Motorola SK28M?
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century tek
Addicted Member
Is it a 3 channel amp? You can still make it a stand alone 'cept with the 3 channel jobbers, its best to run it as such with all 3 speakers.
Motorola was famous for their 3 channel amplifiers so they are not the best candidates for stand alone 2 channel.
Motorola was famous for their 3 channel amplifiers so they are not the best candidates for stand alone 2 channel.
bobrown14
Super Member
What can I do with this Moto 3 channel amp if I pull it?
I guess I'm thinking of amp duty.
Cheers,
Bob
davestradamu
Swimming in Sound
i have a similar amplifier. seems like the best idea is to use the existing speakers (maybe GoldenVoice?). i would like to convert my amp into a headphone amplifier but i have to see what kind of work is involved. i dont do my own mods and it could get expensive....
outlawmws has a similar amplifier and has done a great job with it, and has done some work with goldenvoice speakers. maybe he can chime in with some help. he seems to know a good amount about these moto amps... :thmbsp:
outlawmws has a similar amplifier and has done a great job with it, and has done some work with goldenvoice speakers. maybe he can chime in with some help. he seems to know a good amount about these moto amps... :thmbsp:
So what did you do?
Bob, what did you decide? I just bought the same amp $15 at goodwill, mostly to get into tube audio, but not sure what to do with the 3 channels... seems like it would work well as L/R & subwoofer (since that's essentially what it is, right?) I don't feel too bad about gutting it since the finish is really crazed, prob not worth trying to refinish.
Bob, what did you decide? I just bought the same amp $15 at goodwill, mostly to get into tube audio, but not sure what to do with the 3 channels... seems like it would work well as L/R & subwoofer (since that's essentially what it is, right?) I don't feel too bad about gutting it since the finish is really crazed, prob not worth trying to refinish.
Thats basically what you do with it. Its more of a woofer than a sub, but you get the idea. perfect use for a big orphan speaker though, or you can repurpose the original drivers into an open baffle sort of arrangement since they're likely a good match efficiency-wise to each other and the amp's power output.
Hey gadget73, thanks for the response. I'm leaning towards repurposing as a standalone since: 1) we don't have that much room, 2) I'm good at woodworking and want to build a pretty box to put it in, 3) the cabinet is in rough shape, and 4) I just like the idea of a classy old tube amp CHEAP without the honkin' big console.
Are there any problems using it without a woofer? Can I just run an 8 ohm load across it? What if I hook it up to a modern passive sub? Is there a market for the parts I strip (turntable, tuner, etc.)?
Other questions: what's the best supplier for caps/tubes? If there's an online guide to this kind of rehab project somewhere, point me there, thanks!
Are there any problems using it without a woofer? Can I just run an 8 ohm load across it? What if I hook it up to a modern passive sub? Is there a market for the parts I strip (turntable, tuner, etc.)?
Other questions: what's the best supplier for caps/tubes? If there's an online guide to this kind of rehab project somewhere, point me there, thanks!
You can run it without the woofer but you'll have pretty miserable bass and low midrange output. A modern passive sub might work, if its efficient enough. Keep in mind you're dealing with small power here. The left and right channels are probably good for about 5-6 watts each and the bass channel is about 12-14. Most subs will barely tickle at that level, so you need a speaker that makes a lot of sound without much input for it to work well.
Trio
Super Member
Although: you could use the woofer (as originally design intended) for the low frequencies directed towards the listener, and then with a capacitor for isolation and a rheostat tapped in on that woofer channel- add a self powered subwoofer behind the seating area for the nondirectional bass.
brendandoher
Active Member
Yes, you should just get a 2-channel. the other parts are hardly worth a thing, unless they're special-old jensen or alinco speakers, etc. Magnavox is your good bet for a console- the schematics are everywhere in here, and they were common. the tubes are readily available.
Wigwam Jones
Caesar non supra grammati
Questions about value belong in the D&S forum.
