Hey Terry - I know this is an old thread and I can't believe I haven't seen this one before but, an excellent presentation of how to start on an old amp. I am always impressed by your analytical methods and simple proding around to find issues. You keep it concise. Myself and I am sure many others have benefited from your experience and abilities. Best of the season man.

Terry your power transformer test is exactly backwards of how you should do it. Unhook the rectifier (if its a tube, pull the 5U4, 5AR4, 5Y3, 80, 6X5 or whatever it is) or the solid state bridge rectifier. LEAVE the tubes in and power it up. Leave it running for 10-15 mins... the xfmr should stay room temp. The filaments will be lit, but the HV will be unhooked from the "B+" network. This is the ONLY reliable way to check a transformer ! While testing , you can run the tubes thru your tester (being pre-heated they warm up faster) and that keeps you near the unit so you can listen for any popping or sizzling sounds from the xfmr too.

Man can I relate to your frustration with Gibson White Face Amps! I have spent way too many hours trying to get anything decent out of a GA-RVT 15 Explorer. What a mess! Thanks for taking on the task. When you complete your "re-design" of their tone stack, please make a detailed video with lots of camera time on cap/resistor values and where they are wired on the pots.

@d-labelectronics

7 жыл бұрын

Hello, The re-design is close to completion. I have been making a video, lots involved. Will post it soon. TD

I can not wait to see you rebuild it, the right way... thumbs up as always. Happy New Year Buddy.

I've noticed that old Gibsons don't have the value as some of the other brands. Maybe this is why! Can't wait to see ya make it right. Got faith in ya!☺

It's nice to see you also struggle sometimes . Thank you for all the interesting and fun videos .

My first real guitar amp - so finicky and prone to loud squeals and other marlarkey. It weighed a ton as well. I did not shed a tear when I sold it!

Terry this is just the kind of video I've been praying for! I know of the tone sucking tone circuit that Gibson used. I been told they used it so Fender guitars would not sound good so you would be sold a Gibson guitar! Ha! You will make this amp the amp it should have been in the first place! I'm starting an amp build and any and all info on tone circuits and other amp mods that make an amp the best will greatly help me? The amps you have built have sounded so good. So thank you for sharing and Happy New Year! Thankz

Thanks for the Gibson Saturn video I really thought I was going crazy due to the pranksters who drew up the schematics and/or the actual assembly nothing makes sence values,layout,useless components.I sent an email yesterday with pics of the filter mods from Illinois state,but I sent those before I saw the part of the video that showed you already had them.Got channel one set to kill.Channel 2, ..........wish me luck,I have a Lancer,Minute man,and an explorer yet to be done.alot of these old amps(which I collect) have been molested.

Howdy Terry - first I love your vids - I've used tube amps for 45yrs not knowing how they worked. Now I do thanx to D-lab. Second now you know why Fender amps took off but Gibson amps never did. Guitarists knew they sucked. They sounded bad when new and tone is what it is all about. Lots of Gibson guitars at Woodstock etc but no Gibson amps 😂

Howdy Terry, rumor is these white panel Gibson amps were subject to substitution of component values on the factory floor as dictated by supply. I have only encountered one in my short time servicing amps but I ran into the same issue, burnt-out components and lack of documentation. Luckily I got it back up and running for the owner but it was luck. Looking forward to seeing your Frankenstein monster. :)

@faultlessguitarsandamps1116

7 жыл бұрын

I like your honesty there . Often a bit of luck is what gets a fault found .

Hi Terry! Gibson definitely laid an egg with this model as well as a few others. One gripe I've always had with them is, not many schematics do match the actual amplifier. It's an adventure every time you dig into one. The Twin-T circuit design is a loosing proposition since it robs you of gain and tone. So far, every Gibson from the mid to late 60's that cam in for repair has been an insane adventure. I'm really curious to see what you have planned in the next tube amp theater. :)

I worked on a similar Gibson model, ran into the same type of issues. It became gutted and wired into a cathode biased version of a super reverb and sounded fantastic afterwards.

I agree, I had a second or third hand chassis that resisted repair for years. I would take it out and play with it from time to time and then give up. Years later I eventually realized that it couldn't be wired like the SAMS photofac schematic so I stripped it and rewired and it worked!

