Let's Build the Gibson GA1-RVT.....A 3-Tube Amp with Reverb & Tremolo, Part 1 of 4
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- เผยแพร่เมื่อ 2 ต.ค. 2024
- I've been fascinated with the Gibson GA1-RVT circuit for many years and finally decided to build one, incorporating some updates and improvements. Although the amp has only three miniature amplification tubes (and a 5Y3 rectifier), it offers single-ended output as well as grid-bias-modulating tremolo and a tube & transformer-driven spring reverb.
In this Part 1 (of 4) Video, we will discuss both the circuit and compound tubes it utilizes, then create a parts list, fabricate a chassis from 16-gauge hot-rolled steel, then machine the chassis and prepare it for painting and final wiring and assembly. Additional topics will include making a 2 Meg AT pot and color-changing LED pilot lights.
If you enjoy advertising-free videos like this (we personally do not monetize our videos), please SUBSCRIBE and support our channel by becoming a Patreon patron at: / uncledougsvintageamps or by making a PayPal contribution to dldcam@aol.com. Thanks so much for watching :)
Here is the link to the Parts List: app.box.com/s/...
Here is the code for a 10% Discount on Lacquered Tweed Deluxe 5E3 Cabinet from Mojotone: UD5E3 Should be good for several months.
CORRECTIONS:
1.) I misspoke regarding the insertion point of the "wet" reverb signal. It is fed into the grid of the upper 6EU7 triode along with the dry signal from the 6AN8 triode.
I understand that you are trying to clone the Gibson circuit exactly; but you, or anyone who follows in your footsteps in trying to build one of these, could save the cost of the reverb-drive transformer (and some space on the chassis) by using a capacitor-coupled reverb circuit and a tank of the correct impedance for that type of drive. After all, capacitor-drive reverb was good enough for the famous Ampeg Reverborocket and for vintage Magnatone amplifiers! The only minor disadvantage is that a Fender style reverb tank wouldn't work.
@@goodun2974 Thanks for your helpful input, GU, but the $11 cost of the reverb driver was not exactly a financial burden.
@@UncleDoug I was thinking more in terms of saving some real estate space on the chassis...
@@goodun2974 It's a very compact transformer, GU.
Uncle Doug I have a question. I have an old western auto Riviera AM fm high Fidelity stereo receiver with a turntable. It belong to my parents and I would like to restore it. There is no information on the model number or serial number. Is there anyway to find the schematic for this item? Thank you.
All is right with the world...an new video from "Uncle Doug"!
Thanks so much, ID :)
Uncle Doug is a National Treasure.
You are too kind, BH. Thanks :)
Yes he is. And his dry sense of humor is awesome. The neighbors need to understand that they are host to a national treasure. One that raises their property values.
@@peteleoni9665 Thanks, Pete, but higher property values mean higher property taxes ;)
@UncleDoug
As a guy that refuses to leave his swamp house for life you'd think I would understand. Yep you are right.
Someone asked on Peavey Forum about good books to explain how tube amps work. I told him that Uncle Doug's videos are far and away the best explanations I've ever found.
Dang if it weren't just last night I found myself thinkin about my dear ole Uncle Doug,,,wish you lived closer,you could have free reign in my fab shop
I would enjoy the "free reign" a great deal......but at least I'm no longer using a sledge hammer to form chasses ;)
@@UncleDoug Yeah, but you could *really* use a nice big set of Greenlee chassis punches! If I find myself with $1K of spare cash I'll send you a set. It's just kinda painful seeing you have to do all that deburring and chamfering when there's an easier way... 😉
@@sootikins Thanks, Sooti, but I have a set. I didn't think they were useable with 16 gauge hot rolled steel.
@@UncleDoug I suppose that depends on the specific punches. I know that at least some Greenlees will punch 30mm holes in 12ga panels for mounting switches without damage or complaint.
@@sootikins I'll bet a challenge like that would require a hydraulic ram rather than the manual wrench and bolt.
