The Beatles' Abbey Road SECRET WEAPON - 1960s ALTEC 438A Compressor Preamp Mods (436B RS124)

[@popeye089]

Glad to see you doing these vids again man. It's your channel and you can create what you want, but these classic style "guitologist" vids let us escape from the madness that is todays world. Hope you are well and thanks for these again, these vids are my zen moment of the day

[@popeye089]

@Christine then search them out, I listen to music for music, not for news. If I want news I go look for news

[@TempoDrift1480]

That's gonna be a big 10-4 on that one.

[@JMLRecording]

The Altec 436C modified to RS124 spec is the greatest compressor, Vari-mu or non, available on earth IMHO. I have three pair and use them on absolutely everything. FANTASTIC video. There's soooo many people who covet and hide this information for some reason. It's so cool to see someone giving it away freely, as we should.

[@TheGuitologist]

Glad you enjoyed it, my friend.

[@TheGuitologist]

Glad you enjoyed it, my friend.

[@OneRoundDown]

So cool, just got home from seeing The Cult and Black Rebel Motorcycle Club and you've got a new mod video up!! Great end to the night Thanks Brad!

[@martinreid1740]

That was one of your most interesting videos, really good modifications, well done Brad.

[@TheGuitologist]

Glad you liked it, Martin. Thanks for watching.

[@DerekHerbst747]

The Gettysburg address at the end was a nice and inspiring touch. Great video as always!

[@andrewsmith1520]

I love watching one of your videos and noticing that you’re wearing one of the shirts I sent you. Makes me happy that you like them enough to just wear them. Keep up the awesome work!

[@TheGuitologist]

Heck yeah, man. I wear the stuff people send me all the time. I get a lot of compliments and comments about the Monster shirts.

[@filonome]

love the added info and historical context you brought along with this modification video, Brad! i should put on that beatles doc again, only did ever watch it once so far...

[@TheGuitologist]

Hey Jon. Thanks! I got your text also, just forgot to reply earlier.

[@chokkan7]

Glad to see you doing another 'guitar related' video, Brad. These are my personal faves, but hey...it's your channel. This one was appreciated for its usual quality and content, but I really wanted to thank you for the walk-through explaining how the damned thing works.

[@zandig666]

I've been searching forever for a proper description of what the controls do on a compressor, the needle meter made it easier for me to understand !!!! 🤘🤘🤘🤘

[@DetroitWrecker666]

This is very interesting. I can appreciate someone working on something you don't see very often.

[@TheGuitologist]

Thanks for watching as always.

[@murfmurphy6212]

Great video Brad, super interesting digging into something other than a guitar amp.

[@hestheMaster]

Well done Brad. Fascinating look and rebuild of an unusual type of preamp.

[@MattMonk]

Thanks for another great video, Brad!

[@gregedenfield1080]

welcome back dude!!!!!!!! GREAT VIDEO!!!!!!!

[@lutboy2909]

those unints are soo nice, and surely make magic with a sm57 and a old drum kit, warm and a bit cruchy in the mid tone, definetly a pair of gems

[@DavidSmith-qb1nb]

Great to see you're back at It! Have missed watching the repair and upgrades on amps. I hope to see you finally get to my brothers Epiphone amp. I had talked him into sending it to you and feel bad about time that has passed. He and I both enjoy your repair videos!!!!!

[@TheGuitologist]

Im back at the bench. More amps coming up.

[@shotgunrebels]

Killer video. The mods you did are really well dons!

[@jegr3398]

Really cool video Brad. Very interesting devices there. I really enjoyed this.

[@darrellkelly7614]

Another great video. Glad to see all you do.

[@TheGuitologist]

Thanks as always, Darrell. Good to see you.

[@peterdavies5358]

One of those little things that add a little colour. I think that back in the day those tubes or valves since we're talking about Mullards were made or at least designed and perhaps prototyped at the Bird Hall Lane site in Stockport, near Manchester. Out of school I was a telephone engineer in a van and I used to fix their PABX and their PMBX, (Private Auto/Manual Branch Exchange) The manual one would have an operator and perhaps a 3 unit pegboard setup in dark wood with catseye indicators. One of the other companies on Birdhall Lane once had a fault and I really fancied the receptionist. Now with me being pretty cool and secure by nature, I would've naturally kept a lid on that and she wouldn't've known so when this fault came up I remember saying I would need to check the system to which she replied I needed to check out her reproductive system. To this day I can hear my reply, my voice cracking and me saying ahubbadeebubbady hmmm w'ahoowah er well, gawd she was just so hot, short skirt long jacket, dressed for the job she wanted. Looking back with a second run at it, I believe I said I sooo fancied her I like to think I would've left her at least well and truly earthed. "Enjoy the power and beauty of your youth; oh never mind; you will not understand the power and beauty of your youth until they have faded. But trust me, in 20 years you'll look back at photos of yourself and recall in a way you can't grasp now how much possibility lay before you and how fabulous you really looked... You're not as fat as you imagine."

