ChannelMaster 6600 integrated

Jcricket

not someday, but today
Subscriber
ANyone have any knowledge of this amp. I got it yesterday and it works well. I have opened it up an looked at what it needs fro a rebuild.
It uses a gz34(mullard) rectifier, four 6bq5(ge's), 4 7025(tele 12ax7's) and a 12au7(rca) set of tubes.
The output iron looks okay.
The coupling caps are mica?????

I have ordered an origianl set of the sams photofacts.

So anyone know these amps? have opinions on them?
Here are a few pics.
 

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Does anyone have access to the schematics on this. I have ordered a set but hey won't likely be here for a week or so. I would like to know if this circuit uses coupling caps and what he values are?
I am attaching a pic of the underside. It really suprised me. I do not see any coupling caps, unless those four mica caps are it. ANy ideas????

They are marked .02M - this .02uf? THe seem pretty small for that.
 

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Those caps are ceramics, not micas. They usually don't go bad, but ceramic caps are a poor choice for hi-fi audio work. Replace them with some poly something film caps, like Orange Drops. I also see a wax paper cap, replace it, it's guaranteed to be bad. And the electrolytics usually need to be replaced as well.

See http://greygum.net/sbench/sbench102/caps.html for a discussion of various types of capacitors. Ceramic caps, and tantilium caps have hysteresis loops, which may cause distortion products on the low end of audio (most coupling caps form high pass filter circuits, and bass frequencies develop more voltage across coupling caps than midrange or highs, and distortion products will invade the midrange and muddy the music. The reason we care about this.
 
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Those caps are ceramics, not micas. They usually don't go bad, but ceramic caps are a poor choice for hi-fi audio work. Replace them with some poly something film caps, like Orange Drops. I also see a wax paper cap, replace it, it's guaranteed to be bad. And the electrolytics usually need to be replaced as well.

See http://greygum.net/sbench/sbench102/caps.html for a discussion of various types of capacitors. Ceramic caps, and tantilium caps have hysteresis loops, which may cause distortion products on the low end of audio (most coupling caps form high pass filter circuits, and bass frequencies develop more voltage across coupling caps than midrange or highs, and distortion products will invade the midrange and muddy the music. The reason we care about this.


I knew thaty, my brain just wasn't engaged. Dummy me.

So are thos the coupling caps?
I already plan on recapping all of the electrolytics and the wax ones. THe ceramics don't fail, but if those are coupling caps they should be replaced. I generally use orange drops and spragues for my coupling and power supply caps.

Thanks for the input though.
 
Ceramics aren't very linear components; ditch 'em pronto for best results (in my hardly humble opinion). Orange Drops are a fine replacement (again my hardly humble opinion), or the Illinois yellow tubular capacitors if space is tight.
 
I just ran this unit through some paces. It sounds fairly good - even with the ceramic caps. I have all new caps and the schematic coming. I think this is a real sleepr of an amp. A little tlc and I think this will open up really well.
Once I get a copy of the schematics, I'll scan them in and post them.
 
If those go between the 6bq5 sockets and the 7025 sockets, they're the coupling caps. Electrically, ceramics don't fail that often, but as mentioned, they don't sound great. I replaced the ceramics in my Magnavox amp with orange drops, and the change was obvious. It just sounded less shrill on the highs and overall it was cleaner sounding.
 
Yep,they connet to the center solder lug, and then through a wire they go to the 7025's. They are marked .02M, I assume that must be .02uf? I have never seen a coupling cap in pico farads.
What do you think?

I was thinking of replacing them with .033, as I have those on hand. The corresponding resistor is 470k, I'll change them out as well.

ANy suggestions?
 
In response to your PM, I'd assume 0.02 uf as well but you could always remove one and measure it or wait for the schematic and figure out what you want to do.

Keeping in mind the 1/2piRC high pass filter this forms it would be 1/(2*3.14*.00000002*470000)= 17hz approx. Since that's the -3dB point it actually starts rolling off much higher. Perhaps they're trying to keep the output transformers from saturating with bass they can't handle.

hi_pass_1st_order_freq_response.gif
 
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Hey Scuzzer, thanks for th help!
Measure it? Once again the obvious eludes me.

I thought about the saturation point thing as well. I can say the trannies are beefier than the stuff I have seen on the maggie console pulls, but a little shy compared to my stromberg carlson.

What happens to an amp if you "saturate" the transformer? Or is it what happens to the speakers, if you saturate the transformers?
 
Saturation results in distortion. The peak of the waveform collapses as the core reaches its limit of magnetic flux and the inductance of the winding drops drastically. Every transformer has a saturation point, though ideally it would be below the audible range at the amplifier's rated power. Saturation usually sets the low-frequency limit for an amp.
 
Saturation results in distortion. The peak of the waveform collapses as the core reaches its limit of magnetic flux and the inductance of the winding drops drastically. Every transformer has a saturation point, though ideally it would be below the audible range at the amplifier's rated power. Saturation usually sets the low-frequency limit for an amp.

Hey Tom,
So what does this look like when it happens? Is it like clipping? Does it act similar to a short and send dc voltages to a speaker? Or does the amp go into a melt down mode?
Just wondering if it is safe to experiment a little and see what happens.
Thanks!
mark
 
It's safe to experiment, heck I've been beating up an old console pull OT with my 807 SE breadboard. Hook up your scope and signal source to one of your recapped and functioning amps and measure the output voltage across a suitable load resistor at the onset of clipping at various input frequencies (say 30-100hz). Use voltage squared divided by resistance to figure the watts output.
 
It's safe to experiment, heck I've been beating up an old console pull OT with my 807 SE breadboard. Hook up your scope and signal source to one of your recapped and functioning amps and measure the output voltage across a suitable load resistor at the onset of clipping at various input frequencies (say 30-100hz). Use voltage squared divided by resistance to figure the watts output.

Cool.
That would be easy to do then too. Just do a quick solder of more capacitance on top of what is there and see what happens.
Thanks!!!!
 
Hey Tom,
So what does this look like when it happens? Is it like clipping? Does it act similar to a short and send dc voltages to a speaker? Or does the amp go into a melt down mode?
Just wondering if it is safe to experiment a little and see what happens.
Thanks!
mark

Won't hurt nothin' but your ears...
 
here are some pics of the schematics
Notice the difference between the cap at c4 and c2. One is 150uf the other is 40 uf. Why?
 

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The light for Monaural is green ?
Mine got LED, Red for Stereo and Blue for Monaural (maybe not the right color).
I love this amplifier but it's hard to find informations.
 

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c4 is the bypass cap for the cathode bias on the power tubes (lower voltage) typically 25 to 300 uf @ 25 to 100v. The c2 is in the B supply HV. That help?
 
I had completely forgotten about this amp. I sold it about 3 years ago.

What is cool about seeing this thread is it shows me how much I have learned in regards to these amps. :yes:

mark
 
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