Hammond AO-35 Complete Start to Finish Guitar Conversion & DEMO 

I got an old 3022 Hammond up local for free with a tomorrow deadline. If it doesn't go to someone who wants it, the universe will grant me an amp project. The body of the organ will make a nice guitar studio workstation. Going to place boards where the double keybeds are with rackmounts for some rack gear and the front flat surface will house a vg-99 roland and a Boss GS-10 desktop units. Place a monitor and a power head on top, change out the speaker depending on how it sounds and smile accordingly. This video is a massive help as a primer. So thanks for doing this Brad! You rock!

Got me one,but 67 year old resistors probable drifted,sent mine to Mike Moser,Frugal amps,he wired it up point to point,matchless spitfire,all new caps,and resistors,sounds amazing,volume,tone,master volume,power,and standby switch,iec cord with fuse holder,Jewell indicator light,top notch work.

Amazing sound, well-worth the time and effort you put into it, Brad.

".....and if your amp is a monster...." It sounds incredible! Thanks for this, and the other videos that I've been feeding the sweet tooth of my brain the past few days!

You know why your channel is the best and so do I. I am an electronics engineer/technician and love what you do in these videos. Now I am a subscriber and using youtube more and liking the videos! Gonna be having fun with amps when I get some dough going. Thanks for the killer channel!

I greatly appreciate the help I'm starting my build this weekend and have been thoroughly studying your video. I absolutely love the outcome you got from this setup. Thanks again I always look foward and enjoy all of your vidoes!

This woman gave me an Hammond organ today and it's got the same amp that you just converted...man I can't wait to do mine..thanks so much for your video ....Your awesome dude...Thanks for what you do...God bless..

Great video. Thanks for sharing this. I had a Mitchell 15 watt tube amp 6w6 changed to 6v6 came out of a record player early '50s converted into a guitar amp. GREAT sounding tone

Tip when drilling into a chassis which is already populated with wiring and components, is to use electrical tape to form a little cup, stuck around the rear of the intended hole, to catch the swarf as it gets cut by the drill bit. Saves having to chase the bits out of the chassis before you dare to switch it on.

I love work like this! Kudos! Totally cool of you to post.

1950`s you say? its like somebody just delivered it in a delorian time machine, your vocals were almost drowned out so you must have had the house to yourself i guess! loved it from beginning to end brad thanks ,its a beauty,

Nice Ultra GS! I picked one of these up earlier this year, and I love it.

Blown away by the amp build demo. I got one on the way and am so pumped to get going. Hope to get similar end results.

I tried running the shielding cable to the plate on an AO-35 based Carmen Ghia clone and ended up picking up a few radio stations in my signal chain as well as effectively eliminating any bass from my tone control, YMMV I guess. On another note very informative video that was invaluable in my journey to finishing my build! Thanks!

Thanx Brad, I still miss my M3. I dont play keys well but I loved playin' that old Hammond trying.

I really love it when you have a good build and get all fired up... I'm like happy for you. Wish I wuz there so I could test a couple of my guitars... I know I'd be trippin' keep 'em coming! cheers

That thing is righteous. Nice work Brad

This is a monster, Brad! i like it very much my friend, great job.

Enjoyed the video, well done. I've probably done around 75 of these conversions.

Love your videos. Sometimes it's helpful to have an octal tube base loaded with a couple of diodes to emulate the rectifier tube for when you're variacing the device up. That way you don't have to be concerned with the filament voltage in that tube. Of course use only for testing at lower AC input as the diodes will pass considerably more voltage out at full AC than the tube rect and possibly over voltage the filter caps. Great work.

I usually convert these to Matchless Spitfires with good results. The tube complement and transformers make for an easy conversion. You just pull the board and repopulate it with appropriate caps and resistors. Usually the can cap works fine. There are also a lot of 18 watt Marshall schematics and layouts available for free online. The transformers are very high quality. I have put controls on either side with my conversions. My only misgivings using the side close to the tubes is the heat effecting the pots but it hasn't been a problem. The advantage besides short leads is that the tubes are closer to the outside of a combo so the heat dissipates better. Also there's less drilling into the box.

