Gibson GA 5T Skylark Amplifier Restoration P4 We Have a Major Short Circuit

Welcome back to another exciting episode where we tackle the restoration of a Gibson GA 5T Skylark Amplifier. In this part 4 of our series, we encounter a major short circuit that requires our immediate attention.
In this video, we get the amp ready for it's first power on in decades and find the short circuit. From the initial diagnosis to the final solution, we'll cover it all. This tutorial is ideal for those who have a keen interest in electronics, DIY hobbies, or anyone who wants to learn more about amplifier restoration.
Whether you're an expert in electronics or just starting out, this video will surely provide you with valuable knowledge. So, let's roll up our sleeves and restore this classic amplifier together!
*************************************************************************
Please help support this channel at NO COST TO YOU. If you shop on *Amazon, please use this link: amzn.to/3706t6c *
*I will get a small commission and it costs you nothing. *
*************************************************************************
HEY YOU ABOUT TO POST SOMETHING STUPID:
Yes, I know my hands are large/fat. It's because of a heart condition I suffer from called Congestive Heart Failure. Here's a link to some information about CHF: cle.clinic/2TdS2Ux
One of the symptoms is that it causes fluid retention, mostly in the hands, feet/ankles, and face..
-------------------------------------------------------------------------------------------------------------------
Support learnelectronics:
Amazon Store:
If you are shopping for electronic components, test gear or consumables please consider visiting my Amazon shop @ amazon.com/shop/learnelectronics
Patreon:
Please check out www.patreon.com/learnelectronics and pledge a dollar if you can. It will go a long way to keeping the channel alive. It costs a bit of money to buy all the items and produce these videos. Your help is appreciated.
Paypal:
Or....if you'd like to send a one-time donation you can use this link: paypal.me/learnelectronics
---------------------------------------------------------------------------------------------------------------------
Gear I use:
Multimeter: OWON B33+ amzn.to/3UkTJOo
Oscilloscope: KIPRIM DS1202 amzn.to/3gfJGMN
Signal generator: Junctek JDS8080 shorturl.at/ehTZ1
Component Tester: T7 Multifunction amzn.to/3AYY03v
Soldering Station: Sealody ???????

[@gaspumprepairservice7009]

Handy thing, that dim bulb tester. 👍

[@learnelectronics]

It sure is!

[@EnergyTRE]

wait so i dont have to use my toung to test anymore 🤯🤯😂 always Worth the watch. its looking great sir

[@tenlittleindians]

I just watched a video on the "Learn Electronics Repair" You Tube channel that covered capacitor markings in a three part series. Some capacitors such as those placed across the line power are designed to short when they fail while others are designed to fail open circuit. Gives me a whole new insight into why the old amplifier designers put those death capacitors into their designs. To substitute capacitors just got a whole lot more interesting now that I know there's a difference in how they fail.

[@learnelectronics]

You are talking about safety caps. Class X and Y. None of those here. This 1960s tech. They didn't have RFI testing to pass back then and just used whatever was available, and in the correct range. You see a lot of the blue molded caps and the yellow plastic caps. Those are just plain film caps used for the biasing of the tubes. The main filter caps, those coming off the b+ rail were old oil and paper caps. I replaced them with the JJ can cap. 4 separate electrolytic caps with a single ground.

[@tenlittleindians]

@@learnelectronics Yes, I am referring to X and Y caps. I'm specifically talking about the capacitor that's commonly being removed in KZbin amplifier repair videos and is nicknamed "the death capacitor". I thought this capacitor was across the line voltage coming into these amplifiers. I'll have to pay more attention in these repair videos to where it's at in these older circuits. I find it hard to believe all these old electrical engineers would put something in a circuit without a good reason. I've got a half dozen or more amplifiers around that I've let the magic smoke out of. These are all tube amplifiers from the 40's, 50's and 60's. My guess is they all probably had capacitors fail but I've never opened any of them up to look, I just moved on to another vintage amplifier as my daily driver. Currently using a early 60's Fender Princeton. These old amps have all died the same; the sound quits followed by a puff of smoke out of the amplifier and I quicky pull the power.

[@learnelectronics]

Looks like mine has a blown power transformer. Gonna be on hold until I can source a working one.

