26-04-2022, 09:36 AM
Ah - if "low-powered guitar amp" was the original thought, mentioning that in the question would have saved me including the stuff about T/S parameters (normally when someone asks for specs of a drive unit, that is what they mean). The T/S parameters are about sorting out the bass end, but obviously that's not relevant to a guitar amp. Still, hopefully it helps someone else one day...
Andy, if you didn't use a resistor, I suspect you used a signal generator to drive the speaker directly. The built in source impedance (50ohm, 600ohm, or whatever) would be fine for seeing the resonant peak. It's what I do all the time.
As I say, I suspect this is more a radio speaker than a guitar speaker. Too feeble for serious use, and too much like other Goodmans radio speakers I've seen. As such, it won't be as efficient as a "proper" guitar speaker, but I'm sure it'll be fine for practice. After all, people convert radios with smaller speakers:
https://www.youtube.com/watch?v=HVdG8UF2UMU
As a Hacker collector it's a bit tricky to condone it, but radio side was dead and there's so little on AM these days anyway. The only mod appears to be a hole in the side for the socket (perhaps he used a switched socket that would allow the radio side to work if ever he fixed it?), but a future radio collector could replace that with a DC input socket. Of course, if he'd found a Sovereign II instead, it would already have the input socket.
Based on that video, I'd say that a Hacker A205 would be the ideal amplifier for this project. Just add an input socket and a volume control, plus a couple of PP3s (and perhaps a DC input socket?). The amp has bass and treble controls too - take those from the donor radio. That takes care of the electronics - meaning it's now just a woodwork project. Simple
Of course, if you don't want to "rob" (sorry!) an amp from a working Hacker, just copy the circuit. It's simple enough to knock up on Veroboard or even tagstrip, and the schematic is widely available:
https://www.markhennessy.co.uk/articles/hacker_a205.jpg
Transistors aren't critical - it would be quite possible to use silicon instead of germanium for T3-6, depending on your beliefs.
Andy, if you didn't use a resistor, I suspect you used a signal generator to drive the speaker directly. The built in source impedance (50ohm, 600ohm, or whatever) would be fine for seeing the resonant peak. It's what I do all the time.
As I say, I suspect this is more a radio speaker than a guitar speaker. Too feeble for serious use, and too much like other Goodmans radio speakers I've seen. As such, it won't be as efficient as a "proper" guitar speaker, but I'm sure it'll be fine for practice. After all, people convert radios with smaller speakers:
https://www.youtube.com/watch?v=HVdG8UF2UMU
As a Hacker collector it's a bit tricky to condone it, but radio side was dead and there's so little on AM these days anyway. The only mod appears to be a hole in the side for the socket (perhaps he used a switched socket that would allow the radio side to work if ever he fixed it?), but a future radio collector could replace that with a DC input socket. Of course, if he'd found a Sovereign II instead, it would already have the input socket.
Based on that video, I'd say that a Hacker A205 would be the ideal amplifier for this project. Just add an input socket and a volume control, plus a couple of PP3s (and perhaps a DC input socket?). The amp has bass and treble controls too - take those from the donor radio. That takes care of the electronics - meaning it's now just a woodwork project. Simple
Of course, if you don't want to "rob" (sorry!) an amp from a working Hacker, just copy the circuit. It's simple enough to knock up on Veroboard or even tagstrip, and the schematic is widely available:
https://www.markhennessy.co.uk/articles/hacker_a205.jpg
Transistors aren't critical - it would be quite possible to use silicon instead of germanium for T3-6, depending on your beliefs.
