A Guitar And Gear Support Forum

I think I nailed my final tweaks to my own design, the AMI 20 pictured below. I noticed that since I used a HiFi tube amp as the platform, the HFi output transformer was wicked efficient and had a frequency range much better than the average guitar amp. This made my amp 'boomy' in the low end. Clear and tight, but a ton of low frequencies.

I also changed some tube choices to get the gain structure a certain way. It resulted in a really big, open tweed tone. It is touch sensitive, with harmonics and bloom. But I somehow got around the headroom tradeoff that typically occurs with that. It sounds like a 100w tweed amp and is very pedal friendly. The closest tone I can remember to it would be my friend's Marshall JTM 45 Offset Reissue. I am most happy with it!

For the gear geeks, it has 1 channel, 1 volume, treble control, mid control (internal), a bass control and a presence control (on back). 1st stage is a GE white-star 5751 (volume and tone), into a Groove Tubes 12AX7 (cathode-follower), into a GT 12AT7 inverter, into 2 Gold Lion KT-66 output tubes. I have a switch that takes the B+ voltage down by 35% via a 25w Zener diode. I never clocked it, but would think this brings it down to the 15w range - still very loud.

All point-to-point hand-wired. Mostly reclaimed vintage parts.

I have it feeding 2 Fender Bandmaster cabs, one with 2 Celestion UK Greenbacks (55Hz) and one with 1969 era Celestion G-30H (75Hz). For reference, this is as loud as a Vox AC30.

Pics:

Great looking amp! Waaaayyyy above my knowledge/skill level.

I love using oversized output trannys. Like you said, more bottom end and the amp will sound like it has a lot more watts than it actually has. I bet then KT66's aren't being pushed too hard at all.

mozz wrote: ↑Tue Sep 08, 2020 7:39 pm I love using oversized output trannys. Like you said, more bottom end and the amp will sound like it has a lot more watts than it actually has. I bet then KT66's aren't being pushed too hard at all.

The KT-66's weren't being pushed hard with all the 9-pin's being 12AX7, as they were all compressing. Popped in that 5751 and 12AT7 and I am hitting the KT-66 with more grid current. The sound is awesome.

To your point, I can easily put 6V6 in the output. The output is cathode biased and the max voltage is 370VDC.

Wow