[TenTec] 705 Mic Low Output Help Request

[d.e.warnick at comcast.net]

-------------- Original message -------------- 
From: "Bob McGraw - K4TAX" <RMcGraw at Blomand.net> 

> The Primo EM-60 ( EM-100 in the 1201 kit ) electret cartridge used in the 
> 705 requires 1.5 volts DC minimum to bias the JFET inside the electret well 
> into the constant current region. Actually, 3 to 4 volts is much better. 
> 
> The existing TT design has way too much resistance (24K) in line with the 
> electret such that it's bias voltage never rises much above .5 ~.6 volts DC; 
> and the JFET never gets out of the constant resistance region, and 
> consequently cannot develop adequate gain. 
> 
> To fix your 705 mic, tack solder a 3300 ohm resistor across R11 ( which is 
> 22K now ). 
> 
> You will find that you will have plenty of output after this mod . 
> 
> If you are interested in enhancing the low end freq response as well, 
> increase C2 to .47 uf or larger. 
> 
> Also you should verify that the 705 is being run on at least 7 volts by 
> measuring its operating voltage at the M+ pad on the 705's printed circuit 
> board. Some older Corsairs have 10K behind the mic connector pin 4, which 
> should be reduced to less than 68 ohms. 
> 
> 
> 
> 
> 
> Bob, K4TAX 
> 
> ----- Original Message ----- 
> From: "David & Chris Drake" 
> To: "'Discussion of Ten-Tec Equipment'" 
> Sent: Monday, February 04, 2008 12:03 PM 
> Subject: Re: [TenTec] 705 Mic Low Output Help Request 
> 
> 
> > Don't remember for sure without looking it up. But I think 9-12v. The 
> > mic 
> > runs off a 9v battery if not getting power directly, so it would make 
> > sense 
> > it needs around 9v to work. 
> > David 
> > 
> > -----Original Message----- 
> > From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com] 
> > On Behalf Of Greg Kuczek 
> > Sent: Monday, February 04, 2008 9:15 AM 
> > To: Discussion of Ten-Tec Equipment 
> > Subject: Re: [TenTec] 705 Mic Low Output Help Request 
> > 
> > 
> > I'm running it thru the jack. I haven't checked the voltage at the jack 
> > yet, 
> > thanks. Do you know what the voltage should be? 
> > 
> > 73 
> > Greg W9VOX 
> > 
> > David & Chris Drake wrote: 
> > Are you running the 705 by battery or through the Omni V? If through the 
> > Omni V, check the voltage at the jack first. If by battery, check the 
> > battery. Then check the plug before going inside it. 
> > Good luck, 
> > David 
> > 
> > ----- Original Message ----- 
> > From: "Greg Kuczek" 
> > To: 
> > Sent: Sunday, February 03, 2008 10:23 PM 
> > Subject: [TenTec] 705 Mic Low Output Help Request 
> > 
> > 
> >>I have a 705 mic that I am having low output problems when used with an 
> >>Omni V. I've read that you can change out the R11 resisitor to 3300 ohms 
> >>to 
> > 
> >>help correct this. Unfortunately I don't have a schematic or any 
> >>documentation to help me locate this resistor. Any help identifying R11 
> >>would be appreciated. 
> >> 
> >> 73 de Greg W9VOX _______________________________________________ 
> >> TenTec mailing list 
> >> TenTec at contesting.com 
> >> http://lists.contesting.com/mailman/listinfo/tentec 
> >> 
> >> 
> > 
> > 
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> 
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