I built a whole amp on my channel from stat to finish as and it took so many hours. I enjoy your videos. Wish it was longer.

At about 48:30 when you were wiring up the switch and a bit earlier when stripping the power cord, you may run into a European wiring situation and it even looks like the Hammond amp had a blue wire which should be wired to the neutral or white and a brown wire that should be wired to the hot or blacck. Also, when stripping the outer sheath (or even any bit of insulation) I like to get a really sharp knife or razor blade and cut most of the way through the insulation and then flex the wire to stress pull the insulation apart. The nic usually rips through the insulation and leaves the underlying next layer of insulation or the copper intact. If it doesn't, while the wire is bent i just nic it further and it always works. This is a great video. I just got a B20 amp with I think has 4 6V6s and no preamp. Thanx for the video. I hope that you don't think that I'm dissing you. I'm just a feral human with poor social skills.

I wish there was a button to (EXTRA)- (double) like the videos that one whats more than once.You ROCK Brad!

Sick amp, really does sound good. And sick UFO! It has that nice singing tone to leads with some attack. Not at all harsh despite all the gain and highs. And pleasant crunch. This as two channel amp with cleans having some headroom would be perfect. Some of the characteristics remind me of my Lee Jackson preamp, just with less harsh treble range. I have a feeling it shares some design in the first stages with these kind of small amps that you do, something that does the spanky attack even on drive sounds. I've heard its circuit is following old Fender designs, just with added gain stages. Rock on! These amp servicing/modding videos have been my binge watch during this lockdown time, can't get enough of them. And trying to suck as much info from them as possible. So far gotten great practical bits about trouble shooting, behavior and fixes to common problems in amps. I feel like someone would be able to build a decent amp just by watching a lot of your channel. Perfect nerding out and ruthless humor. And killer guitar playing of course. Anyway, just wanted to say thanks for this content, the info you share feels reliable contrary to how you often have to second guess a lot of stuff you see on youtube. And it's delightful to see every now and then how you and your kid smile to each other.

just love this build. Nice work buddy.!.

It can still happen but it's rare to see these given away now. I got a 1964 M103 for free early last year (2018) and it was seized up. All the tubes we're good though. I had to oil it up and give it a bit of elbow grease on the shaft to get it going again, but it's all there and working well. Caps need to be replaced but I've reserved all that for a full cleaning, tune up and foldback mod later.

Great project Brad! Go for it!

how you do things works,so its good enough for the people who know you are an excellent amp builder.that amp sounds absolutely killer and has wicked dynamics and you have some serious chops my friend.if the amp fixing thing ever stops you could be a gigging monster

The demo was over @ about 1:36:15. Past that it was clear how good the amp sounded by the look on your face/playing lol. You were just having fun after that hahahahaha. Nice work man!

Amazing video! On one of my computers I use a Mullard Altobass / Stereo 44 amp (EF86 - EL84) amp from 1967. Apart from the valves (its on it's third set) everything is original and it does make some popping sounds within the first minute of starting up but works fine, sounds stunning with anything from classical to dubstep. I've got a Trix push-pull EL84 amp in the garage I've been meaning to rebuild for decades - might get on with it now! :o)

Love your show Brad

That amp is a MONSTER!!! I'd love to share my AO-29/ "64 Deluxe Reverb with you. Built by Dave Jones owner of Hook Amps, Greenwood IN. Who doesn't love UFO? You rock brother!!!!

That's an INCREDIBLE sounding amp Bra!!! I'd love to have one to run through a 412 Cab!!!

I should keep it to myself but they are rare enough....old vintage Garnetts are sweet too. Got a couple of those Canadian jems as well. Talked to Mr. Garnett quite a few times before he passed.

Great video sir! I have an AO 35 amp and this will be my first venture into building my own home brew amp.. I am still learning about how tube amps work, but I've been trying to educate myself through great videos like yours as well as Uncle Dougs. Could you by chance put up a link of your final schematic? I've seen others, but I believe you've done things slightly different than the others, and to be honest, I like the sound of yours the best out of all the ones I've heard. Thanks for helping the way you do!