[@seansweeney3532]

Well... having been the ugliest duckling I did have some reverence for the chance... but having spent my entire youth dedicated to musical disciplines; writing and engineering, I promised myself to not be that guy that falls for the first one that noticed Mr after the braces, retainers and rubber bands came off... and held out all my life until I was at the top of my local game, headed for national and the most amazing, singing, reluctantly beautiful tomboy did a Sadie Hawkins on me at a gig... we recorded and wrote for 16 years... never to part, but then she broke everyone's heart... left us all down here... and me to finish our anthology and book. But... in the end the world will miss her and take some of the load off of me. kzbin.info/www/bejne/Zn2Qq2WHhbaopLM

[@rickashford4005]

I'd bet that modded compressor would make a kickass kick drum compressor.

[@TheGuitologist]

I think so too.

[@dnantis]

Brad, YOU ARE A GENIUS !!, THIS CONTENT IS AMAZING !!!

[@davidflamee]

Great mod and the units now have a distinctly better look. Very neat video.

[@dadadrew]

Love this channel. Thanks brother.

[@TheGuitologist]

Glad you enjoy it!

[@Eddy63]

Good and interesting little vid ... Thx for posting ...

[@robnic52]

Great video Brad, nice to see you grafting at the bench again. The Altecs look nice and retro with cream chicken head knobs, they go well with the classy green shade on the original fascia. These preamps were prized for their sound. Surprised they are so simple inside but I guess when a circuit is perfectly designed for its function you don't need complexity. Having preset pots controlling the compression suggests the studio tech would set it to optimum and forget it. Very straightforward, record it, review it and go straight to cutting master vinyl, next! 👍⭐

[@TheGuitologist]

The problem arises when you have parts of a song that are loud or quiet... You might want to change the compression or even turn it off in some parts.

[@seansweeney3532]

I've made these mods and the actual EMI models were calibrated in real time, but it's vitally important to get good new/old tube stock in them or you'll never get the right balance. Abd the neon bulb that EMI installed was wired to light up when you have parity on the two sides, so you get compression without distortion. It was the most complex mod ive ever done.

[@waskerbasket9601]

I'm curious about if that old rectifier has an effect on the sound.

[@seansweeney3532]

@@waskerbasket9601 Which rectifier did you mean?

[@seansweeney3532]

@@waskerbasket9601 the selenium?? They were the first solid state one widely made. But they weren't as efficient as the silicon.... so consequently the voltage coming out of them was lower. Now sometimes you can let it ride if plate voltages were conservative overall and the biasing still adds up, but to be sure you would put some high watt resistors on the supply until you got the appropriate voltage. Once you do this you have effectively no difference.

[@Chinaguitarsceptic]

Love this video brother ❤️

[@TheGuitologist]

Thanks Mike! Glad you dug it. Meandering my way through all kinds of stuff lately.

[@velutumbra]

Thanks for another great video. Allways something new to learn!

[@srtamplification]

To get the best performance out of this, you would want to go into an impedance matched load. I don't know what your bench amplifier is, but it is probably not a 150/600 ohm input like the power amp or mixing board console that this would have outputed to.

[@99David99]

Good to see you back in your wheelhouse. The Sanford and Son stuff was not up to your usual excellent videos. I get it. You needed a break.

[@Damaraja]

How fun is this? Thanks, man 🤙

[@minty_Joe]

The 12AT7, 12AU7, 12AX7 and 12AY7 are all the same pinouts. They are dual triode tubes. Even the ECC81 through ECC83 are the modern replacements and will work without modifications. There is, however, a difference in power factor between these tubes. The AX7 and AT7 will have the higher factor, which means more current draw and less headroom. The AU7 and AY7 have the lower current draw and more signal headroom.