Happy days are here again! A new Uncle Doug video! 👍
Posted just for you, AA :)
Love these videos. It's like I'm "going to school". Thank you Uncle Doug! You're the teacher I've always wanted to find. Sorta like finding the wise man on top of the mountain. Your content and lessons are very appreciated.
That's great to hear, Chad. We're glad the videos are helpful and appreciated.
Glad to hear it, Chad. Thanks !!
Uncle Doug, you're just what my inner peace needed this afternoon.
That's great to hear, Dr. D :)
......and a 3 part series.😎
@@PetraKann To be honest, it may even go 4 episodes, depending on the fine tuning required.
@@UncleDoug No complaints here champ
Cheers
Your videos are my therapy!! Thanks for all you’ve taught to this community. I’m an Electrical Engineering professor and use your analogies in my class to explain how devices amplify. Thank you 🙏
I am quite flattered to hear that, Jorge. Thanks so much for your kind words :)
It's going to be an epic low-watt amp! Thanks, Uncle Doug!
I sure hope so, Ken. It's getting to be a fairly expensive, time-consuming build....but I'm quite optimistic :)
Filled my mouth with cheese and waited with baited breath for another spectacular video! Thank you, Uncle Doug. Can’t wait for parts two and three!
Thanks, A. I was wondering where all my cheese went ;)
Uncle Doug for President!!! You sir are a GEM!
Thanks so much, Lynn :)
Uncle Doug is lucid and sane, and he has actual skills. He is therefore overqualified for that position.
Yay!!! Just got out of the shower, ate food and played with my cats, and there's a new Uncle Doug video one hour ago!!! Maybe I should buy a lotto ticket
It's YOUR day, Nick :)
YAY! Another Uncle Doug video! Thank you sir!
Our pleasure, MJ :)
Hiya Uncle Doug!!😃 Y'know, when you think about it there are very few guys who are proficient in building a circuit like this as well as the metal fabrication, PLUS the woodworking skills to build the cabinet. Not to mention the tweed covering. Well done indeed. Thanks for sharing it.
You're welcome, Dale. I hope you enjoy it :)
I just love this stuff! I too had the let’s build an amp from “scratch”bug many years ago. What a challenge, no internet. Fortunately there were Uncle Doug’s clones everywhere. Still have it and with your videos It keeps pumping out great tones. FYI I had a guitar playing friend bring me his Fender amp to see if I could figure out why the amp had a low but annoying buzz. Couldn’t find anything obvious until I realized the jewel light was way too bright, so I took it out and realized it was LED. Replaced it with the standard bulb and the low buzz went away??? Looking forward to next part.
We're glad the videos have been helpful, BK :)
Nice work as usual Doug. I see the cuts on your hands are related to the amount of metalwork completed 😂
It's all Hollywood makeup to promote pity contributions :)
@@UncleDoug 😂😂
Admire Uncle Doug’s work and was very excited to find this today
Thanks, AQ. I hope it exceeds your expectations :)
Hello Uncle Doug. I was wondering when you'd release your next video -- and to my delight, it's the first of a 3-part series of another scratch build! Can't wait for the next part.
I hope you enjoy the series, Reggie :)
Hey Uncle Doug! Thanks for all the amp wisdom and humor and cars! Tung Sol has started to make 6EU7s again. So anyone building your version will not have a problem sourcing them.
Greetings, Rob. Thanks for the helpful info :)
This looks really interesting. I was considering a bassman clone but this one is intriguing. I’m on board. Let’s do it!!!
I'm glad you share my interest in this efficient little circuit, David :)
What an interesting project. I can't wait to see parts 2 and 3. School is back in session and I couldn't be happier.
That's great to hear, TJ. Thanks !!
Uncle D - love this type of content! Resurrection of old amps! Hope all's well.
Glad to hear it, TAG :) Never better.
