[Lowfer] The transverter's working, but I can't drive the amp !!

[Paul Daulton]

Do you have a scope or rf probe and vtvm? What final circuit are you using. 
the impedance may be way off. A trick I learned from DeMaw , Hayward and Jay 
Rusgrove too, is to keep all stages at 50 ohm in and out.
That way you can calculate power and stage gain easily.

To drive a 63mhz to 439 transverter for atv with a modulator/ch3 box from a 
vcr, I used three MAR-6 mmic in cascade. At our frequencys you could use 
audio chips or just about any audio amp.

Put up a circuit so we can estimaate the impedances. List the rf voltages 
present if possible. I think it may be more of a matching problem than 
power.

If all else fails put some duct tape on it.

Paul
----- Original Message ----- 
From: "Andy - KU4XR" <ku4xr at yahoo.com>
To: <lowfer at mailman.qth.net>; "Part-15 Yahoo" <part15 at yahoogroups.com>
Sent: Saturday, March 27, 2010 11:18 PM
Subject: [Lowfer] The transverter's working, but I can't drive the amp !!


> Home alone today, so I finally built another Class " D " amp to go
> with the transverter. Only problem is; I can't get any measurable
> output thru the amp from the transverter. First thought was I made
> some mistake in wiring the new PA. That all checked fine, why not
> try my known good PA from the " XR " QRSS beacon ?? I did; and
> still nothing. The transverter is generating a signal of some level,
> but it's not enough to drive the complimentary pair amp. I have
> switched out the LM318 in the output stage and get the same results,
> If the chips were fried, I wouldn't think that any signal would make
> it thru the transverter, so I don't believe that's the problem.
> The only way I can get any signal strength at all, is to tap the
> output of the SA612 mixer. I've done all the usual voltage checks,
> continuity checks, look for shorted circuits, everything is clean.
> So my suspicion is that the LM318 OP amp just dosen't have enough
> output to drive the usual amp we use here on LF for 1 Watt.
> I am assuming that the transverter output is a sine wave, so that
> might account for the low output level. Do I need another amp stage??
> If so; Any comments, and suggestions will be appreciated.
> I have to work all day Sunday, so I won't be able to check emails
> until I get home, so if I don't respond to something direct, you'll
> know why.
>
> 73, and good night to all :::
>
>
> Andy - KU4XR - EM75xr - Friendsville, TN. USA
> LOWfer Beacon " XR " @ 185.29875 KHz ( QRSS-60 )
> Coordinates:  N:  35º 43' 54" - W:  84º 3' 16"
> http://www.myspace.com/beaconxr
> http://webpages.charter.net/ku4xr/
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