<VV> Replacement radio speaker options - late model

[Tony Underwood]

At 11:02 hours 04/30/2005, Les wrote:
>Hi,
>
>Original speaker on my '65 (AM pushbutton) is dead. Plenty of 4 ohm 6x9s 
>available; original speaker was 10 ohm.


You *might* still find a 10 ohm 6x9 at your local GM dealership.  Check 
with them.    It won't have the same magnet (it will be round) but the 
impedance will be OK.


>Can I use a 4 ohm 6x9,

Yes but it's a mismatch and the output transistor will tend to draw more 
current and deliver less output, considerably less seeing as how the radio 
is DC/autotransformer-matched to the speaker which is why it uses that odd 
10 ohm speaker... to provide a good imp4edance match to the single-ended 
class-A audio output circuit.   It's a terribly inefficient design, but it 
does get by with using only three transistors in the entire audio output 
circuit.   And, effectively with a storage battery you have practically an 
unlimited source of input power so the efficiency factor is moot.


>or do I need to rig a pair of 5" or so speakers in series to get close to 
>10 ohms?


Kinda complicated, that, although it will work.   Look around for a 10 ohm 
6x9 GM replacement speaker,  or check around for an 8 ohm speaker, close 
enough to not make much difference as far as the output match is concerned.

>How about a 6 ohm resistor in series with the 4 ohm speaker (I know that's 
>resistance and not impedance)?


Not a good idea...  it will drastically reduce audio output to the 
speaker.    Never a good idea to put a resistor in series with a speaker 
since all it does is limit current and thus drop power output to the speaker.


>I tried a 4 ohm speaker here and the output transistor gets kinda warm...


Typical...  a class-A audio power amplifier will get hot, it's 
normal.   The impedance mismatch won't have that much of an effect on the 
output transistor temperature, but it *will* have a relatively large effect 
on audio output power.   Transformer coupled output devices rely on a good 
impedance match for best performance.   Have you tried the vendors for a 
correct impedance speaker...?


tony..