Bravo!

Thanks! I figured this thing wasn't going to be too hard to get going seeing as there isn't much to these old TRF sets, mainly all I had to do was replace a bunch of old crumbling wiring which was pretty easy because all I had to do was steal the wiring out of an old junk desktop computer power supply and use that to replace the old crumbling wiring in the radio and I was pretty much set to go! :yes: :thmbsp:

I hope all your work bears fruit. I've always loved old radios. I look forward to hearing that your radio works. I still have one radio project left.

Yes, me too. I also have a GE L-640 and a Philco 116B up next to finish up and then I have someone on another forum I'm a part of that's sending me a couple more radios to monkey with, and then someone else from that same forum has an eye out for me for some radio parts that came from someone that was part of the Schenactedy Radio Club that recently passed away. So I'll be quite busy for a while. :thmbsp:

When you say new speaker it makes me wonder; have you made sure the speaker impedance is correct in your replacement. 20's speakers were usually some where in the 1k-10k impedance range and new ones are usually 3-8 ohms (which won't sub for a high impedance speaker without a matching transformer).

Don't worry, I found on eBay a speaker that was the same exact speaker as what was in the original speaker box for this radio, which was an American Bosch Model 612 Dynamic Speaker.

Now if the person I bought it from on ebay will actually just ship the speaker (as I have yet to get a notification about it being shipped yet from eBay) I will be good.

See link below to see the speaker I bought for my radio.

https://www.ebay.com/itm/333554478891

OK so I took and hooked up my radio's original speaker up to the radio (I had to use an aligator clip lead with a mini banana plug on the end to hook one of the leads from the speaker up to the radio as the original pin plug was missing on one of the speaker leads and I powered on the radio and it actually worked (albeit with a loud hum) which I assumed was because the set needed neutralizing so I got my signal generator out and set it to 1400 KC and I was able to get the hum to partially clear up, but it still had some hum to it.

So I went to turn the radio off and check something out underneath the power supply to see if maybe a ground wire was loose or something, and there wasn't and so I went to turn the set back on again and now the output tubes aren't glowing anymore and there is absolutely no audio coming out of the speaker except for a little crackling noise when I wiggle the output tubes in their sockets.

I checked the heaters on the output tubes for continuity and they still have continuity but they for some reason just refuse to light and I checked the filiment winding for those tubes on the power transformer and its still has continuity (its not open or shorted).

I'm not sure what's wrong with this radio right now and I'm so close to getting this radio going I'm just not sure what's going on with this thing right now and why the audio section suddenly decided to take a dump on me.

Any ideas?

Also can a tube die and still have continuity on the heater pins? Just wondering because it seems weird that both of my output tubes would of died at the same time but I guess its not completely unheard of just really uncommon.

OK, so I was testing my voltages and my power resistors under the power supply of the radio and apparently my 1.5k Ohm 10W WW Resistor just died on me somehow instead of measuring 1.5k Ohms on the multimeter it measured 14 Ohms which is weird because the 5k Ohm "B" Resistor and the 300 Ohm Bias Resistors test fine the 1.5k Ohm Bias resistor is measuring only 14 Ohms, any ideas as to why that would be?

Which I think that might be why I'm not getting any filiment glow or anything out of the Output tubes because the 1.5k Ohm Bias Resistor is part of the output tube filiment wiring.

Thanks for your help.

EDIT: I removed the 1500 Ohm Bias Resistor from the circuit and retested it and it tested fine, apparently I was just reading the resistance wire windings between the two terminal strips where the filiment wires attached to across the bias resistor to ground rather than the bias resistor's actual value.

I think what actually is wrong is that the output tubes are just bad and I think they failed because the output tubes weren't replaced as a matched pair when one of the tubes failed at one point in time (which apparently according to my Rider's Tube Substitution Guidebook with the 71A tube when you go to replace the tubes when they are in a push-pull configuration they need to be replaced as a matched set or they could fail prematurely due to biasing issues between the two tubes, which I think is precisely what happened in my case).

If the 71 filaments aren't open they should still light. Did you measure the 71's filament voltage, both at the 71 sockets and wherever it exits the power supply?

Edit - Also, neutralizing a Neutrodyne has nothing to do with eliminating hum in the audio. It's purpose is to neutralize capacitance in the RF tubes. Hum is an entirely different problem. Did you replace the power supply filter caps like you planned?

The filiment pins on the tubes had continuity on them, which is the strange part.

Also I measured the filiment voltage on both 71A tube sockets and they both had 5 VAC on them, the filiment winding for the output tubes on the power transformer has continuity, between the transformer and the tube sockets, so its not an open winding either.