Doug. That's a great great idea! Potential to go very viral not that you probably care. Awesome idea, reverb, trem, crunch at low volumes. Perfect I will be building along in some form.
Thanks !! The circuit will be improved as it takes shape, Pete, so be patient.....or creative :)
Thank you for leading us on another cool new adventure. I learn somuch from following these builds!
You're welcome, Peter. That's great to hear :)
Another wonderful project Uncle Doug. Your videos continue inspire, both as templates for creating fun and useful amplifiers, and also as templates for how to share knowledge with the less well informed. And, I like the fact that you're using an unusual design with tubes that aren't often used. This series is truly creative in every sense. I confess I still reminisce about the Supro S6422RT outtakes, but understand not everyone enjoys horror movies. The hot roll you're using is covered in mill scale that forms when the steel comes out of the rolling mill and is cooled and coiled. The oxidization forms a coating that is later removed in an acid bath (the "pickling" process) before going through a gauge reduction mill, annealing and final tempering. Cold rolled steel is typically harder and stronger than standard hot rolled steel, so the cursing and bruising indexes are higher by a significant factor. Good choice.
Thanks for the informative input, GF. Between the grooving and the metal brake, I thought the bends came out quite well.
I was very happy with my mojotone cabinet. A GA-5 8 inch combo cabinet with white tolex and ox blood grill cloth.
Wood and metal working are the big obstacles to my enjoyment of this hobby. Now I buy broken amps on reverb, gut them and use the cabinets, chassis and transformers if they work.
Very excited for the rest of the project. Thanks for the video.
You're welcome, FJ. I hope you enjoy it.
Still without an equal the coolest dude on TH-cam bar none.
Wow....You are too kind, Tony. Thanks !!
Well heck I wasn’t planning on building anything until July or August but since you went through the trouble of making a very thoughtful parts list, I’m tempted to solder one of these together!
Take the parts list with a grain of salt, William. I was a little imprecise with the smaller components and I encourage personalization by the builder. Good luck :)
Let us know ho it turns out, William :)
It's good to see you, Doug! Your channel hasn't popped up on my TV in a while, and it's nice to hear your voice again. I hope you've been well.
That's quite a clever circuit you've got there. Looking forward to hearing it.
Never better, KW. Thanks so much :)
Incredible project - looking forward to the next video. Great job on the chassis design and build! I've often found myself fantasizing that the engineers that design transformers would simply include a piece of paper that's a template for cutting the opening they should fit into. But then I realize that if they did that, I'd never have the chance to exercise my collection of cuss words and I'd never have the chance to ask my wife, "Honey, where's that new box of bandaids we bought last year?"
Thanks, OLW. So true. Even sinks come with cut-out templates :) Also, no matter how careful I am, the holes (all five) have to altered somewhat.
@@UncleDoug Same here - every damn time.
A great video once again, Uncle Doug! Let's hope your neighbours get well soon!
Thanks, Hal......I'm sure they agree :)
glad to see you on air! always informative video!
Thanks, William :)
Thank you for doing this, this might be even more enjoyable than your repair videos.
You're welcome, BMD. I'm glad you enjoyed it.
Great start to another project Doug. Looking forward to part 2
Thanks, Ex :)
Oops, I'm a bit behind, but great to find a new video of yours, and even the first of a mini series! Although, I'm very surprised about that concept - both reverb and tremolo, but with that SE 6BM8 it's only to give about 3.5 watt! Here in Britain they call this 'fur coat but no knickers'! So, I'm curious as to the sound verdict. Looking forward to the next instalment!
Greetings, Reg. Recall that the first Fender Champ amplifiers had only 3.5 watts and nobody seems to complain about their tone and power :) Hopefully the mighty Gibson will sound as good.
The top control opening in that cabinet is 2-1/8" X 12-3/8", and the corners are significantly rounded (so stay clear of the corners). I just measured it on mine.
Thanks, RB. The cabinet arrived immediately after Part 1 was posted (as predicted) and the chassis has been fitted to it.
