I'm itching to build a small bass amp and have a few paths I could take. One potential path would be to repurpose one of several 100W 1900:4/8/16 output transformers I have with a pair of KT88. Now, I recognize that this is an unusually low load for KT88 but I also have a PT that puts out about 280vDC after filtering and the load line doesn't look too bad. It's over dissipation when saturated but the B+ will sag enough to get it into a safer area. The only critical concern I have is that the KT88 is specified for 230mA max cathode current and I would exceed this on peaks but I think would stay below this value on average.
Power would be around 25-30W so a larger OT should be able to play a bit deeper than it would when tasked with maximum power. I'd like some comments though before I go and start wiring something up.
Power would be around 25-30W so a larger OT should be able to play a bit deeper than it would when tasked with maximum power. I'd like some comments though before I go and start wiring something up.
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check with the tube amp forums - I think that's a good p-p load. An output transformer does not need to be huge for bass guitar and size and primary inductance can be reduced vs hifi use. Primary DCR will be lower too.
An unregulated screen with some sag might sound less "mechanical" than a tight screen (?) -
An unregulated screen with some sag might sound less "mechanical" than a tight screen (?) -
What you’re proposing would certainly *work*, but if you look at that load line you could get more oomph out of valves that can push a higher cathode current (say, 450 to 500 mA peak). You will be well below the average Ik and Wp ratings of KT88’s, but you are emission-limited and may be better off with less expensive paralleled tubes. With that load line and power supply you only need a 23 watt tube, but a half amp of peak current capability is needed to fully utilize it. You won’t blow anything, but you’re not going to get full capability out of your power supply/output iron. Four EL34’s can be had for the price of two KT88’s and will give a higher peak cathode current. Sweep tubes that can do half an amp on those low screen voltages are also a possibility (and go for as little as $5). Those will get you even more power out of the same iron.