[AMRadio] 32V-2 speech amp question


Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Mon Jan 23 11:53:29 EST 2006


I agree its pointless to run hifi at 100 watts, but making the rig 
able to run hifi, and then restricting it is a good way to go.

That is why I use the d104 with the 32v, a nice mid range punch, with a bit
of some lows in there to stop it from sounding like a cheap phone.

I hear plenty of weak signals on 40 meters, guys running 50 to 100 watts and
full fidelity, at least the bass, and they are hard to copy over the stock 
sound of most rigs.

I always thought the 75A4 sucked on AM, as most Collins receivers do, 
poor detectors, poor audio amps, poor filter choices.

The Collins design R390/a was good if noisy, but that was the only one I
ever
found to sound good on AM.

As far as bandwidth goes, I hear much more problems from people over
modulating
than from people running hifi audio. That may cause some ssb guys to
complain
about AM. On 40 meters last weekend, I heard 4 stations in the short time I 
was listening (Sunday morning) and 3 were over modding and quite wide.
The scope showed they were closing down the carrier quite well, and were 15
kc wide.


I assume most AM guys on 40 have no way to monitor their modulation and
just turn it up to what the book says, then a little more.
Or they set it up on the scope, and when they operate, they get excited
and talk louder or something.

I feel if you are going to operate AM, you need to be able to 
see and hear your modulation. The ssb guys do not have problems as much as
they have ALC built into their rigs.

Brett
N2DTS
 
 

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of John E. 
> Coleman (ARS WA5BXO)
> Sent: Monday, January 23, 2006 11:19 AM
> To: 'Discussion of AM Radio'
> Subject: RE: [AMRadio] 32V-2 speech amp question
> 
> 	The 32V driver is certainly adequate for the 
> specifications of the
> rig.  I might add that the specifications in fidelity are 
> fine for me.  I
> think it and the 75A4 receiver could do better on THD.  
> However, I think
> Craig was looking for more fidelity.  This might be a good 
> time for me to
> inject the Woos of HiFI.  HIFI is OK for use on ground wave without
> selective fading and of course when the spectrum is void of 
> other QSOs.  The
> problem that I have is the QRM/QRN that accompanies cross 
> country QSOs when
> the band is open for that type of propagation.  I narrow up 
> the RCVR to get
> a better signal to noise ratio and that's when I begin understand the
> problems of having bass without treble.  I'm talking bass 
> below 100 CPS.  It
> sounds great when with a wide band pass and assuming the XMTR 
> is passing
> treble out to 15KHZ.  But when you narrow down to 6-8 KHZ you 
> need to roll
> the lows of starting at 200HZ and eliminate them below 75HZ.  
> I don't like
> 60 CPS hum so I switch to a small very desk top speaker or 
> cheap head phones
> to eliminate the bass.  The XTMR would do better in this case not
> transmitting the low bass but instead putting the energy into 
> low distortion
> limited band width audio.
> 
> This takes me to the new RMs that or in place.  I can see all 
> the sides as
> having made good points.  And I just don't know what to do.  
> I feel that the
> FCC is going to get annoyed at the whole thing and wash there 
> hands of it
> and I don't know where that will leave us.
> 
> John, WA5BXO
>  
> 
>  
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Brett gazdzinski
> Sent: Sunday, January 22, 2006 7:04 PM
> To: 'Discussion of AM Radio'
> Subject: RE: [AMRadio] 32V-2 speech amp question
> 
> Keep in mind, the input impedance is very high, 1 meg at the mike
> input stock radio. No transformer on the mike input in the 32v series.
> I thought the driver transformer was adequate, its very large 
> for a driver
> transformer, the
> DX100 has a postage stamp, the 32v had a fist sized driver 
> transformer.
> 
> I use a pair of KT88 tubes as modulators and don't use the driver
> transformer 
> (gave it away a long time ago). If you run the high impedance 
> mike preamp in
> the 
> rig and want some hifi, you have to run the mike preamp tube off DC.
> I just did 1/2 wave (1 diode) and an electrolytic cap. The 
> size of the cap
> sets 
> the voltage the filament runs at. 
> The DC does not need to be pure, even rough DC will eliminate hum.
> 
> Neg feedback, regulated voltage on the mod tube screens, 
> large coupling caps
> will get you a long way to a good sounding 32V.
> Brett
> N2DTS
> 
> 
> 
> > -----Original Message-----
> > From: amradio-bounces at mailman.qth.net 
> > [mailto:amradio-bounces at mailman.qth.net] On Behalf Of John 
> > Coleman ARS WA5BXO
> > Sent: Sunday, January 22, 2006 11:03 AM
> > To: 'Discussion of AM Radio'
> > Subject: RE: [AMRadio] 32V-2 speech amp question
> > 
> > 	I have not driven it externally before Craig but have some
> > experience with the circuitry and the driver XFMR is a weak 
> > link in the
> > circuit the XFMR barely has enough iron and coupling 
> > coefficiency in it
> > to pass the low frequencies that the rig is designed for.  
> As a matter
> > of fact if the cathode resistor of the driver stage drops in 
> > resistance,
> > as they or known to do with heat, the driver plate current 
> > will quickly
> > saturate the driver XFMR causing the bass frequencies to look like a
> > trapezoid instead of sine wave.  If you were going to go with and
> > outboard amplifier I would include a better driver XFMR as 
> part of the
> > external circuit and go to the grids directly.
> > 
> > John
> > Coleman
> > 
> > -----Original Message-----
> > From: amradio-bounces at mailman.qth.net
> > [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Craig Roberts
> > Sent: Saturday, January 21, 2006 10:19 PM
> > To: Discussion of AM Radio
> > Subject: [AMRadio] 32V-2 speech amp question
> > 
> > Has anyone tried driving the mod input transformer of the 
> > 32V-2 (or V-3)
> > 
> > directly with an outboard mic preamp?  If so, what were the results,
> > please?
> > 
> > Many thanks and 73,
> > 
> > Craig
> > W3CRR
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