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Messages - vidmachine

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1
Amplifier Discussion / Re: Another Randall RG100ES question
« on: May 22, 2019, 11:17:47 PM »
Thanks. I pulled it out and dissected it.  There was literally no carbon left on the track.  I’ll get a replacement and see what happens.   

2
Amplifier Discussion / Another Randall RG100ES question
« on: May 22, 2019, 11:36:44 AM »
Can any one help me identify and locate a replacement for this (see photo.)  It is the mid pot for an RG100 and is believed to be a 2K Linear pot.  There are numbers but I can't seem to find a match.  seems to be a 3/8" bushing and 1/4" shaft.

It has a problem with crackle and the contact cleaner didn't help.  It also has a very small spot where the sound volume jumps up right around 10 o'clock.

3
Amplifier Discussion / Re: Peavey Stereo Chorus 212
« on: May 21, 2019, 12:58:44 PM »
AC hum wouldn't blow both speakers though would it? 

fun story... One of the speakers seemed to break the wire off where it connects to the voice coil winding.  I reattached it with solder and it worked for a while but it seems that the speaker blew again as soon as I turned it up to band level.  Its looking like a bigger mess to me now.

4
Amplifier Discussion / Re: Peavey Stereo Chorus 212
« on: May 20, 2019, 06:52:38 PM »
I’ve decided that I don’t want to blow another set of speakers just to find out the amp went bad.  I tried a voltage reading at the speaker leads and got no real measurement in DC volts but got 150 mv in AC.   Not a pro electronics guy but was wondering if this seems like a big problem.  Thoughts? 

5
Amplifier Discussion / Re: Peavey Stereo Chorus 212
« on: May 19, 2019, 03:34:08 PM »
Well it seems that I blew out the power amp or a transistor.  The volume dropped off a bit and then sound stopped coming out.  Back to the drawing board to fix a new problem. 

EDIT -  The speakers blew...  Can I put 8 ohm replacement baskets on the 4 ohm magnet bodies?

6
Amplifier Discussion / Re: Peavey Stereo Chorus 212
« on: May 11, 2019, 09:47:19 PM »
Thanks Enzo.  It’s in.  The linear pot is goofy and it is still loud as hell but at least it is repaired for now.  It’s an ok amp.   I love putting the Line 6 Pod X3 into the two separate power amps.   It sounds good like that.  I just wanted the ability to adjust the volume when plugged into the front.

7
Amplifier Discussion / Peavey Stereo Chorus 212
« on: May 11, 2019, 05:51:03 PM »
This amp has a broken Lead Channel Post Gain bracket type pot that says 10KA. The folks at Peavey told me I needed a 20KB pot so that is what I got. I opened the amp after the part arrived to see the 10KA pot.   >:(

Any harm in using the 20KB for the post volume?  All I figure is it might be a little less loud.  It is already too loud though. 

Please let me know.  Thanks!

8
Amplifier Discussion / Re: RG100ES Biasing the POWER transistors???
« on: April 01, 2017, 08:47:54 PM »
Ok I swapped them around. And now I'm getting 43.5 mv on both .6's and zero on both .27s. Still have 258 mv on the speaker out to ground.  Maybe a bad resistor somewhere.  Here is an iPhone shot test video.

Except for the iPhone mic compression it sounds pretty good.  Still should be a tad more thumpy but it's good for now. 

https://youtu.be/x6qrPpPfuqk

Additional info Edit:
So the amp sounds good and seems to be chugging as it should but after warming up and playing for a little while, seems to be getting a little bit of unwanted distortion.  Not the crunchy/metal good distortion, but the buzzy kind.   

Questions: Could this be what is meant by Crossover Distortion?  Is this perhaps why the capacitors C31, C33, C34, C35, & C36 may need to be changed?  Can they be tested in circuit?   Would it be better to set bias at 15-30 mv across R55 than at 43.5 mv where it is now? 

Thanks a bunch. You guys are awesome!

9
Amplifier Discussion / Re: RG100ES Biasing the POWER transistors???
« on: April 01, 2017, 03:28:32 PM »
The yellow wire is going to a .27! 

The XP series is supposed to not lose as much volume when you engage the sustain boost.  Would that have anything to do with swapping the resistors around?

10
Amplifier Discussion / Re: RG100ES Biasing the POWER transistors???
« on: March 31, 2017, 12:41:50 PM »
Quote
Looking at the picture I posted starting with the top left .6 Ohm
.6 = 3.3 mV then runs to zero
.27 = 106 mV holds steady

Weird, according to schematic you should have 30 to 50mV across the 0.6 ohm ones, and *zero* across the 0.27 ohm ones.
Maybe somebody pulled them and replaced the wrong way ?  :o

I'll be dipped in dookie.  Every picture I can find has these two resistors opposite of the way they are in mine.  I will trace the circuit to be sure.  I can't imagine that this would have passed QC at Randall but it appears these are originals.  Maybe a trainee or a hungover tech was assembling it?  Gee whiz. 

