Let's Build the Gibson GA1-RVT.....A 3-Tube Amp with Reverb & Tremolo, Part 1 of 4
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- Опубліковано 7 жов 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.
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.
All is right with the world...an new video from "Uncle Doug"!
Thanks so much, ID :)
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
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 !!
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.
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.
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 :)
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.
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 :)
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 :)
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 ??
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.
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 !!
New "Let's make..." video - new tips and secrets from our dear Uncle Doug. What a nice day!
I hope you enjoy it. Thanks !!
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 :)
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.
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 ;)
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 :)
Thanks UD! My fave UA-camr! Great to see you, or rather, hear you. Hope you are well. 👍🏻
Never better, PS. I hope you enjoy it :)
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 :)
Finally I've arrived at more recent episodes... Uncle Doug is the man!
We're glad you're enjoying our videos, Capt.
Nothing better than a UD scratch build series.
I hope it lives up to your expectations, Tommy :)
Great to see a new video!
Glad to hear it, Magnus :)
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 !!
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 :)
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 :)
Hello Uncle Doug. Thank you so much for this new series on a fascinating circuit. I pray you, the wife, an the kittys are all very well. There is not, or will there ever be a channel that comes close to what you put out for us.
Thanks so much for your kind words and wishes, SC. We really appreciate them :)
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.
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.
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 :)
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 :)
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 :)
Admire Uncle Doug’s work and was very excited to find this today
Thanks, AQ. I hope it exceeds your expectations :)
That is awesome that you built your own break to make your own chassis. Your work is inspiring. Great job! I am really looking forward to the series to see how this amp works out.
Thanks, EWR. I too am wondering how it's going to sound. Fingers crossed that it sounds great ;)
Thanks so much for the new video. Your teaching style dovetails nicely with my learning style. I know basic electronics and you make it easy to understand these amplifiers. I have learned a tremendous amount watching you and thank you for including a parts list on this one and plans in the future.
You're very welcome, Michael :)
Another great video series from our beloved Uncle Doug like the robot amp built - so gorgeous and I can't wait for part two and three. Many greetings from Germany Chris
Thanks so much, Chris. We hope to live up to your expectations.
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.
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 !!
A great little amp this will be. Hello Uncle Doug !
I hope so, Tim. Thanks !!
@@UncleDoug A 12" speaker is a good choice for this one...And having the pre-made cabinet all ready to load is worth it X 2..
Cheers !
@@timbuckxxi9690 I thought so too, Tim. The Mojotone cabinet is magnificent.....at twice the price :)
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 :)
glad to see you on air! always informative video!
Thanks, William :)
Nice one. Looking forward to this.
I hope you enjoy it, Andy.
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 ;)
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 :)
Great to see you again, Uncle Doug! I've been wondering if such an animal existed, and if not why not, and out of the blue you show up with a build video for one. I'm excited to see and hear the final result.
Hope all is well.
It's always a pleasure to hear from you, Randy. We're doing quite well indeed. You too, I hope.
Thanks UD. Looking forward to part 2.
It’s nice seing you again ;)
Part 2 will be posted in early May, Aden. Thanks !!
Ya I sidestepped the 6C10 compactron at 100 bones and up! with a couple more readily available tubes 12ax7, 12au7, 12at7's also gives you opportunity to roll tubes for optimum tone works in Super Twin Reverb, six reverb, Champ, Ampeg Jet. I tune in for the chalk talk and the rods appreciate ya always a stellar production. Always "Diggin Doug".
Thanks for your nice comments, A. We're glad you enjoy our videos.
Uncle D - love this type of content! Resurrection of old amps! Hope all's well.
Glad to hear it, TAG :) Never better.
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 :)
Glad to see you Doug! Thankyou as always for the continued sharing of your immense wisdom :)
It's our pleasure, Milo :)
Always great to see a new Uncle Doug vid. Thanks for your knowledge and lessons.
Thanks !! It's our pleasure, Rick :)
I've built two mojotone amplifier kits (Tweed Vibrolux, Marshall 18W) and agree with you on their cabinets...worth every penny.
Thanks for the positive input, CHM. It was even better than I hoped.
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.
Nice to see you give old Gibson amps some love. Folks might be surprised to know which of their favorite albums this amp was used on. I heard Jack saying the same thing in the start of the video ;-)
We hope you enjoy the series, Charlie :)
Those mojotone cabs are amazing quality. Especially the lacquered tweed. I believe mojotone has the contract to build cabs for some major amp builders.
