Hammond AO-43-1 conversion to a blackface princeton?

[UtahAlnico]

I have a Hammond AO-43-1 converted to a Tweed Deluxe that a friend and bandmate built for me years ago and it's by far my favorite amp. Unfortunately, he passed away so I can't ask him about a new build. My question is can this be done/has it been done before? I have seen where people add reverb to the common Carmen Ghia/tweed deluxe type circuit, but I'd rather use the extra tube socket for vibrato than reverb if that's doable. My experience with tube amps thus far has been limited to trouble-shooting, replacing capacitors/electrolytics and basic circuit mods, but I was already close to ordering a princeton reverb kit from mojotone. If I can build a blackface princeton (nonreverb) from my Hammond AO-43-1 it would not only save me $500 but it would be more unique and, based on the tones I get from my Hammond AO-43-1/Tweed Deluxe, I'm guessing it would sound great. I'm hoping someone's already done this and there's some schematics/layouts out there somewhere but I've tried searching online and have not found anything. Any help would be greatly appreciated. I am new to this forum and this is my first post.

 

[UtahAlnico]

Just a quick follow up, I did find some info about a Lil' Tiger AO-3 conversion though it has reverb as well as vibrato and uses a solid state rectifier, so it's not exactly the same thing as I am trying to do. I'd prefer to keep the tube rectifier if possible and would rather not add the complexity of a reverb circuit.

 

[schmee]

Well, at a glance there's enough "stuff" on the AO43 to get there. Of course you will have to punch out two 9 pin locations for octals. Not sure how much of the wiring/components you can use though. It would take time to go through it. Personally, the non rev Princeton is so easy, I would take those trannys off the AO43 and buy a cheap repro Princeton chassis and board to build in. Or a 5E3 chassis, last I saw you can get one for like $40 or so...

For the work involved though, nice to have a nice chassis

5E3 Style Steel chassis and Stainless Blank face plate | eBay

The chassis is "paint grip" galvanized. They are based on the Mojo version.

www.ebay.com

6G2 Brownface Princeton chassis-18 gauge | eBay

It is cut to use Mojo parts and will fit their cabinet. +18 gauge galvanneal (galvanized steel).

www.ebay.com

 

[UtahAlnico]

Well, at a glance there's enough "stuff" on the AO43 to get there. Of course you will have to punch out two 9 pin locations for octals. Not sure how much of the wiring/components you can use though. It would take time to go through it. Personally, the non rev Princeton is so easy, I would take those trannys off the AO43 and buy a cheap repro Princeton chassis and board to build in. Or a 5E3 chassis, last I saw you can get one for like $40 or so...

For the work involved though, nice to have a nice chassis

5E3 Style Steel chassis and Stainless Blank face plate | eBay

The chassis is "paint grip" galvanized. They are based on the Mojo version.

www.ebay.com

6G2 Brownface Princeton chassis-18 gauge | eBay

It is cut to use Mojo parts and will fit their cabinet. +18 gauge galvanneal (galvanized steel).

www.ebay.com

Thanks very much for your feedback. Sounds like a good plan. Basically just use the transformers and start a fresh build with a princeton style chassis and board. I did want to keep the EL84s for the power section, but if I simply add a couple sockets for 6v6's to a new chassis, as I think you're suggesting, then I could just follow an actual blackface princeton schematic/layout instead of trying to "reinvent the wheel" with a princeton style circuit using EL84's instead 6v6s. I guess if I really want to hear it with EL84s I could use yellow jacket converters and that way I could switch back and forth with 6v6s. I like it! Thanks again.

 

[schmee]

Thanks very much for your feedback. Sounds like a good plan. Basically just use the transformers and start a fresh build with a princeton style chassis and board. I did want to keep the EL84s for the power section, but if I simply add a couple sockets for 6v6's to a new chassis, as I think you're suggesting, then I could just follow an actual blackface princeton schematic/layout instead of trying to "reinvent the wheel" with a princeton style circuit using EL84's instead 6v6s. I guess if I really want to hear it with EL84s I could use yellow jacket converters and that way I could switch back and forth with 6v6s. I like it! Thanks again.

I've wanted to try an EL84 Princeton type build, but have hesitated. I bought some convertors once and it sounded terrible, so I guess some other things must have to be done also.

 

[Wally]

I've wanted to try an EL84 Princeton type build, but have hesitated. I bought some convertors once and it sounded terrible, so I guess some other things must have to be done also.

However….don’t those converters also take the EL84 to cathode Biasing? I know the Yellowjackets do. Going from fixed to cathode biased outputs even using the very same tubes results in a difference response from the amplifier.
If one used the very same circuits with appropriate component values, the two scenarios would sound remarkably alike. The circuit makes more difference than does the power tube choice.

 

[Adam912]

I converted an AO-43 a couple months ago. After doing a little research I did a simple conversion in the Carmen Ghia style.
All I did was modify the input circuit with Fender-like values to properly match guitar pickup impedance and added a volume control
pot into the grid of the second stage...I did not add a tone control. With my old Tele it sounds magnificent! Very gutsy, and really nice breakup.
Loves pedals too! Highly recommend you try this simple conversion before you rip everything out of the AO-43!