Can hardly wait for part 2 ... Thx
It's in the works, Eddy.
you're the man, Uncle Doug
Thanks, TM :)
Best YT channel ever, thanks uncle.
Wow.....Thanks so much, HV :)
The deadpan humor at 10:45 is equal to the tech parts of why I love these videos of Uncle Doug 😂
Thanks !! We try to add some levity to wake up our dozing viewers, BH ;)
Uncleeeee.
Another great project as always.
Nice to see you!
Thanks, ITR :)
Man I wish we lived closer to one another. I have my great grandpas old Gibson amp (all I can read is GA then it dives under the body of the cabinet). It isn't this circuit (based on the tubes), but I'd love for you to look under the hood. It works fine, but of there's anyone I'd trust to look it over, it'd be you. Thanks for the great content!
By the way, your videos and advice helped me bring my grandpas old Silvertone back to life from being utterly broken to fully functional. Thanks for that too!!!
You can send some photos of the Gibson "mystery amp" to my FB page Uncle Doug's Vintage Amps. I'm glad the videos have been helpful :)
My first amp was a 1947 Gibson BR-1 that my dad had for his steel guitar (he had the guitar too!) this was late 60’s when he got it repaired for me! It was great for a beginner because it had mic inputs too!! Powered our whole little band! Then I bought a 68 Bandmaster (tall speaker cab) later a Dual Showman! Several Twin Reverbs…. Now I bought an Epiphone Blues Classic 30w… has incredible clean tone! Weighs a ton however!
You've had some fine equipment, Bob. I hope you enjoy our series :)
Great idea extracting so many features from so few valves! It's gonna be very cool! How many watts output will this amp have; a couple?
I watched a couple of Mojotone's videos on the cabinetry they make, & they look VERY good! Like the originals!
Are you going to include a fuseholder or did I miss that?
Supposedly it will put out 3.5W, Neville. The cabinet is fabulous !! Yes, the fuse holder is on the bottom.
been watching since i was 14, now im 24. time flies
...particularly as you get older...
.....especially if you're having fun ;)
Powder coat that thing. Very interesting. I look forward to the rest of the build. Thanks.
That requires outside help, Hugh, which I avoid at all costs.......other than the cabinet for this build (and it showed up a week late).
Good to see this project underway, Doug.
Let's hope the journey ends well, Brad :) I cannot find any reference to this particular amp or RVT circuit on Reverb, the VG Price Guide, or other sites. I wonder if it ever really existed ??
Doug. Please go ahead and send me one of those 12” Jensen speakers. I only need one so that’s good.
I already sent the 3 I had to some needy orphans, David. Sorry ;)
Those are some tricky tubes to find...I used to have two different amps one took a 7199 one took a 6EU7. Both were hard to find I think the 6EU7s were always microphonic
If the 6EU7 acts up, I'll switch to a 12AX7, LAJ :)
@@UncleDoug I havent watched the whole vid so I'm guessing it cant be a direct swap but a rewiring job - which is why Im here - trying to learn more about building tube amps...I had an old Sunn amp that ran 6550s and a 7199 and I ended up selling the head without the 7199 - I couldnt find one at any price at the time - apx 2010s maybe they are easier to find now...I'll watch the whole thing and report back if necessary
@@leveractiongypsy1848 Yes, the tube socket must be wired differently, but that's simply a matter of numbering the socket connections properly in the schematic for the tube actually being used.
Uncle Doug Mini Series - YAY!
We hope you enjoy it, Ray :)
I'm in heaven, brilliant! The input socket wiring is odd in that plugging into the bottom socket seems to disconnect the 1meg ohm to earth resistor I wonder what instrument this would suit? Not a guitar pickup, possibly a mic or a piezo acoustic pickup?
Greetings, Rob. Look closer at the input circuit. Plugging into the lower socket simply adds 94K in series with the 1 Meg resistor to ground.
