Quote from: Loudthud on June 27, 2016, 03:56:00 PM
In a series circuit, the resistor with the highest resistance will have the most dissipation. Calculate the current that will result in that resistor being at it's maximum, then check that the other resistors will be at or below their rating at that current.

In a parallel circuit, the resistor with the lowest resistance will dissipate the most power. Calculate the Voltage that will result in that resistor being at it's maximum, then check that the other resistors will be at or below their rating at that Voltage.

As a practical matter, running resistors at their maximum power rating is not a good idea. If they are on a PCB, it will usually make the board turn black. The resistor or it's solder joints will fail. A resistor's power rating is based on temperature. If they are in a warm environment, they must be de-rated. You can run resistors beyond their power rating for short amounts of time as long as the resistor does not get too hot. To be conservative, don't run resistors more than about half their power rating.

Thanks everyone.

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Quote from: J M Fahey on June 26, 2016, 02:23:23 PM

Quote from: Den. on June 26, 2016, 09:05:31 AM
Thank you. Might this mean then that you would be able to substitute two 29ohm with one 30ohm or maybe even just two 44ohm rated 1/4w and still be safe?

WHICH 29/30/44 ohm resistors?
This question does not make sense since it´s missing data, besides never having heard about them before, certainly not in the above questions.

Sorry, I moved off the test question and am now trying to understand substituting different numbers of resistors with their different watt handling.

Thank you. Might this mean then that you would be able to substitute two 29ohm with one 30ohm or maybe even just two 44ohm rated 1/4w and still be safe?

Quote from: J M Fahey on June 25, 2016, 09:53:42 PM
Sorry Phil, unless stated otherwise they are *all*  in series so 520 + (4*22) = 520+88 = 608 .

I don´t understand how Den can have doubts about this *very basic*  question .

Yes, the way I read the question it seemed that they meant all five resistors wired in series. And I calculated that that would add up to 608. But, it was the power handling aspect I was unsure of; using four 1/4w resistors when one watt is required.

I had this TRUE or FALSE question on a written test recently: You can change the resistance in a circuit that uses a 520ohm 1w resistor to 608ohms by adding four 22ohm 1/4w resistors in series to the existing 520ohm resistor.

I answered true but now I'm not sure of my answer.

Quote from: Peggyr420 on November 03, 2015, 02:55:39 PM
... Keep trying to post a pic but keeps saying already a file with that name n won't let me post pic

http://0.tqn.com/w/experts/Electric-Guitars-3419/2015/10/gibson-amp.jpg

What's the deal with unplugging a guitar cord while the amp is on and the volume is up? I've seen some people panic if the volume isn't turned down first. But I've heard some people state that "it doesn't matter with a SS amp; it's only important with a tube amp."

Found this:
http://tinyurl.com/b5ydkg5

Well, good news and bad news and more good news. The first good news is that we've figured out what was wrong. If you go back to my original post where I am describing the amp, "It worked fine at low volume while I tuned my guitar. Then it started to sound fizzy." That was the bad news. It turns out what I was describing was the sound of a Peavey speaker failing. Tonight the speaker failed your 9v battery test then plugging the amp in to an extension speaker cabinet brought it to life. The rest of the good news is that I have a couple of extra speakers laying around that will match up to this amp just fine. Thanks for your help guys.  Den

Quote from: Enzo on January 29, 2013, 09:55:10 AM

Does the headphones jack work with phones?   

The schematic is for both the Studio Pro and the Envoy and points out the different components to install and omit. The Studio Pro does not have the headphone jack.

Here is the schematic:

Thanks for your reply.

You have FX loop jacks, so plug the guitar or some other signal source into the FX return.  Get sound?  That checks the power amp.

No sound.

Plug a spare cord from FX send to FX return, any help?

No. Still no sound.

Turn the reverb up midway and rock the amp back and forth to crash the reverb springs.  Does that noise come out the speaker?

No reverb crash.

Plug the guitar into the regular input jack, and set the controls as normal.  Connect a cord from FX send to the input of some other amp and speaker.  Get sound there?

Yes. All of the controls and channels and mode switches work except for the T. Dynamics knob.

Obviously there are other things, any point in the signal path could have failed.  You have mute transistors that could be stuck on or failed, and so on.

Here's the latest. The LM3886T arrived the other day and I soldered it in. I screwed the amp back together and tested it. I started with the clean channel. It worked fine at low volume while I tuned my guitar. Then it started to sound fizzy. And cutting in and out. The more I played the fizzier it got. Same in the lead channel. Hardly any volume too. No amount of knob twiddling had any effect on the sound. Then, after about 5 minutes, it quit...nothing.

I opened the amp up again and the LM3886T looked fine.

I started looking around and spotted this honey colored stuff underneath these two caps. It's dry which made me think that it had been there before and I just didn't notice it.

I checked around all of the other caps and other components didn't find any sign of the honey stuff.

I'm prepared to replace those two caps if that looks like the problem.

I bought an inoperable 2001 Studio Pro 112 and quickly found the damaged LM 3886t. I've removed the 3886 and I am ready to order a replacement. Is there anything/anywhere else I should look for related problems?

The grill cloth, tolex, tilting back of the speaker in the cabinet, control nomenclature and position all remind me of early to late '80s Peavey combos.

http://search.ebay.com/271101755857


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