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 Post subject: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Wed 29, 2017 2:12 am 
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Joined: Nov Thu 22, 2007 11:31 pm
Posts: 819
Location: Johnston, Iowa
All, I've rebuilt dozens of antique radios but this will be my first stereo. Does anyone have schematics for these? Any idea how they will sound? Were the Knights all sold as kits? I've got lots to learn.
Thanks,
Keith


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Wed 29, 2017 6:04 am 
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Location: Ft Worth TX
EICO Dyna and Heath sold preassembled as well as kits. Not certain about Knight, lean toward yes.

I built a KG50 long about 1965. Very satisfied. College was ~40 miles into fringe and it worked fine. Earlier built EICO HFT90 and MX99, preferred the Knight. Interchannel hush on FM and the stereo decoder 'seemed' more transparent.


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Wed 29, 2017 2:59 pm 
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Location: Fernandina Beach, FL
Here is a scan of a scan of the amplifier, KG-250 that I could find in my files. It is an earlier schematic but the same amplifier.

Image

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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Wed 29, 2017 3:08 pm 
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Don Cavey wrote:
Here is a scan of a scan of the amplifier, KG-250 that I could find in my files. It is an earlier schematic but the same amplifier.

Image



And the tuner will be in two separate scans. I don't have Photoshop on this computer so I can't stitch it at the present moment.

Image

Image

I can email the scans to you later today if you wish.

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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Wed 29, 2017 3:26 pm 
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I have worked on a few of the KG-250 Knight amplifiers (and its earlier version, same circuit). One thing that was always bad was that huge electrolytic capacitor. What I did was to install discrete individual capacitors on the terminal strip. Plenty of room to do that.

I also found most of the 220KΩ (red-red-yellow-silver) ½-watt plate resistors on the 12AX7 tubes to be either open or very high in value. You might check them out.

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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Thu 30, 2017 1:04 am 
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Joined: Nov Thu 22, 2007 11:31 pm
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Location: Johnston, Iowa
Thanks everyone, I picked it up today and it appears to be in good condition but one of the speakers is missing. The single remaining speaker is a Utah coaxial speaker. I'm suspect I need to find another one so the sound is balanced. Can anyone recommend a speaker replacement that will sound good with this setup? The tuner and amp came in a home made cabinet with a record player that looks better than it does in this photo. I think I'll paint it black and add new speaker cloth. I'll change all caps and swap out any out of spec resistors before I power it on. Here are some pictures.
Keith


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Utah back sidejpg.jpg
Utah back sidejpg.jpg [ 219.12 KiB | Viewed 1508 times ]
utah front.jpg
utah front.jpg [ 247.29 KiB | Viewed 1508 times ]
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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Thu 30, 2017 2:57 pm 
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That's a 12" speaker, right?

What you could do is connect the one speaker to a decent amplifier and see how good it sounds. If it is a sound you like then all you need to do is find another Utah like that one.

If it doesn't sound good to you then find a good quality pair of 12" Coaxial speakers such as Goodmans, Olson, JBL, Altec ETC...

That Utah speaker is actually not a coaxial. It is just a regular speaker with a whizzer cone.

A coaxial speaker will have a tweeter where the whizzer cone is and will have a crossover.


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Fri 31, 2017 1:19 am 
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Joined: Nov Thu 22, 2007 11:31 pm
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Location: Johnston, Iowa
Quote:
That's a 12" speaker, right?

What you could do is connect the one speaker to a decent amplifier and see how good it sounds. If it is a sound you like then all you need to do is find another Utah like that one.

If it doesn't sound good to you then find a good quality pair of 12" Coaxial speakers such as Goodmans, Olson, JBL, Altec ETC...

That Utah speaker is actually not a coaxial. It is just a regular speaker with a whizzer cone.

A coaxial speaker will have a tweeter where the whizzer cone is and will have a crossover.


Yes, it's a 12 inch. I haven't had time to look at the speaker but I suspect it's trashed. The builder of the cabinet wired the amp speaker wires onto a standard 120V outlet on the back side of his cabinet. He then wired the speakers using standard 2 prong extension cord. I remember the guy who sold it to me said he plugged the speakers in and they didn't work. I'm guessing he plugged them into a 120V outlet. When I look for new coaxial speakers do I need match the wattage to the amp?
Thanks,
Keith


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Fri 31, 2017 1:35 am 
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The KG-250 when working properly is about 10 watts RMS per channel output. So, you would need rather efficient speakers. Bass reflex comes to mind. Sealed, acoustic suspension speakers often need more power to push them.

Klipsch speakers are supposed to be a good match but have a pair and I am not all that impressed with them. AR speakers often needed quite a bit of power to push them.

I also have a pair of JBL L100 speakers hooked up right now. They are reflex cabinets and have good response. But it appears that they have become popular and are quite expensive.