6GH8 is a good sub for 7199, AND there's a plug in adapter for the conversion if you've got an old Ampeg or Seeburg that needed 7199. I have a pair of 6GH8 in my Seeburg and it works well.
I hope the 6AN8 works out well, DK :)
Dug deeper in the crates, found a pair of 6GW8/ECL86 beauties, one's a Mullard! Game on!!
You're well on your way to a successful project, OAR :)
This circuit looks really fascinating. I want to hear how this sounds before picking my next build now… can’t wait to hear the finished product!
I too am curious about the outcome, VS. Will the output power, tremolo, and reverb all be worth the time, trouble, and expense? We'll see.
@@UncleDoug😮😮
Neither can I, VS. Thanks !!
Amazing as usual Doug . I'd love to make this amp just can't afford it right now , but one day soon it's going to happen. Thankyou so much for the inspiration Mark
Thanks, Mark :)
Hi Uncle Doug.❤from 🇬🇧
Greetings, Peter, from the desert Southwest, USA :)
The very last scene of this video is my favorite. I love a pile of parts spread out on a table and a plan inside one's mind coming together. Question: what's the key fob for? Is this amp going to have an alarm? Good idea - keep all the wonderful tone safe and secure. Eagerly awaiting part 2. Thank you, UD!
You have a sharp eye, TP. I ended up looking everywhere for that buried fob when I had to go to the Circle K for my 44 oz. Polar Pop.
I know. 1 last question. Where did you get the dials? Sweet work. Sir. Thank you again kind sir🌹❤️
They come from Antique Electronic Supply......in their knob section.
Please Doug wait until you get the cabinet to measure it before cutting your steel to ensure it fits ok. :)
Too late, Rob......but it fit just fine :)
Very interesting!
I might build a variant using european tubes :)
Good luck, BS.
@@UncleDoug ordered all the tubes :)
I heard it helps youtube channels if we comment so, great job and thanks for all the years of teaching and sharing!
It helps me when I hear from viewers, Steve. Thanks to you too.
Unbeliveable work, as always! That chassis will be a survivor after nuclear Armageddon! Have you ever considered using compactrons like the 6AV11 (triple triode) or maybe 6AF11 (which could be a whole amp in one tube)?
Thanks, Sterling. I hate to design or build a circuit around tubes that are virtually impossible to get. That was part of the problem with this circuit.
Rummaged thru the crates, I found a whole sleeve of NOS 6GM8s, and that was it dang it! So close, lolol!!
Close.....but no BM. Wow, that doesn't sound good ;)
I love a scratch build series and that's a cool circuit design. I'm a hop, skip and a jump from where the Gibson factory was in Kalamazoo but I've never owned anything Gibson. I don't know if you've pre-shot this series and it's all done but using heat to "blue" that steel to a straw color and clear coat it would be pretty unique. I built the mojotone champ kit several years ago and the cabinet was very nice. I had an issue with the speaker it included and customer service was excellent.
I thought about clear-coating the blued steel, JV, but on this build will probably go with a colored lacquer finish. The Mojotone cabinet arrived today and is spectacularly nice. I am quite pleased.
Is there any functional problem with cutting my own pine and just staining it instead of tolex or tweed?... Is the Tweed doing anything for tone?
No, in fact it may be reducing the resonance of the cabinet. Bare pine would probably be the best of all "finishes".
Awhile back I built an amp and cabinet per your videos. Lots of fun. A tip for those of us who don’t weld: the chassis ends can be filled with 1/4” to 1/2” hardwood blocks epoxied in. Works fine.
Find a small local fab shop or laser cutting place with a TIG welder, us welders are very food motivated, like labradors. Take some chocolates in and those corners will be welded up in 5 minutes.
That's a trick that Valco used a lot, Sax, but they used screws instead of epoxy.
@@Jonathan_Doe_ Chocolate......or 44 oz. Polar Pops work for me :)
Hey! You liked a video before you watched it!?
