1960s Gibson GA-5T Skylark Amp Service, Restoration & Demo

Here we'll go completely through a vintage 1965 Gibson Crestline era GA5T Skylark Tube amp and service it. We'll also restore the handle, make a custom repro logo, look at some schematics, and slightly modify the circuit to remove the 'tone sucking' network and change one coupling capacitor to enhance bass response and gain and make the tone less tinny and harsh. Finally we'll demonstrate the amp with a Gibson SG Standard and a Fender '52 Telecaster.

[@Partsocaster]

Stumbled onto your channel a few days ago and have been binge watching. There are guys who know their way around a tube amp, and there are guys who know their way around a fretboard. You are one of the rare ones who knows both. Bravo.

[@TheGuitologist]

Thanks so much for watching. I appreciate that.

[@douglaszolton8985]

Is this why Gibson amps failed in their sales ,then stopped production ? What was their last date of production ?

[@abecene]

I've been designing and building tube guitar amps for the last 15 years or so, over 100 and counting. Found your channel and now I'm hooked. Excellent job explaining how the circuits function and making it simple for the masses.

[@StainedGlassColors]

Your videos on vintage gibson amps are really a source of great information on both tones and all that is possible for these amps. Thanks

[@musicguy9299]

Long time fan here. You find so many amps I really used.and wanted, that I will be watching your videos a lot! Thanks! ps, Your knowledge and presentation is amazing and impeccable. Genius.

[@decsnspace]

Another great video! Was a long player, but very enjoyable to watch. I really liked your discussion and comparison of all the various schematics for the versions of this amp and your in-depth focus on the tone sucking component. With your mods and service the amp now sounds awesome! Love the cleans and the breakup on it is killer!

[@TheGuitologist]

Thanks Bud. I appreciate that. Yeah, I try to keep my vids under 30 min, but this one got away from me somehow. Whoops! :D

[@MichaelKLee-jf7qs]

Just so happen to get my hands on the non tremolo version of this amp, with the same emblem on the back of the speaker. This video is a godsend, wow!

[@FredFacker]

I just picked up a 64 model, and I really appreciate the fact that you put this together. Going to have to chase down a hum and figure out why the tremolo isn't working exactly right.

[@lowheadroom]

Man I forgot how thoroughly you document. Love watching this again now that I know how it all works :)

[@lowheadroom]

I am repairing a Gibson GA8T. Gonna recommend the “tone sucking” network be taken out. The trem is working too fast and there is low amplitude

[@bassdale17]

nice to see and hear a amp tech with soul

[@TechBrewGamer]

i actually like watching your videos in the background as i am working.

[@CitrusDistress]

^^^ this

[@ericr5431]

Brad, as usual another great video. I found one of the amps in the garbage in the early 90's minus the speaker. I installed a Eminence legend alnico and recapped it. It sounded awesome. I gave it to my nephew. Mine did not have the tone sucking circuit. I have always theorized Gibson used that circuit because as I recall, Gibson supplied all it's guitars and basses with flatwound strings. That tinny tone sucking circuit may have given the flatwounds a brighter sound.

[@geraldbaranski8983]

Thanks man. This will be my first foray into amp mods. (or any amp work, for that matter). The GA-5T I have has the same black electrical tape- seems to be factory tape. Thanks for the Knowledge & inspiration !

[@srvfan454]

I have one exactly like that! And it's almost like new! Got it cheap off of ebay about 13 years ago. It's awesome!

[@mike60510]

Thanks, Your video came at a great time. I was looking to buy Gibson amp at a local music story. Always enjoy your videos!

[@TheGuitologist]

Thanks Mike! What model you looking at? I have a few for sale including this one if you can't get that one.

[@mike60510]

I was looking at a Scout that does not work and a GA5T like the one you repaired. I've seem most of your videos and it looks like you have a lot of gear., I'd assume some for sale. Do you have a web site or do you prefer to work individually. I can contact you through the e-mail listed on the "about" page.

[@TheGuitologist]

louisville.craigslist.org/search/msa?query=1103 That link will take you to my current listings. I ship with Paypal.

[@anthonydallarosa8314]

Just picked up a 64 GA-5 today at a flea market for $130. I feel like I stepped in Leprechaun poop. I haven't removed the tone suck couplet yet and it's already one of the best sounding amps I've ever played hands down. Takes pedals like a champ and is loud as fuck for a lityle 10 watter. Had I not seen this video a while back I probably would have passed. This thing is amazing. Thanks Brad for opening my eyes to this incredible little amp.

