Quote from: BMWFREQ on March 30, 2011, 06:05:21 PM
So, it sounds like you have modded your RG100ES...  If so, what did you mod; why and what was the outcome?

...

I didn't mod it, just replaced the electrolytics and a couple of transistors.

Bravo!  Craigslist is a good source.  People just want it out of their garage or closet and if they don't play it doesn't mean a thing to them.  Tell us how you progress with fixing the hum.

The program has help and instructions.  It's pretty straightforward.  You just click on a component to open up a window to change its value.  The sliders at the bottom represent the rotation of the pots.  The default is halfway, or "5" (and, sadly, Nigel, these do not go to "11"  ).  The graph is a plot of gain versus frequency, so it is telling you at which frequencies and by how much the circuit is cutting or boosting.  Its like  a drawing of whether you hear less treble or more bass.  The caps and the resistors work together to determine the frequencies at which you start to lose gain, but generally, if you add capacitance, the effect will be to boost the bass end of things.  With guitar you are concerned with the middle of the plot, from about 80 hz to about 1,000 hz.  Playing with the pot and cap values for the bass should tell you what you might expect out of any tweak you are doing and then you could experiment by trying a few values yourself.  The pots are easy to get at, but the caps are on the board, so you have to at a minimum lift the board up to desolder.

Also, a note on randall board:  some of the caps that I replaced seem to have been cut with the world's dullest nippers when installed, they didn't want to come out of the holes, so I had to de-solder, push into the hole and nip the bottom ends, then pull back up to remove (if that makes sense?).  What I'm saying is, the ends of the leads were flattened after installation.  I don't know if this was intentional, or whether my board was made by a guy with old nippers, but it was annoying. 

JM Fahey:

On your third picture, there is a small blue elctrolytic cap from circuit board to chassis.  It lands right near the PS filter caps.  What is that cap?  What part of the board is it attached to?  I ask because I don't have that on my amp.

Regards,

JHow

It's all personal preference... but I like my JRC4558-based BYOC "British Blues overdrive" in the effect send-receive of my rg80 - I'm not going for hardcore metal, but it leaves a lot of room for rude sounds in the red channel.  Think of Zep live Killing Floor.  If you want extra crazy, you can turn on the diode-clipping.  The green channel I like with the reverb up high and no boost.  Think Earl Hooker  on dust my broom. 

The modification I am most interested in for the randall is the trick to set it up to switch the channels via relays.  I have read that people have done this to cut some of the noise introduced by the long footswitch cable.

Have you played around with the duncan tone stack calculator?

http://www.duncanamps.com/tsc/download.html

It's a marshall-style tone stack.  You can plug in values to simulate the rg100 and try switching in lower values for the bass cap.  You can also simluate rotation of the pots to see response at various positions.

It looks better in full size.

I think these do have a three-prong plug, but still with line-cap-to-chassis.

Looks familiar.

Do you have any issues with hum, by the way?  I have low hum that I can't figure out yet and hiss in the reverb circuit.  I dig the reverb (even with the hiss) on this. 

Also, even with the switch, I turn down the gain and volume on the channel you're not using.  If you are on green, the red channel can still assert itself.

Quote from: J M Fahey on February 02, 2011, 03:22:51 PM
...Really groundbreaking....

J.M.:  What part of the design do you consider the ground-breaking part?  Or do you mean the sound is groundbreaking?   I know that I like it but I don't have enough knowledge to know what makes it great.

Thanks for the responses.  I can see  the BC s at mouser.  I will give those a shot.  Yes it is differential pair. 

Can you guys suggest some replacements for TIS-98, which seem to be hard  to find?

I was looking at PN3568 or BC637 from mouser, they seem to be similar.  Application is Rg-80 Randall.  Collector to Emitter is just over 40V in the circuit.

Hello:  I am new to this group (first post here) and am also owner of a fairly beat-up Randall RG-80 (circa 1983).  I have been working on it (which I detailed on another amp forum so I won't go into it here), but this being a forum dedicated to Solid state I am wondering if there are any fans of the RG 80 here?  By fans I mean that you use one and like it.  I really dig it (despite the hum problem I am working on), the "red" channel is really fun when cranked, it is quite loud for what it is.