[@DarrenForbes]

This was an awesome video. Thanks for this.

[@TheGuitologist]

Thank YOU for watching! I really appreciate it. Tell your friends.

[@MiximusMaximus]

I had 2 of the 436c units that I dug out of the trash. Traded one for a Groove Tubes CL1s. The Altec is an interesting beast. The 436C has a release and threshold adjustment. Had to recap my units, they don't suck and the value has shot up over the years.

[@MiximusMaximus]

Guess I should have watched the entire vid before commenting since you brought in the 436C.

[@TheGuitologist]

It seems like everything that eventually becomes expensive and highly sought after goes through a period where some people are throwing them away first.

[@TheFULLMETALCHEF]

Saw one rack mounted in a video about an old Nashville recording studio. Said they still used it for the lo-fi sound.

[@TheGuitologist]

Interesting. I’d like to check that out.

[@framusburns-hagstromiii808]

Dang but that old Altec gear is Cool! Serviced a bit of it back in the day......well engineered and well built stuff. Good job as usual! CHEERS!

[@golgothaassassin5035]

I would like to see some of the Neve preamp circuits explained. I love the repair/rebuild videos, and it is a great escape from the headaches of our utopian world of cheaper is better. Great video as usual!!!

[@jasonwright7513]

Brad nice to see you in my feed again a real shame that people are punished now for telling the truth or even voicing their opinion but that is the insane world that we live in now.

[@embreesmith7613]

Thanks, Brad. 🙂

[@ronfrey5327]

Very cool to see great ideas.

[@TheGuitologist]

Hey Ron, how are you? Good to see you.

[@patprop74]

Next time you do something like this, could you go more depth about the process of replacing a selenium rectifier, please.

[@TheGuitologist]

Yep. In this case, I just removed the full wave selenium and replaced with a full wave bridge in silicon.

[@jeremiahlyleseditor437]

Excellent Job.

[@TheGuitologist]

Thanks, Jeremiah. Glad you dug it, dude!

[@JaniceLalla]

I enjoy whatever you do

[@ado7098]

Great stuff ! What a nice project, love that technical stuff !

[@jenniferwhitewolf3784]

Nice to back to the bench👍🏻👍🏻👍🏻

[@TheGuitologist]

It's time. I sowed my oats elsewhere for a while, but now it's time to soothe the misses.

[@HP_____]

6AQ8 is essentially the 6v version of 12AT7, both with a mu of 70. It draws more current than 12AY7. 6BC8 is a semi-remote cutoff tube where is 6BZ7 is not a remote cutoff tube, I believe so it's not suitable for gain reduction. I worked on a UA 175 and it uses 6BC8 and it simply does not compress as smoothly as fully remote cutoff tubes like 6386. All tubes will compress or affect gain somewhat when their bias is changing current draw but remote cutoff tubes are designed for gain reduction. Looks like a fun project!

[@robertross7491]

Yes, you can see at 33min, the threshold isn't that dynamic - result of the 6AQ8. A remote cutoff is touchy with small negative voltage dips but less sensitive at the larger negative biases. A normal uniform triode as seen gives a linear response, even less smooth!

[@jeremylhay]

That's pretty damn cool!

[@vintagetubeamplifiers]

Could you make an episode dedicated to your use of an Oscilloscope and go over the basics of operation?

[@emilytvmusic]

hey what is the green waveform sci-fi tv lookin thing in the back haha it’s so cool

[@biasrocks]

Cool conversion. Fyi. The Hold control on the Abbey Road version allows you to put a 'hold' on the amount of compression to avoid a large spike when the track first starts. The idea is to play the track or stereo mix into the compressor, engage the hold control locking in the gain reduction. The when you start the track again you release the hold after the track has started playing. I imagine this feature was mostly used when the compressor was on the entire mix. A better implementation of the two volume controls would be to have a line level input which bypasses the mic input stage and goes directly into the 4651 transformer, with a switch to disable the mic input stage. The threshold seems a bit redundant since with the fixed threshold you can simply hit the compressor softer or harder. I get that it's a trim pot on the original but it maybe better to leave that as a trim option rather than a main feature. I think a better addition would be an output level control on the output stage to better manage how much level is being passed to the next device in line.

