Just a query about the correct audio bandwidth of the 19 set. I have been using a fully restored Mark 111 through a Mk 2 amplifier a lot recently and speaking to a lot of amateurs using 'modern' a.m. rigs. The combination puts out a healthy 12 watts of carrier and is achieving a good range, but the usual comments are of poor or 'thin' modulation. Monitoring my signal on speech via a scope reveals that full modulation is in fact being achieved, but another amateur with signal monitoring facilities told me that most of the audio in the received signal is around 1.4KHz - 3KHz. Measuring the output directly of my mike capsules (non-carbon) of which I have six show that they all indeed have an audio output profile of this form. Is this in fact typical of the 19 set audio performance of the capsule - which may have been intended by the designers to eliminate some of the low frequency noise in the tank. Direct insertion of the audio to the microphone transformer bypassing the capsule shows that the set itself has a broadly flat response fro 300Hz up to about 5Khz
I wonder whether anyone has installed a modern low impedance capsule in the headset to give a more acceptable signal? If so which one!
Phil 2W0KGP

Do you own a serviceable 19 Set? yes

In reply to your question:

1. For the Intercom Amplifier Fidelity Test (EMER FZ 254/3 para 68) the
specification is as follows:

Adjust the input to give an output of +4.3 dB at 400 Hz
at 150 Hz the output should not be less than - 1.8 dB
at 5,000 Hz the output should not be less than +1.24 dB


2. Under the "A" Sender Tests (same EMER para 157) the modulator should
do the following:

"As measured across the audio oscillaror terminals, the input voltage
required for 75% modulation shall not exceed:
1 V (rms) at 400 cps
5 V (rms) at 150 cps
7 V (rms) at 5,000 cps"

3. As far as the original capsules are concerned, I have always found
them to be very low in output. I attribute this to age and stiffness of
the cone. I know someone who used to use an adjustable, amplified mic for his
19 Set. We did not use it often but it seemed to work fine. I replaced
the guts of a capsule with a small, plastic 40 ohm Radio Shack speaker
(perfect fit). That arrangement is the the best mic that I have.

4. Hope this is of some help. Checking on an oscilloscope is the only
way to tell what is really happening.

Cheers...Dave

Do you own a serviceable 19 Set? Yes