I can tell the amp has had a repair before I bought it. A power transistor appears to have been replaced before I bought the amp used.  I can tell because there is evidence that there was an overheat. (bluing on the metal straps inside the chassis and the part looks like a later model with different silk screening on the top.)  Maybe that is why the owner traded it in.  "Hey man, this amp doesn't like Lynch or Dime.... blah, blah"

It sounded great for the 19 years I had it but something is off for sure. 

Thanks for the details on the voltage readings.  I am so grateful for your help.

The jpg file at the other thread looks like mine and has the two op amps and TL604C switcher.  Compared to my amp, the resistor's position is different.  (from https://www.ssguitar.com/index.php?topic=2847.0)

ADDITIONAL INFO: 
Yeah the resistors are definitely in the wrong place.  I have 46 mV on the .27 labeled R55 In my attachment.  There is 243 mV on the speaker outs.  Is this reading due to the manufacturing defect/botched mod/repair?  Would there be permanent damage?   Can we verify that I identified the correct parts with the markings on the image attached?  Also a photo of the QC tag for shame.  :trouble

The XP series is supposed to not lose as much volume when you engage the sustain boost.  Would that have anything to do with swapping the resistors around?

11
Amplifier Discussion / Re: RG100ES Biasing the POWER transistors???
« on: March 30, 2017, 12:16:43 AM »
Measure with DC millivolt range.  One probe at each end of resistor.
Post your results for each and specify whether .6 or .27 resistor.

I put the controls all at noon, no signal plugged into the input, reverb off with footswitch, and both channels on with fs-5 footswitch

Looking at the picture I posted starting with the top left .6 Ohm
.6 = 3.3 mV then runs to zero
.27 = 106 mV holds steady

next bank next to the molded connectors
.6 = 6 mV then runs to zero
.27 = 83 mV holds steady.

I have adjusted the trim anywhere from .550 to .650 Volts.  And there is a sweet spot that sounds pretty decent, but I can feel the back heating up a bit more than yesterday.  My initial reason for the investigation started when I noticed the Bass was sounding loose and flabby.  I changed the filter caps to 6800 uF - 50V cans.  Some of the ever-present hum cleaned up, but the bass was sounding off.  It was suggested on the thread https://www.ssguitar.com/index.php?topic=4201.msg33508;topicseen#msg33508 to change a few capacitors that I haven't had a chance to swap. 




12
Amplifier Discussion / Re: RG100ES Biasing the POWER transistors???
« on: March 29, 2017, 08:36:46 PM »
what are the symptoms of a bad transistor?
It doesn´t work that way.
You tell us what is the actual problem with your amp or describe its symptoms, then we proceed.


I was double checking the bias based on RG and PRR's post here http://www.diystompboxes.com/smfforum/index.php?topic=31737.msg899678#msg899678

It has me concerned. 

When I measure my R55 & R56 .6 ohm resistors across the terminals I get a reading that quickly decreases to zero mV.  One of the .27's is in the 48 mV range and the other is about half of that. They do not decrease.  I have 43 Volts going into the set closest to the molded plugs. Oddly I get a chassis voltage reading of 43 on either leg of both of these. Maybe I am doing this wrong. This was with no signal attached and both channels on with the volume cracked open a little.  The other set of .6/.27s shows about 250 mV on either side to ground. 

13
Amplifier Discussion / Re: RG100ES problems - new owner/new poster
« on: March 18, 2017, 12:10:12 AM »
How do you play the amp (i.e. Style of music)? Do you use the effects loop? How long were you playing the amp and satisfied with the tone?

My amp is a RG100ES XP.  Mostly I use it for practicing hard and heavy rock, some metal.  I have had the amp for at least 19 years and it always sounded awesome.  Now it just seems to sound "pretty good."  The tone change is obvious to my ears.  The low end is not really defined or clearly boomy/thumpy anymore.  It is loose, woofy, and flabby sounding.

Speaking of the effects loop, I have never been able to use it.  It always has a terrible buzz if anything electronic is connected to it.  I can plug a guitar into the Return side and it sounds clean and clear.  But any preamp or the Pod XT plugged in or out just buzzes so bad... 

Do you guys like sound samples?  I'll attach and mp3 with the current sound.  It is mic'd on axis with the cone.  It is a CAD TSM 411 microphone.  I'm looking for some old recordings to compare it to.

The guy who suggested the transistors maybe going bad was a guy at the office, nobody here..

14
Amplifier Discussion / Re: RG100ES problems - new owner/new poster
« on: March 17, 2017, 10:13:08 AM »
Thanks for the reply, Doc.

Yes I tried some other speaker setups.  I used a 1x12 Peavey cab, the 1x15 in my Randall bass combo, and also the 1X12 "special design" in my Fender Studio 85 with some wiring adapters.  I can't say they had the exact same issue because those speakers are drastically different.  None of these sounded "bad."  But something changed from what it used to sound like.   Normally I use a Tour cabinet loaded with 2 8 Ohm Peavey Scorpions wired down to 4 ohms. 

The problem appears to point to something in the Randall head wearing out or breaking down.  Don't get me wrong, it still sounds good but it used to sound awesome.

15
Amplifier Discussion / Re: RG100ES Biasing the POWER transistors???
« on: March 16, 2017, 11:36:30 PM »
what are the symptoms of a bad transistor?

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