<VV> 30 watt or 80 watt replacement speakers

[Tony Underwood]

At 09:52 AM 3/9/2012, corvairduval at cox.net wrote:
>Not only is 10 watts all you have in a stock radio, you also only have ONE
>channel, mono. So why two speakers mounted in one opening? In case you
>upgrade later to a stereo radio?
>
>Frank DuVal



I'd wager that the factory Delco radio is hard pressed to deliver 
more than about 5 watts output so there's little chance of damaging 
any speaker you may attach to one.


Now, the interesting part about the Delco radios of that vintage is 
their Class-A output circuitry.   It's designed to work best with a 
10 ohm load, as in a single 10 ohm speaker.   It is also very 
inefficient, drawing something like 15 watts of power continuously 
even when idle, no output at all.  But, they're working with an 
almost unlimited current source (the vehicle's battery/charging 
system) so the inefficient Class-A output circuit is useful in a car 
radio because its internal amplifier only has about a dozen 
components which cuts down on costs in manufacturing although the big 
finned heat sink on the output transistor and the mandatory matching 
transformer tends to offset this.

These radios are somewhat critical regarding the impedance of the 
speaker attached to them... anything much lower or higher than 10 
ohms will cause a mismatch and a loss of volume which can also, 
depending on how far off from 10 ohms, can end up causing distortion 
if you crank the volume up a bit.

Two speakers attached to a Delco Class-A output radio without a 
balanced fader control could present problems since it's unlikely 
that the pair will be wired so as to present a 10 ohm load to the 
radio... as in a pair of 20 ohms in parallel or a pair of 5 ohms in 
series.   Two 4 ohm speakers in series *could* work out well enough, 
but what layman has the know-how to be aware of this and wire them 
correctly without getting them out of phase etc?

Better to stick with a single 8 ohm speaker... although most car 
speakers anymore are usually only 4 or 3.2 ohms.   I'd not wanna use 
a 4 ohm speaker on a Delco car radio from the '60s.  The power output 
is gonna drop and if you crank the knob up to compensate there's not 
much headroom before it distorts.  The 8 ohm speaker is close enough 
to a match that you won't hear much if any difference.


tony..