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 Post subject: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 2:12 am 
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Posts: 20
I picked this up today in a shop in PA. I had not heard of this Radio before and am have trouble finding much info on it.

The set is in remarkable condition. It employs 4 UX199 tubes.
A typed letter found inside the chassis area states that this radio was purchased from the estate of a collector who was. An electronics engineer and radio expert who revamped it to work on AC instead of batteries.

It has three tunning pointers, High and Low Volume and an Antenna Switch 5 positions.
I attempted to get this going but get nothing so far. I also don't understand the 3 tuning dials?

If anyone has one of these models or knows anything about it the info would be greatly appreciated.


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 2:53 am 
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Location: 08033 Cherry Hill Jersey
Very cool radio! You mention it runs of ac - does it have an external power supply?
Would like to see that.

In those days battery radios could have any number of tuning dials, many had three dials.
Looks like it is very well made.

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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 3:10 am 
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Joined: Jul Thu 29, 2010 5:35 am
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Location: Simonton, Texas
I do not have one of these but it looks simular to an Atwater Kent model 20 and should operate simularly.
The manual for the model 20 is here: https://www.atwaterkentradio.com/AKInst ... okVol2.pdf
Tuning instructions start on page 31.
I would start at the beginning of the manual as it guides you through antenna, ground, speaker and power supply set up.
Should you have more questions just come back to the forum and ask.
Good luck.

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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 3:18 am 
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Going read that now. Thanks Koby


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 4:15 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: S. Dartmouth MA 02748-1225 USA
The inverse duplex is a reflex receiver that feeds detected audio back through the RF stages in reverse. Homemade designs of this type are difficult to layout and make work. If there were substantial modifications to the receiver for AC there could be problems. If the receiver is unmodified and a power supply properly designed the radio would operate as intended... Of particular concern are the audio transformers, these are carefully selected and phased so stages do not oscillate. There maybe an audio transformer whose markings do not co-inside with the actual hookup. That would be normal connection for a reflex. May also find all the frames of the audio transformers are wired to B-. Note separate "B" sources...


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Last edited by Chas on Oct Sun 18, 2020 4:18 am, edited 1 time in total.
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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 4:18 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 3064
Location: Austin, Texas
Here's the Radio Museum link for that radio:
https://www.radiomuseum.org/r/grimes_in ... ex_4d.html

To download the schematics, click on the schematic page in the right window. Then click on it in the left window when it appears there.
You can download three schematic pages per day.

Good 199 tubes are hard to find. We hadn't yet learned to make good metal to glass seals at the time of those tubes so most have leaked their vacuum.

Jay


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 4:35 am 
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Well i do not even know to start with this. I outstanding cosmetically inside ans out. I can't even figure how to get started. 3 of the tubes appear to be fused to the floating sockets. A 199 has separated from the base. Since there is no chassis to pull. Everything seems to have to be disassembled from the top down?

Bewildered and confused!


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 5:48 am 
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Joined: Nov Tue 14, 2017 5:09 am
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Location: Austin, Texas
Some of the 199's have short pins and are bayonet mount. You have to rotate them to remove from the socket.
Attachment:
199.jpg
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Your radios is supposed to have the long pin tubes but that could be wrong.
The 1924 model has bayonet mount tubes. The 1925 model has long pin tubes.
Rechecked the picture and your radio appears to have the bayonet mounts.

The chassis is often attached to the front panel and removes from the front.

Jay


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 3:17 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Some early tube sockets as well as tube bases are prone to both shrinking and swelling. That will bind a tube nearly solid into the socket. The bayonet socket key on some molded sockets cannot be seen, requires the tube to be pushed down then turned anti-clockwise, the turn amounting to only just a few degrees. If the tube will not push down it is likely stuck from swelling... The tubes are replaceable at some cost. The socket will be very hard to find unless if it is of a particular brand... Sockets are not alike from manufactures.

Applying a heat gun, carefully around the socket could help release the tube. Once removed determine of it is the tube or the socket that has swollen and trim to gain clearance again.

