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Old 27th January 2013, 11:30 PM   #141
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Is there a pair of transistors your would recommend that I can substitute for these small transistors?

I'm still trying to figure out if there is a name for these small transistors that are cylindrical with a flat on one side.

Since all of these transistors are connected between the -/+ 42 rails the transistors have to handle 84V?

BR
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Old 28th January 2013, 04:25 PM   #142
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Quote:
Originally Posted by badraven View Post
Is there a pair of transistors your would recommend that I can substitute for these small transistors?
My normal small signal devices are BC107 and BC177, but these aren't high enough voltage for some in the amp (see below).

Quote:

I'm still trying to figure out if there is a name for these small transistors that are cylindrical with a flat on one side.

Since all of these transistors are connected between the -/+ 42 rails the transistors have to handle 84V?
No, only some of them - many only ever see a single 42V, and some less than that.
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Old 28th January 2013, 11:24 PM   #143
Enzo is offline Enzo  United States
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The amplifier is in current production, so those transistors should be available, from Fender if from no one else.

The small cylindrical transistors with the flat side are called TO92 packages. TO means "transistor outline" and most common shapes have a TO number.

None of your 2N400x series transistors are in the signal path. The actual amplifier circuits use Japanese series transistors. Your 2N4003 and friends do things like turn LEDs off and on, and act as switches turning 16v off and on to control things. Also a couple of them turn on and off the power amp mute. These are not critical types, and something like 2N4401/2N4403, or 2N3904/3906 should work.


I recommend if you replace the 2Nxxxx types with something else, you stick with American types. Electrically you can do fine with the BC series or some 2S Japanese serie4s parts, BUT the legs are in different order. AMerican types will go right into the holes, the other types will have to be mounted sideways or backwards so the leg pinout will fit the existing board holes.
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Old 29th January 2013, 12:34 AM   #144
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Default Enzo

Thanks for explaining these things to me. I figured out earlier today that these small transistors are TO92. Or should I say, I found some info that indicated that to me and then you confirmed what I found. Thanks!

I understand that the FM212R is still in production, which makes me wonder why these parts are so hard to find. They apparently have updated the parts they use or are running on previous stock. As for purchasing from Fender, they are real proud of their stuff. I don't think it would be feasible to purchase from them. Unless of course I can figure out exactly what it causing the problem and replace just that.

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Originally Posted by Enzo View Post
The amplifier is in current production, so those transistors should be available, from Fender if from no one else.

The small cylindrical transistors with the flat side are called TO92 packages. TO means "transistor outline" and most common shapes have a TO number.

None of your 2N400x series transistors are in the signal path. The actual amplifier circuits use Japanese series transistors. Your 2N4003 and friends do things like turn LEDs off and on, and act as switches turning 16v off and on to control things. Also a couple of them turn on and off the power amp mute. These are not critical types, and something like 2N4401/2N4403, or 2N3904/3906 should work.


I recommend if you replace the 2Nxxxx types with something else, you stick with American types. Electrically you can do fine with the BC series or some 2S Japanese serie4s parts, BUT the legs are in different order. AMerican types will go right into the holes, the other types will have to be mounted sideways or backwards so the leg pinout will fit the existing board holes.
Thanks for leading me in the correct direction.
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Last edited by badraven; 29th January 2013 at 12:37 AM.
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Old 29th January 2013, 09:27 AM   #145
Enzo is offline Enzo  United States
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Transistors may be American types, but that does not mean they are made in the USA, in fact very few transistors are made here. Not all transistors are distributed in the USA. These could be among them. The Frontman series are imports. I can think of any number of times I wanted some part, and bumped into "not available in the USA".

I am not sure what you mean by proud of their stuff. You cannot just call Fender and order a part, but any Fender dealer or service center can, and there are places that sell Fender parts. Guitar, Amplifier, and Korg Keyboard Parts | NATIONAL PARTS DISTRIBUTOR FOR KORG, VOX, BLACKSTAR. PARTS FOR FENDER, GIBSON, GRETSCH, HOFNER, SWR, GUILD, AND MUCH MORE is an example.


But as I mentioned, these transistors are used in control circuits, so would have no effect on the sound quality, and most anything of sufficient ratings would work. I would just make a substitute if this amp came to my shop.
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Old 30th January 2013, 02:09 AM   #146
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Talking Enzo

Quote:
Originally Posted by Enzo View Post
The Frontman series are imports. I can think of any number of times I wanted some part, and bumped into "not available in the USA".
Yeah, I think you nailed that one on the head. Import amp = import parts = pain in me ****!


Quote:
I am not sure what you mean by proud of their stuff.
Proud of their stuff = "high priced". Check any "Authorized Dealer" of any persuasion and you'll get quoted the "OH, you want factory parts? Step this way..." price.

Quote:
But as I mentioned, these transistors are used in control circuits, so would have no effect on the sound quality, and most anything of sufficient ratings would work. I would just make a substitute if this amp came to my shop.
I have been reading a different article about SS amps that is way more informative that the last one I posted here. This fella has really got me thinking. I stiff don't get the whole picture and the whys and such of how power splitting via resistors etc. but I am getting there. The more I read the more I see and the more it makes sense.

