Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on June 05, 2016, 09:13:33 am
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Im working on an amp design to achieve a good metal/down tune tone. It seems that the SLO 100 style is pretty popular. Where I am with the whole thing is this. I have plenty of preamp designs but I am curious as to how the power amp affects what I am looking for. I understand that the more iron (higher wattage) means a thicker bass response, so my initial thought is ok lets do a 100 watt power amp, but I've played some of the lower watt Freidman amps and those things have excellent/thick heavy metal lead tone capabilities. Theres not a WHOLE lot of difference when it comes to a marshall 100 watt power amp or the slo 100 power amp so im trying to decide on the kind to throw in there and do I really need the 100 watts because I considered a 50 watt as well.
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While nobody can exactly know what another means by "good metal/down tune tone" it's my opinion that the greatest mileage comes from additional gain in the preamp stage. Obviously, you cannot get the kind of speaker driven effects of standing in front of a Marshall stack with a 12" combo amp sitting off to the side on the floor. I stated in another thread that at one time I had added just a simple extra gain stage to a stock Princeton Reverb. Just 1/2 a 12AX7 in a straight-ahead copy of a Fender gain stage and thing turned into a complete brat, really on the edge of feeding back on almost every note and with a very aggressive tone. That amp had been hotrodded to dual-6L6 power with transformers swiped from a Dynaco Mk IV (dual EL34's in its stock config) I was pretty much trying to clone an original Mesa-style amp and wanted a controllable-gain stage in between the fairly normal preamp and the fairly normal output section. Well, it worked.....as long as I controlled the "mid" gain to about 2-1/2!
So to me, since you cannot hear a schematic diagram, the smart way to come up with what I think you are talking about would be to select a range of output power based upon your requirements for what sized venues you use the amp in and how many speakers you think you'll want to drive, and just build whatever you decide on with room for and a socket installed for one extra 12AX7 (or other) tube and an extra hole in the front panel for a control. If you never use it, big deal. This is on the assumption, perhaps wrong, that you are looking to experiment some as opposed to finding, auditioning, and copying an existing design.
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Well, ive built the jcm 800. It wasn't enough. I know a lot of guys on here will think thats crazy, and I understand. My favorite amp is an el84 driven 30 watt Ive built and my ideal setting is with the gain at about 11 o clock (and thats with a 12aY7). So im not one of those guys who crank the gain and muddy up the tone. But I do know heavy guitar and the 800 isnt there. I have even built an 800 and tried some diode clipping. That wasnt the rout i needed. I have studied the slo100 a good bit. Ive actually almost completed drawing the schematic in JSCHEM. I want to throw this on my board but I havent decided on a power amp. The slo100 is cool. I like the adjustable NFB and I like the presence. But I may just do something very simple. gain, bass, mid, treble, master. I havent decided.
But like you said, this is for me to experiment and not to copy any design. But I do need a starting point. According to the weber version of the slo 100 (i have never played any slo 100 not even a clone) it can take 2 kt66 and two el34. Im not sure what the pros and cons are of this. If you can shed some light on it I would appreciate it.
Now this may get me even more stink eye, but I plan to use Mercury Magnetic on this build. Why? Only for the fact that I have never tried them and they seem to have a lot of OT for the style of amp I am going for. Ive used Hammond almost exclusively so far with the exception of some ClassicTone. So my point is, this is going to be expensive. And I want to be very sure as to what kind of power amp I am using before I buy the iron. I definitely do not want to do a cathode bias power amp. The heat from those just make me nervous. I am least experienced when it comes to power amp sections of an amp so maybe this will be a good experience for me. I would like to have a simple 6l6/el34 100 watt power amp with the posibility of adding or removing (undecided on these features) a presence and resonance/depth/whatever.