Yamaha CA-1000 What will go?

[sssboa]

I was thinking about buying CA-1000 as I love CR-1000.
I had CA-1010 though and I didn't like that class A thing, a lot of heat, two relays, setting bias for each mode, etc.
Now I read that if you switch to class A while the amp is on you will break it.
But what will exactly go in such a case?
Can I somehow disable class A? I could lower the bias for class A to the level of AB bias, but will it solve the problem?

 

[willyrover]

Switching between Class A and Normal is accomplished by switching secondaries on the power transformer.

The CA-1000 accomplishes this directly through a DPDT switch on the front panel. Supposedly, switching modes while powered on can wear the contacts on this switch and they aren't exactly off the shelf replacements.

The CA-1010 accomplishes this through RELAY that is controlled by the front panel switch. The relay generally solves the problem because the contacts can handle more current. Relays are also more easily replaceable since they are off the shelf parts.

Can you disable class A? Sure, just leave it off - don't use it.

Can you lower the bias in class A mode to run cooler? Maybe. But Yamaha designed the class A mode to run hot. Also, the Class A and B bias pots are interdependent (at least on the 1010). The adjustment of one pot in one mode affects the second pot in the other mode. This is why bias adjust is done by alternating back and forth between A and B several times until the readings are correct.

 

[blhagstrom]

Correction.

The switches for the CA-1000 are off the shelf parts.
I've rebuilt 2 of them and have another in the queue.

The A/AB switch is on the front panel. I doubt switching while powered on is a bad thing since its right there! I have accidentally done it without problem. The wives tail probably started because units died because they were in bad condition to start with.

Typical issues are bad switches, fusistors that have gone bad. Old capacitors are now a concern.
The last one I rebuilt had bad solder joints on the input board which is buried in the back panel.
Toss in the fact that they are 40 years old and other parts may go bad and you are squarely dealing with vintage gear.

The more gear I restore, the more its obvious that restoration is the best path on vintage gear.

Note: The traces on those are a little delicate so its best to use quick accurate desolder skill when rebuilding them.

If you don't want class A, then don't use it or don't buy the CA-1000

 

[zaibatsu]

Switching it while powered on won't "break it".
It's just been recommended to not do that regularly as high current is being switched, some techs have seen the switch contacts welding together from regular powered-on switching.
http://audiokarma.org/forums/index.php?threads/yamaha-ca-1000-running-hot-in-class-a.216279/

You've already asked the same question once before and you've misunderstood avionic's reply.
http://audiokarma.org/forums/index.php?threads/class-mode-switch-ca-1000.713739/

Logic would indicate that if you replace the switches with new ones (in case originals are partially damaged) and don't sit there flipping it on and off all day while the unit is powered on, it won't be a problem. Doing it once or twice accidentally certainly won't be.

If you don't want class A, then don't use it or don't buy the CA-1000

Agreed.
Why bother buying an amp if you are against what is probably its best feature?

 

[Jpete9]

You can just leave it in normal mode. No issue, nothing to disable, just dont flick the switch.

If its a working one, budget for a coupler switch, micro switches for the Class A function. These seem to be the main parts that are end of life after 40 years. All off the shelf and super cheap and DIY.

 

[tubed]

I've had my flawless looking CA-1000 since 1975, used as my main amplifier up until 2007, never used the Class A extensively, still original, still sounds good and dc offset at the speaker terminals is a usable 28 and 47 millivolts.