I Lied About this Amp and Speaker (the details)

[andrewsrea]

From the multiple speaker swap tales and threads of 'What's on your Workbench,' here are the more detailed story on my AMI Lil Giant:

The objective of my AMI Lil Giant design has always been to have a very portable guitar amp, which was equally sublime at home, studio or gig. With or without the 4x10 Marshall cabinet loaded with (2) Weber Alnicos (like the Jensen's found in the 1964 Super Reverb) and (2) Weber Blue Pups (like the Celestion Alnico Blue).

Background: This amp was built using donor parts, which a music store was going to scrap: a 1974 Fender Princeton Reverb chassis and cab, with July 1967 Fender Bassman transformers.

I have had multiple expensive and inexpensive speakers, 'internal' to this amp and have struggled to get it to sound 3-dimensional 'big'. Problem solved. The 'lie' is. that the Sunn 128G looked like a keeper. The 12" Celestion Creme Alnico is back in and now sounds huge at any volume. Which clean, is a pretty loud 42watts and distorted & dimed - a crushing 85 watts! Master volume preserves the tone really well at all levels.

While addressing the power transformer (1967 Fender Bassman) running a bit hot, it dawned on me that the combination of things I did to create 'thump' (which is typically diminished in small combo format) was creating massive sub-harmonic spikes. Since the output trans (also a 1967 Bassman) couldn't translate that into sound, it was causing the other frequencies to 'squish' and have phase problems.

The results are, this is one of the best amps I have heard. Equally great at internal dirt or as a pedal platform.

Corrections I made yesterday:
1.) Replaced the EH-6CA7 output tubes with a NOS (early 70's from my stash) Sylvania 6L6GC STR. They both sound similar (phenomenal), but the 6L6 puts less strain on the power transformer. The downside is, the unicorn NOS 6L6 tubes are probably worth >$500 for the pair and I'll be putting some wear on them.

2.) Simplified the negative feedback (Presence) circuit by substituting a 56K resistor and 0.1uF bypass cap, for the overly complex resonance type circuit.

3.) Applied a 1500pF bypass cap between the lead and ground fo the reverb control pot, to mellow the reverb and allow it to fit more in a band mix.

[jtcnj]

"The search is over, you were with me all the while"
Glad you got it sorted Rob!!

[tonebender]

That is a lot of amp. You continue to amaze me.

[andrewsrea]

That is a lot of amp. You continue to amaze me.

Thank you - you are very kind!

I built this in 1989 and it has a lot of attributes of a Dumble ODS and a rich clean 1965 Fender Pro Reverb. Way before I ever heard of Dumble Amps. I arrived at this by accident through a lot of trial and error, while keeping in mind what worked well in a mix and sounded good.

It was a different direction for me, as I was probably modding a 100w Marshall every other month at that time.

Kind of what goes into my music builds, whether it is an amp, pedal or pickups. If it doesn't do at least one thing exceptionally well and reliably, it gets scrapped. And I and still learning, often conferring with our own @mozz .

[mozz]

..........As i take the back off a amp i built a few years ago, hhhmmmm, appears to be champ, but with a 6550 output tube. Wonder if i measured how many watts this was. I really need a notebook. I do have a nice power transformer and output transformer here for a 50 watter, plexi of course. Maybe later this year before the snow flys. Need to do another tube inventory, finish these 3 strats, oh look, a Tele roasted neck, have to get a body for that.

[andrewsrea]

..........As i take the back off a amp i built a few years ago, hhhmmmm, appears to be champ, but with a 6550 output tube. Wonder if i measured how many watts this was. I really need a notebook. I do have a nice power transformer and output transformer here for a 50 watter, plexi of course. Maybe later this year before the snow flys. Need to do another tube inventory, finish these 3 strats, oh look, a Tele roasted neck, have to get a body for that.

That 'champ' sounds like my old neighborhood friend's grandmother's 1964 Belvidere 4-door sedan. It was a pastel green and looked like she just drove it to church. But it was a total sleeper. It had a 426 Hemi, dual Holley 4 barrel 760 carbs, headers, a more radical cam, a shift kit in the trans, Mopar race wheels (very subdued) and 4.11 posi differential. This car would run 11 second quarter miles all day and he made a ton of money street racing it.

[mozz]

Older sister's boyfriend, this had to be back in the late 70's early 80's, old Dodge Polara (i think), 440 4 barrel, 4 door, ugly car but fast and he eventually wrecked it. Another friend of mine actually bought a Belvedere from someones grandmother, slant 6 , 4 door, slow, ugly, rusty. Suspension was so worn, we used to joke you had to step down to get into the car.