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December 09, 2023, 07:19:34 AM

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#1
The Newcomer's Forum / Re: Carvin sx amp build
Last post by smsuryan - December 08, 2023, 07:32:43 AM
Quote from: Tassieviking on December 05, 2023, 06:57:33 AMDo you have a SX-50 still ?
I am wondering as we will have to identify some transistors (FET's) as they don't seem to be marked on the schematic.
Q21 and Q22 are most likely JFET's in a TO-92 casing so we need to identify them.
The LED's D1, D3 and D5 are most likely red, but best to make sure, they should be on the PCB as well.

Yes I still have it, play through it daily.  What sources are available to buy PCB boards?
#2
The Newcomer's Forum / Re: Randall RG50-112 Distortio...
Last post by LBeast - December 07, 2023, 04:44:46 PM
No problem.

I opened up the amp, removed the board, and took some pics (see attached).

It appears to me that this amp has had some work done to it previously. The 2" green wire was very curious and the scrub through the board below where the wire attaches to the relay area made me go "Hmmm".

Let me know your thoughts.

As far as measuring values, I'm not gonna lie, never done it before and am a bit wary of doing that on a live amp for fear of frying myself. I did try reheating some of the solder joints which appeared to possibly have issues, but the amp has been sitting unplugged for a week so I was pretty sure the caps were no longer live. Nothing changed in the amp when I put it back together. So it didn't hurt anything, but I also didn't make any headway really.
#3
The Newcomer's Forum / Re: Randall RG50-112 Distortio...
Last post by Tassieviking - December 06, 2023, 12:18:56 PM
Thanks for the Reverb Tank info, I am definitely putting this amp on my to-do build list.
If you have the lid of the amp you could measure the voltage across the 12v Zener diode, I think it's the one behind the big resistor so it might be a bit tight to get at.
You can also tap some components in that area with a plastic or wood chopstick to try to make the LED's flicker on, it is an easy way to look for bad connections.
Make sure the chopstick is plastic or wood only and it should be safe, plastic is the preferred type of course.
#4
The Newcomer's Forum / Re: Randall RG50-112 Distortio...
Last post by LBeast - December 05, 2023, 10:52:32 AM
The reverb tank is an Accutronics 9" model#: 1FB2A1B. The stamped model number on the reverb tank doesn't show up well in the photo. Here is the pic of the back of the tank.
#5
The Newcomer's Forum / Re: Carvin sx amp build
Last post by Tassieviking - December 05, 2023, 06:57:33 AM
Do you have a SX-50 still ?
I am wondering as we will have to identify some transistors (FET's) as they don't seem to be marked on the schematic.
Q21 and Q22 are most likely JFET's in a TO-92 casing so we need to identify them.
The LED's D1, D3 and D5 are most likely red, but best to make sure, they should be on the PCB as well.
#6
The Newcomer's Forum / Re: Randall RG50-112 Distortio...
Last post by LBeast - December 04, 2023, 08:41:03 PM
Quote from: Tassieviking on December 01, 2023, 12:42:31 PMWould you be able to check the reverb tank for the model ?
I might build myself one of these and the reverb tank information is not on the schematic.
If you could provide all information you can see on the tank I should be able to work it out.
Thanks
Mick
Hey Mick,

Be glad to. I'll pull her apart tomorrow and send you some pics/info. It is an Accutronics brand just like Fender uses. That much I know of off hand.
#7
The Newcomer's Forum / Re: Carvin sx amp build
Last post by smsuryan - December 04, 2023, 02:39:57 PM
Quote from: g1 on December 04, 2023, 12:32:28 PM
Quote from: Tassieviking on December 03, 2023, 10:17:37 PMhttps://carvinaudio.com/pages/guitar-amp-schematics
Excellent.  From the SX package on that page, the SX50 is pg.14 and 15 of the pdf.

Quote from: smsuryan on December 03, 2023, 08:50:50 PMnot sure how to distinguish where the "blues button" is located and omit the clean channel. 
The blues button puts back the 500Hz that is notched out for metal and hard rock tones.  It is only on ch.1.
It is shown as S1A and S1B around IC's A3A and A8A.
Around Vol.3 pot (which should be labelled Vol.2?) you can see the 500HZ notch circuit with no defeat switch.

Wow! Thanks for your help! I'll check that out!
#8
The Newcomer's Forum / Re: Carvin sx amp build
Last post by g1 - December 04, 2023, 12:32:28 PM
Quote from: Tassieviking on December 03, 2023, 10:17:37 PMhttps://carvinaudio.com/pages/guitar-amp-schematics
Excellent.  From the SX package on that page, the SX50 is pg.14 and 15 of the pdf.

Quote from: smsuryan on December 03, 2023, 08:50:50 PMnot sure how to distinguish where the "blues button" is located and omit the clean channel. 
The blues button puts back the 500Hz that is notched out for metal and hard rock tones.  It is only on ch.1.
It is shown as S1A and S1B around IC's A3A and A8A.
Around Vol.3 pot (which should be labelled Vol.2?) you can see the 500HZ notch circuit with no defeat switch.
#9
The Newcomer's Forum / Re: Carvin sx amp build
Last post by smsuryan - December 04, 2023, 10:08:04 AM
Quote from: Tassieviking on December 03, 2023, 10:17:37 PMI was looking at the schematics as well and we really need to know what model we are talking about, there are differences between the different size amps.
We might also need help identifying some of the components as they might not be marked the schematic.
I was pleasantly surprised when I found  the schematics on Carvins website.
https://carvinaudio.com/pages/guitar-amp-schematics

It's the sx50 model..the smallest one.  Might not be much different than the 100 model?
#10
The Newcomer's Forum / Re: Carvin sx amp build
Last post by Tassieviking - December 03, 2023, 10:17:37 PM
I was looking at the schematics as well and we really need to know what model we are talking about, there are differences between the different size amps.
We might also need help identifying some of the components as they might not be marked the schematic.
I was pleasantly surprised when I found  the schematics on Carvins website.
https://carvinaudio.com/pages/guitar-amp-schematics