It arrived and exceeded all expectations.......beautiful !!
They build some Gibson amps
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.
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 :)
Wow! What a great looking project! You have amazing talent. I love buying from Antique Electronic Supply. I've bought from them for 30+ years without any issues and they are about the cheapest around, especially for the price. Those tapered drill bits are a MUST for thin metal! (unless you LIKE stitches). I'm looking forward to hearing it play. Take care.
Thanks, W1. Let's hope it sounds even better than we expect ;)
i love these!
We're glad, K :)
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 :)
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 :)
Great to see another build series coming up!
We hope you enjoy it, Matt.
Wow! A new UDoug vid just minutes ago! So happy to see you back on my UA-cam channel
Thanks, Rich. It's good to be back :)
Still without an equal the coolest dude on UA-cam bar none.
Wow....You are too kind, Tony. Thanks !!
I can hear someone in the future calling that chassis a gem !
Great work UD
Stewart 👍🏴
I sure hope so, Stewart. Thanks !!
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.
Wow Doug...Just a fab project..Love it and all the info is incredible to this newbie here..Looking forward to the next videos...Take care..Ed..UK..😄
Thanks, Ed. It's always good to hear from you :)
A great video once again, Uncle Doug! Let's hope your neighbours get well soon!
Thanks, Hal......I'm sure they agree :)
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 😂😂
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 :)
This is gonna be a hoot!!
I hope so, C09. Thanks !!
Can hardly wait for part 2 ... Thx
It's in the works, Eddy.
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.
Great start to another project Doug. Looking forward to part 2
Thanks, Ex :)
Great project! I started building one of these a while back using a 6U8a for the input pentode and reverb driver. Can't wait to see how this goes!
6EA8 and 6GH8 are the other tubes that are similar to a 6U8 and conceptually similar to the 7199. There is also a 6AN8 but like the 7199 those are pretty uncommon nowadays. I have to wonder if owners of vintage Dynaco hi fi amplifiers snagged up all the 7199 and 6AN8 tubes.
I considered using a 6U8, Martin, but was able to find a really nice 6AN8 at a reasonable price.
you're the man, Uncle Doug
Thanks, TM :)
Uncle Doug thanks for the upload ❤️🇺🇸
You're welcome, Rusty :)
Doug; I have one of these amps if you need photos. The tank was dead when I got it so we put in a long tank.
Are you SURE that you have a GA-1RVT......and not a GA-1RT? I have never seen or heard of an RVT actually existing, but the RT model is relatively common.
Can’t wait for parts 2&3 Uncle Doug
Part 2 is almost finished, Blair :)
Best YT channel ever, thanks uncle.
Wow.....Thanks so much, HV :)
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).
Great to see another educational and informative video! That metal work appears to very tough on your hands with several wounds appearing.
Thanks, Harvey. The wounds are all fake......to stimulate pity contributions ;)
Fun new project, looking forward to more.
Thanks, Andrew :)
Great new video thanks uncle Doug, I really learn a lot and enjoy them
Thanks, K. We hope you enjoy it :)
Uncleeeee.
Another great project as always.
Nice to see you!
Thanks, ITR :)
Uncle Doug is a true jewel 💎
Thanks, Mr P. You are too kind.
Excited to hear this one.
Me too, TM. Thanks !!
The tube never tells me about your videos anymore? I guess they wanna decide what we watch. Glad I check on my own!!!
It's a conspiracy, Ben ;) Possibly because we don't monetize our videos.
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 :)
I think you are the Bod Ross of amp techs.
Thanks, T78 🙂
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 :)
A "festivus miracle"! 😂 Shipping is chaos these days...thankfully you got the goods
Indeed. I have noticed a huge decline in shipping efficiency lately. I guess the world's madness has rubbed off on the transportation industry.
Uncle Doug I missed this one❤❤
We're glad you found it, Charles :)
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.
UD this is epic! Can't thank you enough!
We hope you enjoy it, James.
Still fun Doug. Thx.
I hope the audio testing is fun also ;)
Antique Electronics suggests a 6U8A as a replacement for the 7199. They provide instructions for moving 3 wires on the socket.
I did the 6U8A/7199 swap in a mid 60's Ampeg Gemini 1, which uses it for the phase inverter. Works great!
The 6U8 is indeed another good choice to replace the rare and expensive 7199, Dan.