My "secret" is to do away with the amplifier and replace it with a series 470K resistor. This is actually an old-timer's trick to mellow out the frequency response of the D-104 head. The amplifier is enhanced uselessness for our radios. It will happily drive just about any radio this way and you get rid of a failure point (actually two if you consider potential battery leakage). This works with any T-UGxx stand.
My understanding is that later D-104 heads used a ceramic cartridge. The same fix applies. The D-104 head likes to see a high impedance load, the higher the better.
I have three T-UGxx variants that I have done this to and tested on the air with good reports. And they can be used with VOX.
73
-Jim
NU0C
On Fri, 23 Feb 2024 08:26:30 -0800
"jerry-KF6VB" <jerry@...> wrote:
I have a D-104 that I use with various radios. I always get good
reports.
The secret? It has a JFET source follower in the base. The JFET
presents
an extremely high impedance to the Rochelle Salts element. Multiple
megohms.
This improves the low frequency response.
I powered the JFET with a 9V rectangular battery switched through the
PTT.
Disadvantage is that I can't use this mic for VOX.
- Jerry, KF6VB
Jim Shorney