In answer to your question about the amp itself, I have a 3 channel Moto and I like it very much. But you use it as a 3 channel amp; too much work to try to make it a 2 channel amp. I'm not sure why people get so squicked by that idea; I think 3 channels is fine. But if you absolutely must have a 2 channel amp, then you should buy one of those; this isn't one and won't be made into one easily.
center channel speaker?
Wigwam, thanks, do you have your set up as a standalone with external speakers, or are you just using the console. If it's a standalone, what do you use as a center channel speaker?
Wigwam, thanks, do you have your set up as a standalone with external speakers, or are you just using the console. If it's a standalone, what do you use as a center channel speaker?
Wigwam Jones
Caesar non supra grammati
I was given the amp sans console, but it did come with the original preamp, so at the moment, that is how I am using it, just standalone. I have been running a pair of Boston Acoustics HD5 speakers as the L and R and using a big gigantic 15" Fisher woofer (also given to me by a friend) as the center channel. My eventual plan is to mount both 15" speakers in an open baffle arrangement, as they were originally used in a console which was not sealed. I plan to run both 15" woofers as the center channel, and a set of 'normal' speakers as the L and R. The woofers will be placed L and R, but obviously won't have any stereo separation themselves, as they will be running a single channel output. Just aesthetics, they won't be plopped in the center of the room.
In a sense, this is a 2.1 arrangement, as others have mentioned. It's also worth noting that bass frequencies are somewhat directionless, so I won't lose a lot of stereo separation (I will lose some, but I'm OK with that). My particular Motorola 3-channel has 6BQ5 tubes. The L and R are single-ended and the center channel is push-pull. Very fascinating design, and I like the way it sounds. If memory servers, the crossover point is about 600 Hz, which really allows the woofers to not have to work at playing any higher frequencies, and gives the same break to the woofers in the smaller speakers I'm using, not making them try to play anything below 600 Hz. At the moment, the system sounds just fine even with the jury-rigged setup I am using, just propping the single 15" woofer up on its side. I'm really pleased with it.
Wigwam, thanks, that's exactly what I thought. If I can get a few $$ for the speakers (especially the 15" Jensen woofer) from somebody doing a refurb on a console, I'll get myself a decent passive sub and set up the pre/power amp in a box. Do passive subs have xovers? Even if they did I could bypass since the amp already filters. If nobody wants teh speakers I'll just put the 15" in a standalone cabinet, hook up some sensitive L/Rs and call it good.
Ok, so I've been working on rebuilding the amp. Today I used a hole saw to make walnut knobs for it, I'm going a bit overboard but I think it will be nice. Anyway, I was thinking what I needed was a good passive subwoofer that I could use for the center channel. A week ago I picked up a Bose Acoustimass 3 Series iii at a yard sale for $10. Today it occurred to me that the Bose system IS a passive subwoofer, with a couple satellites. Except I can't find any documentation on the system. The user's manual says you're not supposed to connect the speakers directly to the amp, only through the subwoofer. Any idea why? Would the sub likely not handle high enough frequencies? Any thoughts on using the Bose system with this amp, connecting the satellites directly to the L/R and the subwoofer to the center channel?
Wigwam Jones
Caesar non supra grammati
If I had to guess (and it is indeed a guess), then I'd guess that the reason you're not supposed to connect the satellites directly to the amp, but to the subwoofer instead, is because the subwoofer contains some crossover circuitry that keeps the low frequencies out of the satellites.
If there is any way to check the crossover frequencies of your Bose speakers, that might help you out in deciding. If I am not mistaken, the center channel of the Moto handles everything below 600 Hz and the left and right handle everything above that frequency. You would want something to match that in your Bose setup. If not, you could end up with some serious holes in your frequency response at best, and damaged components at worst. That is my guess; if others have better information, I'd defer to them on this.
century tek
Addicted Member
Yup! :yes: That's what it is! :thmbsp:
The satellites may be perfect for use with your Motorola amp as the satellite speakers are basically a mid/high driver, and the left & right channel frequencies from the Motorola are also mid/high outputs so this might work perfectly for you.
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Wouldn't it be safe to assume the amp itself has some filters built into it (no point sending frequencies to the tweeters or woofer that they aren't capable of)?