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 Post subject: What did I buy?
PostPosted: Jun Fri 22, 2018 8:44 pm 
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Location: saint clair shores, michigan
I picked this up at an estate sale for $5. When looking at it I thought it was an amplified extension speaker that mixed right and left stereo channels into mono. After taking the back off, I see a reverb tank. Also I don't understand the hook up diagram on the back showing another speaker. The reverb has two springs - so I assume for stereo. The tube lineup is 50EH5, 30A5, 12AU6. It looks to be in almost unused shape, I got it for next to nothing, but what is it?


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 Post subject: Re: What did I buy?
PostPosted: Jun Fri 22, 2018 10:24 pm 
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I think you are right, it is a reverb add-on speaker with a built in amplifier.

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 Post subject: Re: What did I buy?
PostPosted: Jun Sat 23, 2018 12:01 am 
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I found a model - SK-256 - that indicates it is indeed a amp\reverb\speaker. Trying to find instructions and or detailed description.

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 Post subject: Re: What did I buy?
PostPosted: Jun Sat 23, 2018 1:14 am 
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They were very popular in the "good old days" of audio.

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 Post subject: Re: What did I buy?
PostPosted: Jun Sat 23, 2018 12:04 pm 
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A reverb was used with a monaural signal source to simulate a kind of “stereo”. Made me laugh when a friend had one in his 1966 GTO and we hit a bump or especially went over railroad tracks. Quite a sound!

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 Post subject: Re: What did I buy?
PostPosted: Jun Sat 23, 2018 1:45 pm 
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I remember reverb units being used in cars in the 60's as a couple of friends had them in their cars. The sound was interesting at best especially like Don says when driving over a railroad track or on a bumpy road. They sort of sounded like stereo coming out of a monaural AM radio. If I remember correctly, the reverb units were sort of a fad and didn't stick around too long. The only reverb unit I've seen in recent history was in a Fender Twin Reverb Amplifier that I restored last year which actually sounds pretty good. Harry


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 Post subject: Re: What did I buy?
PostPosted: Jun Sat 23, 2018 6:27 pm 
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The SK-256 was designed to work with mono or stereo receivers/amplifiers, etc. to achieve that "concert hall" echo effect. The schematic shows an AC input transformerless design so safety is important when diddling with the SK-256. And roughly 10 years later, we started playing with passive 4-channel setups. Unless you're running the SK-256 in a mobile home and constantly riding and bouncing over railroad tracks, the reverb mechanism in it is fairly sturdy.

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 Post subject: Re: What did I buy?
PostPosted: Jun Tue 26, 2018 4:45 am 
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I hooked it up tonight. The knob is push on \ push off for power, in addition to volume. There is a stylish (for the time) neon power indicator lamp behind the speaker cloth, underneath the Lafayette badge. The sound is equivalent to the car reverbs I have heard over the years. In other words, a twangy echo. All in all, IMHO a cool piece of vintage "hi-fi" equipment, although from the stereo era.

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 Post subject: Re: What did I buy?
PostPosted: Jun Fri 29, 2018 2:11 pm 
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Well if you can disable or bypass the reverb, you might have a handy amplified speaker unit for the bench. Otherwise you could attach a quarter inch jack to the high gain inputs and advertise it as a tube practice amp with reverb, for the guitar players.

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 Post subject: Re: What did I buy?
PostPosted: Jun Fri 29, 2018 5:44 pm 
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You'll have to add an isolation transformer for it to be good for anything.

-David


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 Post subject: Re: What did I buy?
PostPosted: Jul Sun 01, 2018 7:29 pm 
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That may be the case, but, what is the transformer on the board for?

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 Post subject: Re: What did I buy?
PostPosted: Jul Sun 01, 2018 9:56 pm 
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Excellent question! An isolation transformer would need capacity for 35 watts, but the transformer on the board looks much too small for that.

-David


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 Post subject: Re: What did I buy?
PostPosted: Jul Sun 01, 2018 11:18 pm 
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dberman51 wrote:
Excellent question! An isolation transformer would need capacity for 35 watts, but the transformer on the board looks much too small for that.

-David

Is it an impedance matching input transformer?

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 Post subject: Re: What did I buy?
PostPosted: Jul Sun 01, 2018 11:19 pm 
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wazz wrote:
That may be the case, but, what is the transformer on the board for?

Input coupling.

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 Post subject: Re: What did I buy?
PostPosted: Jul Mon 02, 2018 3:42 pm 
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That should be adequate for isolation as well, as long as nothing touches the chassis.

-David


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