Yeah, it's Uncle Doug. Guaranteed to be good.
Thanks, MRM :)
Great Channel !
Thanks, ND :)
Hi, Uncle Dough. I think there is an error in your explanation of the schematic.
18:55 The amplified signal from the reverb tank is not mixed to the wet signal via the two plate resistors of the 12ax7, because they are both connected to the +230V rail.
Greetings from Germany, Wolfgang
I missed the tiny dot showing connection to the rail, Wolfgang. The wet signal is instead fed into the grid of the upper 6EU7 triode along with the dry signal from the 6AN8 triode. Thanks !!
It's really because that sub-rail is decoupled to ground via the 10uF in the middle of the schematic. Curiously there is no further decoupling for V1. I suggest you add that. 10k+10uF between the 22k and the 470k plate resistor would be enough. It will help with stability as well as hum.
@@EJP286CRSKWThanks for your helpful input. I was concerned about inadequate filtration with only 20, 10, 10uf......but the addition of another node resistor and 10uf cap would definitely make sense.
I used some colour change LEDs in a fuzz box once, looked cool but they were noisy - there seems to be a tiny chip in the LED which ramps the individual red, green and blue LED sections up and down in brightness and - no doubt due to the high gain of the fuzz - was audible on the signal. I managed to reduce it by adding significant decoupling caps on the LED power but it was less than ideal. Of course, a vintage amp is very different to a fuzz box so chances are you will be fine with those LED indicators but thought it was worth sharing my experiences.
Thanks for the input. The fellow I got them from warned about possible noise. We'll see :)
Great video! I’ve built several old Gibson amps that use a 6EU7 in the first position/amplification stage. And even though the 6EU7 and 12AX7 have similar electrical characteristics, they do sound different. I used a 6EU7 to 12AX7 converter A/B test this and the 6EU7 tube gain is much smoother, warmer, and more natural sounding than most 12AX7’s I tested. Now this model Gibson uses the 6EU7 in position 2 so it probably won’t make nearly as much of an audible difference here which tube is used. But to my ears, the audible difference between the two is definitely notable in V1. And I liked the 6EU7 much better in the Gibson circuit than the 12AX7 in the same circuit. It’s unfortunate that 6EU7’s are very hard to find now a days and can be expensive if you do find them. Just thought I’d share my experiences with the 6EU7.
Thanks for sharing, DCA :)
I followed your directions for scratch building a cabinet once and that was the last time I will ever do that. Just take the glue, after about 5 minutes slathering all over the cabinet and tolex I was hallucinating and drooling and my long dead grandfather came pedaling in on a unicycle wearing a tutu and singing Deutschland Uber Alles. No thanks, nobody needs that, I'm with you, shell out the $350 for a pre built one.
Agreed, M7, especially with the discount......only $315 !! Regards to your grandfather ;)
Wow! , I've been looking for a single ended tremelo/ reverb schematic . I'm glad you showed this, this looks like a really cool project, can't wait to see it finished.
Nor can I, Daryl. The wiring is proving to be quite a challenge within the rather claustrophobic chassis. Thanks !!
During the pandemic I came across this awesome channel. How transformers works.. vacuum tubes.. etc
The way I was able to understand it was unreal. You are so good at teaching that made me fall in love with this world. I’m starting an electrical engineering degree at 28 😂 😂 Better late than never!!
Thanks for your work and effort. It really inspires other people.
Greetings from Andalucia!!
Wow!! That's great news, Alva. Thanks so much.....and best wishes for success with your continuing education.
6F3P russians will do for 6BM8's, look for NOS Svetlana gold pins. Should be able to still get a pair for about $20.
Which primary winding are you using on the output transformer Doug, 5K or 7K (or is it 8K? Faded on the specs...)
There's a 5K/7K eBone trafo with 16/8/4 ohm secondaries for about $40, search for OT10SE. 3 different ones, 2 bell end mounts and an open coil for $1 less.