At 26:45: You just just broke it, as near as I can tell! I have a 62 Baldwin that I want to repurpose all the things inside from... once I figure out which end to hold the soldering iron at. This is great, thanks so much for sharing it!!!

THANK YOU for your remarks regarding saving the Hammond Organs. All of the amps you showed are out of A-100 organs, which are identical organs to the famous B-3. The AO-44 also came in the M-100 series, which are spinet organs. Generally, the M-100 series organs do not have alot of value nor alot of demand. But there are plenty of them.

EPIC! Great work...I'm a fairly intelligent person but I can't even wrap my head around the world of electronics/schematics and the level of work you do. The amp sounds fantastic. You should put together an online class to teach amp repair. Mojotone occasionally has 2-day workshops at their headquarters where you build your own amp.

Enjoy the information in your videos, Brad. I've just picked up and AO-35 and wonder if you'd pick a different tone stack if you were redoing? Thanks.

Hi Brad, thanx for the careful explanation & builds. With reference to the feedback, a lot of guitarists do like it - why not retain it as an option? Make it switchable. I think it was Uncle Doug who made one of his projects with variable feedback. On drilling into the chassis, to make things a bit safer, sleeve the drill bit with a piece of wooden dowel leaving just enough business end sticking out to go through the metal but no further. Works a treat!

So I've got one that I've just finished my initial mods to which follow many of the suggestions that have been mentioned here. I'm amazed at how quiet the amp is even though the only new parts are in the tone circuit and input. I've also completely removed the NFBL and the zobel network (this was done for me when I powered on the amp and the resistor in the zobel network burned up). The issue that I've come across is that at about 3-5 on the volume, I get some high pitch squeal. Above that the squeal goes away but the volume is substantially lower and there are a lot of what I assume are odd order harmonics in the distortion (to be honest I'm having a hard time finding a video demonstrating odd order harmonics to be able to confirm my suspicion. The controls are in the same location as the CG and I ran across another thread a while ago (of course I can't find it now) that mentioned having the controls that close to the OT, can cause some interference and that if that's where you're going to mount it, that you need to have it shielded. Anther possible cause? I have 2 new, matched output tubes coming as I think I've ruled the pre-amp tubes out through swapping out with some that I had on hand which I knew were good. Open to any feedback. P.S. amp sounds great at the volume below where I experience the squealing.

I have a few of these I've done. My favorite conversion is using AO-35 and making a Matchless Spitfire. I usually install them in old dynamite crates. The layouts and schematics are readily available online

There is an amp that has been in my dad's attic for as long as I can remember. With it, is a metal plate with oiling instructions and indicates it is a Hammond model M amplifier, serial number 11836, 115 volts AC, 60 cycles, 93 console watts. There is one larger transformer that has no corrosion, as well as a smaller one, also without corrosion, that has AO-20936-0. The tubes look okay, and are as follows: 5U4, 6BA6, 6V6, 6V6, 6SC7, 6J7, 6J5, & 6SJ7. On the "front" are various screws, that look like wires have been attached, as well as a couple of what looks like RCA inputs. The best I could read with my old man eyes: "Pedal Cutoff" "Key SW" "Decay SW" "Sus SW" "Pedal In" "Voice Coil" "Ped" "Att-Key" "VIB"(?) The RCA looking inputs have (best I can tell) "Radio Phono" & "Spec Input" So……would this make a good guitar amplifier? I know absolutely nothing about electronics, but do play guitar, and love the different colors and temperatures of tones that tubes can produce. I am not asking how to do what needs to be done, because I am sure I will be finding someone to be with me every step I take…..I've just not seen anything other than amplifiers from M3's, M2's, or M100's anywhere. I DID, however, find the schematics, block diagrams, wiring for the organ itself….but what is the amp called? AO-20936-0??? Thanks, and sorry for asking so much ! Ke & Ri

You and I need to get on the phone and start talking turkey man rite up my line. Keep the great videos coming. Also love the one with Tony Dorris of Volition amplifiers.