[@jonathanstrand2474]

Some folks only do guitar Amps, but you are a far broader entity, but it’s like Jimi Hendrix, he goes back to England and all they want is his first incarnation, not the new and improved model.🙂 Old outboard gear is very cool, and certainly NOT useless! Just maybe a bit more power hungry I play an all original Altec 12 guitar speaker from the 60’s. And my stereo has 2 Vintage Altec 15’s. Same era…..Probably both could use a recone, one aluminum dome is missing, but they work perfectly, with a crossover….good volume match left to right…..so I know they work fine Sometimes I don’t watch your other stuff, I just click the like because overall your videos are far more interesting, you are always worth supporting!🙂you and uncle Doug. And He’s got a hot Rod! Eclectic is good!😀

[@TheGuitologist]

I try to branch out where i can.

[@mikepalumbo4362]

@@TheGuitologist Brad, didn't you have one o them British Jaguar hot-rods?

[@TheGuitologist]

@@mikepalumbo4362 Yeah. I currently own two Jaguars. I have owned an 80s XJS in the past and a 1976 XJ-12C.

[@sparkletune]

Hope all is well Brad!!

[@fireantsarestrange]

I used to have a nice pair of Altec Lansing home speakers. They were great. Nowadays I just use Yamaha studio monitors with the sub.

[@LanceHall]

These and the custom EQ boxes were literally the sound of those recordings.

[@KalikaWeerasinghe]

Like the logo intro 💖

[@alexbozas887]

Brad, thanks, that was awesome to watch the build transition. Are these your own personal units?

[@TheGuitologist]

Not mine, Alex. These belong to a fellow in Florida.

[@alexbozas887]

@@TheGuitologist after your superb mods, he is going to be a happy chap.

[@iaingraham4911]

Excellent video keep well

[@tdtrecordsmusic]

Just found your channel. Cool stuff ! =sub

[@osomedude1]

Wow those things are cool

[@angelic_slayer]

Killer video Brad.

[@motomoog]

I have the software version of this now I understand and learning more about these amazing units is fun thanks.

[@donbutler8760]

Check the date codes on the pots. That should give you a good idea about when it was made.

[@kevinshea4776]

I would had done my Kennedy inaugural speech voice ... "Let the word go forth, from this time and place. Friend and foe alike...That the torch has been passed to a new generation!"

[@aerodynamicfilms4119]

I have an Altec 438c, it powers up, passes signal, input pot works great, all the tubes check good. plenty of gain, but no compression.

[@christopherallen5603]

Hey Brad, just wanted to shout out an early Happy Birthday to ya.. Don't remember what day it is exactly, I just remember that you're only a few days older than me :) great video btw

[@aaax9410]

Really cool Brad 👍

[@drummerman8698]

Fantastic! I've been wanting to install a bypass on my 436c ever since I read the note in the manual that the compression circuit can be disabled by removing the tube. I was wondering how exactly to do that and why I had not seen it before. I was not going to go fiddling around in there trying to figure it out and risk destroying it. Thanks for the simple (but much needed) mod! Were the resistors installed at the switch originally on the tube socket or were those added for some reason? If they were added, can you let us know why and the values?

[@theoloutlaw]

Aww, was hoping to hear how a Gee-Tar would sound through it.

[@mrromantimothy]

Altec Lansing was what immediately came to my mind I don't know if the Lansing denoted Michigan or was maybe somebody's surname but definitely a pioneer in audio recording equipment. all their shit was very good. those schematics are a game changer, anybody would be a lost puppy without them. lol

[@electrolytics]

Lansing was John B. Lansing...creator of JBL and Altec.

[@joesalyers]

So are these Diode Bridge compressors or a Vari-Mu or a combination of both? I've own some Altec compressors over the years and I always thought they were Vari-Mu designs but after looking at your video these seem similar to the 1960s Neve Diode Bridge Compressors like the Neve 2254 or 254.

[@colinricgmailcom]

Have you heard any more from Boaz since January?

[@javierjanaid]

Thanks for that!!!!

[@carldybowski4338]

Cool video. Curious about the one after the "c" model. Forgot the model number but has 4 digits.

[@carldybowski4338]

Also wondering about attack and ratio in comparison to release and threshold.

[@kwgm8578]

Nice job and a good explanation of signal flow. Don't you think that the AX7 has too much gain? I'd like to hear the AU7 as originally spec'd, especially for a mic jack input. I have an old Motion Sound rotating horn unit that I use with a Hammond organ as Leslie 122 units are way too expensive in my area. It was shipped with an AX7 preamp similar to that compressor, which I always thought was harsh sounding above 20%. After I swapping it for a Sovtek AU7, it delivers a sweeter tone over a wider dynamic range, making it more responsive to the pedal. Thanks for the redesign example.

