• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Resistor in D104 mic


Active Member
Jul 7, 2015
Ok so i dug out one of my old D104 amplified mics and it seemed to burn thru 9v batteries rather faster than i remembered,
So i noticed i had a 1/2watt 47k in it, so i thought i would swap it out for a 1/4watt 33k as i was out of 47k's and it seems
to work fine. Is there any reason that it is a problem or could cause any problems? If it matters it is bein used with a Cobra
2000gtl. Thank you for reading and i await for those much smarter than me to comment.


Well-Known Member
Aug 4, 2017
In the D104 manual (see attached) it suggests installing that resistor in cases where the gain from the mic is too hot. The best use of the mic amp circuit is to have the gain of the mic about 1/2 way up so you can benifit from its equal amplification within its frequency range. I have seen some instances where folks use the mic at about 5% gain and it really does not sound as good as it could (not that it sounds bad though). Remember, many tube radios use an unamplified D104 and they can sound great as well. There are soo many different factors that it is impossible to say that one way works across all radios.


  • astatic_d104_manual.pdf
    503.8 KB · Views: 4


Analog Retentive
Apr 3, 2005
Louisville, KY
The resistor serves two possible purposes. To reduce the excessive drive level to the radio's sensitive mike input, or to reduce a feedback-squeal problem caused by your transmit signal being rectified in the mike's preamp circuit and making it oscillate.

If the battery runs down prematurely this suggests that the switch is not shutting off the battery in receive mode.

  • Like
Reactions: Holydvr

Help Users
  • No one is chatting at the moment.
  • @ BJ radionut:
    he's begging....he's run a huge pile-up and looking for more
  • @ BJ radionut:
    G8DX WIDE 20kc wide ..7L at 80ft and limit on 28.491 20 over here in Ind
  • @ BJ radionut:
    band wide open to Euro's on 10m
  • @ Joseph23:
    can anybody help me with a cobra 139 ssb 23ch. no modulation indicated when keyed up. any help would be appreciated also looking for a NEC1307 1K64C.