Speaker selection advise

[BJosephs]

I have done quite a bit electronically regarding home built tube amps and modification of tube amps that I buy. I have always used whatever speaker was lying around to play them through. I am now approaching some new territory in that I have an amp, an Egnater tour master, that I think is lacking somewhat in the tone department. I think the most appropriate modification are the speakers. The combo is stock with two Egnater custom celestions that are supposedly a variation on the Celestion Classic Lead.

I would like to curb the treble a bit. I could do this electrically but I don't want to affect the high end "drive".

The bass is a little loose so maybe a speaker is the answer there as well. The cabinet is half open - does anyone think completely closign the back would tighten the bass?

As ridiculous as it sounds I kind of want the amp to sound a little more like a 4X12. Not exactly like a 4X12 just a little closer...

I put some G12t-75s in there today and didn't get to where I expected.

I am not expecting a clear answer from anyone just some advise or past experiences form people that have gone down this path.

Thanks

[Rob Mercure]

BJ,

While I don't know this amp's circuitry does it have a negative feedback loop?" The symptoms you mention - excessive treble and loose base sound like classic lack of NFB. If the amp doesn't have an NFB loop starting with a fairly high value potentiometer you can play with the setting to see if you can find a sweet spot you like. If it has a existing NFB loop you might want to replaced the fixed resistor with a pot to vary it and perhaps bypass the resistor with a high value cap - say 220 pf to start - to limit the highs some. But the NFB loop is a pretty robust playground and you can put some fancy corrective networks in it to tailor your sound. Ordinarily I'd think, as you suggested, that the speaker's the problem but the way you describe it I wonder if it isn't the lack of or inappropriate NFB.

Rob

[BJosephs]

Fantastic suggestion. You know, I had been thinking about how unresponsive the Presence and Density controls (which would typically be in a feedback loop if one exists) were and figured the culprit is that there isn't enough NFB to keep gain down on the midrange frequencies. I hadn't drawn a connection to the low end being muddy.

I have requested a schematic but I haven't gotten a reply in two days, my other questions were answered the next day.

I may be forced to find the feedback path myself.

I have posted in the general guitar amps forum with gut shots of this amp if you wanted to have a look. It's a multi-circuit board monster, made in china but definitely well built.

[Rob Mercure]

If you want to post them here feel free but I tend to avoid other forums due to the heavy bull dada and commercial streaks - I'll stick around here as I've spent 11 years or so comfortable years here.

Rob

[BJosephs]

Well, I feel silly but think I might have ben on the wrong path. I have been waiting on a quad of EL34s and when they arrived yesterday, I put them in, re biased and they sounded perfect. The bass is way tighter and far more pronounced. The treble is still way too sensitive but, with the G12T-75 in the amp is pretty close to where it needs to be. I might try the stock speakers one more time with the EL34s to make sure I am not cannibalizing a 4X12 for nothing.

I will still investigate the NFB as well. Thanks.

[Steve Conner]

Well, because EL34s have more gain than 6L6s, one effect of changing to EL34s is to put more gain inside your NFB loop, so you effectively have more NFB. (I bet the presence control works better now.)

Rob, I think he posted the stuff in the "Guitar amps" section of this forum.

[mac1amps]

You had also been talking about open-back vs. sealed enclosure. A "sealed" enclosure (especially a well made one) is ALWAYS going to have a more "pronounced" bass response. Sometimes even too much for some "bass efficient" speakers (like an EV, for instance). There is also going to be a reduced brilliance (i.e. Treble) in a sealed cab. as well.

[BJosephs]

I'm embarrassed to say that, somewhere along the line, I wired my speakers out of phase. I had just thought the G12-T were quieter, but when I switched back the stock speakers, I knew something was wrong. It wasn't until I got close to it that I heard that out-of-phase "pull". Sure enough I swapped the wires around and the thing started cranking.

The amp sounds amazing with just the EL34s. I really feel that this amp was designed for this tube and not for 6L6's- maybe I just got a flabby set. I don't think I will pursue the the speaker change after all. And with all hte bass the EL34s produce I will probably leave the cabinet alone too.

Thanks for the help everybody.