[@hugh-johnfleming289]

My hand to God I understand about 2% of these schematic ramblings and yet I am still fascinated. What the flock is wrong with me?

[@charleslambiase5670]

Hey buddy I got a bag of ECC 85's amperex RCA etc could you use them.... They have no use for me

[@TheGuitologist]

Email me. I’ll take them for sure: bradlinzy at gmail

[@charleslambiase5670]

@@TheGuitologist just sent you an email my friend check it out!!!

[@BigTrouble324]

Now you juat need an EMI console and a four-track Ampex machine.

[@Twobarpsi]

Awesome watch!

[@R3TR0R4V3]

Very cool. 😎

[@canigetachannel]

Very nice !

[@zandig666]

Dag nabbit great project man !!!! 🤘🤘🤘🤘

[@RealGengarTV]

Interesting video, i really like this kind of content. Although I'd wish you'd connect a 10 hour drum loop from KZbin instead of talking in a feeding microphone but beggars can't be choosers i guess

[@jonnybeck6723]

Did you try running a guitar through one these suckers (?) (!)

[@newtronix]

Definitely more usable but sure bang goes the resale value drilling holes in the front panel?

[@TheGuitologist]

The resale value is greatly enhanced with these mods. This is a working studio tool, not a museum piece.

[@newtronix]

@@TheGuitologist Cool, all good then. A great mod!

[@tunabob]

I think the cream chicken knobs look GREAAT! perfectly goes with the green faceplate and Vu meter

[@user-tw5ed1od5l]

GReat Job!

[@steveg219]

Cool topic!!!

[@georgeshaw8925]

Can’t wait, just tested positive for Covid, still get to hang with all my people. Gotta love technology! 😂

[@krietor]

Yeah!.... Wait. What?

[@georgeshaw8925]

@@krietor yep I have Covid and am having a hard time breathing. I hope it doesn’t get any worse.

[@tinicum54]

Good luck, I had it 2 summers ago, took about 6 weeks. That hard time breathing is rough.

[@mikepalumbo4362]

Gee! Did you get the jab?

[@georgeshaw8925]

@@mikepalumbo4362 No sir I didn’t, when you have to have 15 boosters for it to be legitimate, maybe they’ll to go back to the drawing board before I get stuck.

[@richreid7098]

Excellent

[@royrogers7644]

So what is a compressor good for?

[@TheGuitologist]

Compressors equalize parts of the music so they are of similar volume. Loud parts get squashed down. Quiet parts can be set to be closer to full volume.

[@tunabob]

Peaks n valleys.... Btw Brad, I love em! Stellar job, man...also, I did put em inline and part of a mix chain and these little beauties (tho not optical), I'm sure will do well, where my requisite.L2M mark 2 sits n will give em a run for the money, lol...... Thanks again, tuna...

[@timothyb1559]

Awesome!

[@scottgarrett744]

Music equipment!!! Yea!!!

[@rager-69]

I'm surprised you put the release knob on the left and the threshold on the right. The normal layout would be the opposite and it looks like the wiring would a little shorter if you had done it that way.

[@TheGuitologist]

The 436 has the Release on the left and Threshold on the right also. It's shorter wire runs this way.

[@cubistone]

Those Altec would be very much at home in a wwii museum. They look the part. I'll bet they saw action against the Luftwaffe at Dover.

[@TheGuitologist]

Looks like something from the instrument panel of a bomber.

[@cubistone]

From a flying coffin B24 Liberator storming onto the flak filled sky of Third Reich Germany.

[@alnorman6846]

It Sounds distorted, is that normal ?

[@jefflitchfield4950]

I highly recommend using a chopstick or another piece of wood or something when taking a tube that is powered up with sound going through it. I washed a friend shoot a lightning bolt out of his elbow when he touched it tube on a radio while keying the mic. Use a piece of wood, humans are very conductive.

[@TempoDrift1480]

Fuck yeah! Getting back to good.

[@srtamplification]

Jimmy Carter Lincoln?

[@Ricobass0]

Zaerux valves were Russian. They had a shop in Tottenham Court Road, London, England in the 60s and 70s. Mullard valves had totally different printing on them.