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

how in the world do you troubleshoot under that chassis!!? most likely, i would've given up 5 hours into the job and burned the thing....

sure looks very pretty though. great job!
 
Well, I just picked up one of these as well. Thankfully, it still has all of the original 7591 output tubes and they test very good. I know that I have my work cut out for me. But I have done several Scott amplifiers and a Sansui 1000A so I am not too worried. Much will be replaced before the first electron passes through the power cord. No evidence of thermal melt down so I am happy.

Thanks for the heads up on the resistors. I usually don't check them unless voltages are bad. So, as I go, I will check them. Obvious power supply rebuild is in order...
 
Great tip. I'll keep that one in mind. This one has SS rectification and rectifier bypass caps as stock issue.




wa2ise said:
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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I find that the leaky caps cause tube & OPT failure in this receiver more frequently than any other I've worked on. I have a spare OPT if one of yours is bad.




kvflyer said:
Well, I just picked up one of these as well. Thankfully, it still has all of the original 7591 output tubes and they test very good. I know that I have my work cut out for me. But I have done several Scott amplifiers and a Sansui 1000A so I am not too worried. Much will be replaced before the first electron passes through the power cord. No evidence of thermal melt down so I am happy.

Thanks for the heads up on the resistors. I usually don't check them unless voltages are bad. So, as I go, I will check them. Obvious power supply rebuild is in order...
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Assume that the black is the common lead. With a good VOM, measure the resistance between the other leads and the black one. The more the resistance of the winding, the greater the value, i.e, the 16 ohm tap will have the greatest resistance.

Hey, are you the same fellow who posted this question to me on eBay?




iswind said:
What is the wire color coding for 0,4,8 16 ohms
Black, white,yellow and blue ?
Thanks
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Good to see all those grey caps removed! I still have to check all the resistors on my earlier Kenwood (Trio actually) which runs ECL82s. But I agree that these receivers are very enjoyable to listen to.
 
The Kenwood 1100A has a truly "fixed" (i.e. unadjustable) bias that was designed back in the days when line voltages were lower and output tubes were readily available and cheap.

The stock circuit will run your 7591s too hot, and so it's a good idea to put 10 ohm 1/2 watt resistors on the cathodes (so you can measure current) and install an adjustable control for the bias. A good potentiometer can be mounted on one of the pieces of L-shaped sheet metal in the chassis.
 

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BuzzK said:
I find that the leaky caps cause tube & OPT failure in this receiver more frequently than any other I've worked on. I have a spare OPT if one of yours is bad.
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Thanks for the heads up and the offer. Unfortunately, this little guy will have to wait his turn in queue since there are many more receivers and amps in line for restoration.
 
After eleven years, guess what is on the bench? I do have audio flowing and the tuner works well. Dial glass cleaned without damage. Pictures to follow soon.
 
Pio1980 said:
How offer do you all find bad control pots in these vintage tube receivers?
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Interesting question! In just about every HH Scott amplifier that I have worked on, controls are almost always scratchy and need to be cleaned. Slide switches often will not work even after cleaning!

In this Kenwood 1100u, I did clean the controls after initial first power up. But I encountered no problem whatsoever, not even with the selector switches or rocker switches. Could it be possible that they were coated with a lubricant from the manufacturer?

I have another 1100u that is not as nice as the one on the bench. My intent is to just get it going, not do a full out restoration.
 
depends on your definition of bad. Slightly annoyingly off-value so the sound is shifted to one side? All the time. So bad it doesn't function at all? Not so often. The volume pot in my PAS was so bad that the sound shifted side to side as I changed the level. That one had to go. If its just consistently skewed a little one way or the other and I can fix it with the balance pot I don't care so much.
 
gadget73 said:
depends on your definition of bad. Slightly annoyingly off-value so the sound is shifted to one side? All the time. So bad it doesn't function at all? Not so often. The volume pot in my PAS was so bad that the sound shifted side to side as I changed the level. That one had to go. If its just consistently skewed a little one way or the other and I can fix it with the balance pot I don't care so much.
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I have an early version of the Sansui 1000 and a Kenwood, both with bad useless loudness pots that have sidelined them. Assuming leaky Suzuki blocking caps killed the carbon tracks.
Oddly, the Sansui SM 80 from which the early 1000 resembles pot is fine and fully functional.
 
Once had twice a go at restoring a 1970's Kendwood valve based transceiver - the copper wires kept on breaking off as soon as one moved them ever so slightly. Some issue with the copper wire they used - never again.
 
My best looking 1100u made it to the bench. It is certainly a labour of love working on them. Very cramped conditions. The largest power supply capacitors were leaky and replaced. However, the multi-cap farther down the line is good so it is staying.

Now for the coupling capacitors, they were leaky and replaced. Also, all small "Elna" capacitors test open and are being replaced slowly. Right now, it is playing on the bench. However, there are more small electrolytic capacitors that will be replaced.

The tuner works well but there are few aluminum cased paper capacitors that will be replaced, slowly, methodically and retest after one or two.

More coming...
 
More small Elna electrolytic capacitors replaced. Every time one is replaced, it just sounds better and better. Proceeding s---l---o---w---l---y and testing after each pair of capacitors replaced.
 
image0 (3).jpeg


More to go but so far, so good. All Japanese tubes, Hitachi output tubes and many Matsushita small tubes. All tubes test good.
 
Some of the capacitors replaced. Mind you, ALL low value electrolytic capacitors are testing open; dried up. The larger ones are leaky at the rated voltage so they went away as well. Resistors replaced only as a convenience. They all were testing well within the tolerance. Since the voltage doubler power supply diodes were old, they were replaced as well on precaution with 1N5408 silicon.


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I find that a lot of high-value resistors in the model age to a significantly higher value!

I installed a bucking transformer for the AC mains. Amazing how cool the power transformer runs, and the filament voltages are now in spec.

I used the 5V tap, not the full 10V winding to bring it to spec.


KW1100 Bucking.jpg
 

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