RA100: Best Preamp Tubes

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RA100: Best Preamp Tubes

Post by bandit2013 » Tue Dec 05, 2017 10:26 pm

Recently I have been playing the RA100 more than usual. Yes I have the TC-50 and a few other amps. However, when I had rolled in some tubes sometime last year the amp sounded incredible. More than I ever expected. The Clean channel had a unique tone to it that just lets you know this is a British Voiced amp, The vintage Lo definitely reminds you this is not what it sounded like out of the showroom or out of the box, and vintage Hi definitely makes you think twice and helps you forget you thought you wanted another amp. Sure this amp is heavy, much larger than most mesa heads and sounds so damn good with the right mix of tubes in the preamp. Now the run down.

The following combination works incredibly well for the Hi/Lo channel. If you have seen my post "TC-50 will not replace my RA100" this is the reason why.

V1: Mullard CV4004 . I have tried this tube in my other amps before I got the TC-50 and JP-2C. It was good in the Mark V and interesting in the Roadster. Just wow in the RA100. The CV4004 does have a scooped tone but yet does not choke off the midrange. Bass response is a bit more refined than stock tubes.

V2: Mullard 12AX7A Re-issue long plate: This tube definitely has a well balanced tone with a slight bit of high frequency roll off. This definitely helps cut on the brittle tone and yet warms up the amp for both lo gain and hi gain channels. Also this tube position is the driver for the tone stack. The long plate Mullard definitely adds what the lo gain channel has been missing. It deepens the bass but remains bold and much tighter than the stock tube. Dial in more bass without any mud.

V3: stock Mesa 12AT7 tube. I have tried an RFT NOS 12AT7 as well as the JAN/Phillips 12AT7. Not bad but the Stock tube works well for the FX loop.

clean channel tubes
V4: Svetlana 12AX7. Yeah, looks just like the Mullard CV4004, Tung Sol and EHX tube but has a different character to it. It seems to be much brighter than the stock tube. The clean channel does need some help in controlling the bottom end and gaining some top end chime. Perhaps this tube has a lower gain characteristic but it works in this position quite well as it is the first stage for the clean channel.

V5: Mullard CV4004 (again). Not exactly sure what the plate voltage is on V5 but the slight scooped tone and gain character of the CV4004 helps in this position. I am not exactly sure where the tone stack is on the clean channel. I would assume it is between V4A and V4B. When you push the gain on the clean channel this tube definitely takes over as the hard driven clean channel never sounded so good.

V6: I am currently using a JJ ECC803S long plate tube. It probably does not matter what tube you use here. I have used others but seem to like the long plate ECC803S for the reverb.

V7: Sovtek 12AX7-LPS. It is similar in appearance to the Mullard re-issue but is more suggested for the Phase Inverter. This tube position can influence your tone too. I have experimented with other tubes to see what works. Sometimes the stock Mesa 12AX7 tube may be a good complement to the Mesa EL34 power tubes or the Sovtek may be a better fit. I have even used the Mullard tube but that has more treble roll off for use as a phase inverter.

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