Sadelta mic advice

Discussion:

Sadelta mic advice

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Islander

2007-02-27 01:03:07 UTC

I am new to the group. Renewing my interest in CB and can find very
few let alone any with electronics in the CB group.

I just purchased a good condition Tram TitanII from ebay.. and from
another source on Ebay a Sadelta echo-plus classic.

The rig I always wanted back in my cb days in the 60s n 70s. I was
looking for a D104 and a demco power modulator preamp.. Lots of D104's
out there but few good tube type mic preamps. so.. the easy option
that has it all seems to be the Sadelta echo plus mic.

I go to hook them up and the tx relay kicks in no matter what. I
have checked all the wiring. and rewired the Tram to stock wiring
according to the schamatic I have. As soon as I connect the brown wire
from the mic. TX key off, the TX comes on on the rig. No mic wire
hooked up no other wires hooked up... Yes my digital ohm meter says it
is a wide open circuit. TX pin on the rig has 270V on it.. as soon as
I hook up the mic it drops to 40.. when the tx key on the mic is
closed it drops to zero.

anyone with any ideas where else to look and how. Please..

cheers
Marv

Islander

2007-02-27 01:08:37 UTC

Permalink

Oh and does anyone have or know where I can get the schematic for
this mic.. The Sadelta echomaster plus classic base station mic.

thanks again.
Cheers
Marv

i***@sbcglobal.net

2007-03-11 08:35:17 UTC

Permalink

I'm not familiar with the transceiver or mic, but it sounds like the 270
volts exceeds the zener breakdown voltage of the mic's keying transistor, or
perhaps there's a diode across the switch. Something is dropping that
voltage, regardless of your (very low voltage) ohmmeters reading, and it's
only happening with high voltage applied to the circuit.

Also, 270 volts seems like an ***awful*** lot of voltage to be running into
a microphone. This voltage is potentially lethal. Does the rig's schematic
indicate this is normal? If not, don't try to use it. Instead, take it to
a qualified repairman. A repair shop is cheaper (and a heck of a lot more
pleasant) than a funeral.

If the 270 volts is normal (and you're competent to work on high voltage),
I'd run low voltage to the mic (i.e. 12 volts DC) and use this to key a
relay *at the transmitter*. If you're not sure, take it to a shop.

BTW the D-104 is a crystal mic, and per Astatic requires a minimum 1 megohm
impedance to function properly. Its rated impedance is not even measured in
ohms, but is listed as "equivalent to a 390 pF capacitor". Do the math
(Cutoff frequency= 1/RC). I use a 741 OpAmp voltage follower (infinite
input impedance) with a split 9v supply with excellent results. Unity gain,
but the crystal element is plenty hot when properly matched.
--
-IronMan Mike Curtis
http://www.ironmancurtis.com http://www.SouthlandBlues.com
Need a web host? From $3.99 per month http://1and1.com/?k_id=10346266

Post by Islander
I am new to the group. Renewing my interest in CB and can find very
few let alone any with electronics in the CB group.
I just purchased a good condition Tram TitanII from ebay.. and from
another source on Ebay a Sadelta echo-plus classic.
The rig I always wanted back in my cb days in the 60s n 70s. I was
looking for a D104 and a demco power modulator preamp.. Lots of D104's
out there but few good tube type mic preamps. so.. the easy option
that has it all seems to be the Sadelta echo plus mic.
I go to hook them up and the tx relay kicks in no matter what. I
have checked all the wiring. and rewired the Tram to stock wiring
according to the schamatic I have. As soon as I connect the brown wire
from the mic. TX key off, the TX comes on on the rig. No mic wire
hooked up no other wires hooked up... Yes my digital ohm meter says it
is a wide open circuit. TX pin on the rig has 270V on it.. as soon as
I hook up the mic it drops to 40.. when the tx key on the mic is
closed it drops to zero.
anyone with any ideas where else to look and how. Please..
cheers
Marv

Islander

2007-03-16 16:24:44 UTC

Permalink

Thanks Mike This gave me some clues as to what to look for. I am
unable to find a schematic for the mic anywhere. So I carefully dove
iinto it, to see where the wires go on the pc board. Sure enough it
is not to the switch direct but to something that is not your normal
ic. A largerdevice with no known numbers on it. Rather than modify
the mic or the rig a good old mechanical relay is the answer. I had
one in the parts bin and a dc supply to run it next trip to the parts
store I will pic up a box to put them in and the appropriiate
connectors. Thanks for the suggestion.

cheers
the islander

Post by i***@sbcglobal.net
I'm not familiar with the transceiver or mic, but it sounds like the 270
volts exceeds the zener breakdown voltage of the mic's keying transistor, or
snip
input impedance) with a split 9v supply with excellent results. Unity gain,
but the crystal element is plenty hot when properly matched.

Howard Bingham

2007-04-12 08:24:57 UTC

Permalink

Instead of spending money on CB gear, why not take the technician
class ham license..?

All it consists of is 35 multiple choice questions & if you know any
radio theory, you should be able to ace the test..

Then the whole world of high teh communications opens up, as with ham
repeaters on 2 meters & 70cm, one can talk coast to coast with not
much more than a HT (Handi Talkie, or hand held tranciever for the
uneducated.

Howard Bingham
KE5APJ - EL29gq

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