Repair question re: threshold 400a

[Apogee]

Originally posted by moamps


You can't be serious! I'm afraid you're grossly mistaken if you honestly believe that anything can be fixed by anybody with a little help from the forum(s), particularly if "anybody" happens to be a complete newbie with an attitude and "anything" is a very complex and valuable piece of equipment.

If you think this particular amp is not difficult to fix, I invite you to share your superior know-how and experience for everyone's benefit.

Regards,
Milan

I have helped a number of newbie's in the past and if you'd bother to search you'd already know that.

There is no reason that he can't tackle this with some help.

The outputs don't even have to be matched. He could just measure them and vary the load sharing resistors as a cheaper alternative.

You post gets exactly to the attitude that I called Anatech on. How do you know that the guy isn't extremely bright and wouldn't pick this up in no time. You don't, and instead decided to make a judgment before he was given a chance.

Give me a break!

[anatech]

Hi Nelson,
He received the amplifier disassembled with an estimate for repair. Some resistors burned.

He may possibly be able to repair it, but more likely not if he can not take advice.

No, you do not have to match the outputs, but the performance is better if you do. He has an opportunity to do this. It is normal service procedure with good tech's to do this.

Remember too Nelson that when you receive transistors from the manufacturer, they are normally in the same lot and will be close in beta. In service quantities they can be easily out by three to one.

-Chris

[anatech]

Hi Steve,
Okay. I'll call you on this. I agree to let you contact him off line and let you start a thread for him. I will not post or moderate this thread. In other words, you can attempt this with the help of the entire forum and no interference from me. Milan may agree to this as well.

I will apologize here and now for my reaction to this member.

What do you say?

-Chris

Edit:

The outputs don't even have to be matched. He could just measure them and vary the load sharing resistors as a cheaper alternative.

No. Emitter resistors affect current sharing at higher currents. It's the crossover region where beta makes a larger difference. So do not play with emitter resistor values.

Just a thought.

[Apogee]

Sounds good.

You guys don't have to disappear from the thread, just give the guy a chance that's all.

I already tried emailing him directly as well. Haven't heard anything back...

[Q]No. Emitter resistors affect current sharing at higher currents. It's the crossover region where beta makes a larger difference. So do not play with emitter resistor values.[/Q]

Ok - just figured he might be able to more easily get close to the good ones he still has in the amp.

Thanks,

[anatech]

Hi Steve,
Given my personal feelings about this member, and his probable feelings towards me .........

I will not have any contact in your thread. It's cleaner that way.

My feelings are not hurt and I am not upset. I think you and he deserve a chance to get working.

-Chris

[Apogee]

Hi Chris,

Okay, we'll see if he comes back. If so, we'll start a thread for him.

I was editing my last reply at the same time you were typing.

Thanks for the crossover region tip!

[Zen Mod]

Originally posted by Apogee
Anatech - Understood.

However, the point is that's not a call that you, I or anyone else is entitled to make.

He bought it because he respected Nelson and wanted that amp. He also knew it was broken when he bought it.

He wanted to try fixing himself so he could learn something.

With the talent on this forum, we could have easily guided him through the process.

Yes, it might have cost him more money in the long run than taking it somewhere. So what? It's his money, and if he's excited by the prospect of learning, then more power to him.

I would have suggested that he stick it in the closet for a little while and first try building a Zen or something simple to get his feet wet. Then, once that was done have him tackle this. If he insisted on jumping in straight-away then so be it and we could have helped him with it.

Instead, now we have someone who was excited about our hobby that has been turned off by the attitudes on this board.

That, to me, is a shame.

post No.3 :

I can install parts.. but as for matching.. no way.. I have no scope for starters..

it's easy ,with help,when you are not stubborn
no further comment

[moamps]

Originally posted by Apogee
I have helped a number of newbie's in the past and if you'd bother to search you'd already know that.

As we all have.

There is no reason that he can't tackle this with some help.

There is a reason: people were bending over backwards to help him and all he had to say was that the thread was a complete waste of time. I'd expect an apology when/if he comes back.

How do you know that the guy isn't extremely bright and wouldn't pick this up in no time. You don't, and instead decided to make a judgment before he was given a chance.

He was given a chance (see above).

I repeat, it is quite unreasonable to try to make a complete newbie repair a piece of equipment running at +/-70V and using 16 output transistors per channel. The best thing that may happen is that he destroys the amplifier beyond help and the worst thing is that he could get seriously hurt in the process.

In another thread, barchetta did not know what a cascode was. Does anyone really expect him to be able to check transistors/parts to see whether they're working or not. Besides, the amplifier looks like it was serviced (butchered up) a few times before and only God knows what awful things may have been done to it. Even if barchetta were the next Tesla, it would still be a challenge to fix that mess.

Regards,
Milan

[anatech]

Hi Milan,
I think we should back away and let them try.

I came on strong enough for both of us, wouldn't you agree?

-Chris

[moamps]

Troops withdrawing... Over to you NP.

Originally posted by Nelson Pass
So let's start with the first step:

How do we know this unit is broken?