AO-44 Bedroom Special

[lord preset]

This one is based on the tiny AO-44 reverb chassis that uses a pair of triode/pentode combo ECL86s as both PI and power tubes. Reportedly these put out about 8 watts which seems about right. The chassis is only about 9 inches wide. Used the existing cap can which seems absolutely fine and left the power section mostly intact other than removing negative feedback. I tried a stripped down AB763 front end ala sluckey's schematic. It sounded OK but was just too quiet even for a bedroom amp and stayed fairly clean all the way up. To me the point of tiny amps are to allow cranking up at moderate volumes so I reverted to a Spitfire-ish front end with tone bypass and a cut control.

[drew]

Nice job. How's it sound? I've had one of those AO-44s sitting on a shelf for a long time; ought to do something with it.

[Teleguy61]

Love that Hammond iron.
Did a conversion of a AO-35 to a Phoenix (Ghia) and it is
a very cool sounding little amp.

[lord preset]

Nice job. How's it sound? I've had one of those AO-44s sitting on a shelf for a long time; ought to do something with it.

i

It has a very nice medium gain overdrive, especially with the tone bypass engaged. You need to use the Cut to dial out the buzz. It is a nice bedroom amp - not really gigable but possiblywith a 12" speaker it might be. I was lucky that the cap can was good as there is no room for axials a inside the chassis.

[sluckey]

I tried a stripped down AB763 front end ala sluckey's schematic. It sounded OK but was just too quiet even for a bedroom amp and stayed fairly clean all the way up.

Very interesting. Mine is too loud for a bedroom amp. It has a nice clean scooped AB763 sound at low volume but gets dirty by the time you get above normal conversation level. Wide open it's just kinda ugly sounding to me.

Could you share your schematic? I'd be interested in trying your preamp.

[lord preset]

I tried a stripped down AB763 front end ala sluckey's schematic. It sounded OK but was just too quiet even for a bedroom amp and stayed fairly clean all the way up.

Very interesting. Mine is too loud for a bedroom amp. It has a nice clean scooped AB763 sound at low volume but gets dirty by the time you get above normal conversation level. Wide open it's just kinda ugly sounding to me.

Could you share your schematic? I'd be interested in trying your preamp.

I didn't create a schematic but it's really just a standard Spitfire preamp mated to the existing power section, with NFB removed and a cut control (like your AO-39 AC15 conversion). As for the difference in perceived volume it could be that I did something wrong on the original build, or the elc86 tubes in my chassis are tired, or we have different ideas about how loud is loud.

[lord preset]

I was getting ready to put this one the block and decided that it just wasn't meeting my low standards. It sounded good wide open with the cut control set just so but that was mostly it, and the tone control wasn't all that useful. After playing around wide various tweaks I decided to ditch the ecl86 tubes, wedge a second 12ax7 in and try a 18 watt Lite IIb type circuit. The layout has an exploded fishing reel vibe but it all fit. I went to SS rectification to bring up B+ to run the Russian 6P14Ps at 312v. I kept the tone bypass switch and turned the Cut control into a Spitfire style master volume. I had tried it with the original AO-44 and it sounded like angry bees but in this case it works well. When I first tried it the cleanish and edge of breakup tones sounded kind of dull and stuffy. I ended up changing the V1 plate resistor to 100k (from 120k) and the cathode from 1.5k/50uf to 2k/25uf which ended up regaining some sparkle. Now I'm done. Unless this is still around when I'm waiting for parts for another build and get bored.

[donzoid]

I'll bet that is getting "plenty" of volume now...thanks for sharing Preset.

I have one sitting there "waiting" for something also. You're really close to what I was thinking to do 'cause those stock tubes are spendy and 6p14p's are a great sounding tube imho.

[lord preset]

Cleepz:

https://www.youtube.com/watch?v=1owWWVBpNxU

[donzoid]

Gets pretty hairy indeed when its dimed. Curious how 2 6p14p's are only yielding 8 watts...is it transformer limitations or just setting up your bias so they aren't running too hot? Seems like 300+ volts would give you the ability to yield more watts.

What kind of speaker in that little cab?

[lord preset]

Gets pretty hairy indeed when its dimed. Curious how 2 6p14p's are only yielding 8 watts...is it transformer limitations or just setting up your bias so they aren't running too hot? Seems like 300+ volts would give you the ability to yield more watts.

What kind of speaker in that little cab?

It's just a guesstimate. The original ecl86 power section was reportedly 8 watts and the el84s produce more or less the same perceived volume. I assume it's transformer limited because the iron is indeed pretty tiny.

The speaker is a Fender/Emi 10" from a Pro Jr.