 

[schmee]

However….don’t those converters also take the EL84 to cathode Biasing? I know the Yellowjackets do. Going from fixed to cathode biased outputs even using the very same tubes results in a difference response from the amplifier.
If one used the very same circuits with appropriate component values, the two scenarios would sound remarkably alike. The circuit makes more difference than does the power tube choice.

I never got back into it but I thought the cheap converters I had just were direct pinouts from 6V6 to EL84.

 

[vampwizzard]

You'll have a better time converting to a deluxe or a one channel AB763. Its certainly doable.. many AO-43's have been made into good 6V6 amps.

 

[ok_state_blues]

If you have a chance, you should make a pass through the amp garage page. 14 pages worth of Hammond organ repurposing. I built a 5E4A circuit with organ parts and am right in the middle of a matchless lightning with organ parts. Albeit my donor chassis is different. Also captain foldback's webpage can provide you a schematic of your donor if needed

 

[UtahAlnico]

I've wanted to try an EL84 Princeton type build, but have hesitated. I bought some convertors once and it sounded terrible, so I guess some other things must have to be done also.

Thanks for your response. I had a late 60s Deluxe Reverb as my main gigging amp for years and it sounded awesome with yellow jackets (sparkly cleans, earlier breakup and really creamy overdrive), but I've also tried them in other amps and they sounded really bad, especially in vintage champs/vibro-champs, but then I tried a single yellow jacket with EL84 in my VHT Special 6 head and it sounds really good. I'm sure there's a technical reason related to the types of circuits/bias. I believe the Special 6 has a solid state rectifier.

 

[UtahAlnico]

However….don’t those converters also take the EL84 to cathode Biasing? I know the Yellowjackets do. Going from fixed to cathode biased outputs even using the very same tubes results in a difference response from the amplifier.
If one used the very same circuits with appropriate component values, the two scenarios would sound remarkably alike. The circuit makes more difference than does the power tube choice.

Thanks for your response. I suspect this is why they sound good with some amps but horrible in others, maybe it depends on whether they change the bias in an undesirable way. I will say I feel like I can hear a difference between EL84s and 6v6s, but that's only based on using yellow jackets in a late 60s Deluxe Reverb. To my ear, the 84s have a bit less low end and breakup earlier with a tighter overdrive.

 

[UtahAlnico]

I converted an AO-43 a couple months ago. After doing a little research I did a simple conversion in the Carmen Ghia style.
All I did was modify the input circuit with Fender-like values to properly match guitar pickup impedance and added a volume control
pot into the grid of the second stage...I did not add a tone control. With my old Tele it sounds magnificent! Very gutsy, and really nice breakup.
Loves pedals too! Highly recommend you try this simple conversion before you rip everything out of the AO-43!

Thanks for your response. I actually already have a hammond organ based tweed deluxe (which I think is very similar to the Carmen Ghia) that a friend and bandmate built for me years ago and it was and continues to be my favorite amp of all time. Mine does have a tone control, which I have set at about noon all the time so it's probably not needed. You can just use your guitar's tone knob. My donor amp came with tubes, and included an amperex bugle boy 12AX7 which still works and sounds amazing. My love for this amp is what led me to consider a blackface princeton build from a hammond amp with 84s.

 

[UtahAlnico]

You'll have a better time converting to a deluxe or a one channel AB763. Its certainly doable.. many AO-43's have been made into good 6V6 amps.

Thanks for your response. I've ordered everything needed to build a princeton reverb combo, except the transformers and a few other things I will take from the AO-43. Based on what you're saying it sounds like those transformers may limit me to a single input, which I can definitely live with, but was not aware of, so thanks for the heads up. I realized the AO-43 transformers might not be a perfect match.

 

[Wally]

I have a couple of tube high fidelity stereos that use EL84s. There is no lack of low end. Circuits determine what is going to happen much more so than does tube choice, ime. One good example of this is the Fender Pro Sonic, which has three modes of operation with regard to Biasing and rectification. Those three modes give three very different results despite the fact that the rest of the circuit is not affected by those options….except for B+ voltage due to the Biasing and rectification options.
imho, there is no fair comparison of the two tube types when using a set of Yellowjacket adapters in a DR.
Good luck with the project.

 

[Ronno25]

Here is an AO43 I turned into a 5E3. I used the transformers, chassis, and board. Using the chassis is a pain but works well if you’re careful about where you place your parts. Good luck with your build!

 

[Lowerleftcoast]

I realize you have already ordered...

FYI the Marshall 18 Watt style chassis is drilled for EL84. There is a version with tremolo. The 18 Watt circuit is not the same as the Princeton so some tweaking would be needed to change it to Princeton.

 

[vampwizzard]

Thanks for your response. I've ordered everything needed to build a princeton reverb combo, except the transformers and a few other things I will take from the AO-43. Based on what you're saying it sounds like those transformers may limit me to a single input, which I can definitely live with, but was not aware of, so thanks for the heads up. I realized the AO-43 transformers might not be a perfect match.

Not the transformers.. the chassis size if you were using the AO-43. If chassis size isn't a problem you can go with the full deluxe. Princetons can be finnacky in the phase inverter but if you really want to build the princeton it should work.