Service Data Request: Kenwood KA-5700 Integrated Amp

[bob p]

Nice flowing profile on the connie.

yeah, that was a sexy airplane.

Here are some photos courtesy of Flightline's "Airliners of the 50s" web page:

[bob p]

Enzo, it turns out that the final results of the mods to the fan's dropping resistors was pretty simple after all. Remember those four 47K resistors that were wired in parallel as R3 to yield an impedance of 12R? I removed three of them and left one, so that R3 was 47R. Add that to the R4 value of 18R and the R1 value of 1R, and the results were:

Low Speed: 66R, 12 VDC (nice and quiet for the living room)
High Speed: 19R, 14 VDC (lots of air at idle for stage use)
Thermal Bypass: fast as hell and loud as hell too.

The really good news is that the mod was very simple and recycled its own parts. Yeah, Baby!


(more photos -- i couldn't resist)

[Enzo]

Hmmm, I don't remember them with tip tanks, as some of your photos include.

I recall Ike's plane as named the Columbine, and sure enough it was:

[bob p]

nice photo of Air Force One.

i think that the tip tanks were a howard hughes idea, for when TWA took the Connie transatlantic. that's a photo of him in the TWA cockpit, btw.

[Enzo]

Yes, I recognized him. Tanks are a fine idea, I just don't remember ever seeing them. Then again I hardly remember last week.

Well, we have come a long was from Kenwoods in this thread. Maybe we can trade chili recipes now.

I looked up Arthur Godfrey, and came upon this. You might find it interesting. I cannot vouch for it, since on my dial up, I can't do videos well, but it should be flying the connie as seen from the cockpit.

http://www.archive.org/details/Flyingwi1953_2

Arthur got in trouble for buzzing the tower at an airport once.

[bob p]

Well, we have come a long was from Kenwoods in this thread. Maybe we can trade chili recipes now.

Funny, I had chili for lunch yesterday when you wrote that...

Yes, Kenwood to Carver to Connie. I'd like to shift the conversation back to the Carver fan motors again. Although the dropping resistor method seemed to quiet the amp down nicely on the bench, when I put it in the living room I found that its still far too noisy.

If anyone has a good idea...

[bob p]

Looks to me like the replacement fans have higher voltage, lower current motors than the originals, so the dropper resistors have much less effect. However, remember that the behaviour of a motor is affected by the back EMF constant (volts/RPM) as much as the DC resistance, if not more. But a higher DC resistance may well mean more turns and hence more V/rpm.

The confusing thing (to me at least) is that the fan motors are made by the same manufcturer and share the same model number, yet they are different.

As it turns out, the old fan was made in Japan and the new fan (of course) is made in China. I haven't done any forensic analysis the old motor or one of the new ones to see if the wire gauge and the number of turns is different. I guess that could effect DCR and operating current. I guess wire gauge and assembly methods could be one of the issues that came with moving production to China. I guess it could also be that the new motor's bearings are just so lousy that even a new fan makes awful noises.

Steve, you had mentioned something about using caps on an AC fan. what is it you were trying to accomplish? Granted, this is a DC fan, but I'd still like to ask about your approach.

For my DC fan I've used the dropping resistor approach, and I'm running out of ideas. I'm thinking that my only option is to add enough serial Z until I get to the point where the motor really slows down and almost stops turning. I was wondering if there's a better way to tackle the probem.

[bob p]

well, i got tired of soldering parts in and out, so I decided to be a bit more analytical in my approach and I soldered some wires to the board and hooked up a rheostat. i took a bunch of measurements and plotted the results.

just as ohm's law would predict, the plot of DC voltage as a function of series resistance yielded a linear function with a negative slope equal to the rated current of the fan in mA and a y intercept equal to the motor's rated operating voltage.

regression/extrapolation to the desired series resistance was pretty easy, and it was simple enough to re-scale the fan control's voltage divider components to yield the desired result. now the fan is nice and quiet and the fast and slow speeds are just right. it looks like the project is done.

Steve, you made a good point earlier that I did not fully appreicate when you made it:

Looks to me like the replacement fans have higher voltage, lower current motors than the originals, so the dropper resistors have much less effect.

i didn't fully appreciate what you had said until i plotted the function and realized that you were saying that the slope of the function was very shallow. as they say, a picture is worth 1000 words.

Steve and Enzo, thanks again. now all that's left for us to do is to exchange recipes.

[poirson]

Hello Bob

I purchase a carver pm1.5 few time a go. I change the motor fan cause some times it had difficulties to start or made scratchy noises.
I use now a 24v 150mA. First I remove the résistors, replacement R4 by 68 ohms and R2 by 22 ohms. But the amp become hot quick (few minuts), I put parallely of R4 68 again and on R2 22 ohms again.

It's the same.

The voltage of the motor could explain the problem ???

The motor you use it's a 35v ?

Thanks to help me. Renaud

[bob p]

This thread seems to have become more popular than I ever thought it would be. It seems that anyone who's working on a PM-1.5 with dead fans gets linked to this thread, because it's the only one on the web that details how to re-scale the voltage dividers in the fan control network to adjust the fan speed. Enzo and Steve, thanks again for your help when I was working on this project way back when.

Funny thing, because of this thread I periodically get emails from guys who are looking for OEM replacement fans. The good news is that I still have some of the fan motors that I got from CarverPro when they were going out of business, and that I don't think I'll ever need them as spares during my lifetime. The bad news is that I can never seem to remember where I put them. I guess that comes with being an Old Timer.

[NIM006]

This thread seems to have become more popular than I ever thought it would be. It seems that anyone who's working on a PM-1.5 with dead fans gets linked to this thread, because it's the only one on the web that details how to re-scale the voltage dividers in the fan control network to adjust the fan speed. Enzo and Steve, thanks again for your help when I was working on this project way back when...

I could not agree more with this statement!!! I'm referb-ing a PM-1.5 myself... my fan is DOA. I could go with a direct replacement, but I'd really prefer to drop in a modern brush-less model... I have a 12vdc, 1.6a 60mm server fan with PWM control, I'm thinking of building a replacement fan supply board and using a regulator to keep the fan supply at 12vdc, a second regulator at 5vdc to drive the PWM circuit, and mounting a variable R in place of the push-button speed switch to control the speed. Obviously this circumvents the thermo-switching features of the OEM fan, but even at half speed, this fan will push 180 cfm so I'm thinking of setting the speed to a comfortable roar and leaving it there, always on... does anyone see an issue with this theory?

[The Dude]

I've been servicing Carvers since their inception. Long ago, I was an authorized service center. If you don't want to go through all of the hassle of fan circuit modification, check this out. I've been using these for years. It's a near exact replacement. No modification required at all.

RadioShack Super Speed 9-18VDC Hobby Motor : Hobby Motors | RadioShack.com

[NIM006]

I've been servicing Carvers since their inception. Long ago, I was an authorized service center. If you don't want to go through all of the hassle of fan circuit modification, check this out. I've been using these for years. It's a near exact replacement. No modification required at all.

RadioShack Super Speed 9-18VDC Hobby Motor : Hobby Motors | RadioShack.com

Thanks! I'll definitely keep that in mind I still would like to go the brushless route if possible, my only concern is the possibility of the PWM signal being fed spuriously back into the 25V rail. I may repost this to the main forum, I really want to know if anyone out there has tried something like this.