I had just read in a Rider's tube substitution buidebook that I have that the 71A tubes need to be replaced as a matched set or else they will hum which these 71A tubes were NOT a matched pair, one was the original RCA Radiotron branded 71A tube and the other was a Tung-Sol branded tube, which I think might of been where the hum was coming from the fact that the tubes weren't matched.

Yes I replaced the filter caps like I said I would, I replaced them both with 4 MFD 450 VDC Electrolytics wired in the exact same spots as the originals were.

I just rechecked the filiment voltage for the 71A tubes and they were only measuring about 300 mV and I rechecked the continuity between the wire going from the terminal strip for the output tube winding to the tube sockets and I'm getting intermittent continuity and I looked at the wire and there was spots where the wire was bare and was shorting against the output transformer and the chassis of the radio so I think if I replace the wire going from the terminal strip to the tube sockets I think it might fix the problem.

Sounds like you found your problem, hopefully before you damaged the winding. Partial grounding of one side of the filament could have something to do with the hum too. For such reasons it's a good idea to keep the set plugged into a dim bulb tester until you're very confident everything is working reliably.

The problem with this thing is that the wiring is so hard to get to in this portion of the chassis and trying to clean the solder off the holes where the wires go into on the tube sockets is a pain in the butt because the ouptut and the interstage transformer are in the way and I can't move them very easily.

OK, so I got the wiring replaced for the 71A tubes and that fixed the issue, now I just need to figure out how to properly neutralize this set and get the tuning dial to track correctly because several of the known local (and distant) stations are not showing up at the correct positions on the dial and one of the local high powered Mexican stations on the AM Dial is showing up on two spots on the dial.

OK well she's good to go now, all I need is a period correct cloth cord (a reprodution one of course), and this radio will be ready to go back together! :music::thmbsp:

This thing is super sensitive for a TRF set because most of the time these TRF sets get a bad rap for being very lousy at getting anything in (radiotvphononut for example says these things are horrible as DX'ing) but I was receiving stations from Cincinatti, Chicago, Waterloo, Iowa, Fort Wayne, Indiana, etc on this radio earlier this morning with no problems and all I had hooked up to it was a 6' length of wire.

Sounds like a fun radio. With 4 tuning stages and push-pull audio I'm sure it was a pretty impressive performer back in it's day. :yes:

I'm sure it was! :yes:

I got a glimpse of the radio that mine is based on (the American Bosch Model 28) and it was made of Mohogany with a Maple Inlay around where the tuning dial went and the speaker for that radio looked like a Gothic Cathedral, it was quite an impressive looking set.

I noticed that my radio has 2 volume controls, one that is a potentiomenter that is controlled by a knob that is linked to the potentiometer with 2 pulleys and a belt (dial string), and another one that is a knob linked to a of some sort, any ideas as to what those two volume controls are for?

Also the inside of the speaker cabinet has some chunks of wood missing from where the speaker itself attached to the cabinet and the cabinet took a tumble at some point in time in its life and the weight of the speaker was enough to blow out the wood around where the screws were that fastened the speaker to the front of the cabinet, do you have any suggestions about how to repair that damage?

I was thinking of using a wood epoxy of some sort if such a thing exists and filling in the missing wood chunks and then putting the speaker back in the way it was originally.

Hard to say without seeing where second is wired into the circuit. A guess is that someone added a second volume at the input to the 1st audio amp so they could run the gain of the RF stages higher.

Wood glue or epoxy mixed with sawdust pressed into the voids. When it hardens sand flush and re-drill the holes.

I just realized that the second volume control you speak of must be the variable antenna coupling transformer? I guess you could say it's a second volume control, although technically an antenna tuning control. It has something to do with the very good selectivity. :thmbsp:

TRF radios are known to be sensitive but not selective. Superhets were the "cure" for the problem. You found out that some TRF designs were as good, or better than superhets. Grebes were known to be excellent DX radios!

Kevin:
I think you might be right on the money for the one "volume control" because it is a coil that moves with the knob and depending on how the coil is positioned it makes the selectivity of the radio better or worse (better or worse separation between stations on the dial and also makes the overall reception better or worse depending on the position of the coil) and the second "volume control" which is the one that is actually a rheostat type control is the actual volume control because the overall volume of the set is made louder or quieter when that knob is turned.

Titan1a: This radio I think is on par with Grebe as far as being a great DX'ng TRF set because as I said previously this radio was picking up stations loud and clear from as far away 300+ miles away or more, and this radio is still using the original bypass caps for the RF cans!

Also I got my replacement speaker in for this radio's speaker cabinet which was an American Bosch Model 612 8" Dynamic Speaker just like what was in there originally so right now I'm working on repairing the blown out wood around the original screw holes that were used to hold the original speaker in place when the speaker was made back in 1927, and I'm making the repairs with Elmer's Stainable/Paintable and Sandable Wood Filler that also resists shrinking and cracking.

