GGG Rangemaster Mods

[YouAre]

I'm working on building a Rangemaster on perf. I'm doing a Negative ground so i can daisy chain it. I bought the magical OC44 from Smallbear.

First is the silly question. I wasn't sure which way the transistor was oriented, so i tried it in both directions. One direction yielded an odd hum, while the opposite sounded fine. I want to make sure of everything. There's a red dot that indicates the orientation, can anyone tell me if its for the collector or emitter?

Also. The 68k and 3.9k resistors....Keeley replaces them with 100k and 5k trimpots respectively. Do you think thats necessary? Or is it for really fine tuning the bias?

regards,
murad

[soulsonic]

I believe the red dot is the collector.

The trim pots are only really necessary if you're wanting to be totally anal about biasing it a certain way.  Sometimes you have to mess with the bias a bit if it's not working right, but if yours is working I wouldn't worry about it. RG's essay on the Rangemaster gives some detailed notes about biasing it so it's voltages and response exactly match an original, so you can check that if you want. But if you used the resistor values that were listed on the sheet of paper that came with the OC44, it should already be biased up just right. Small Bear tests them to have the same bias as suggested in the GEOFEX article when you use the resistors recommended on the sheet.

For other mods: I highly recommend fooling with the values of the input cap, it's really easy to make big changes in the tone by switching to smaller or larger values. It's alot of fun to put the different ones on a switch so you can try all the different possiblilties. This makes way more of a difference than messing with the bias.

[YouAre]

excellent. i appreciate the help man!

now when it comes to the input cap, does anyone know what the values are for Treble, mid, and full boosts?

[Rick]

Hmmm, can't totally agree that messing with the bias isn't always necessary. Maybe you'll get lucky with matched sets from Smallbear and get the sound, and maybe you won't.
Anyway in all fairness I've built many TBs but all from scratch misc mostly 2SB trannies and these all really benefited from biasing (at least using one trimpot). It was really like fine tuning a hotrod engine ...the sound improvement can be quite impressive! Do the input cap mods after the engine is in perfect running order IMHO. Fun circuit for sure.
later ...Rick

[soulsonic]

I had Atlas check the OC44 I got from Small Bear just to make sure, and the red dot IS the collector.

For the input caps; .0056uF is the stock value and it has kind of a mid-peaky tone, so I always call that "Mid". For Treble, just try smaller caps and select according to taste, and for Full, try larger caps and select to taste. I'm not telling the secret values I use for mine!

[zotch]

I used trimpots with the NPN unit I just built, even though it was one of those 'pedigreed' CV7112's from Small Bear. It was a gift (Stepson's guitar-playing friend going back to England-I sent 'im home with a bit of British Musical History, heh) so I just got it running to RG's specs and sent it off. Didn't want to fool w/my first build. The one I build for self will get trimpots too; not terrribly extravagant/anal--my Chandler Tube Drivers have a panel-mounted 'bias' control, and I found it useful back in those rack-mount days...

I've seen orig. input cap values listed as .0047 to .0068uf, and posts regarding .1uf as a full boost (Tommy Iommi mod?); I used a toggle between .0068 & .001uf. My mileage:

Smaller cap: I found Brian May in my amp (neck & neck/bridge humbuckers); bridge alone made Ratt's 'Lay It Down' jump right out. Larger: a bit thick for neck, but fattens up the bridge; all positions in my strat like this cap.

I tried a glass .01 cap, but I found the green 'chicklet' to be the choice at the time--just a bit more detailed? I've got a few .01 & .1 glass to spare to anyone who'd like to try em.

I haven't gone larger than .01uf yet, but my own unit will have a second footswitch for the first two values, and a toggle for other-value pairs or some such madness. I see three input cap sockets minimum for this one...changing caps is so much cheaper than rolling tubes in my amp, and I don't have to snipe on eBay to get 'em!

I see a use for an output pot in mine, unless I find that juicy tone at the far end of 'boost set' is lost by not driving the amp as hard. I'd trade a bit of it to even out the difference in volume when byp'd. Maybe I'm trying to make too much out of it, but I need to build courage before I start the mods on my unfinished NeoVibe.

tom o   

[zotch]

Whoops, typo in last wordy post: my R-mastr had .0068 & *.01* caps.

Apologies,

tom o

[YouAre]

zotch i'm sorry i misunderstood your correction that you made.

Your rmaster had .0068 and .01 caps? And .1uf is the fullrange mod?

[zotch]

Yes, you got it right; but I checked the Geofex site again and and the highest cap value mentioned was .15uf  gotta be tough on speakers at that range!

The first Black Sabbath album was said to be recorded with a large cap, .1 to .15uf IIRC; have fun rolling caps to get your tone (cap socket highly recommended).