There are certainly some Hammond models that are much more desirable than others, and Hammond, in addition to making some magnificent instruments, has just as certainly produced a staggering number of 'clunkers' over the years! Sadly, there's not a whole lot that can be done to salvage those. A couple of years ago, I was fortunate enough to rescue a 1953 C2, that was headed for a landfill, from a church that had been convinced that digital was the only way to go!! I donated a few hundred dollars to the church (otherwise, I really would have felt as though I was robbing them!) and explained the instrument's worth before carting it away! Shortly thereafter, I found an almost equally ridiculous deal on a basic Leslie (Model 25) which I am now in the process of converting to 2-speed and adding rotating horns. While I am all for salvaging older electronics, and converting them for use with guitar and/or bass, the magnificent power of a proper Hammond is where I have to draw the line!! Unless it's totally beyond restoration (which is seldom the case), the amp is a significant part of the Hammond-Leslie sound, and there are plenty of devoted Hammond players that would pay handsomely for many of those old amps (including the AO-29, and AO-35 reverb amp). in addition, many old Hammond and Leslie amps include parts of the Leslie switching circuit, which I can tell you is a real pain to replicate correctly...without resorting to solid state add-ons and/or expensive Trek II parts. Love your videos....I just have a major soft spot (Yes, probably in my head!) for Hammonds.

Why would anyone thumb this video down? Just get out if you are not interested. I'm guessing 4 people accidentally clicked the wrong one, or left the youtube page open, and their cat walked on their keyboard. No, there couldn't be 4 people that trollish to thumb this down. Not on the internet, right? Good job on all your videos. I watch this because in 2010 I successfully converted a Crate BV120H (Blue Voodoo) with 6L6's to a (v1)Plexi 1987-(v2)JCM800 2203 with (v3)reverb. I then bought all the components to build a new one from scratch but still haven't made the board or finished it for 7 years. I drew up schematics and still have my converted amp to reference, but before I get started i needed to refresh my knowledge on the stuff. These videos help me a lot. I may do some things differently this time. I use a 12v dc relay with 1 jack to switch channels, and a 12v dc relay to switch reverb. Of course I get a pop when I switch, so I may try the opti switch thing. They seemed hard to implement w/o losing some tone. I already use 3v dc filaments for v1 and v2, and 6 vac for the rest. I'll stick with that. So yea, thanks for the videos. They help me get my mind re-primed to start doing this again.

Actually at 1:08:00 it wasn't a bad resistor. You had installed capacitor C5 in backwards and it was causing excess current build up on the plate of the 6AU6 tube leading to the problem. I know this because I have watched a video where someone fixed some old electronics on youtube.

Hi What model Hammond organ used the AO35 speaker amp? I have a source who has inherited an old Organ shop by way of a real estate transaction (bought the building with a basement full of old organs) and there are 5-6 Hammond’s in the bunch

Great video, this is helping me out a ton! Question - what value fuse did you use for yours?

What a wonderful sound, cant beat valve (tube) amps

admittedly i skipped to the end. sounds fantastic!

Hey Brad. I like the videos. Iam an Uncle Doug fan as well. I was wondering; those ceramic disc capacitors you replaced with orange drops.. is it microfarads. in the AO35 ? I only have a basic volt meter and. cant test the capacitors. Thanks.

I have watched a few of your videos. Quite a bit of information, where did you learn your techniques for upgrades/mods?

Wow, that sounded good.

John Hammond invented the tube Amp. If your ever in the Salem Mass. area go check out Hammond Castle. Really COOL place. And they have a couple of his first amps on display. You won’t believe how big they are. Great video although quite long. Lol 😎🎸🎶✌️

Nice. Now thats shredding with soul.

Uncle Doug is my hero. Nice video !

Oh my goodness ! That thing sounds a bit like a Dumble ! Yeah I said it ........! That thing has a million dollar tone my friend ! Great job !

Lol, I always just intuitively (since I don't actually know shit) dealt with shrink tubing precisely the same way you did it at about 53:00. Works like a charm.

Several quick questions please. 1. What did you do with the green wire you clipped from the terminal strip at the beginning of the video? 2. Where is the tone stack wired in at? 3. Where is the lamp wired in at? My project is almost complete and I need you assistance.

