Adapting a D-104 "Silver Eagle" to an HTX-100

[W2PSK]

Hello. I was hoping some of you might be able to share your knowledge in how I can adapt a D-104 "Silver Eagle" microphone to an HTX-100 10m radio. I have read about how the D-104 is a "Hi-Z" microphone and "modern" transceivers are "Lo-Z". I am unsure if the HTX-100 qualifies as a "modern" transceiver or not.

Any insight would be appreciated.

[W9GB]

I am unsure if the HTX-100 qualifies as a "modern" transceiver or not.

YES.
The easiest dividing technology for Medium-Z (~ 600 ohms) or High-Z (~ 50 Kohms) microphone/audio input was usage of vacuum tubes versus solid state (transistors, ICs) in that audio input stage.
There were a few exceptions, especially hybrid radios, which is why you should double check the owner's manual for the radio !!

w9gb

[K9STH]

SSB:

Although many people refer to the "modern" transceiver microphone input impedance as "low" it is really more accurately described as "medium". The microphone input impedance these days is usually in the 500 ohm to 600 ohm range. A true "low" impedance microphone usually has an impedance considerably lower, generally below 20 ohms.

The D-104 microphone stands with the transistorized preamplifier work fine with "medium" impedances. Just be sure and do NOT overdrive the input which is very easy to do. Basically this means to adjust the drive control, which is accessible through a small hole in the bottom of the base, to a very low level. In fact, start with the control fully counter-clockwise and gradually increase the level. The transistorized preamplifiers were designed so that the D-104 could be used with "CB" equipment which generally had the 500 ohm to 600 ohm microphone impedance.

I believe that all of the "Silver Eagle" D-104 microphones came with the preamplifier base although there may be exceptions. Also, since the "head" can be detached and used with all sorts of bases, this is also possible.

Glen, K9STH

[W2PSK]

SSB:

Although many people refer to the "modern" transceiver microphone input impedance as "low" it is really more accurately described as "medium". The microphone input impedance these days is usually in the 500 ohm to 600 ohm range. A true "low" impedance microphone usually has an impedance considerably lower, generally below 20 ohms.

The D-104 microphone stands with the transistorized preamplifier work fine with "medium" impedances. Just be sure and do NOT overdrive the input which is very easy to do. Basically this means to adjust the drive control, which is accessible through a small hole in the bottom of the base, to a very low level. In fact, start with the control fully counter-clockwise and gradually increase the level. The transistorized preamplifiers were designed so that the D-104 could be used with "CB" equipment which generally had the 500 ohm to 600 ohm microphone impedance.

I believe that all of the "Silver Eagle" D-104 microphones came with the preamplifier base although there may be exceptions. Also, since the "head" can be detached and used with all sorts of bases, this is also possible.

Glen, K9STH

Thanks for the info, Glen! So all I have to do is wire it up for the radio and turn the input up slowly? That's great news! After reading around on the net and not finding anything specific to the HTX-100, I was under the assumption I was going to have to do work to the base of the mic and replace the element. Thanks again!

[K9STH]

Make sure that the microphone element in the D-104 is still good. Unfortunately, they go bad all the time and Astatic is no longer making the replacement element. If it is bad then replace it with a Kobitone element that Mouser sells for around $5.00. The part number is 25LM022. You will have to make a spacer out of something like styrofoam because the cartridge is much smaller than the original. However, the Kobitone cartridge works great.

Glen, K9STH

[W2PSK]

Make sure that the microphone element in the D-104 is still good. Unfortunately, they go bad all the time and Astatic is no longer making the replacement element. If it is bad then replace it with a Kobitone element that Mouser sells for around $5.00. The part number is 25LM022. You will have to make a spacer out of something like styrofoam because the cartridge is much smaller than the original. However, the Kobitone cartridge works great.

Glen, K9STH

Do you have any opinion on the Heil HM-5 or HM-4 elements? I've read about people replacing the elements with those too.

[AC0FP]

KC2SSB,

Here are some general electronic engineering rules for "matching" audio impedance's that might make things easier.

1. If you have a high output impedance, you need to drive a high input impedance (load) of the same or higher value. Not obeying this rule can result in excessive audio distortion.

2. A low output impedance can drive any higher value of input impedance (load) without and consequences. In the case where an output impedance such as 600 ohms is perfectly matched to an input of 600 ohms, there will be no penalty except you will lose 1/2 of the source impedance's voltage amplitude in the load.

Good Luck,

fp

[K9STH]

You can spend the money on a Heil microphone cartridge or you can go with the Mouser. Frankly, in my opinion, the Kobitone cartridge sounds just as good as the much more expensive Heil.

Glen, K9STH

[VO1GXG]

Make sure that the microphone element in the D-104 is still good. Unfortunately, they go bad all the time and Astatic is no longer making the replacement element. If it is bad then replace it with a Kobitone element that Mouser sells for around $5.00. The part number is 25LM022. You will have to make a spacer out of something like styrofoam because the cartridge is much smaller than the original. However, the Kobitone cartridge works great.

Glen, K9STH

You can also replace the D-104 elements with Mouser # 25LM032 which is a 500ohm dynamic Kobitone element. I did with with my D-104 since it did not have a TUG base ( the pre amp ) and the orignal element was shot.

[K9STH]

One thing to remember is that Heil doesn't manufacture microphone elements. What he has done is to locate elements from various manufacturers that work very well. For this knowledge he charges a premium.

Glen, K9STH