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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 5:57 pm 
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Joined: May Sat 30, 2015 11:49 pm
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Location: Keystone Heights, FL, USA 32656
As mentioned, the tubes are UV199 tubes. Push down and turn a bit counter clockwise to remove. Grip them by the base, not the glass, if possible. I think the engineer made a power supply to replace the batteries; it is not possible to "revamp" the radio to work on AC. It has to have DC voltage to function. Picture of the power supply, please?

The whole radio pulls out the front after the screws are removed. I don't see any need to pull it out, at this point. Voltage at the tubes can be checked at the metal tabs on the sockets.

For tuning start with the condenser plates fully closed; the pointers should all point at 100. Turn them together about 10 points at a time, rock the #2 and #3 dials a bit back and forth to find a station. Try this with different settings of the antenna switch.

Make sure the loop/antenna switch inside (missing knob) is turned to "antenna".

Touch each end of the grid leak to see if you can get some sound out of the speaker; should buzz or hum.

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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 6:09 pm 
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Joined: Nov Tue 14, 2017 5:09 am
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Location: Austin, Texas
Do you have a speaker? I didn't see mention of one but may have missed it.

Jay


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 6:17 pm 
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Joined: Feb Fri 13, 2009 5:09 am
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Location: Santa Clara, CA
Yes, please describe the speaker you are using, and also your antenna and ground setup.


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 7:39 pm 
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Joined: Jan Sat 03, 2015 4:09 pm
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I have this radio conneceted to my working Atwater-Kent Type E Speaker. I am also using the same antenna setup I use on the Atwater-Kent. The info on the bayonet sockets was helpful. The glass tube in 199A has some slight wiggle and is obviously come lose from the base. None of the tubes appear to have burn spots or are hazy. They are UV199 tubes with the stubby pins.

I will forward more photo's once I figure out how to slide out he workings without damaging the wooden case.

I am new to this and have only successfully recapped and restored one 1946 Philco. I am slowly learning the terminology. I need to find a good book for beginners in Antique Radio Repair and electronics in general.


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 8:15 pm 
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Joined: May Sat 30, 2015 11:49 pm
Posts: 1374
Location: Keystone Heights, FL, USA 32656
Before you take things apart, did you try the test at the grid leak like I suggested? The grid leak resistor looks like a fuse. Put the tubes in, turn the "Battery" knob up about 3/4, and touch each end of the grid leak to see if you get any noise.

You can also check the voltage at the tube sockets, they are marked; F and F is filament; G is grid; and P is plate. Should have 2.5 to 3 between F and F on each socket.

NOTE: This is nothing at all like the Philco you did.

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“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 9:24 pm 
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Jeff, I did as you suggested. No sound touching the grid leak. The filament looks good and I did check continuity.

Checked voltage F to F and got .007 on each.


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 9:25 pm 
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I do not have a tube tester yet but I did check continuity on all.


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 10:52 pm 
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Joined: May Sat 30, 2015 11:49 pm
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Location: Keystone Heights, FL, USA 32656
.007 volts? Did you have the power supply on and the battery control turned up? I meant one meter lead on F and the other lead on the other F at the socket. Should be 2 to 3 volts and the tubes should light.

I think tube filament resistance is around 7 ohms; measured on opposite pins of the tubes. Don’t remember which pair.

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“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 11:25 pm 
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Tubes were at 7 ohms. I had the battery up and got nothing.
The battery knop feels like it is connected to nothing.
Maybe because it was converted to AC?

Possibly the Transformer is bad.


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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 11:29 pm 
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jwehberg wrote:
Tubes were at 7 ohms. I had the battery up and got nothing. The battery knob feels like it is connected to nothing. Maybe because it was converted to AC? Possibly the Transformer is bad.
Explain please what this power supply is and take a picture of it... Might have to test the supply at its terminals if there are any, for the correct voltages and again under load (radio turned on). There could also be a mechanical problem with the battery setting rheostat, loose wiper or other... chas

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 Post subject: Re: 1925 David Grimes 4D Inverse Duplex Radio
PostPosted: Oct Sun 18, 2020 11:55 pm 
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These are a few photos I took holding my cellphone underneath. As you can see the collector who owned this radio did some extensive work. Everything appears completely new. I will have to pull it out of the cabinet this week to get a better look and do some voltage testing.
Also a phot of the document I found inside the case.


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