Need advice for an EL84 two channels 18W range project/layout...

[Fabio65]

Dear all,

Please allow a small foreword despite the bulk of my question is in the subject already...

I'm looking for a project of a small (18W) head which matches the main characteristics
of the Hughes&Kettner Tubemeister 18 which is giving a lot of troubles and which I fear
not enough reliable for heavy gigging (see my other thread on H&K TM18)...

What I need the most is:

A switchable two channel amp with a real clean and a lead/overdriven channel
Separete eq controls for each channel or at least a real eq with three controls shared by the two channels

Preferred but not mandatory:
12AX7 + EL84 and tube rectifier based schematic
a layout clearly understandable (I'm not new to tube amp construction but I'm not that confident to
stard a new project based on a plain schematic only.

I was very happy of the sound and versatility of my TAD retubed H&K TM18 but I can't afford to go gigging around with an amp that after two hours of work starts to make volume up & downs...

Thanks a lot for any of your thoughts and comments...

Fabio

 

[enorbet]

Since you already have and basically like the H&K may I suggest you discover why the volume fluctuates after only 2 hours of playing? Some component is drifting off value likely due to heat so it shouldn't be very hard to determine the culprit. You can rule out the speaker in 2 hours simply by plugging it into an extension speaker and disconnecting the original. A tech can use a heat gun (tight nozzle recommended for "pinpoint accuracy) on a low setting to work backwards from the output stage and narrow the possibilities, possibly to the one component but even if things are so tightly packed you can only narrow to one stage that's few enough components to find the culprit in th next few minutes. Knowing if the ups an downs are gradual or sudden also narrows the field.

Anyway unless there are other problems it is likely better to work with a known rather than begin again exploring new and unknown territory. Tiny repairs or tweaks are easier than wholesale changes in most cases.

 

[Fabio65]

Thank you enorbet, yes I do like the TM 18, it's nicely sized to my needs and after the retubing with TAD premium tubes I got the sound I was looking for. My concern with mods/repairs on such a small PCB based amp is that the board is crowded and pcbs are sensible to soldering... and I now tend to rely on sturdy PTP boards which I may build myself as I did for my 5E3 and the Ceriatone JTM45 which I've heavily modded...

I'm looking now the 18Watt TMB with the EF86 pre tube circuit which on paper has the characteristics I'm looking for (a bit bulky but that's not the main concern). If I can add to that schematic a channel switch I'm home.... maybe )

Fabio