08-01-2021, 09:01 PM
Any 50mm speaker of appropriate depth (17mm) can be used but you'll have to increase the series resistor to a higher value to limit the output current.
Altronics has a 50mm one that is marginal on its depth (18.2mm) and Jaycar has 40mm 0.25W both are 8 ohms impedance.
Ideally as not to cook the driver transistor this should be around 120 ohms for 8 ohm and 75 ohm for 50 ohm speakers when running your microbee from +12V.
When running on lower voltages you can use appropriately lower values. Doing this may affect its volume.
You can also install a flyback diode on the back of the speaker to control the back emf generated and also install a serial high pass filter capacitor to preventing the constant DC from flowing through the speaker.
Those speaker clips were are a standard item back in the early 1980's.
Many microbees were assembled with the speaker upside down and glued in when the clips were out of stock (or couldn't afford them).
You can make your own clips from your 3D printer or just fashion your own after you get the replacement speaker so you can alter it appropriately.
You can actually remove the 74LS92 for the conversion between 2MHz and 3.375MHz.
The change of Font ROM is not because of the 13.5MHz crystal but to provide a smaller font for the additional 80x24 mode.
However, the Font ROM used must have a sufficiently quick memory cycle time to run at the higher 3.375MHz.
Even some of the custom masked Dual Font ROMs are not fast enough and require upgrading. (That's an embarrassing faux pas.)
Someone also gets the same error message for clicking photos.
Altronics has a 50mm one that is marginal on its depth (18.2mm) and Jaycar has 40mm 0.25W both are 8 ohms impedance.
Ideally as not to cook the driver transistor this should be around 120 ohms for 8 ohm and 75 ohm for 50 ohm speakers when running your microbee from +12V.
When running on lower voltages you can use appropriately lower values. Doing this may affect its volume.
You can also install a flyback diode on the back of the speaker to control the back emf generated and also install a serial high pass filter capacitor to preventing the constant DC from flowing through the speaker.
Those speaker clips were are a standard item back in the early 1980's.
Many microbees were assembled with the speaker upside down and glued in when the clips were out of stock (or couldn't afford them).
You can make your own clips from your 3D printer or just fashion your own after you get the replacement speaker so you can alter it appropriately.
You can actually remove the 74LS92 for the conversion between 2MHz and 3.375MHz.
The change of Font ROM is not because of the 13.5MHz crystal but to provide a smaller font for the additional 80x24 mode.
However, the Font ROM used must have a sufficiently quick memory cycle time to run at the higher 3.375MHz.
Even some of the custom masked Dual Font ROMs are not fast enough and require upgrading. (That's an embarrassing faux pas.)
Someone also gets the same error message for clicking photos.