superheterodyne.  However, fidelity may have suffered in superheterodyne sets, especially in earlier sets with low IF frequencies of between 48 and 250 KHz.
  

Hope this helps and glad you got this old-timer playing again!

[dconant]

Thank you MrFixr55. I get it.

Dan

[dconant]

What I didn't tell you guys was since the radio appeared to be a cross between the early and late schematics and several unique parts missing and a hodge podge of wiring and being fairly simple, I removed everything from the chassis except the tube sockets. I then set out to repair the antenna coil and then rewire the chassis and replace all caps and resistors. Not many of either. The main candohm was totally shot. I rewired the chassis according to the early schematic. The only problem I had was one of the antenna coil wires (gird cap) got shorted to the can. Once that was fixed it play nicely. I always wanted to try that. I did make notes for the transformer connections.

Dan

[MrFixr55]

Congrats on restoring this piece of history, Dan, especially the fact that you practically completely rebuilt it! This will now play for many more years and will surely see its 100th birthday!

On to the next one!

[radiorich]

Hello Dan,
Wow, that wonderful news it sounds like you have been very busy !

Sincerely Richard