5E3 Gain Question - Mod Questions

[leucein]

I built an amp based on a 5E3 circuit with a single input and designed to handle EL34's. Since I have half or my preamp tube open I was thinking about installing a mod similar to the Hoffman Hot Mod <http://www.hoffmanamps.com/projects/hotswitch.htm>. In talking about this to an old electronics teacher I decided to check the current configuration on an o-scope to see what the waveform looks like to see of the mod would be useless. I am using a 12AT7 in the preamp and the wave starts clipping on the top at about 9o'clock with a 100hz input. Is this how the wave should perform or am I seeing a problem? Could this be the tube going out, or needing to be rebiased? The gain control also seems to have little effect past about 12o'clock.
Also, are there any other mods out there that anyone would suggest? I have heard of a few in reading different forums but Haven't considered any that may just make the amp better overall?

[stokes]

When you say "9 o'clock" are you saying the volume control turned 3/4 full?If so that wouldnt indicate a tube failure,most 5E3's will clip at about 1/4 full on the volume,and halfway to full you wont notice a lot of increase in volume as you turn it up further.Adding another gain stage to a 5E3 like the Hoffman Hot Mod would be too much,in my opinion as these amps overdrive very easily just as they are.As for other mods,what is it you are trying to accomplish?A mod I think would make the amp "better overall" may not sound good to you,or be what you are looking for.If you could be a little more specific as to what you are trying to get,I am sure there are plenty of opinions people would be happy to share with you.

[leucein]

When I say 9o'clock i mean about 1/4 vol, 0 being about 7o'clock and full being about 5o'clock. I thought that this may be how the wave should react based on how the distortion of the amp should be, but I just wanted to make sure since the guy who was helping me didn't know that much about guitar amps in particular, but seemed to think this might not be right.

I am thinking about switching my 12AT7 to a 12AY7 that the original design calls for so as to not get distortion quite so early. As far as other mods are concerned I was thinking about the Paul C. P.I. mod for a little more clean headroom. Would also be curious about some of the "de-farting" mods since the amp seems to fart out for most of the volume range (most of my guitars have humbuckers). In general I am looking for mods to make the amp a little more versatile since it is my primary amp at the moment. (Have an early 90's 160w Peavey halfstack that I adore, but I don't really need the volume for anything that I am doing at the moment so I don't really use it because of the size and weight). So I guess that I am looking for more clean headroom and tighter bass, possibly if I could get the clean headroom high enough then maybe use the Hoffman Mod so that overall I can get more clean and crunch tones.

Otherwise I still have a half half of a preamp tube to play with if anyone has any suggestions as to what I might do with it.

Also, what is the easiest way to check bias, not that I am having any issues that I think may be related to this, but because it seems like an important issue that I would like to know more about.