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I love the tone of the clean channel of my Marshall JTM60 when the channel vomle is turned down low, about 10 o'clock, with the master volume cranked up. However, this just isn't loud enough to gig with. If I turn the channel volume up the amp loses 'sparkle' and I start getting some nasty pre-amp distortion.

Anybody know of a means to solve this this? The amp is rated at 60W. Is there anything I can buy (cheap, I'm still at school) that's gonna sort this out? Thanks.

small PA system?

You could try a lower gain tube in V1 or V2 (which ever controls your clean channel), say a 12AT7. That will give you a little more headroom. Also, a speaker that handles more wattage will not distort as early either. However, that's part of the charm of an EL34 amp....you'll never have as much headroom as with a 6L6 type amp.

You must play pretty loud! I've played quite a lot of gigs with a JTM60 and never experienced a lack of volume! Having said that, I never used that channel totally clean - I typically had the clean channel volume at 1 or 2 o'clock.

Jeff's suggestion of trying a 12AT7 (ECC82) pre-amp tube is a good one. Pre-amp tubes are cheap and you won't damage the amp. I have a feeling that in a JTM60 V1 affects both channels and V2 is for the dirty channel only. So changing V1 may lower the gain on both channels, which isn't necessarily a problem if you don't play high gain on the dirty channel. I remember reading posts on a Marshall Forum a few years back about changing V2 on a JTM60 to a 12AT7 deliberately to sweeten the distortion on the dirty channel.

If changing a pre-amp tube (cheap option) doesn't work, the next step might be to look at getting some power tubes with more headroom (would they be called softer or harder? ) and getting the amp biased. If the bias is wrong this will affect the clean headroom, won't it?

Ironically, Jeff and I can both tell you how to get MORE gain from the clean channel, but LESS is more of a challenge.

Thanks for your help guys. If I put an EC882 in will I have to do anything else? Like re-bias the amp. I don't really understand how that stuff works so I'll take it to a tech. Also how will I know which valve to change? There are four ECC883s in the amp and one is seperated, kinda. I've been told it's a rectifier(?) or something.
Cheers


Originally Posted by benjaturnerThanks for your help guys. If I put an EC882 in will I have to do anything else? Like re-bias the amp. I don't really understand how that stuff works so I'll take it to a tech. Also how will I know which valve to change? There are four ECC883s in the amp and one is seperated, kinda. I've been told it's a rectifier(?) or something.
Cheers

If you're changing pre-amp valves you don't have to worry about biasing or matching - that only applies to the pair of EL34s in the power stage.

When you look in the back of the amp there are six valves. The two big ones (EL34s) are the power amp valves. The small one next to those is the phase inverter. Ignore that for now, you're supposed to change it when you change the EL34s.

Then there is a group of three small ones. The one nearest to the phase inverter provides the gain for the parallel effects loop (I think). The middle one is V2 (extra gain for the boost channel), and the one on the far end is V1 (works on both channels). It's V1 we were talking about changing. ECC82s are the same size as ECC83s. You just turn the amp off and change it like you would a light bulb. You won't need a tech to do that.

I can't guarantee that will fix your problem, but ECC82s are relatively cheap and it's something that's quick and easy to try.

If you start with your amp's master volume full up and the clean channel volume all the way down (then gradually turn it up) are you sure you can't get a clean sound that's loud enough?

Simon is right on. You can swap the pre-amp tubes at will. Order or go out and buy several different types of tubes. Go to KCANOSTUBES.COM or call Bob at eurotubes. Instead of giving money to a tech, spend that $$ on more pre-amp tubes. You'll thank yourself later.

Have fun!