I'm gonna finish watching this later, but I just wanted to say I have a H AO 22111 coded (on transformer) Hammond amp I'm going to use for something 6V6-powered. Not sure what kind of design I want to use, so what's your favorite 6L6 amp? I'm still working on a 6L6-powered 5E3-P Fender design first. I used wide terminal strips from that AO 22111 chassis for it so far. The 5E3P uses iron from a free Wurlitzer that had 6L6-compatible tubes (forgot the number codes of them) .

NICE TONE

Interesting video. Would you please post a link to the schematic you ended up with in the description?

thanks again for your help

My practice is to go to fuse or circuit breaker first..... When the guts of the switch fail, you will have the fuse to open, instead of an overload. In rhe days of 2 prong plugs, it did not matter, as it was random which side was hot. and with AC its always changing ‘direction’. With a grounded chassis, you probably want to have power interrupted before the first potential failure point.

Zobel circuit used to balance loud speakers with different sound pressure level outputs by attenuation of the higher SPL speakers signal.

Is it possible to convert this amp for guitar and keep the reverb? Maybe adding an additional tube to drive the tank? I’d love to get some feedback on the best way to do that.

Half way thru the vid and subscribed. Just salvaged a M111. Not sure whether to do a conversion on the AO-35 or figure out how to adapt it to a stand alone reverb if possible. Great demo, love the little things, like saving that wee chunk of wire. Same stuff I do he he.

That Bucherot cell looks like a typical Zoebel Bridge, used to adjust for speaker impedance?

Nice Job Brad.

Wow a monster amp indeed! Sounds a lot like a Magnatone. A couple of those with a stereo tremolo effect and Billy Gibbons might come knockin! :)

Hello, I see you have several Hammond preamps, I was wondering if you have any transformers from the percussion amp section left over. Since you won’t be using it for the guitar amp convention. I’m looking for one for my organ. Thanx

There are tools for striping cable outer insulation, cheap and they make the work one twist of the wrist. Also no cut thumbs :D

When you inserted the tone stack did you go from the .022 capacitor right into the grid of the 2nd 12ax7/ phase inverter? Did you solder it to the board or directly to the tube socket? Was the 1meg resistor removed where you have circled to insert the stack? Thanks any and all help is appreciated

This is GREAT! Thank you. I just re-capped mine and hope to wire up the pots soon. One question though, I have a reverb unit I salvaged from a marshal amp. How would I wire in a "effects loop" with a Pot to control it?

thanks for this- Great job and so helpful- I'm struggling with some the very issues you address and will now try your mods!Only request is for a post of your final schematic.

Wait, at 52:00 I must have have heard wrong. Yeah, I sorta did hear wrong. A 12AX7 plate is around +210 volts above ground so don't forget and wire the other end of the coax to the input jack end to ground. I've heard of only grounding one end and float the other end so that you don't have ground loops. I'm trying to figure how that works. The thing that I'm coming up with is the DC doesn't flow but you get a counterpoised (180 degree out of phase) signal on the sheild. Do you know what gives here?

LOVIN THIS.

Removed the Boucherot from an Ao-44 and it did seem to make the tone a bit less “grey” to my ears,at least. I haven’t added a 12ax7 to it so it’s fairly stock other than a bright cap of an unusual value since I experimented with what I had on hand. Always wondered what that part of the circuit was supposed to do. Completely gutted the Ao 35 I have besides the transformers and tubes.. Prolly do the 18 watt thing. Watching this to see where u go with it. :)

Great conversion it sounds nice and crunchy. Do you still have these amps ?

Hi Brad! Wow you really did create a monster of a guitar amp didn't you? It sounded fantastic with lots of nuances & different sounding effects with just your simple, untuned tonestack! That filthy crunch & breakup was awesome! I'm guessing that a lot of the components you removed from the amp were there because it was originally set up as more of a stable, hifi amp. You obviously removed the right bits!

