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Old 26th January 2013, 01:13 AM   #131
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Default Nigel Goodwin

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Originally Posted by Nigel Goodwin View Post
As someone who repairs amps professionally I would definitely say 'toss the old transistors', often one of the earlier stages can be intermittent, and blow the rest. It's good practice to replace all transistors in the DC chain, and gives a MUCH better chance of a lasting repair.
Well I can see the benefit of changing them all, especially if it is a common scenario of having repeat visits from a customer because of an intermittent transistor causing a "Comeback" as we call it in the auto repair industry. Then again in my industry we call people that throw parts at a problem a Hack. Of course this is a different industry so I will not make assumptions where I have only a basic knowledge.

These is something I am confused about. I am looking up a 2N4003 transistor which my amp uses several of. The schematic shows Q6 and 7 show a PNP transistor but when I look for that item online I not only see that it is obsolete but the datasheet shows it to be an NPN. Am I missing something here? The arrow is pointing inward in the schematic, that makes it PNP.


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Originally Posted by Nigel Goodwin View Post
A TIP31C isn't an RF transistor, it's a normal NPN medium power audio transistor, and complimentary to the PNP TIP32C. Personally I only stock the TIP41/42C which are higher rated versions of the 31/32, and commonly use them for drivers in power amps (or even outputs in smaller amps).

So TIP31/32 are perfectly fine for your situation.
Well I was asking because the receipt shows the description for each item I ordered and it states that the one is an RF and the other is a Bipolar. If you say its not that I will take your word for it.

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DC coupled amps are VERY difficult to repair, you need to understand how they work and why they were designed that way, and even then a slight mistake blows everything again
Yeah I am quickly gathering that. This amp really is a cluster f___!
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Old 26th January 2013, 01:41 AM   #132
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Can someone recommend a Capacitor Tester that is reasonably priced. I was looking on ebay and I just don't know if I am looking at reasonable items. There are several US retailers on there.

Thanks!

BR

Capacitor Tester in Test Equipment | eBay
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Old 27th January 2013, 11:37 AM   #133
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Originally Posted by badraven View Post
Well I can see the benefit of changing them all, especially if it is a common scenario of having repeat visits from a customer because of an intermittent transistor causing a "Comeback" as we call it in the auto repair industry.
Same in the electronics trade.

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Then again in my industry we call people that throw parts at a problem a Hack. Of course this is a different industry so I will not make assumptions where I have only a basic knowledge.
Replacing all faulty parts isn't 'throwing parts at a problem' - if you replaced the piston rings in an engine no doubt you would replace the big-end shells, the gaskets, the oil and filter etc, etc. - none of which were faulty. It's EXACTLY the same.

Quote:

These is something I am confused about. I am looking up a 2N4003 transistor which my amp uses several of. The schematic shows Q6 and 7 show a PNP transistor but when I look for that item online I not only see that it is obsolete but the datasheet shows it to be an NPN. Am I missing something here? The arrow is pointing inward in the schematic, that makes it PNP.
Q6 and Q7 are definitely PNP, as is Q17 (complementary to Q16).

Quote:


Well I was asking because the receipt shows the description for each item I ordered and it states that the one is an RF and the other is a Bipolar. If you say its not that I will take your word for it.
Both are 'bi-polar', but so are most RF transistors

They are audio drivers/outputs, your receipt was completely wrong.

Quote:


Yeah I am quickly gathering that. This amp really is a cluster f___!
Like I said, you need to understand how it works - for example you could leave out Q16/17 for initial testing (they are simply over current 'protection'), likewise you could ignore Q6/7 and short Q7 together collector/emitter (it's just muting and anti-pop). Once the rest of the amp is working, you can then reinstate non-essential sections.
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Old 27th January 2013, 11:41 AM   #134
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Quote:
Originally Posted by badraven View Post
Can someone recommend a Capacitor Tester that is reasonably priced. I was looking on ebay and I just don't know if I am looking at reasonable items. There are several US retailers on there.

Thanks!

BR

Capacitor Tester in Test Equipment | eBay
There's little need (or use) for testing capacitors - with the HUGE exception of ESR of electrolytics - by far the most common fault in electronics equipment over the last couple of decades. Here is the one I use, easily available in the USA - a normal capacitor tester doesn't test ESR, which is almost entirely the fault with electrolytics.

Peak Electronic Design Limited - Atlas ESR PLUS - Equivalent Series Resistance Meter and Capacitor Analyser with Audible Alerts - Model ESR70

However, it's not very often a problem anyway in linear amplifiers, more so in switch-mode power supplies.
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Old 27th January 2013, 06:11 PM   #135
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Nigel

Thanks for the clarification. You are correct, when you replace the rings you also replace bearings and seals and gaskets, all of which may or may not have any problems. But it saves a world of irritation and "free" labor in comebacks if you don't take care of these things while the engine is out. I stand corrected sir.