[@spencerfreed6947]

Just watched this older video and what a great episode Brad! Thanks for the content man! These Skylarks were never on my radar till about a year ago and I've been keeping an eye out for the right one. I really think they're serious sleeper amps! Try and buy a '65 Fender amp for under $700...ain't going to happen. Anyway thanks again, I constantly learn shit watching your channel and I love it! Keep it up and be well my friend!!

[@TheGuitologist]

I have another Skylark video in my “Secrets of the Classic Amps” playlist. Be sure to check that one out.

[@whynotme5926]

Neat video, for sure, nice playing. You have a good ear.

[@cassvirgillo3395]

Hey Guitologist, I hope your doing good. I really enjoy your videos and as a sub look forward to new releases. Thanks for sharing your knowledge and experience and the time and effort making videos. I am learning a lot. I like detailed explanations of certain aspects of tube amps, the how and why. Take care, C.

[@TheGuitologist]

Thank for watching and taking time to comment. It's good to know someone out there is getting something out of it.

[@wadenkrangguttenberg3750]

+The Guitologist plus one for me. your videos are like an online course in amp repair. thank you

[@TheGuitologist]

Everyone is welcome to learn from my mistakes. ;)

[@davidclink1425]

Need some input for a Gibson Skylark Amp the size of a practice amp. It powers up but makes a loud hum or buzz. serial # is 111053 and it has three tubes 6BMB/ECL82, the others have some numbers missing. P28-?? 62-??, and a 61-48 (or B) 274. Tubes say Gibson on them so likely original. Will replacing all three tubes remove that buzz? I cleaned all the connectors and tube sockets with tuner spray. I saw the main amp tube for sale but noting on the other two tubes which aren't the ones you cover here. Hope you can help.

[@EurekaRecycler]

Do you have to preheat the old components on 60 vac for a bit first ? Thanks

[@christselectedservantrealt5077]

@The Guitologist i was given an amp exactly like this one the other day the fuze is missing i think it doesnt come on when i plug it in but it appears to be in almost mint condition other than the fuze how do i get it to power ???

[@NortonG15CSR]

I have a 1964 GA5T and need to replace the handle, so this excellent video is very helpful. A few questions: I see the bolts you used have a gold tint - were they brass? I can't tell from the video, but did you use lock washers or loctite to keep the nuts from coming loose? Did you avoid stainless steel for any reason? The cleaned up brackets seem to also have a gold tint - did you do something to color them? Thanks again for this wonderful video.

[@dolemite84]

I came so close to making this amp beautiful watching your video. I made the .022 cap change and removed that goddamn Sprague wafer from the “loudness” pot. The problem is, I placed the lead of the .022 cap to the (looking from underneath) third lug of the vol potentiometer… and now, the vol is always all the way open. Did I just burn it up with my iron? Is this the wrong way to bypass that shitty, value drifted Sprague wafer? Thanks for any input.

[@georgeallison6228]

Man..that guitar and amp..you're set ol Dickey!!!! :)

[@marscounty]

What is the black plastic you used for the logo backing?

[@comajoebuck999]

Love that asphalt tile floor.

[@trey8069]

What did you use to clean up the control plate? Yours looks pretty spankin clean at the end of the video.

[@charlesshaw9090]

Interesting vid. So, nothing wrong with the power transformer in the end? Maybe the old DC power cap was really dead causing the fuse to blow. The single BQ5 version is an alternative 5W circuit but the twin BQ5 with diode rectification is an 18W version so not a GA5 amp at all. Surely the chassis should be removed from the rear?

[@audiotechlabs4650]

Great as usual! Did you have to mount that upper back plate to the chassis before you put the chassis back in the cabinet? It seems worked on GA5 that had the same configuration. Thankz

[@TheGuitologist]

Thanks for watching. You have to put the chassis back in FIRST, then the baffle or the back panel next. Just depends on which nuts you prefer to put in blindly. It's a weird design. They could have at least made the screws go all the way through the back and used sheet metal screws directly in the chassis.

[@cdemeo2]

Great video! What did you use to clean the chassis faceplate? Just picked one of these up for a really good low price. The chord was replaced with a 3-prong grounded cord, the old speaker was replaced with a new Jensen and some caps replaced. Mainly the tone killer was removed. Loving it.

[@cdemeo2]

*cord :)

[@TheGuitologist]

I don't recall what I used here, but you can use baking soda or baking soda toothpaste and an old tooth brush with good results.

[@vintageaxeworks2777]

I know this is an old video, but the guitar hunting up on the right with a cream P90, bridge and stop bar; is that a Junior, or a Melody Maker?

[@alaricmusic]

Cool video. Thanks. That thing still sounds kind of boxy. Is it safe to assume the speaker sucks?