A Zobel network is really pretty simple, it is just the inverse of the speakers inductance due to capacitive reactance, I’m not sure why you’d really want that here. They are used when you have a 2 or 3 way speaker design to present the passive crossover with a constant impeadance rather than an inductive rise as frequency goes higher, this makes designing crossovers easier, that’s pretty much what’s its used for in practice... For instance, a 4 ohm 12 inch speaker might be 3.8ohms at DC but at 500hz it might be 78ohms, this circuit would make the impeadance more flat, so you’d have 3.8ohms at DC and 5 ohms at 500hz, so this would help the amp see the speaker as more resistor like than inductor like, it should not have all that much effect on tone if it’s designed correctly. There is no just putting a capacitor and resistor in the circuit and seeing what it sounds like, this network needs to be specifically designed for the exact speaker it’ll be used on... Wikipedia doesn’t have very good information in this case, this would not be the best method to tame a misbehaving amplifier that’s oscillating, although it would probably work. It might have been used for that 80 years ago, but obviously electronics has changed just a little bit since then.

At about 40:00 that pilot drill bit that you were using looked like one of them rotary butterknives.

Once finished that makes a great plug and play amp. Sounds excellent and really cooks. I have two of the AO-40 amps. At a quick glance theyappear to be very similar to the AO-35 shown. Anyone know if the the conversion process should be nearly the same?

fantastic !

My B3 burnt in a house fire. I can't tell you how much I miss it!!!! :(

What is the ohm rating of the speaker you're using? I have an AO-35 on the way and I'm piecing together exactly what I'm going to be doing with the circuit but the one thing I don't think I've heard anyone mention is the speaker requirements. Thanks for the great vids! Keep them coming. Between you and uncle doug, I've got way to many project ideas than I have money to see them through with.

Another item my father left me a Hammond and it's great and an old Moog.

"Take your time with these kind of things, you don't want to make a mess. Eye protection is recommended." That's what she said.

Hey Brad, you should have like 250k subs in a year, no problem. i build amps and play as well. in a weird twist of events you have actually inspired me to move from restoring old crts in 80s arcade games, back to working on music gear which is how i got into electronics in the first place. I ripped a bogen chb 14 off my shelf and converted that, into a guitar amp. it actually turned out great, and I also shot a video on it which i will post up soon. i have videos on my channel but its arcade related electronics and a few other repairs. But so cool. Great work, and wicked chops.

The first thing I did on mine (that I will finish some day) was to add L brackets so the board is horizontal - much easier to work on.

Brad I love the sound of your amps and have been watching voraciously! Let me ask you, which Hammond, the A0-29 or A0-35, is the simpler conversion and which do you think makes a better guitar amp? Or is it just a matter of taste and power difference between the EL84's vs the 6V6's ? Also, your tremolo circuit sounds fantastic in the A029 conversion! Also, in your A0-29 conversion did you simply cut out the un-needed circuits or did you pretty much gut it and rebuild ? I was going to build a 5e3 kit but man your amps sound better than the kits I've heard!

Funny, I used the same tone stack diagram as you did and had the same issue with the tone pot being backwards. Easy fix to reverse the wiring. What size speaker are you using?

On top of being super knowledgeable in electronics, your a hell of a guitarist to boot.Also, you seem to get a good variation in tones with just the tone controls on that guitar.The sound comes out pretty well with just your camera phone. The little bit of distortion from the little camera mike suits my ear just fine. Oh ya, the amp sounds great too. Cheers

@1:11:36.........Brings back memories of my childhood....when the stomping was rendered useless, the main power fuse(for the basement) was extremely effective...lolol

Why would you run the hot wire to the switch BEFORE the fuse?

Love the channel. Did you win that drill from one of those crane games at an arcade?

How do you upgrade the memory in those amps? Say I wanted to go from 2Gb to 8Gb where do I plug in the SCSI cable? Also how do I make it pay mp3's off an SD card? The SD card has more wires then the input on the amp. Can you just tie the extra wires together?

how hard would it be to use an EF86 as the first preamp tube? I have an old AO 35 that's been lying around the shop for years. thanks for posting this. Uncle Doug demoed one but didn't get into the details of the conversion like you did. great job.