Bang & Olufsen S45-2 speakers (Not to be confused with S45) are quite a match for tube amplifiers. But don't forget, we are talking 10 watts per channel, something like the output of a pair of 6V6 PP.

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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Mar Fri 31, 2017 2:30 am 
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Had he plugged them into a 120Vac outlet the one speaker would have easily visible damage and have a smoke smell.

Now if you want some great sounding efficient speakers find a pair of 12" capehart field coil speakers which were made by Jensen as I recall. The field coil of each will be 750 ohms. The voice coil is 8 ohms. They were used in one of capeheart's high end consoles with two per console.

I have a pair I use in my Magnavox CR-198C console and they sound real good and can easily go down to below 30Hz and would be perfect for a 10 watt amp.

Just need a decent tweeter and a proper crossover. The tweeter could be mounted in front of the 12" driver unless there's room in the cabinet to cut a hole on the speaker baffle.

That said a pair of Altec 811B horns with Eminence PSD2002s-8 drivers would work as well and they can sit on top of the speaker cabinets.


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Apr Thu 06, 2017 5:16 pm 
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Keith, I got your emails and read them about the MPX adapter and tuners etc. Lots going on right now so I am not ignoring your questions etc. I think that you are on the right track. Allied Radio Kinght-Kit audio was and is good stuff. I have had a lot of it over the years and have my Dad's original 18-watt 6973 output mono amplifier as well as his matching tuner.

http://www.alliedcatalogs.com/html/1959-180/h247.html

http://www.alliedcatalogs.com/html/1959-180/h249.html

And this is the predecessor to the KG-250

http://www.alliedcatalogs.com/html/1959-180/h246.html

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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Apr Tue 11, 2017 11:25 am 
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Joined: Nov Thu 22, 2007 11:31 pm
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Location: Johnston, Iowa
I managed to restuff the 5 section orange electrolytic capacitor on the kg-250 and all the resistors are within specs so I'm ready to try out the amp. The selection switch has me confused. There are 8 connections for inputs but I'm not sure how they match up with the switch. For, example there are 3 aux setting, two are aux and one is aux rev. What does the rev. stand for? Here are some pics.
Keith


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firecracker.jpg
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Knight KG250 inputs.jpg
Knight KG250 inputs.jpg [ 169.94 KiB | Viewed 1346 times ]
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IMG_1010.JPG [ 169.32 KiB | Viewed 1346 times ]
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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Apr Tue 11, 2017 1:06 pm 
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This should explain it. Simply, one position reverses the channels from the other of the same input.

Image

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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Apr Thu 13, 2017 12:58 am 
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Joined: Nov Thu 22, 2007 11:31 pm
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Location: Johnston, Iowa
Thanks Don!!, That's exactly the info I need. I've got everything recapped and ready to go. I just need to find the time to plug it in.
Keith


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Sep Fri 08, 2017 6:22 am 
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I got an email asking for the scan as a file since the resolution is not that great here. I am in Australia right now and can't get access to the files and can't respond to the email. So, if you are waiting for a response, please be patient. I will be back in the US soon...

Send me a PM to confirm please.

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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Sep Fri 08, 2017 11:47 pm 
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Joined: Jan Thu 17, 2013 8:57 am
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Just got a kg 250 (no cabinet) Hoping to recap it and use it In my family room as my daily driver.


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Sep Wed 13, 2017 7:17 pm 
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Joined: Sep Tue 05, 2017 7:12 pm
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Me too, got a kg250 and the matching tuner with the wood cases. Starting with the amp...tested the tubes (all good) and waiting on the filter caps in the mail. Hopefully it'll be pushing speakers soon.
Was hoping to mod it with some pre-outs to feed a separate power amp to drive my Magnepans.
My early research shows this will not be trivial.
Any advice on such an endeavor?


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Sep Thu 14, 2017 12:21 am 
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There is a preamp output which you can use as is if the amp you are going to use it with is tube.

If solid state you will need a buffer.

I can provide a schematic of one using an OP-AMP tomorrow.


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Sep Fri 15, 2017 1:05 am 
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As far as I can tell, there's only a mono out from one channel of the phono section, before the tone control or volume control, or am I reading the schematic wrong somehow?
It is a sold state power amp, with 100kohm input impedance, so from what I've read I'm looking for the preamp outs to have an output impedance in the 1-5 kohm range.
What's the buffer for, and how does it work? I've read of tube buffers for giving a tube sound to a SS preamp before going to a SS power amp, but not of SS buffers for tube preamps. I'm kind of new to this...


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 Post subject: Re: KG-50 tuner and Knight KG-250 amp schematics needed
PostPosted: Sep Fri 15, 2017 1:23 am 
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On the amp itself there's no output jacks after the volume control so this cannot be used to control any other amp unless you were to add the correct jacks.

What the OP-AMP buffer does is takes a high impedance source and enables it to drive a low impedance load while keeping the output voltage the same.


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