Kenwood 1100u - I'll never redo another one!

BuzzK

AK Member
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I think this is the 3rd Kenwood 1100u that I've done, and assuredly my last. I didn't keep track of the hours, but I'm sure I have 30-40 in it.

I purchased it on eBay. It arrived with no output tubes; most of the others were weak. One of the OPTs had caught fire and had been replaced by an odd one that was bad, too.

There was a small fire or two below deck. I had to replace a binding strip and a lot of wire. The multi-cap had leaked corrosive goo. All electrolytics were replaced, along with every non-disc coupling cap, safety cap, etc.

Several out-of-spec resistors were replaced as well. I added an adjustable bias control and 10 ohm safety resistors on the cathodes of the 7591s.

I undid some "mods" that a previous owner made, and then modified the headphone circuit slightly. I relubed all of the controls; replaced lamps, etc.

I had a pair of Sansui OPTs from a 1000A - they bolted in place with minimal fuss. They were slightly bigger than the original Kenwoods; they didn't have a 4 ohm tap (which was used for the headphone circuit exclusively). Otherwise, they were a great fit.

I bought some EH 7591s from Jim McShane. Plate voltage on these is 506 VDC! I've got them biased at 22.5 mA which is under the 70% recommended bias setting.

I fired it up and it works. FM MPX needs some adjustment (no surprise) and there is a bit of hum in the AM section to track down, but the AUX sounds glorious.

I think the Sansui iron is an upgrade for this model. If any of the other 1100u's that I worked on sounded this good, I wouldn't have sold them!
 
BuzzK,
I haven't called it quits on receivers as jaymanaa has, but they've definitely got a lot of stuff in them both under and above the chassis.
Well, will you keep this one?
 
As an aside I am listening to a Sansui 1000a as I type this, I picked it up at a yard sale all orginal but in good cosmetic shape, I consider myself an advanced novice, I have rebuilt some simple phono amps AA5 radios etc but when I looked at the underside of that Sansui I decided I was over my head so it went to a tech. He also re aligned the tuner and tweeked the multiplex so it is a sweet unit now.
 
Recievers are fun, though I've never had to mess with an MPX decoder. Definitely a lot more stuff than an amp or an integrated but the challenge makes the results so much more worth it.
 
I intend to keep this one to use in my shop.

I had a Sencore FM alignment tool, but sold it for lack of use. I wonder if I can find service info on the MPX alignment process.
 
Kenwood kw-1100u

HI YA..
I am also working on one of these old Recievers.. this would be my first all tube stereo to restore..for sure it is packed with Capacitors..I have ordered all Caps already..and tested and tested the tubes.. output tubes seem fine, all of the 6BN8's are weak.. interesting thing is this does work (without output tubes in) , and picks up FM Really nice and in stereo.. Stereo indicator light is very dim.. least of my worries yet..but as you can see from pics i think a few things in the power supply have been replaced already..2 large wirewound resistors i have been trying to figure out as the diagram only give the wattage.. R4015.. ( i think it is R401 in reality).., it's the large ceramic white wirewound and I think it's a 5 ohm 10 watt wirewound but hard to say as the lettering is all burned off and in the Diagram the designation numbers are so close together, and the other is the green one that someone stuck in, which is R 402.. I think it's a 470 ohm wirewound..look at pics and you will see..can anyone give me a proper Value of these..?
if you see anything that does not look factory before I begin please let me know as the manual is hard to read...(poor copy)
thanks!!
 

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KENWOOD KW-1100U
if anyone Can tell me if for sure "R401" is actually a 5ohm 10 watt wirewound, my service info is hard to read in the area where the page was creased..otherwise everything else is clear..this will be a change from working on Vintage Televisions to something different.. a all tube stereo..:)
 
Yes, that is the correct value for R401 @ 10 watts. R402 is 470 ohms, 5% @ 4 watts.
 
Kenwood kw-1100u

I think it has been a Month or so since I posted the before "pics" of this RX.
I have been working on this off and on after work and weekends, you really would not beleave the number of way off value Resistors..Just yesterday I replaced 19 of the 1/2w carbon resistors, everything seems to be doubled in value.. I have spent so much time on this and still have a bit to go..I have to put this away and get other things done..! but as it is it sounds GREAT..!..the Tuner is Fantastic..I also replace the 7591's but the original ones were fine..I still have the Phono Preamp section and the 2 safety caps and power cord..the only power supply filter I did not replace yet is the 4 x40uf multiCan section cap, I was able to find NEW ones for the other 2 multisection lytics ..I can't find anything new to replace the 40uf x 4 can, the old one seems ok as it has good ESR and Value is close,.this has been an expensive and time consuming project..and try and find screw base 9 volt lamps..??.. HA..!
I seen one of these on *-bay last week.. but it looked like it was never Recapped.. boy is the new owner for a shock..I still have to "re-shape" 2 of the clamps for the new Smaller caps under the chassis, I placed them back around the Caps so I would not lose them..this has been a gear change from Vintage Televisions and Solid State amps..
here is some latest pics..
it sure does sound great though..!..So BUZZK is for sure right about the amount of time he has spent..these amps are much more difficult to work on than the typical SS amp, I have to work off only a diagram, I ordered a manual and it was suppose to be the whole service manual but I was shocked to open the envelope and find only a diagram.. sucks and a waist of money, so I have no alignment steps for the tuner, but it seems fine so far..
 
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Honestly since this is my First sort of tube amp ,I think they sound Fantastic, for sure not harsh on my ears and this thing has got some punch for a tube amp, I had a friend over who does sound systems for night clubs who hates tube amps and he was impressed..I have pioneer SX-1980's that I am used to and this amp for sure has a different sound , very nice sound..so yes they sound great..!, I just don't like the way they sit in the tube sockets, they look sort of wobbly..but I am picky..
 
Very nice. I restored a Pioneer receiver a while back that was a similar rats nest underneath. Definitely gives your soldering iron a workout but, as you've already discovered, the results can be quite rewarding.
 
there is a bit of hum in the AM section to track down, but the AUX sounds glorious.

If it's hum that shows up on some stronger stations and not others, try placing small bypass caps across the rectifiers. Like 0.01uf with voltage ratings at least 4 times the secondary's voltage (you want some safety margin, ceramic caps will be fine here) What can happen is that some AM radio signal will travel over the powerline, and pass thru the rectifier tube while it is conducting at the top of the AC waveform, and not conduct at other times thru the AC cycle. This in effect modulates the AM station with a buzzy hum.

Sometimes it can be the rectifiers in another piece of equipment that is connected to the receiver. You can spot that by disconnecting it while tuned to the problem AM station.

If the engineering at the AM station isn't as diligent as they should be, they may be the source of hum. Check the station by tuning it in with a good car radio system in the car.
 
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