my Egnater Tweaker 15, the tubes, and volume for home use....

wordy

hi all,

I play through an Egnater Tweaker 15 at home which I've had for about six months.  Like all tube amps I suppose, it can get pretty loud for playing at home on an evening.  I think in the past I'd always had that master about half-way, and the gain knob turned right down.  I wasn't unhappy with the amp, but I'd long suspected that it must sound better if I could get it cooking a bit.

Last week I mistakenly thought I had an issue with the tubes, so I ordered some new ones, and this week I replaced all the stock tubes.  The amp comes with three 12AX7 pre-amp tubes.  I did a bit of reading and found out that the X part seems to represent the gain produced by that particular tube.  I decided to buy three 12AU7 tubes and put them in.... thinking that a drop in volume might be quite desirable.

The difference is massive... the volume has been cut, but I now feel I'm in proper control of the amp.... I can now get both master and gain past half way, and the amp, to my ears has come to life.  Mostly clean-ish but with lots of sustain and lively singing tone.... and if I turn the gain up I can still get it to break up.

I suppose I've now got less-efficient pre-amp tubes.... but I'm now able to get the whole amp working a bit harder as a result.

I thought I'd post this, as I'm sure there are other people with the same issues I had.  If I hadnt thought I needed to change my tubes, I could well have gone on for a few years.... not really getting the best out of the amp.

And of course, its dead easy to swap the tubes back at a later stage if I decide I need more volume.

Looking forward to the weekend now.  Missus out tomorrow getting her hair done.  Big job.... could take most of the day.  Brilliant.

Cheers.

ICBM

Be careful, because *some* of these substitutions can be a risk to the valves, the amp, or both.

I think you should be OK with 12AU7s in that amp, though. The problems are more likely to happen with 12AT7s or 12AY7s, or in amps with higher voltages. (Typically 30W and above, although the voltages are not always directly related to the power.)

The 12AU7s are not less efficient, and the amp is not working harder - but you have changed the gain structure and the frequency response quite a bit. Most people find the drop in gain from a 12AX7 to a 12AU7 too extreme, but it can be very useful if the amp has far too much gain normally. You can always mix and match types too - you'll find some of the positions have more of an effect than others... not always the same ones for gain and for tone.

wordy

tbh I did manage to find a precedent online for these valves in the amp.... I wouldn't have been game to do it otherwise.  There's a fairly long list of compatible valves apparently.... something to do with the amp being 'cathode biased'... whatever that means.

There are three pre-amp tubes.... the second is for the effects loop, so I think one and three are the ones which matter most.  Number three is something called the 'phase inverter'.

The three 12AX7's I pulled out were Electro Harmonix tubes, I guess putting one of these back in could be interesting.... hmmm.... might try it just out of interest.  Pretty curious now.

The two power-amp tubes were Ruby 6V6's, which I replaced with TAD's.

Thanks for the info and the word of caution.... its not like the amp costs a fortune, but ideally I'd rather not blow it up.

ICBM

Preamp valves are almost always run cathode-biased, that's not the issue - it's that in certain amps, 12AX7s can be run in a configuration called a 'cathode follower' which results in the cathode being at an increased voltage, above the rating for a 12AT7 or 12AY7, so they may fail if used in these positions. (Even some 12AX7s sometimes do.)

Also, 'lower gain' valves typically have a higher current draw, which in some amps with higher voltages, can then exceed either the power rating or the maximum voltage rating of the plate resistor, and blow it. This applies to the 12AU7 even though it has a cathode voltage rating high enough for cathode followers.

So you really need to know before you try any substitutions - probably 90% of the time or more, there's no risk, but it's worth checking before you cook a valve or a resistor.

The power valves in this amp are also cathode-biased (I'm pretty sure) so you can change *brands* safely without having to adjust anything, but again be careful before trying a different *type*, unless you have it on good authority that it's safe.