I have been told by several people that they keep TIP41 transistors in stock because they cover many others used in various cases. And that makes perfect sense to me. My question is: Is this the same for these smaller transistors and JFETs used on my amp? Meaning: there are several smaller sized transistors on my board.
For instance, my PCB contains:
3) 2N4001 - NPN
6) 2N4003 - PNP
5) J111 - N Channel
2) 2SC3262K - NPN
2) 2SC2383 - NPN
2) 2SB1236 - PNP
1) 2SA1013 - PNP
1) 2SA1016K PNP
and
1) 2SD1857 - NPN

Is it a matter of buying transistors that simply meet or exceed the electrical requirements for a circuit or will changing to different ones cause a change in tone and/or operation?

I ask because I have been looking these up and most of these appear to be obsolete. SO I have to figure out what will interchange. I have been downloading datasheets but I have not been able to find all of them yet. And of course there is learning to interpret what I am reading.
So please don't get the idea that I am trying to get someone else to do my research for me. I am just asking if these are similar "Shortcuts" like with the large transistors?

Thanks for your time.

BR
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Old 27th January 2013, 06:31 PM   #136
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If you are struggling finding all the obsolete transistors then maybe it is time to cut your losses and buy a new amplifier module ?

There are dangers with replacing transistors with newer versions that could cause oscillation. I suppose you could still alter feedback to get rid of oscillation.

At least you would end up with a new amplifier which should give many years of good service and it would be easier to find components for if required.
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Old 27th January 2013, 07:43 PM   #137
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Nigel W.

Of course you have a valid point. I actually have my eye on a tube amp. A Bugera V22. Combo. Its not a big name brand but it sure does have some nice tones.

In the mean time I am kind of treating my current amp as a learning tool.

When you say buy a new module, you mean buy a new amp right? Because it sounds like your might be saying get an updated PCB.

BR
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Old 27th January 2013, 08:54 PM   #138
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Originally Posted by badraven View Post
Nigel

Thanks for the clarification. You are correct, when you replace the rings you also replace bearings and seals and gaskets, all of which may or may not have any problems. But it saves a world of irritation and "free" labor in comebacks if you don't take care of these things while the engine is out. I stand corrected sir.

I have been told by several people that they keep TIP41 transistors in stock because they cover many others used in various cases. And that makes perfect sense to me. My question is: Is this the same for these smaller transistors and JFETs used on my amp? Meaning: there are several smaller sized transistors on my board.
Again, it's a question of understanding how it all works, and what each transistor is doing - as I've previously mentioned I only stock the TIP41/42C as they are essentially higher rated versions of the 31/32 - so why keep four types in stock when you can keep just one.

Quote:

For instance, my PCB contains:
3) 2N4001 - NPN
6) 2N4003 - PNP
5) J111 - N Channel
2) 2SC3262K - NPN
2) 2SC2383 - NPN
2) 2SB1236 - PNP
1) 2SA1013 - PNP
1) 2SA1016K PNP
and
1) 2SD1857 - NPN
These are a mix of American and Japanese numbers, so I'm not familiar with them - but I doubt any are critical.

Quote:

Is it a matter of buying transistors that simply meet or exceed the electrical requirements for a circuit or will changing to different ones cause a change in tone and/or operation?
'Tone' is an imaginary and unmeasurable term used in regard to the degree of distortion obtained from valve amplifiers - it doesn't apply to transistors where the quality is much higher and not subject to such terms. Different transistors make little or no difference to a correctly designed amp.

Quote:

I ask because I have been looking these up and most of these appear to be obsolete. SO I have to figure out what will interchange. I have been downloading datasheets but I have not been able to find all of them yet. And of course there is learning to interpret what I am reading.
So please don't get the idea that I am trying to get someone else to do my research for me. I am just asking if these are similar "Shortcuts" like with the large transistors?
Generally you use transistors you have access to - often having to replace obsolete ones with more modern devices.
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Old 27th January 2013, 09:16 PM   #139
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Nigel W.

Of course you have a valid point. I actually have my eye on a tube amp. A Bugera V22. Combo. Its not a big name brand but it sure does have some nice tones.

In the mean time I am kind of treating my current amp as a learning tool.

When you say buy a new module, you mean buy a new amp right? Because it sounds like your might be saying get an updated PCB.

BR
There are loads of amplifier modules you could buy to fit inside your case.
Or you could just simply buy a new amp.

You could fix your amp and treat it as a learning exercise.
It depends on how many transistors you find are obsolete.
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Old 27th January 2013, 09:59 PM   #140
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Nigel G

Believe me, I UNDERSTAND that I need to understand how items and circuits work. I assure you I know this at my core, that is why I have been reading everything I can get my hands on over the last few weeks pertaining to guitar amps. . Believe me, I know the necessity of understanding something in order to troubleshoot it. I am asking questions because some of this stuff is still over my head and I am anxious to get my amp operational again.

Your input is very much appreciated sir, as is that of others here. Thank you all!.

BR
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