Gibson changed amp schematics from year to year... or half year to half year... and never changed model numbers. I have a GA-5T. The schematic on Gibson's site isn't the one for my amp. I have the original schematic from it thank heavens. I actually like it so much, I want to build a variant of it with a few changes of my own.

Hey Terry, thanks again for the vid. It's gonna be a big reconstruction for this amplifier! How is it possible that the schedelbeen is so different? The amp is certainly in good hands! Have Fun with rebuilding it! Happy new year! Grz

Excellent video!

I think with the later Gibson amps their first priority was to design an amp that would sound better with humbucker pickups over single coils since fender didnt use humbuckers in their guitars. The problem is they tended not to sound great with any guitar.

Those Gibson amps were factory assembled by amatures. Paid by the hour at the lowest wage..what do you expect.? Unfortunately back when they were built, the price was the bottom line, not quality of construction. Then there was those stupid Sprague tone sucking networks..what where they thinking? They were so afraid not to make their amps sound like Fenders, they more or less went out of their way to make them sound different.,muddled. Jim Marshall OTOH, built their designs on Fender using the European tubes..and their own design tone stacks and their success story is history.

I've never seen an electronics repair channel that uses the main theme music from Caligula.

I really enjoy the videos and appreciate all the effort. This is just a little constructive suggestion. Most filter caps are not shorted or even leaky enough to fry a power transformer if you bring the amp up slowly as you have but also with a bulb limiter and current meter for good measure. Personally, I would never do that much work on an amp before I know if it basically will function after doing all the B+ and bias voltage testing as you have. If any of the filters were obviously leaking or shorted I'd then clip one end and tack in a temporary replacement & then fire up the amp before doing all that hard wiring replacing work I'd then bring up on variac while monitoring the output bias & then inject a signal to get a relative idea of the condition of the rest of the amp (as you have) eg: output transformer, other tubes, etc. When I was making a living doing this work my time was very valuable & I'd alway minimize the time necessary to do an estimate so that I wouldn't get to the point of having replaced all that stuff I could have just hung in for testing purposes... I Did that way too often when younger and it cost me $$$ especially when I was working for someone else on commission then in my own business just cost me valuable time which of course also translates into $$$. Maybe that's a suggestion after the horse left the barn, but there are other beggining techs that could benefit from that experience. Thanx for the great videos. The next generation of techs have a huge advantage with the internet as a source of what you used to would only get if you apprenticed with someone like yourself.

Your very talented in what you do man. Cant wait to see what you do with it.

I just bought the same amp a few days ago for $525 off craigslist. The seller handed me an invoice for service done this past February. All new caps were installed and I verified that by removing the chassis for a visual inspection. It does have all new caps. The board and everything else looks very clean and in great shape. All the tubes are 100%. Everything seems great. However, when I turn it up past 5 or so it starts to break up a little, not much, but enough to ruin the tone. This video gives me very little hope! LOL. I don't want to turn it into a Fender! It sounds fantastic at moderate volumes, and I don't gig anymore, I just play at home, so I may just leave it as is. I'm not sure if it needs replacement speakers or not. I'm not that savvy with amp repair. I hope that's all it it though. Incidentally, the '65 Saturn I bought used to belong to Phil Brown of Little Feat, and I know it's a fact because the seller bought it from him and showed me a picture of him and Phil standing next to the amp. There are certain marks and blemishes on the amp in the picture that match perfectly with my amp!!

All I can say id D-Lab gives up and walks away. It really has to be bad. Thanks for sharing Terry. Just had a power supply kick my butt due to someone installing wrong components, but all fixed now.

Oct 1975 my very first combo amp was a Gibson. two weeks later my very first amp head was a Blackface Bassman. The Jazzers were using Ampegs.

These can be really challenging I have fixed a few over the last 40 years. Here's the inside secret there are 3 versions of this model! First production with all the filter circuits and more complex. Mid production the power amp section changed some and other changes to reduce parts. Final production is what you came across with very circuits on the preamp and power amp and less parts overall and much louder and more gain.

Hard to fix one if you have the wrong schematic. It is always a good idea to do a quick "sanity check" if the documentation does not seem to be lining up with the device.

