05-10-2018, 05:00 PM
Personally, I wouldn't. It's too big a jump. If it was less of a leap - say, from 8 to 4, then I'd be more relaxed about it.
The amplifier runs from 18V, and uses AC128/176 output transistors. They are already on a pretty reasonable heat sink, but the prospective output currents are the problem. If we pretend for a moment that the amplifier can swing over the whole 18V peak to peak range, that implies a peak current of 2.25 amps! Obviously that won't happen in practice, but the output transistors are only rated for 1 amp, which is 8V peak to peak into 4 ohms. Any attempt to play louder could damage the output transistors if the VAS stage driving them can source the current. 4V peak into 8 ohms is 2 watts. With the original speaker, I'd expect to get about 1.5 watts, give or take... At only 250mA peak, give or take...
Sets using 4 ohm speakers tend to come with the AC187/188 pair (and run from 9V rather than 18V). These are rated at 2A.
These speakers aren't hard to come by, so I'd wait until an original turns up. I might have one - I know that I have several RP33s, but without checking my database, I can't remember if one or more of them is a "donor". I've seen them fitted to loads of other UK radios.
The amplifier runs from 18V, and uses AC128/176 output transistors. They are already on a pretty reasonable heat sink, but the prospective output currents are the problem. If we pretend for a moment that the amplifier can swing over the whole 18V peak to peak range, that implies a peak current of 2.25 amps! Obviously that won't happen in practice, but the output transistors are only rated for 1 amp, which is 8V peak to peak into 4 ohms. Any attempt to play louder could damage the output transistors if the VAS stage driving them can source the current. 4V peak into 8 ohms is 2 watts. With the original speaker, I'd expect to get about 1.5 watts, give or take... At only 250mA peak, give or take...
Sets using 4 ohm speakers tend to come with the AC187/188 pair (and run from 9V rather than 18V). These are rated at 2A.
These speakers aren't hard to come by, so I'd wait until an original turns up. I might have one - I know that I have several RP33s, but without checking my database, I can't remember if one or more of them is a "donor". I've seen them fitted to loads of other UK radios.
