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My RD 50 Mods

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Mike (mike_h)
Username: mike_h

Registered: 06-2006
Posted on Friday, July 01, 2011 - 03:19 pm:   

This is the 3rd RD50 I�ve owned. But, the first 110RD50. The clean channel is great as is, as most already know. Here�s what I�ve done to the �Limiter� channel to get rid of the mud and make it a usable channel worthy of being matched with the clean channel.

1. Replace R18 with 820 ohm resistor. This mods the tone stack to decrease the mids. In a previous amp, I replaced R18 with a 1K pot to adjust the mids. I kept this amp simple and matched the clean channel tone stack. I played with different values at C4, but the .0068u worked best to prevent a farty bottom.
2. Removed R10 and replaced with a jumper wire to keep the power even to both sides of the 12AX7.
3. Replaced C6 with a 400v cap (same value) to handle greater voltage.
4. Replaced R9 and R11 with 150K resistor. This increases the voltage on the plate, which makes the tube sound much better. 100K in R9 is also a good choice with a 1.5K at R12. A bit sweeter sound, but less gain
5. Replaced C10 with 4.7uf cap. If you go more, the channel gets farty. Less sounds thin.
6. Replaced R12 with 2.2K resistor � pretty standard plate/cath ratio.
7. Added a 4.7uf and 2.2K resistor to V1/8 and ran to ground rather than V1/8 direct to ground as original. 1st half and second half of tube now the same.
8. Changed C35 to 22uf 350v cap. More power in reserve to meet the 12AX7 draw, 10uf would probably be ok as well.
9. Changed R61 to 1K (1 watt which is greater than necessary but I had one). This pumps up the power to the 12AX7!!!
10. Changed C33 and C34 to 100uf 350v. This cleans the power better and tightens the amp.
11. Added a 100pf bright cap across the lugs of the limiter volume pot � very important to carry some highs through the channel.
12. Still have the original MM 10� speaker in, which sounds very good. I have a Rajin Cajun and Legend 105 on order just because I�m curious. But, the MM10 is a very beefy speaker weighing in at 7.5 pounds!

The results:

My amp has about 185 volts on the plates of the 12AX7. The channel has a great blues sound and can do a nice classic rock overdrive. The mud is gone from the channel, and both channels sound great! The plate voltage on the 6L6 is up to about 600 volts as well. I did do a cap job as well with the original values except as noted above. All of the Mallory 20uf caps I took out read around 30uf. I used Atoms except for the 100uf and 22uf.

Mike
Mike (mike_h)
Username: mike_h

Registered: 06-2006
Posted on Friday, July 08, 2011 - 08:26 pm:   

also added a 68K grid resistor to V1/7. I may up the value to 100K to roll some highs off a bit.
Ed Goforth (ed_goforth)
Username: ed_goforth

Registered: 06-2006
Posted on Friday, August 05, 2011 - 02:31 am:   

Hi Mike, here's Bob's schematic if you need it. Follow the thread, maybe you have this info?
http://music-electronics-forum.com/t2411 3/

Good Luck!
Ed
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Friday, August 05, 2011 - 03:45 am:   

Is this thing still putting out 50 watts? some of those mods may be pushing the transformer to put out more watts wouldn't it?just curious?
Ed Goforth (ed_goforth)
Username: ed_goforth

Registered: 06-2006
Posted on Saturday, August 06, 2011 - 02:48 am:   

It kicks ass! The last RD-50 mod I did for Jeff Prine will soon be on Youtube. He is really happy with the tone! He plays a lot like Dicky Betts (with the Allman Brothers) and then some! He wanted a great Deluxe and vintage Marshall tones with some balls (50 plus watts) He said this amp sounds better than any Mesa he's heard which in most cases is true with many amps these days, if you find the new Boogies are harsh sounding. This amp will do Classic Fender and the Vintage/modern Robben Ford and Chris Cain thing well according to Jeff. The Clean channel now keeps up with the Limit channel, Jeff says that he can solo on the Clean channel All night and be happy now!
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Saturday, August 06, 2011 - 03:21 am:   

were's my rd-100 mods ,lol
Ed Goforth (ed_goforth)
Username: ed_goforth

Registered: 06-2006
Posted on Monday, August 08, 2011 - 12:47 am:   

Right around the corner, what are you looking for specifically? I have a RD-100 here and will starting on it soon. Some things I will share, other things I will keep to myself since I will be building something similar, hopefully to market at some point, but there is a lot of competition these days, and who can compete with the Chinese market? Maybe I will do a small run or just keep the mods for my own use. Can't seem to make any kind of living at it, and I cannot afford to have a website designed....
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Monday, August 08, 2011 - 08:55 pm:   

well anything to enhance the solid state preamp ,and you to chevk out kt- 88's in that head.big difference to my ears.
Ed Goforth (ed_goforth)
Username: ed_goforth

Registered: 06-2006
Posted on Sunday, September 01, 2013 - 05:25 pm:   

Using a 1k resistor in the 12ax7 power supply string will cause more hum since there is no choke. So YMMV...
Rhcp.schipper
Rhcp.schipper's picture

Mike (mike_h)

Mike,

Are you still around on this forum?

Tim

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