[@altcountyemo]

The EA 50T from Epiphone looks a lot like this amp you are working on. I have one that the PT is sizzling and when I remove that primary white ground wire on the PT the amp is much better. The resistance from that primary ground to the red/white CT for the secondary is 2K ?? An internal semi short?? I am stumped, but the amp is OK with the Prim ground isolated. The chassis is grounded with a new 3 prong cable.

[@SuperCarver2011]

I've been watching your amp repairs with a lot of interest. Years ago, when I wore a younger mans clothes, i used to work in a guitar music store between 65 and 68. I used to repair guitars and some amps too, using tube manuals and learned to read schematics. Later on I went to electronic college to learn tube theory..anyway I remember fixing some new Epiphone amps, since we were strictly an Epiphone dealer,. CMI would not give us the exclusive on Gibson as another dealer had that line. The Epiphone amps did not sell very well, we practically had to give them away when other items were purchased.; The solid state rectifiers used to short out after a while. I was watching your episode on the GA-5T (Skylark) with interest (as well as your other repair episodes) and found it very interesting. You do a very good job of explaining the circuitry, repairing it and then testing it out with various guitars. What year is the SG you are playing in the Skylark episode? (I also play guitar myself.) Going back to the differences on the various versions of the Skylark. Especially '65 models during the Ted McCarty era, the Gibson amp department was first outsourced to CMI (Chicago Music Industries) the parent of Gibson before McCarty left in '66. The Gibson electronics dept was set up by Walt Fuller and Seth Lover, (inventor of the Gibson hbucker). Some amps before the electronics dept was set up in Kalamazoo were farmed out to CMI in Chicago, who may have farmed it out to a commercial manufacturer. Later on, before they were discontinued due to poor sales, they were limited production with Seth Lover in charge and he may have been influencial in design of some of their amps. . Gibson amps were designed to be used with their humbuckers which are more mellow than the Single coils of the day, and perhaps that was the reason for the experimentation using the "tone sucker"? Gibson amp production ceased (after McCarty left) due to poor sales. Seth Lover left Gibson to work for Fender in California around then. .

[@waynegram8907]

I would like to know how to make those Gibson Tone Sucking Networks sound good because each one of those Couplets are a custom RCR/C network with different values. Each one of those Custom Couplets won't have the same values internally.

[@wbajzek]

Hi! I have the non-tremolo version of this amp, which I've really liked but have felt is not quite there. I just jumpered around the "tone sucking circuit" to see if that would do the trick, and boy, did it ever! I was wondering, is there any harm (to safety or tone) in just leaving the jumper in there (it's an insulated wire with rubber-insulated alligator clips)?

[@TheGuitologist]

I would not personally leave gator clips inside an amp. Get an iron and do the mod.

[@wbajzek]

Yeah, I think you're right. I'm gonna do it this weekend. Even if it's not a safety problem, the wire's probably acting like an antenna.

[@wbajzek]

Done!

[@richardwalley2862]

I noticed these amps are pretty bright as there anything that can be done to add more bass to the sound aside from just using the tone knob

[@cassvirgillo3395]

Hey G, How come the non grounding jack only had a resistor to one lug and the other had nothing? I know the resistor goes to ground, no input lead from what I could see. C.

[@TheGuitologist]

The resistor goes to the grid of the first tube amp stage. The empty lug is a ground lug. No need to solder a wire from there to ground because the jack housing is touching the chassis already. The 100k and 1M resistors add up in series to become the grid leak resistors when you plug into Input 2. No other components are necessary

[@contrabandjoe7974]

I recently subscribed to your channel (it was a youtube search of vintage Fender Deluxe reverbs, I own one and was curious about the one you repaired over the winter). My question is about amp parts, you talk alot about fuses. I never take spare amp parts to my gigs (and been gigging since the 80's)... where would I buy spare fuses? guitar center etc? and what spare amp parts would you recommend a guitarist keep on hands at a gig?

[@TheGuitologist]

Thanks for the comment! Spare fuses are nice and you can find those at Radio Shack, Advance Auto Parts,Harbor Freight, or Wal Mart in the Auto section. IF a fuse blows during a gig though, there's probably something else going on that made it blow. Be careful just plugging in another fuse and going ahead. A spare set of tubes is also nice to have on hand.

[@williamnichols6253]

I wonder if the tone sucking network was intended to make vocals sound better?

[@jasonaustin3270]

I have been a fan for a long time, but I just found a skylark on the side of the road and went back to this for some info. But yeah I found a cool sears amp, and an old single ended power section skylark in the garbage.

[@TheGuitologist]

WTH is wrong with people?!