Thanks for the input, OaR. As will be discussed in Part 2, I used the 5K winding., not the 8K.
Such a pleasure to see a new Uncle Doug series. I re-did a silver face Bassman 50 a few years ago with Uncle Doug's tutelage - all the way from from 'tube amp basics' to actual Bassman 50 vids. I had MojoTone install a couple of 12" speakers (I don't recall the specifics - but one was supposed to be a bit Les Paul-ish and the other was supposed to be a bit Strat-ish) into a Bassman-like cabinet. All I can say is that the amp/speaker combo sounds amazing with anything from a Tele to a Les Paul. Thanks so much, Uncle Doug!
We're glad you're enjoying the video, Michael. Perhaps you had a ceramic speaker and an alnico speaker ?
Wow this is going to be good! I have a Gibson Kalamazoo Reverb 12. It's circuit is very similar except it's double ended and uses 12ax7s and 6BQ5s, Terrible hum! Good Luck!
Thanks, OMG. I hope you're right :)
Your chassis hand tooling is exemplary and impressive ,😇👍
looking forward patiently to the next exciting instalments ...
thanks so much uncle doug, creating an oasis of sanity in this
batshit crazy world😎😊
Thanks so much, MT. It's good therapy for me too.
Hello Uncle Doug. Great video(s) as usual. I also noticed that there has never been a reported physical sighting of this amp, either on youtube or any of the auction sites. Just the GA-1RT. I want to try to build one also(I'll be anxiously awaiting the next 2 videos). I don't know if I'll be able to get a 2MEG potentiometer where I live but I think I have an alternatie: instead of the pot I'll use a 2 MEG fixed resistor and I'll put a 1Meg pot instead of the 1MEG fixed resistor in the reverb return line. Does that sound workable?
Greetings and thanks :) No, a fixed resistor and pot in series won't function as you expect it to. No matter how low you turn the pot resistance, the line resistance cannot go below 1 Meg. Check with Weber.....they are purported to have 2 Meg pots.
Look forward to this build Uncle Doug with its suspense and drama! After this build why not make a push pull amp using an ECL800 (triode and dual pentode) valve. Hagstrom made a guitar amp using this valve in the output stage. You'd lose tremolo but you'd have a preamp, reverb, phase inverter and push pull output still with three valves! Love the proposed speaker by the way.
Thanks for the suggestion, AG. I'll keep it in mind for the future :)
How about the holes with garments for the power supply filter caps wiring to enter and exit the chassis?
They will be covered in Part 2, Joe.
Unfortunately if the trem osc signal is fed to the g1 of a SE output tube, audible thumping will probably be a problem if the OT is good enough to pass through low frequencies well enough. The best solution would be to use push-pull output stage if the tremolo effect is achieved by modulating output tube bias. Even in the case of a push-pull output stage, thumping can be a problem if PI circuit loads trem signal assymmetrically, as for example cathodyne PI does.
Thanks for your input, J. If the tremolo input to the 6BM8 grid is noisy, perhaps I could change it to the cathode of the 6EU7 upper triode, as in the fender Vibro-Champ.
New "Let's make..." video - new tips and secrets from our dear Uncle Doug. What a nice day!
I hope you enjoy it. Thanks !!
I'm very interested in how this might sound with a harmonica. I've been looking for a compact harp amp that will fit in an Atwater-Kent pedestal speaker frame from the 1920's.
I don't have any harmonicas for testing purposes, LG. Sorry. Perhaps you could build one and test it yourself.
Uncle Doug has vintage 60yr old 12in Jensen speakers stashed... I have a piece of chocolate cake stashed.😢 life aint fair, kids got it.
I would trade you, but since the cake is gone......I guess not ;)
I finally got a break from honey-do's and was able to watch this. Fantastic content as always. Your attention to detail is a mark of a true artisan and an inspiration to us in the next generation..
