D-104 UG8 Stand Question

[CM-4441]

I dug up an old D-104 with the UG8 stand. I used this back in the 70's on a Browning R-27 S-23 base. If memory serves me correctly (it usually doesn't) someone added an amplifier to it. I don't think it originally had one.

I want to run it on my Galaxy DX-2547 without the amplifier. It also appears to have a different mic cord. Here are a couple of pics. How do I wire this thing up?

Terry

 

[Shockwave]

The choice of being able to use an unamplified D-104 mic went away once transistor radios came out. You only have this option when the radio is tubes. It all comes down to the input impedance of the first mic amp in the radio. If it uses a tube it will have high impedance that matches the element in the D-104. The FET transistor can also provide this high impedance input however, they are not used as mic amps in CB's.

The purpose of the pre amp inside the D-104 is not just to add gain. It also has a low impedance output that matches today's radios. If you use it without the preamp on the 2547, it will have low modulation and no low end frequency response because the element will be heavily loaded.

Also, from looking at the picture the preamp is disconnected. As I recall the green wire on the preamp is the AF input and the white wire is the output. They have been disconnected from the terminal strip and taped together. I think the yellow wire going up the neck of the mic needs to be attached to the green terminal on the right. The white wire from the mic cord needs to attach to the left terminal with the other white wires. Then this mic will match your 2547 radio.

 

[CM-4441]

Okay, thank's a lot I'll have to see if that still works!

Terry

 

[EDUK8TR]

Good Call Shockwave.

 

[CroMagnum]

I dug up an old D-104 with the UG8 stand. I used this back in the 70's on a Browning R-27 S-23 base. If memory serves me correctly (it usually doesn't) someone added an amplifier to it. I don't think it originally had one.

From the schematic on the bottom cover, the lack of an E/R Switch, plus the awkward hole drilled through the base plate, I'd say you have an original UG8 stand that someone added an Astatic TU-KIT to later, but now has bypassed back to an unamplified stand.

Here's a clean copy of your original wiring:

I want to run it on my Galaxy DX-2547 without the amplifier. It also appears to have a different mic cord. Here are a couple of pics. How do I wire this thing up?

Shockwave is right in that a bare crystal element won't work very well plugged directly into a low-impedance solid state radio, so you really need to hook up the amplifier again. Here's a scematic and wiring diagram from the TU-KIT:

Hope this helps!

 

[CM-4441]

Thanks for the 2 diagrams. I think that will do the trick.

Terry

 

[CM-4441]

Okay, I have the base wiring straightened out now. In doing some looking around on the net I find 4 and 6 wire diagrams for the plug going into the radio.

Astatic (4 wire)
1- Shield
2- White
3- Red
4- Black

Astatic (6 wire)
1- Shield & Blue
2- White
3- Red
4- Black
Yellow NC

I have 5 wires: Blue, white, shield, red and black. Should I follow the 6 wire setup?

Terry

 

[Robb]

Yes . . .

 

[CM-4441]

Thanks, I appreciate it!

Terry

 

[CM-4441]

I tried it out today. It keys the radio but there is no modulation. Is there any way to check just the head unit? Maybe that is the problem.

Terry

 

[CM-4441]

Bump

 

[Robb]

All of the Silver Eagle and TUG 8 mic heads use the same mic element inside. If you can borrow the top section from a friend long enough to see if it works; then you can be sure that is the problem.

Having said that, you have the option to get a replacement element for it. They no longer make new elements from Astatic. The real Astatic 'New/Old stock' ones found on eBay go for a pound of cash. The other options are getting a crystal replacement element from Mouser Electronics - or a similar one sold as replacements from eBay. I did that; and they sound 'tinny' - not very good. The other option is to get the Heil replacement element - which converts it to a condenser and cost about $35.

 

[CroMagnum]

I tried it out today. It keys the radio but there is no modulation. Is there any way to check just the head unit? Maybe that is the problem.

First I'd thoroughly buzz out all the wiring again. After dealing with several "modified" D104s you never know what people are going to do to them. I'd check for continuity from mic socket pin 3 to terminal 3 and pin 2 to terminal 2 & ground, and make sure pin 3 has no connection to ground. Forget about the colors, just check them all with a meter.

Assuming everything is wired correctly, you could always just pull the battery and jumper terminal 3 to terminal 8 and try it. Of course the modulation would be really low, but you should get something. If not, it's the mic head. If you do get something, then it's probably the amplifier board.

Like Robb said, the easiest thing to try first is swap heads. This is where having more than one D104 comes in handy. If not, find someone in your area and try one.

If it's the amplifier board, you're in luck because there's only two semiconductors and they're both 2N2712 transistors. These are easy to find as NTE85. I've heard of people substituting 2N3904 with good results, but I haven't done it myself. If you try this, keep in mind the the 2N2712 is ECB and the 2N3904 is EBC so you have to switch the leads around.

If you have to replace the element, I hope you go with the one from rbmicro.com so you can give us a review before I buy one.

 

[radiohobby]

I was just looking at that kit from RBMicro. I think I would get that one if I needed one. All this talk about these things made me go and dig mine out and hook it to my 148. I had it on a 2000 a long time ago, put a new batt in it and it is talking like the day I put it away back in 1983. It was so long ago when I used it last I can't remember why but I have a resistor added into the white wire circuit. Sure is nice getting all the old gear out and getting back on the air.

 

[Shockwave]

The resistor was probably added in the output audio line to scrub some gain off the preamp and remove a squeal caused by RF feedback. This can also be cured with the use of a ferrite bead on the mic line and sometimes requires a bypass cap too.