Hammond A0-39 conversion

[AaronP.]

Hey guys!

I just got this little hammond power amp from BB organ here in Minneapolis (anyone here from the area?) as part of an A100 sale/trade.

http://theatreorgans.com/hammond/faq/a-100/schem3.jpg

Kinda been looking at the available components and wondering if it'd be possible to do One gain stage like a Vox AC-30 and a split load PI to get a Preamp and PI out of the one 12ax7. Do you guys think this will work? If not I'll probably just punch another hole for a 12ax7 and go from there.

Or, if you guys have suggestions for other ideas or designs that's awesome too! Single ended perhaps?

Thanks for any useful knowledge and time spent helping out a learning hobbyist.

-Aaron-

[AaronP.]

Oops, didn't realize the single stage preamp in the Vox was running a pentode.

Still open to ideas...

[AaronP.]

maybe I'm asking dumb questions...

[RWood]

I think I'd be tempted to make it into a one-channel AC-15. It'll need another 9-pin socket as you suggested, for the EF86 pentode input.

http://schematicheaven.com/voxamps/ac15.pdf

If you'd rather use a 12AX7 in V1 there is a ton of info available on the Lite IIb circuit, a popular variant of the Marshall 18 watt circuit. It is a great combination of simplicity and great lead tone.

[AaronP.]

ok, well i figured I'd update this...

Traded up to an AO-35!

http://www.webdatasystems.com/images/AO35_3.jpg

Now things are looking just fine for conversion options.

[cminor9]

I am working on a conversion from an AO-35 to a Matchless Spitfire. I have to say, it's quite the tight fit and the spitfire is a pretty small circuit in terms of board space. Every inch of that chassis is crammed. I am considering just pulling all the hardware off this chassis and starting over in a larger chassis.

I have no idea how you'll cram an AC-15 in there!

[AaronP.]

yeah, i figured I should convert it to something a little closer to that actual circuit than an AC15. Modify the front end and gain/frequency to be guitar friendly, three prong/fuse, 1/4" jack, on/off, standby. the usual...

Maybe just a volume and tone.

Just checking around for schematics that would suit this little guy.

I heard there was a famous little boutique amp that started out as an A0-35 conversion project. I won't get into that discussion though....

[doctorfixit]

Here's a layout I am doing for a LiteIIb conversion using the AO-39, adding a 12AX7 for the PI and using the original 12AX7 for the 1st gain. We'll see how it works.<BR>

[cminor9]

I heard there was a famous little boutique amp that started out as an A0-35 conversion project. I won't get into that discussion though....

yes, I've heard of it! If this spitfire doesn't float my boat, guess what I am going to convert to?

[AaronP.]

Hey Doc, nice build in progress there. I only wish I had the 39 and the 35 now. Good thing is I can always track down an AO-39 easier than the infamous AO-35.

C_9, i considered the spitfire as well, but I think I'll opt for the later option and do the "CG" because of the minimal changes (Or so I've heard) and controls on the face plate.

[doctorfixit]

Updated AO39 Conversion

The added 12AX7 is shown as V1 on the schematic.

Basically , an 18-watt Lite IIB front end on the Hammond power tubes.

Note that this conversion leaves a lot of the power tube setup as-is, with the exception of the new fixed bias. (I started with 150R bias per the LiteIIb, but this was way too hot!)

This amp is terrific! Excellent high E string performance near the bridge. Incredible sustain. This amp performs better than my AO35 "carmen ghia" conversion, IMHO.