Other Amps

Building a A0-44 based Peewee

1

Getting going on building this Steve Luckey mod of an A0-44 reverb amp. I've made some deluxes and a vibrolux using hammond chassis and transformers. I might make this one as a mini, band volume distortion machine to do some amp switching with...or at least that's the rationale. This little unit has been kicking around for a while, probably would make good donor parts for a tweed deluxe and or princeton too. I like the cute little shielded PT. Already gutted the relevant bits. http://sluckeyamps.com/PeeW...

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I'm hoping to mount it in this little 10" speaker cab I made out of some old organ and a reel to reel case.

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I love using the AO-44 for a guitar build. Voltages are pretty low for a 5E3 or 5F2a, but can still make a little screamer. I've built a number of preamps into these. Just remove everything before V1a and use it for the tone stack recovery. This amp has a 5F10 Harvard 6AV6 preamp, which can be swapped for a 6AT6 for lower gain. As long as everything checks out, I leave everything after V1a as is, including the conjunctive filter on the output sections of the ECL86's. V1a also has NFB and an unbypassed cathode resistor, which lends itself to other boost mods.

4

Here's the layout I use running a 12AX7 preamp in parallel. Basically a Marshall Popular without the tremolo.

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Cool! Can you PM me that schematic. I can't seem to make it larger and I can't read some of the values. I like the simplicity.

6

I use AO-35 often.

Usually I build a Matchless Spitfire or Marshall 18 watt style amp.

Mod to taste.

7

yay they're cool

I've built 3 deluxes (2 deluxe reverbs and one 2 channel deluxe) using AO-43s

8

The AO-44 is half the size of an AO-35 and still allows you to build a 10+ watt PP amp that can get very loud.

This micro head is about the side of a Nerf football.

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Cool Nice amp and cabinet! I'm hoping to end up with a distortion pedal/box that's roughly 14" a side and about 7" deep (My accordian speaker cab) Good for recording sessions and amp switching.

10

Hey do you think it would be possible to shoehorn a tiny tremelo circuit (probably bias vary) into an AO-44

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Hey Powdog instead of using the 12AX7 in paralell, what would happen if I just used half of it and the other half fro a small bias vary tremelo circuit?

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Something like this would work fine. Might need a few tweaks.

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So I got this thing up and runnning Might do some tweaking as it's pretty &^&^ loud

Powdog. My Ao-44 is slightly different than yours and Steve Luckeys(Hoffmans amplifier site guy) But I stuck the min preamp you sent me in front of it. I am currently using only using one have of the 12AX7 in case I want to ad a simple tremelo

-I also used a 33k resistor on the input instead of 68K

-and because I wasn't paying attention I put a fender style cathode bypass on it 1.5K resistor and 22uf 25 V cap

i have a few questions

  • will there be a change in preamp gain as a result of just using one half and not having them in paralell? (was the paralelle use of teh tube the reson for the 820 resistor 5o uf bypass)

  • I know the 33k input resistor will make it louder is it a bad idea for noise etc?

  • what will the different cathode bypass resistor and cap do?(see above)

-Also I see you have no negative feedback. Would a little help to tame this monster??

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The parallel 12AX7 adds gain but not double. The 820 was for the paralleled cathodes. I currently use a single triode 6AT6 preamp with a 1.5K/25uF cathode network. The 33K input resistor is fine. More for RF suppression than gain control. I'd replace the 82K NFB loop to reduce gain. If still too gainy for your taste, try losing the bypass cap from your first gain stage.

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Cool thanks I have this version of the AO-44

I reattached the 82K negative feedback and put in 68 K input resistor sounds a bit more reasonable now.

The .0047 cap (.005) from the plate of the preamp to the Volume control on your schematic would seem to knock down the bottom end a lot. I noticed it didn't seem to have tonnes. But i couldn't turn it up very loud in my apartment Was that intentional? I heard somewhere else that these little guys can produce a lot of bottom end.

Or am I completely wrong/

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Here's what I have so far. For fun I might try swapping in a bigger (say .01 or .02) coming off the 12ax7/ecc83 plate to see if it lets more bottom end through.

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Does it sound thin?

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hmm When i think think thin I think too few mids or over-scooped

It sounds like there isn't tonnes on the bottom end Maybe I'll try a bigger cap there for fun and see if it makes a difference

i just realized you can't make my schematic bigger,,rendering kind of useless!!

19

Tried a .02 Maybe this preamp gives me too much of that tweed sort of sound Tonnes of mids, less highs and lows. Always sounds kind of congested to me. Maybe I have to give up on the tremelo idea and go with an AB763 tone stack? Not really room for another tube in there!

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Hey Powdog IS the micro layout you drew out supposed to be basically the same as the tweed harvard preamp about?? Because it's pretty diferent or were you giving me another option?

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The layout preamp is different than a 5F10 Tweed Harvard preamp illustrated above. There are a lot of preamp/tonestack combinations you can use on this amp.

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The really cool thing about an AO-44 over all the other Hammond monoblocks is the absense of a circuit board. It's all point to point. Tweaking and changing coupling cap values is really easy. The pentode section of the ECL86 is basically a 6AQ5/6BQ5, so you can build up this amp using Marshall 1974x values, or Vox AC15 or Gibson Skylark etc.

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Totally. I started off messing with point to point wired cheaper mono hifi amps. I've also recapped a few Klempt Echolettes...that's pretty well like brain surgery! It wasn't till I got into the AO-43s etc that I started reusing those hammond cone boards and doing conventional fender type layouts. I'll see how this amp sounds at volume tomorrow before I decide to monkey with it further

25

Yeah I ended up putting in fender pre using both sides of the triode. that way I could make sure nothing was amiss as i know what the fender pre sounds like. it sounded good but to get it loud enough to distort fully (to use like a distortion pedal) it completely flattened the loudest clean signal i could get out of my 2x10 deluxe. Thiswas through a Rola 12' speaker. Hilarious! It was too powerful! When I use distortion I want ti to be a little louder than my clean sound. i use it in an arrangement sort of way as a different sound rather than just a 'lead' sound So for the time being I've put it aside to decide if I want to reconfigure it in that chassis. I've been pondering a combo stereo amp and thought the transformers might work. A couple of them together might make a cool stereo amp. But I'd have to put one in a bigger chassis cause I want to have reverb and tremelo.

Just ideas right now.


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