My only concern was with the multi-colored LED. Some of these devices operate off a PWM, which uses an oscillator and a counter to regulate how much red, green, and blue LED is used for each color. Depending on the oscillator's frequency and the refresh period, it could be a noise source for the audio signal. I thought a flicker bulb would be a cool pilot light for a build a couple years ago, but it inserted too much digital noise into the circuit. Of course anything can be filtered or shielded if one is determined enough.
I appreciate the helpful input, NN, and will heed your warning. It's such a neat effect I hope it causes no noise. We'll see.
I like those indicator plates where did you find those? Once my transformers get here I will be starting my 30w bass amp and cabinet. I'll have to share it with you once I finish. Just waiting on edcor.
I like the simplicity of this, but my fear of the triode/pentode combo tubes is microphonics.
See the parts list, Aaron. We'll see if there are any issues. The Hammond AO-44 seems to do quite well with triode/pentode tubes.
Uncle Doug-enjoying this video. I may pursue it myself. I was watching the chassis layout section of the video and missed where you are going to put the fuse socket holder. I assume it will be accessible outside, but just wanted to clarify it’s location. Best.
It's on the bottom of the chassis, next to the rectifier :)
Please do a plaid chassis!
The chassis is metallic gold, Jeff, but plaid is a good suggestion ;)
Thanks UD! My fave TH-camr! Great to see you, or rather, hear you. Hope you are well. 👍🏻
Never better, PS. I hope you enjoy it :)
Nice 2 meg hack! I’ve got a falcon with a problematic 2 meg audio taper pot. Problem solved!
The combination of two 1 Meg pots can create a 2 Meg variable resistor (2 terminals), but unfortunately cannot duplicate a potentiometer with 3 terminals......at least as far as my experimentation can determine.
I can't reply to your replies ... makes me worry about TH-cam,
anyway,
it's an elegant design, a good choice for it, and it will be neat to see it come together.
Thanks so much, Rulgert.
Thanks for not gutting a vintage radio to use its cabinet as a case for this project (it happens). You idea is much better suited for your overall design than that would have been...
Looking forward to the next installment!
I am not a fan of gutting nice old radio cabinets, Joseph. Thanks for your nice comments.
this is fantastic. glad you are dealing again with gibson amps. question: when you say the reverb is long do you mean the length of the springs or the decay. i changed a reverb pan to one of shorter decay and liked it much better. of course, that is subjective. thanks!!! p.s. interesting choice of 4 ohm!
The tank itself is 17" long, Michael. I had the speaker....it just happened to be 4 Ohm.
Hey. Got. A 6BM8s. And some scarier 6gw8 or so. Out of Hammond organs. ❤️🎶
We'll see if the 6BM8 makes a good dual purpose amp tube, 300......stay tuned :)
nice I might try and build that 😎💚💙👍👍🍺🍺🍻
Please do, Walter, and let us know how it turns out :)
Glad to see you are still going strong...I recently watched a video of a gentleman adjusting the bias on a valve amp that had a screwdriver adjusting control. The thing is he said he would turn up the adjuster and turned it to the left.. I found this odd ,,would turning it down not be to the left and up to the right ? regards for any reply.
Thanks, Mr. A. It all depends on how the bias pot was wired. Left could be up......or down in resistance.
Uncle Doug, you're an inspiration. I have an old solid state amp chassis that I may try turning into a tube amp.... or it may wind up at the firing range holing a target!
Thanks, David. Few if any parts from SS amps are adaptable to tube circuitry. The target range may be the best bet ;)
Doug, have you ever heard this amp before? Not great……but it should be a cool build.
I don't believe anyone has ever heard an amp with this circuit, Pete. It is completely different from the GA-1RT, and may never have been sold by Gibson.
I had a shipment of amp parts take a three week trip all over the western U.S. that went USPS Ground advantage. Never again.
Agreed, Brian. Requesting USPS Ground Advantage is tantamount to saying that you're willing to wait weeks or months for the parts being ordered. It is the Titanic of shipping methods......the worst !!!