clean headroom

[chuckedup]

wassup guy's.. only just starting to tryn learn about amps so please bare with me.. i've gotta kid who likes jazz and i'd like to mod one of my lil amps to give him a bit more clean headroom. i've a champ 600 anda blackheart little giant. as i understand it changing the tubes will help a bit. a more powerfull speaker will help. and a larger output transformer will create more headroom.

now the questions... which amp would work best? which, if any, of these little tweaks will give a noticable diff? are there any other minor mods that will help me to this end? and by the by, the blackheart already needs an output transformer. a few suggestions on a replacement OT would also be great..

many thanks.............laters...chuck

[Chuck H]

Let me open by saying that a 3watt amp isn't the best candidate for clean headroom. Also, class A single ended amps, while they are great for jazz, also aren't notorious for clean headroom and don't afford the same level of tweakability as class AB1 amps for cleaning them up. All you can really do with a 3watt class A single ended amp is:

bigger OT

more efficient speaker (possibly bigger too, and a bigger cabinet)

convert to fixed bias (this won't really make the amp louder, but it will improve punch and dynamics)

bigger PT (not in volts, but mA secondary rating. This also won't really make the amp louder, but improve dynamics)

reduce resistance in the power supply (if you have a rectifier tube, change to a diode rectifier, as long as this won't raise the Vp too much for safe class A operation. this will have a similar effect as the stronger PT. Also, if there is a resistor in the B+ rail between the plate and screen supply, consider replacing it with a choke. This also improves dynamics but not volume)

higher value filter caps (the filters are there not only to decouple AC from the power supply, but also to act as a power reserve for heavy current situations, like big bass notes and punchy chords. Since class A is biased in the ctr of the tubes range and already drawing max current at idle you might not think that greater reserve power would help much, but it does seem to. If you stick with a rectifier tube you must be aware that there is a max uf for the input filter. Too much uf on the first filter after a rectifier tube can cause the tube to fail. Check tube data for your tube type but also know that you can fudge up a little from there. So if max uf is, say, 22uf, you could probably get away with a 33uf or even a 47uf, but definitely not 80 or 100uf. if you use a diode rectifier you can use any value filter you want to)

While your at all this, if you decide to change the OT and the PT you could upgrade enough to use a bigger power tube. Like a kt88 or 6550. That would get you well over five watts and probably closer to seven or ten. If you did that AND all the above mods to improve dynamics you would have a truely potent little monster on your hands. You also will have spent enough $$$ to buy a different amp at that point. But where's the fun in that

Chuck