I admire your honesty.

awesome....cant wait to see the next video

I had one 25 years ago. Two 10 inch CTS speakers and it worked fine. I did one tube mod to it.

Interesting,,, looking for the next part on this.

I have same thing on a REL sub. No schematic at all. You can even to go to the parts! very difficult to repair and service unfriendly, better yet, NOT to repair. Had to demolish a lot. Then those SMD parts. I think I have replaced 3 ic's in 3 fold, and no sound yet. Decided to throw in the towel. Normal in factory they replace the whole pcb.

Oh nice, we get a 2 for one out of this amp!

I had a Saturn 45 - VT years ago first tube amp.

Really excited to see what comes of the amp :D Terry what would you recommend for someone who wanted to start building/designing amps? Math courses, physics? Just trying to get pointed in the right direction. I do have the book 'Design and Construction of Tube Guitar Amps' by Robert Megantz, which is very good, I'm just getting hung up on the math once you hit equations with Resistive dividers and I/O impedance. Sorry for the long comment, and thank you for all the effort you put into your videos and this community! Take care.

According to the schematic the bass pot has connections to all three terminals of the pot but when you showed the pot, there were only two connections and the end was unconnected.

your awesome !!! i love your logic!!!

i have a Saturn and hope to see what you do ........ I Want to rebuild mine as everyone seems to hate them

Part 2, The Fender effect has been posted kzread.info/dash/bejne/h4WizLt9hMXIZMo.html

Awesome Video Terry ...Gibson snobs ..lol

Worked on a dead Gibson GA-30 RVT got the first channel working flawless 2nd all a got was a loud hum. I gave up

Mine works great and has worked great for over 2 0 years. Effects are beautiful.. Wonder what the deal is with this one ?

Terry in the case of the first major cap you removed, it was a dual 20 500. what did you replace it with? not sure how to work that one out. Thanks

heheh...Had to laugh watching this. :D Gibsons take a LOT of patience.

@d-labelectronics

7 жыл бұрын

Yep, it just burned up lots of bench time

Hi Terry,watched the Gibson GA 45 RVT many times,and was very frustrated with the irregularities with the schematics and reality.I want to get an AB 763 board as you suggested.Can I get the part or reference number,so I can get the same board you used from Watts? Thanks.

YAYYY! "PIGARAMUS!" (3:10)

What value & wattage resistor did you use to discharge the caps. Great video!!!

@bucyruserie1211

7 жыл бұрын

Uncle Doug has a video on how to make one. I used an old scratch awl or center punch with a wood handle, a 5 watt 100 ohm resistor soldered to it, a piece of wire with an alligator clip soldered to the other end of resistor. I wrapped the resistor and wire with electrical tape. Put the clip to the chassi or ground, then touch the tip of tool to the positive side of cap for 10 sec. That should be enough time to discharge. Do it to all of them. Obviously do not touch the metal portion of tool, or the chassi when discharging them. Take care, Tom

@Finom1

7 жыл бұрын

Thank you, my family always looks forward to your videos. We are very excited to see the new improved version of this unique amp!!! Well done.

Just curious: Are you (ex) military? I don't hear too many people other than those in uniform use the term "INOP" :) Cheers!

@d-labelectronics

7 жыл бұрын

Yes Sir, 12 yrs USAF

@garymadore5674

7 жыл бұрын

Pleased to meet you, Sir. 34 years active RCAF service here (35 complete as of May 20th)... Flying a desk in our version of the Pentagon these days. Time to retire: I'm nealy INOP myself ;)

@kujawat

7 жыл бұрын

anyone in aviation will use INOP as well..

@garymadore5674

7 жыл бұрын

We tend to use N/S or U/S up here but, yeah, now that I think about it, I've seen "INOP" in civil aviation (e.g. flags on U/S instruments)

Get those old Cigar butts Out a there!!

r u guys still selling fender amps?

@d-labelectronics

7 жыл бұрын

Hello Greg, I only sell used amps and newly build Boutique type. Is there a certain Fender model your seeking?

Gibson is (was?) a guitar company that happened to make amps :)

Get those old cigar butts outathere.

typical gibson quality