[AMRadio] FW: Homebrew receiver

[Brett Gazdzinski]

On all my AM rigs, I had to go with dc on the mike preamp,
otherwise, I had a lot of hum on the high impedance
input circuit, likely its better with a 600 ohm setup.

Its easy to do tho, a diode and a cap, the size of the cap
sets the dc voltage.
The dc does not need to be pure at all, a little filtering 
reduces the hum to where you cant hear it.

If its a problem with the 7360, you could do the same,
and add a 6.3 volt zener diode...

 
Brett
N2DTS

> -----Original Message-----
> From: amradio-admin at mailman.qth.net
> [mailto:amradio-admin at mailman.qth.net]On Behalf Of Donald Chester
> Sent: Saturday, November 08, 2003 3:26 PM
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] FW: Homebrew receiver
> 
> 
> 
> 
> There are several beam defection tubes in circulation during
> >the 60's time frame. Unfortunately, none of them are directly
> >interchangeable with each other unless one is willing to 
> rewire several
> >pins on the tube socket. Spec wise they are very close to each other.
> 
> If anyone  has the data, maybe you  could post a list of all the beam 
> deflection tubes of that era.  I think they were widely used 
> in tube-type 
> color TV's.   Sometimes the TV ones are cheaper than the 
> 7360, but on the 
> other hand, the cheap sweep tubes of the 60's now cost 
> several times more 
> than 6146B's.
> 
> One problem I  had with the 7360 was that the a.c. filament 
> current would 
> introduce hum into the circuit.  The magnetic field from the 
> filament would 
> modulate the beam deflection enough to modulate it slightly 
> at 60~.  I am 
> sure this was never a problem with the  slopbucket rigs of 
> that era since 
> everything below about 500~ was rolled off anyway to produce 
> "communication 
> quality", but it was certainnly noticeable in my homebrew SSB 
> generator.  Of 
> course there is a very simple fix: use reasonalbly well 
> filtered DC on  the 
> filament.  I have found that to be necessary even with the 12AX7 1st 
> amplifier stage of my mic preamp.
> 
> _________________________________________________________________
> Crave some Miles Davis or Grateful Dead?  Your old favorites 
> are always 
> playing on MSN Radio Plus. Trial month free! 
> http://join.msn.com/?page=offers/premiumradio
> 
> _______________________________________________
> AMRadio mailing list
> AMRadio at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/amradio