[linuxworks]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Glad to hear it! ... and thank you for not giving up. We've had one or two that did that when they realized a mistake with the output transistors.

raises hand, embarrassingly

I soldered in all 4 transistors in the wrong 'mirror image' holes but fortunately found my mistake BEFORE applying power. I have a good desoldering gun (hakko) so it was not hard to fix but man, that would have bummed me out had I not caught it before power-up time.

check check and visually check again.

I do think that to make things more user goof-proof, the extra set of holes should not really be there and people should just get the right parts as long as they're not *impossible* or overly expensive.

that was the only gotcha in my build.

 

[patton713MW]

Quote:

Originally Posted by aphexii /img/forum/go_quote.gif Just curious, what gauge wire are you guys using for your hookups?

22 gauge from Navships, just like TimJo said.

 

[tomb]

Quote:

Originally Posted by linuxworks /img/forum/go_quote.gif raises hand, embarrassingly I soldered in all 4 transistors in the wrong 'mirror image' holes but fortunately found my mistake BEFORE applying power. I have a good desoldering gun (hakko) so it was not hard to fix but man, that would have bummed me out had I not caught it before power-up time. check check and visually check again. I do think that to make things more user goof-proof, the extra set of holes should not really be there and people should just get the right parts as long as they're not *impossible* or overly expensive. that was the only gotcha in my build.

I suspect almost as many builds were made with the 2SC2344/2SA1011's as opposed to the 2SC3422/2SA1359's. Those transistor pairs go on opposite sides from each other. So, the extra holes are needed.

Also - we've been surprised since the start of the MAX/MiniMAX builds when people have messed up, because it appears that reversed output transistors are OK every time. Get the TO-92s mixed up and in the first instant of applied power they're fried, but the TO-220's take quite a bit to blow. I guess they melt easier than they short out, because mistakes in over-biasing have burned up more than have the incidents of soldering them in backwards.

P.S. Glad you recovered, too.

 

[aphexii]

Quote:

Originally Posted by patton713MW /img/forum/go_quote.gif 22 gauge from Navships, just like TimJo said.

Thanks guys, i'll place an order tonight!

 

[tomb]

Quote:

Originally Posted by aphexii /img/forum/go_quote.gif Thanks guys, i'll place an order tonight!

Yep - John at John's Silver Teflon Wire Shop (navships) is a good guy. Last time, we started a thread for him and it gave him some of the biggest business he's ever had.

Study his selections though, and pay attention to the total diameter and insulation thickness. Look at all the other 22 ga to make sure you're getting the thinnest stuff. Some of his wire has got some really thick insulation on it (it can be good for certain things, but just be sure you're aware of the difference). Likewise, stay away from the Kapton stuff.

 

[patton713MW]

What's the difference between the Kapton and the other silver/copper?

 

[tomb]

Quote:

Originally Posted by patton713MW /img/forum/go_quote.gif What's the difference between the Kapton and the other silver/copper?

From what I remember, Kapton makes the wire stiff as all h*ll and it also has abrasion problems from what I've read. It's just more trouble than needed for our stuff. Stick with the normal teflon-spc.

 

[eitel]

Hi guys,

I am almost done building my minimax, but could need some help figuring out a noise issue.

When I touch/tap the volume knob, chassis or pretty much anything on the amp, the tap itself is amplified through one of the audio channels. When I switch the tubes around the tapping ends up in the other channel. Could this the result of a bad tube?

I also noticed that if I bias the tubes(12FM6) at 13.5V and then switch them around, the bias is 11 and 17 volts. Is this normal?

Any help is appreciated.

 

[rds]

Quote:

Originally Posted by eitel /img/forum/go_quote.gif Hi guys, I am almost done building my minimax, but could need some help figuring out a noise issue. When I touch/tap the volume knob, chassis or pretty much anything on the amp, the tap itself is amplified through one of the audio channels. When I switch the tubes around the tapping ends up in the other channel. Could this the result of a bad tube? I also noticed that if I bias the tubes(12FM6) at 13.5V and then switch them around, the bias is 11 and 17 volts. Is this normal? Any help is appreciated.

The tap issue is what people mean when they say a tube is "microphonic". The tube itself is picking up the vibration and turning it into electrical noise. The solution is to replace the tube.

The bias thing is normal too. That is the reason we bias the tubes to begin with (if that makes sense).

 

[tomb]

Quote:

Originally Posted by eitel /img/forum/go_quote.gif Hi guys, I am almost done building my minimax, but could need some help figuring out a noise issue. When I touch/tap the volume knob, chassis or pretty much anything on the amp, the tap itself is amplified through one of the audio channels. When I switch the tubes around the tapping ends up in the other channel. Could this the result of a bad tube? I also noticed that if I bias the tubes(12FM6) at 13.5V and then switch them around, the bias is 11 and 17 volts. Is this normal? Any help is appreciated.

Yes, rds is absolutely correct.

If I've supplied the tube in question, please let me know - I'll send you another. All my tubes are tested, but microphonics is not something that shows up in a tester - you have to plug them in an amp, first.

As rds says, every tube will have a slightly different bias point. That's why we have the tube bias adjustment in the first place.

 

[eitel]

Quote:

Originally Posted by rds /img/forum/go_quote.gif The tap issue is what people mean when they say a tube is "microphonic". The tube itself is picking up the vibration and turning it into electrical noise. The solution is to replace the tube.

That makes sense. Thanks a lot.

Quote:

Originally Posted by rds /img/forum/go_quote.gif The bias thing is normal too. That is the reason we bias the tubes to begin with (if that makes sense).

What I meant to ask was if it is normal for the bias point to be that much different for a matched pair of tubes. But based on your and Tom's answer I guess it is

 

[tomb]

Quote:

Originally Posted by eitel /img/forum/go_quote.gif <snip>What I meant to ask was if it is normal for the bias point to be that much different for a matched pair of tubes. But based on your and Tom's answer I guess it is

Think of it as two people - one shorter than the other, but both of them can jump the same amount. Their jumping "output" is the same, but they start from a different level. Put a step stool under the shorter person so that they start at the same height, then their jumps will reach the same level. Tube bias adds the step stool.

There's also some compensation going on in the circuit, too. Even if the two tubes were perfectly matched in bias, there may be subtle differences in the two CCS's, slightly different resistors/trimmers in the circuit, etc.

Or, I may have just messed up and the tubes aren't really matched (assuming I supplied them).

 

[ssoaos]

hi, a few days ago I reported some noise issues from my new MiniMax. Some of you jumped right in to help. After talking to Tom he sent me a new 12AE6 to replace the noisy side and the problem was solved.

I wanted to thank you all and Tom's offer.

Regards,
Stanley

 

[ruZZ.il]

ENJOY!

 

[THE_SOURCE41]

Quote:

Glad to hear it! ... and thank you for not giving up. We've had one or two that did that when they realized a mistake with the output transistors. Hopefully, it wasn't that hard for you. Bring on the pics!!

I will be posting pics as soon as i get back home. I am on spring break in london for the rest of the week.