I have a theory. My amp works for several minutes before the output transistors, well Q21 anyway, get hot and the amp stops working.
The sound is distorted on the clean and the drive channel. Now in this article, this fella explains a situation where you get oscillation. His description sounds like what my amp is doing. (Yes, Nigel has mentioned this possibility in past posts) The problem is, the oscillation this fella is talking about is in the power amp section. The distortion I am experiencing is on all three channels. This tells me the problem is right in the beginning of the preamp circuit. U1, U2, U3. Or one or more of the resistors in that section is not restricting.

Last night I was checking resistors in the power amp and found that R106, which is supposed to be 47 ohms was actually 3k2. And even though I went to Radio Shack yesterday to get some 47, 470 and 47k resistors when I got home I have two 47k and one 470. So I swapped in a 470 to see what would happen. Nothing!

Anyway, I am thinking maybe the same "problem" might be happening in the preamp.

I'll update tomorrow...

BR
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Last edited by badraven; 30th January 2013 at 02:23 AM.
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Old 30th January 2013, 05:21 AM   #147
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"Proud of their stuff = "high priced". Check any "Authorized Dealer" of any persuasion and you'll get quoted the "OH, you want factory parts? Step this way..." price. "

Oh? Pardon me, but my shop is an "Authorized Dealer" for many brands, and I find it offensive to be accused of such an attitude. I don't charge any more for parts someone wants for themselves than I do for any repair. In fact, I support local amateurs wanting to learn. A guy walks into my shop looking for a 470k resistor, I usually just give him a couple. And advice is free. In fact, if you walked into my shop wanting those 2N4003 transistors, I would tell you I could order them, but I would also tell you what substitutes we could use, and I would have them in my drawers ready to go, no ordering required. COnsider I normally charge $60 an hour for the very diagnosis I give you for free. As do a bunch of other folks on this forum. It is easy to just label an industry professional as some sort of underhanded used-car-salesman cliche, but in reality the majority of us are honest prefessionals trying to help people.
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Old 30th January 2013, 12:37 PM   #148
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Default Enzo

Enzo please dont be offended. I have run in to many "Authorized Dealers " with very high prices. Im sure you have too! Of course being in the auto repair industry, I see a lot of gouging, and I hate it! Perhaps my perception of dealers in the music eletronics world is slightly off center, fair enough?

The fact that you are here (as with others) helping amateurs with their woes shows your true colors. Its people like you, Fahrey, the Nigels and others that remind us that there are people that do give back to the community.

So please, dont be offended. I assure you, you are more than appreciated.

Now, about that twenty bucks...
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Old 31st January 2013, 03:53 AM   #149
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Default OpAmp U8

I have been having this idea that the fuzzy sound problem has to do with an OpAmp. I have some sockets and plenty of OA's so I removed them one at a time till I ran out of sockets. I'm short by two. I started with U1, installed a socket, inserted a TL072, plugged in the amp and tried it. Still fuzzy, U2 etc... I skipped u4 because it has to do with the reverb tank. U5 had a strange shinny pattern on top, I honestly expected that to be my problem. But I replaced it and nothing changed.

I should note here that two of the OpAmps are TL072 and the others are BA4560's. I have RC4580's which are nearly identical to the 4560's according to the datasheets.

The last one I changed is U8 and when I turned it on the amp was dead silent. No hum, no nothing. I thought for a moment I had shorted something and the amp wasn't on. But I cracked the volume on the guitar and there it was, smooth, no fuzz, sounding as pretty as the day I bought it. I played all three channels and it sounded wonderful! I kept checking the temp on the heat sink and it took longer this time but it was still getting hotter that "I" think it should. I still don't know what is normal. "Normal" must be pretty hot since it uses such a think heat sink. Anyway, I was playing and then suddenly it went fuzzy again. I checked the temp and it was about 135 on the heat sink. So... apparently the problem is on the same circuit as U8-B.

Last night and tonight I have been checking the value on each resistor beginning with R1. Most are right on the money (within 5%) but some are off by a noticeable amount and some are WTF off! Like thousands of ohms off. I am up to R115 so far. Below are my results so far. Those that are off but are in the ball park are not listed. Only the ones that are WAY off.
Those with no letter are ohms (<999) I'm sure that's obvious but...

Item listed actual
R19 47k 8.3k
R25 5.1k 21.8
R29 33k 3.07k
R31 220k 180k
R44 100k 44.1k
R50 47k 27.5k
R64 1m 93.1k
R88 47 80k
R106 fu47 3.3k changed to 470 - didn't have a 47ohm to install
R107 150 107
R108 390 107
R110 150 107
R111 390 107
R114 .22 0
R115 .22 0

That's all I have for the moment.


BR
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Old 31st January 2013, 04:35 AM   #150
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In the section of the schematic where U8 is I assume that since the mid contour switch is shown to the left, that means that its in the "out" position or "Normal" and pushing it in makes the signal go through the section where U8 is?

But that section would still pay a part at all times wouldn't it, since it is connected to the circuit at all the times? Its just that the signal is directed through that section when the button is pushed in?

BR
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