Once I'm done repairing the damage I'll re-drill the holes back where they were originally and install the speaker and put it back together and wire up the speaker and test out the radio with the newly repaired speaker and see how it sounds and works. :thmbsp: :music:

It is finished! I have uploaded a video showing the after results of the restoration including what it sounds like with the speaker repaired (I actually had to repair the replacement speaker because apparently the speaker I got off ebay even had some damage to it (fairly minor damage compared to the original).

Enjoy!

Pictures below showing what the radio looks like.

YouTube Video Link Below:

https://www.youtube.com/watch?v=P-1rXkXH_IY

You did real good, it sounds very nice for a radio from that period. Now if you only had an outdoor antenna away from buildings with a shielded lead-in connected to a good ground, you could lose a lot of that buzz riding on the rf. With an indoor antenna you're actually picking up a lot of your signal that's being re-radiated from your AC wiring. In other words your houses AC wiring acts like a long wire antenna, but it's also got all the noise on it.

Well Unfortunately I don't own my own place so a long wire antenna is just going to have to suffice for the time being since I can't drill holes in the wall at my place.

Understandable. Sometimes just getting the radio connected to a good earth ground can help, or even a separate long wire connected to the antenna ground can act as a counterpoise and cancel out some of that noise. Often it takes a lot of experimenting to find the best solution.

You did the best you could. To cut through the "crud" I use a very expensive amplified loop antenna. Listening to WSM as I type.

I was able to pick up WSM just fine on my radio with just a long wire antenna at 10 o'clock at night, I was also able to pick up the Oldies station out of Toronto, Ontario, Canada just fine on my radio as well on my radio at 10 o'clock at night one night with just a longwire antenna.

Excellent! Maybe I need to get one of these.

Yes, this radio actually has really good sound for its age and also it has great DX'ing abilities for a TRF set.

I know I'm late to the party here, but I own two of these. Mine are Model 2's, which are the same radio but in a green metal case. $75 is a good price; I paid about $100 each for mine.

On a whim I powered up the nicer of the two and was surprised to find it still worked! It's encouraging to hear it'll be a decent performer after restoration. I'm not a big fan of 1920s sets, but the Art Deco styling of these won me over.

Yes, I've always wanted a 1920s radio so that my radio collection could be rounded out to include all of the various style of radios ever made over past 100 years.

One question Tim, did your radio when you powered it up make a high pitched whistling noise out of the speaker while it was warming up?
The reason I ask is because my radio when its first powered on and while its warming up makes a high pitched whistling noise out of the speaker before finally putting out an audio signal.

The reason is that your detector tube , which should be a #27 if I looked at the right schematic , is an indirectly heated cathode type of tube , whereas your #80 B+ rectifier and #71A audio output tubes are directly heated cathodes . When you turn the power on the directly heated cathode tubes are conducting pretty much instantly VS the one indirectly heated cathode taking it's sweet time to begin passing signal . For all that time you have the audio amp section operating wide open but with no signal to process . In the absence of signal to force a bit of bias onto the circuit the tubes become very sensitive to "Microphonics" , having loose elements in the tube actually rattle and give off squeals . This is of course assuming that you did a full recap on the radio (haven't kept up with the entire thread here) because an electrical cause could be if the capacitor listed on the schematic as "43 - By pass condenser .002 mfd." were bad that could cause the amp to squeal till the detector warmed up and began supplying it with audio as well .

I did not replace any of the bypass caps just the filter caps, and that's how it operates.

No. 43 the .002 MFD Cap is a mica cap so I didn't even bother with that cap.

If you want the squeal to go away I'd try replacing that cap , yes I realize it's mica but in very very rare instances those can fail and go open just like any other cap .

Always remember , NOTHING in life in infallible , from the "unsinkable" Titanic to our "Always good" mica caps :thmbsp:

Ok, I'll give it a shot. But taking this thing apart again is going to be a pain because of the way they have this thing assembled into the case.

The whistling noise it makes when it first powers on isn't that annoying , because it does go away once the radio is warmed up, it doesn't really bother me that much it was more of a curiosity than anything.

If it's a difficult set to take apart and the brief warm up whistle doesn't bother you then I wouldn't blame you in the least for not going after it . If it does ever have a future failure that requires opening it maybe then would be a good time to try replacing that cap .

That's what I was thinking, because the radio works great with just the power supply reworking, and the rewiring job that I did.

The bypass caps probably should of been replaced because when I listen to more distant stations (late night DX'ing), the stations will cut in and out sometimes (the station's volume will go really quiet for about 2 or 3 minutes and then get blaring loud for about 20 minutes or so and then back down to barely listenable levels again for a couple of minutes, so on and so forth).