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Hammarlun SP-210 speaker
Hello all, I've been given an old Hammarlund SPR-210. It needs a good amount of restoration but appears complete inside and outside. I've seen on the manual that it has 600 ohm speaker output and I was wondering where to find such a spekear with this impedance. Probably there's need for an external audio transformer to use any low impedance (I have many in the 16-4 ohm range) speaker? Any hint is welcome. Best regards Frank IZ8DWF |
Hammarlun SP-210 speaker
On Oct 6, 8:22*am, frank wrote:
Hello all, I've been given an old Hammarlund SPR-210. It needs a good amount of restoration but appears complete inside and outside. I've seen on the manual that it has 600 ohm speaker output and I was wondering where to find such a spekear with this impedance. Probably there's need for an external audio transformer to use any low impedance (I have many in the 16-4 ohm range) speaker? Any hint is welcome. Best regards Frank IZ8DWF The usual fix is to use a 10-watt, 70-volt line to voice coil transformer. The 10-watt tap on a 70-volt line to voice coil transformer will provide a decent match to a 500/600 ohm output. In a pinch, an ordinary filament transformer will do. Get a transformer with a 120-volt primary and 12.6-volt secondary and connect the 120- volt winding to the receiver and the 12.6-volt winding to the speaker and you are done! --Ed |
Hammarlun SP-210 speaker
frank wrote:
I've been given an old Hammarlund SPR-210. It needs a good amount of restoration but appears complete inside and outside. I've seen on the manual that it has 600 ohm speaker output and I was wondering where to find such a spekear with this impedance. Probably there's need for an external audio transformer to use any low impedance (I have many in the 16-4 ohm range) speaker? Any hint is welcome. If you wound a 600 ohm voice coil on a speaker, it would be so heavy you'd have no high end at all. SO, what we do is to put a 600-8 ohm transformer behind the speaker; lots of communications speakers have mounting points on the back so you can bolt the transformer right there. A 1W transformer for a 70V PA system has about a 600 ohm to 8 ohm ratio, and will cost less than $5 at an electronics supply house. Or ask a guy who installs 70V PA systems for piped-in music in supermarkets for an old one. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
Hammarlun SP-210 speaker
Hello Ed!
Ed Engelken wrote: The usual fix is to use a 10-watt, 70-volt line to voice coil transformer. The 10-watt tap on a 70-volt line to voice coil transformer will provide a decent match to a 500/600 ohm output. In a pinch, an ordinary filament transformer will do. Get a transformer with a 120-volt primary and 12.6-volt secondary and connect the 120- volt winding to the receiver and the 12.6-volt winding to the speaker and you are done! --Ed thank you for the suggestion, I do have a spare 120V primary transformer lying around (I live in a 240V country, so no use for it). I could also wire my own transformer, but that would take some time. I don't know what a line to voice coil transformer is, can you explain better this part? Thanks a lot. Best regards Frank IZ8DWF |
Hammarlun SP-210 speaker
On Tue, 6 Oct 2009, Richard Knoppow wrote:
"frank" wrote in message ... Hello Ed! Ed Engelken wrote: The usual fix is to use a 10-watt, 70-volt line to voice coil transformer. The 10-watt tap on a 70-volt line to voice coil transformer will provide a decent match to a 500/600 ohm output. In a pinch, an ordinary filament transformer will do. Get a transformer with a 120-volt primary and 12.6-volt secondary and connect the 120- volt winding to the receiver and the 12.6-volt winding to the speaker and you are done! --Ed thank you for the suggestion, I do have a spare 120V primary transformer lying around (I live in a 240V country, so no use for it). I could also wire my own transformer, but that would take some time. I don't know what a line to voice coil transformer is, can you explain better this part? Thanks a lot. Best regards Frank IZ8DWF I've used filament transformers many times and they work well. While the fidelity may not be as good as a special purpose audio transformer I doubt you will be able to tell the difference in this application. Of course, one solution in the old days was to use a 400Hz transformer, which were cheap and available as surplus, and which didn't have much use in the average ham shack at the time. The idea being that since it's intended for 400Hz, the upper frequencies might get through the transformer better, and the loss of lower frequenices didn't matter since for voice you didn't care about much below 300Hz. Nowadays it may no longer be a solution, given WWII is so far in the past and the stores that might have them for next to nothing nearby are gone too. Michael VE2BVW |
Hammarlun SP-210 speaker
Michael Black wrote:
Of course, one solution in the old days was to use a 400Hz transformer, which were cheap and available as surplus, and which didn't have much use in the average ham shack at the time. The idea being that since it's intended for 400Hz, the upper frequencies might get through the transformer better, and the loss of lower frequenices didn't matter since for voice you didn't care about much below 300Hz. Nowadays it may no longer be a solution, given WWII is so far in the past and the stores that might have them for next to nothing nearby are gone too. 400 Hz transformers are still very popular for modern aircraft applications. There are still lots of them on the surplus market. They catch fire if you connect them to a 60 Hz source because the series inductance is very low. They actually aren't very good as audio transformers even. Really, they aren't good for anything. If you want some, let me know. I even have a bunch of sealed 120VAC-200VDC supply modules, 400 Hz only. Not useful. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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