[@BenPrevo]

Hi brad -- I have the earlier Ali chassis GA5T -- 6.3 v pilot -- no tsn and nice redwood cab -- it took me a while to figure out how to get it apart to service ! It was vastly improved with a new jensen C10R -- please put the hot of the line on the fuse tip for safety == not the ring-- I also would have changed the bypass caps -- keep on rocking !

[@TheGuitologist]

Yeah dude..they sure as hell didn't want people getting into these did they? It's like having to solve a troll's sick riddle before you can proceed.

[@BenPrevo]

Yup it took me a while to find the 2 'mystery' nuts -- then a couple of minutes to figure I had to pull the baffle too -- wacky gibson designers -- and only on that model as far as I know -- go figure....

[@teddee7900]

I have a question about the tone sucking circuit i just acquired one of these if you could message me back it would be greatly appreciated.

[@stephenbarton2625]

How can I get one of those logos?

[@MyNameIsMcBad]

How much do these cost nowadays? Hard to find

[@douro20]

The 6CZ5 and the 6CM6 are actually better in terms of power dissipation than the 6AQ5. The 6CZ5, which was designed for audio output in TV receivers, is actually a near equivalent to a 6973 with the difference of the screen grid connection.

[@lepetitnabot]

And here I was thinking I was the only weirdo listening to Bob Ross while working :-o

[@coldbastard6859]

Nice SG ^^

[@nfausman]

Man ive got s/n 765626 date mid 65ish, and its so similar yet so different, and im baffled as hell on it

[@richardross4747]

9:20 - Those bolts on the 'back door' are for securing the back door to the chassis. PITA to undo that first every time, and if you leave it connected to the chassis, you can't use the cab as a natural workbench as it was intended.

[@richardross4747]

14:08 Ah! You got it. And yeah.. it's weird.

[@DeadKoby]

Sorry to be a bother, but I've still got it in my head to build a 6AQ5 push pull. Knowing that the max plate volts for 6AQ5 is 250v, do we know what the transformer's main secondary is? 250-0-250 perhaps? The rectifier tube should sag a little, and leave us right around 250 I'd think... with a full wave rectifier anyway.

[@TheGuitologist]

Probably a little higher... like 275-0-275 with no tubes in. The 6AQ5 is a hearty tube, and you can always bias however you like for plate dissipation. I'd err high on tranny selection.

[@TheGuitologist]

Anything designed for PP 6V6 will work perfectly, so on second thought, something more like a Fender Deluxe replacement 330-0-330 will be ideal. www.tubesandmore.com/products/P-TF41316

[@DeadKoby]

The 275-0-275 makes sense if I wanted to hit 250... I've had some very bad things happen as a result of excess plate voltage... having 6v6, 5881, and 807 do some very bad things when max voltages were exceeded. My 807 amp runs right on the max voltages, and all is happy there... but any more and weird things seem to happen. It's been said that a 6AQ5 is a heck of a lot like a 6V6... but it does show lower volts on the spec sheets. plus, 2 6AQ5 in p-p are roughly 10w music power. 2 6V6 in p-p are usually 18... I'm a classic over-thinker... but the mains at my home are strong.. 120V RMS and really don't waver.. I've seen mains voltages in my town as high as 135v... I'd rather error a little low.

[@VeryVeryVeryHigh]

You look and sound like Clapton! \m/

[@johnharlan7205]

Maybe it’s the RF that breaks down the Sprague Black Beauty caps?

[@williambock1821]

I wonder how those “tone sucking networks” sound with humbuckers and P-90’s compared to Fender single coils. Maybe they wanted to keep Gibson amp owners buying Gibson guitars. Haven’t gotten through the entire video yet so sorry if you mentioned that later. :-)

[@wonderwomanguy]

The crest is a goose that opened a can of pringles and then scattered the chips everywhere.

[@williamgregory6684]

A speaker replacement would work wonders.

[@francesnieznay6623]

same as Cass,Thanks.

[@GerSHAK]

Absolutely beautiful demo-ing as usual. :) Hope you don't mind a small pedantic note - standard pronunciation is TREMmo-low, not tre-MOlow. :)

[@GerSHAK]

Awesome ending, too :D

[@TheGuitologist]

Should have put stings on that SG. Man, they sound dead. :(

[@kardRatzinger]

Is that a Les Paul Junior Doublecut on the wall?

[@kaypolo]

The symbol is a Coat of Arms.

[@Agenthoover1]

I used to be into car stereo systems in a big way... many times people thought it was a good idea to use silicone to seal sub woofer enclosures, however, i was lead to believe that silicone was a big no no as the silcone fumes could actually rot speaker cones.... anyone ??

