M4 Tube Replacement Questions

[UnderDriven]

Hi. This is my first post. I'm an owner of an original M4. I've never replaced the tubes (I'm a casual player--I'll play for a while, stop, and then start again). I'm starting to play again, and I suspect that some of the tubes are shot. I've been having some dropouts (no sound, sometimes it comes back and sometimes I have to do a power cycle). Can anyone help me identify the three chassis tubes by location (function and type)? I never use the FX loop--do I need to replace that tube? Also, any recommendations for tubes would be appreciated (I have DLX, BMAN, and SL+ modules). My M4 has Sovtek 12AX7WA tubes in the modules--I haven't looked at the chassis tubes yet. Is there an M4 manual online? Mine is buried somewhere due to a move...

 

[mboogman]

Not sure about the first run M4s, but with my 2nd gen M4 the tubes are all just plain old Sovtek 12AX7WA's, and I think that's probably the best/easiest thing to replace them with. You'd want the tubes in the modules to provide the tone, so the chassis tubes should be (in my opinion) just a good reliable tube like the Sovtek. On my M4, I can get to the chassis tubes from the back without having to take any panels off. Since your M4 has a loop on it, that would actually be the first place I'd check for the dropped signal. Sometimes without much use, those contacts can get a little corroded. As prescribed by Bruce when I had a similar issue on a Mod50 I used to have, he said spray a little con act cleaner (DeOxIt?) in the jacks, and then take a plug and plug it in and out a few times to clean the jacks. worked like a charm. If you haven't played the M4 too much, I doubt that the tubes are in that bad of shape. I'd only replace ones that you find are failing. Hope my ramblings help!

 

[UnderDriven]

Not sure about the first run M4s, but with my 2nd gen M4 the tubes are all just plain old Sovtek 12AX7WA's, and I think that's probably the best/easiest thing to replace them with. You'd want the tubes in the modules to provide the tone, so the chassis tubes should be (in my opinion) just a good reliable tube like the Sovtek. On my M4, I can get to the chassis tubes from the back without having to take any panels off. Since your M4 has a loop on it, that would actually be the first place I'd check for the dropped signal. Sometimes without much use, those contacts can get a little corroded. As prescribed by Bruce when I had a similar issue on a Mod50 I used to have, he said spray a little con act cleaner (DeOxIt?) in the jacks, and then take a plug and plug it in and out a few times to clean the jacks. worked like a charm. If you haven't played the M4 too much, I doubt that the tubes are in that bad of shape. I'd only replace ones that you find are failing. Hope my ramblings help!

Thanks for the reply. Sorry if I misspoke--I meant to say that I am the original owner, not that I had an early version of the M4...

That's good advice on the chassis tubes--a reliable, low-noise tube is probably best. I'm thinking about the Sovtek WC as an alternative to the WA, only a couple of bucks more and possibly a bit quieter (based on info at TubeDepot.com)...

It's a parallel loop (I think) because it has a volume control. I keep it turned all the way down. In any case, I'll try the contact cleaner...

Well, the SL+ is sounding poor as well, which is why I was thinking at least some of the tubes are bad. I'm going to try swapping the tubes from the DLX into the SL+ to see if that has any effect. I use the SL+ most of the time, and hardly ever use the DLX. I'm not sure whether use contributes to tube failure or not...

 

[UnderDriven]

Okay, after swapping the tubes from the DLX module to the SL+ module I can hear a big difference--much better with the rarely used tubes. So I think I'm going to retube the SL+ and the chassis tubes. I'll stick with the Sovtek WA's for the chassis, but I may try some other tubes out of curiosity in the SL+. Based on this page: http://www.knzaudio.com/tubeampsecrets/tubetest/ it appears the Sovtek tubes have some very different properties compared to other tubes (low transconductance and low gain). If the preamp is set up to use these tubes, other tubes may sound very different--possibly a good argument for sticking with the WA's...

 

[mboogman]

I've had really good results with the JJ 12AX7's, and the EH 12AX7's. I can't remember which I used where, and exactly what variety, but definitely good stuff.