[@TheGuitologist]

That sounds pretty dubious to me.

[@SuperCarver2011]

I've used it in the past to repair small tears on speaker cones. it depends on the power and type of amp. On a 15 inch bass amp speaker, too much of it on where the cone vibrates a lot, can still lead to the repair becoming unglued, but for most guitart speakers especially smaller ones..it seems to work.

[@kaypolo]

Spreading school glue on torn cones works wonders. I've repaired some trashed cones and they play loud and sound fine. Just let it fully dry.

[@Drew_Gliebe]

I have a ‘64 #’d 754835 Add that to the list too

[@DeadKoby]

I've got the earlier brown Skylark. I left the schematic at default... It loooves humbuckers, but will bite your face off if you put singles in it... Roll back them tone knobs for maximum cool. 6AQ5's baby.

[@TheGuitologist]

Yeah, love 6AQ5s. If you have a much earlier Crestline Series Skylark, you may have one before they added the 'tone sucking network' to it. Open it up and see if you have that Sprague component in there.

[@DeadKoby]

Note.... mine is PRE-Sprague red-brick of doom.

[@TheGuitologist]

Yeah, yours is pretty much identical to this one after the mods

[@DeadKoby]

The First thing anyone says about these is.... ARRG the treble... However there's no tone knob... so it makes the tone knob on your guitar IT... I find that rolled half way back is the happy position. I've had tone knob-less amps that didn't have enough treble... that's more of a problem to me, since I can reduce treble at the guitar.

[@TheGuitologist]

That's true, but the amp was designed to stay clean most of the way up the dial with humbuckers. Hard to make break up. Even with these minor mods, the amp is still plenty bright, but there's a lot more gain on tap now, so you can still dial back the volume and tone on the guitar and dial in your sweet spot and have room to step up to a solo.

[@Uraim]

try out in this the bass

[@utooberblooper]

bob ross is almost as brilliant as the guitologist,two simply amazing phenomenons in the personal entertainment world(mine at least)both are much better than fake drama bullcrap that proliferates television and mainsteam media these days.

[@akkudakkupl]

That little bridged-T notch filter is -17dB centered around 460Hz. That's close to where the MID control on a Marshall sits frequency wise. I'd say try rebuilding that with discretes, but the 2 resistors could be replaced by 68k fixed, 250k pot and 100k fixed. Wiper to 5n cap. Should work as a variable mid cut from -10 to -20 dB.

[@javiceres]

Isn’t that the frequency region where most Fender blackface are also heavily scooped?

[@bobcs71]

Tried that with my '63 & somehow I ended up with a ghost note

[@TheGuitologist]

Check tubes. Could have a noisy or microphonic tube that just didn't show up until you changed the frequency curve of the tone network.

[@bobcs71]

Thanks. Tried swapping tubes with no luck. Compared to the schematic I have, my amp has 2 6EU7s & the schematic shows a 6EU7 & a 6C4.

[@TheGuitologist]

You may need a grid stopper resistor on the control grid of the stage following the original tone network. Try adding about a 100k-220k resistor there. If I was a betting man, I'd bet that'll kill your ghost note problem.

[@williambaldwin7611]

I bought an amp like this GA-5 crestline off ebay where they guy had already done this mod. It had a ghost note. What I found was that there were 3 20uf filter caps coming off of the B+. The first 2 were wired in parallel after the 1k resistor coming off the rectifier...leaving no path to ground for the center tap except through that resistor. It burnt up the resistor and also caused a ghost note. I took one of the filter caps and moved it before that 1k resistor and all is well now. Also I changed out the cathode bypass caps with 25uf it took a little of the sting out of the high end. Although I kind of miss the way the amp used to hurt me a little. I might put them back :) anyhow just sharing in case your issue is similar to this.

[@donrutter6765]

Has a non flattering fuzz at high gain,, sounds like the amp, not a speaker problem.

[@bengalvin9932]

i keep watching these videos thinking this will be the amp even THE GUITOLOGIST can not make sound any good but no it sounds killer again! by the way it is not fair that you can be both great at working on amps and great as a player too NOT FAIR! tell me you can't cook give me some thing to make me feel better about my self!

[@Angelum_Band]

45:00 Nah! Naaaah! Naaaah! Naaah!

[@josephlama4097]

It's in a good condition but it needs a new makeover.

[@jrcstudios3803]

Hot glue for paper speaker cone?? NO.

[@TheGuitologist]

Yes. It's the best fix for a cone. Makes a sturdy, permanent repair. Done it many times with excellent results.

[@bengalvin9932]

THE GUITOLOGIST............THE PEDAL KILLER!