[@tenlittleindians]

@@learnelectronics That's about the worst news given the fact that most old amplifier transformers haven't been made in decades. Somewhere I seen an old radio restoration where he installed modern electronics into an old transformer housing to keep it looking original. It was one of those transformers with the metal can cases and he just gutted the old windings to make room for the tiny modern circuit board. I can't remember if it was just a DC to DC booster or a complete buck converter style power board. The bottom line is you do have options but it might be a hell of a rabbit hole you need to dive into before you come out the other end. Let's hope you get lucky and source a transformer.

[@learnelectronics]

We have a replacement on the way.

[@harryshector]

With the amount of corrosion evident in that chassis, I’m not surprised that the power switch is reluctant. It looks like it was ‘stored’ out in the woods, somewhere. Transformers are difficult to test with multimeters. You can get a pretty good idea of condition using a signal generator, or powering the primary with a low voltage source, such as a filament xformer, and measuring the outputs. The ever decreasing availability of incandescent lamps will make building dim-bulb fixtures more difficult. I’ve built up a small stockpile. They are fragile.

[@learnelectronics]

I wonder myself if it was submerged at one point.

[@mikemoran5439]

Hey Paul! Where did you find that can cap? It would be perfect for my old tube radio.

[@learnelectronics]

I buy all of my tube amp replacement components from Tubedepot tubedepot.com/?gclid=CjwKCAiApaarBhB7EiwAYiMwqnYZHESSbiUy6MW5E0zkeDlYkR6ZoDH4wXzXg589oC5hnGIWbkCL5BoCJw8QAvD_BwE

[@sethmarquez409]

Hi, what is the best pinter neptune 4 pro o ender 3 ve ke? (quality of print)

[@learnelectronics]

I don't have an answer yet...I will this week.

[@sokoloft3]

Wonder if some deoxit would make that switch come back. Heard it can actually damage whats left of the material inside. Dunno for sure tho

[@learnelectronics]

It had plenty of CRC Contact Cleaner. I may tear it apart and have a look inside.

[@bblod4896]

Yep, light bulb! Hopefully not the transformer, that may be difficult to source another one.

[@arielinoa9161]

Now I have to research how Dim bulb works.. and then buy one lol

[@mikehensley78]

make one.... you put the bulb in series on the HOT (black) AC Mains line... then run that to an outlet with the COMMON(white) wires ran through not broken. so you want the incandescant bulb in series. ---(blackwire)----*light*-----(outlet)----| |----------(white wire).

[@mikehensley78]

also... im sure google has a way better diagram/schematic than my ASCII art. lol!!! but yeah, dim bulb tester is super simple to make.

[@learnelectronics]

I just showed you how in yesterday's video...kzbin.info/www/bejne/faqoiIlsbdOqabs

[@EnergyTRE]

😂

[@mikehensley78]

@@learnelectronics LoL!!! i work alot...i didnt see yesterdays video. i am gonna watch it now.

[@robtitheridge9708]

RFI cap if there is one bridge rectifier mains transformer (hope not)

[@learnelectronics]

There's no bridge rectifier. It's half wave. My guess is the mains Xformr too. I say that because what you didn't see was me spending about an hour testing every component for shorts to ground. We will find out as soon as I get enough courage up to go on the hunt. I dont want to spend $170 on a new Xformr.

[@harryshector]

Seems odd to spend the money to provide a power xformer, then cheap out with half-wave rectification…

[@learnelectronics]

It was the 60's, what can you say.

[@robtitheridge9708]

Sorry to hear that .the worse possible outcome

[@learnelectronics]

Yep, it's shot!

[@paulperano9236]

You've already checked the primary. Don't remember if you checked the secondaries. Also the 'death cap' looks like the original - get that replaced.

[@learnelectronics]

The death cap will go. I found a short on the filiment heater leads. Fixed that. Now, no short, but only a volt or 2 out of the B+. I'll isolate the transformer next and go through it, but I think it's blown.

[@paulperano9236]

That's a real bummer. Amazon won't have one of them little buggers.

[@learnelectronics]

Transformer is shot. New one on the way.

[@SteveHacker]

Link to Part 4A: kzbin.info/www/bejne/qoSZmnt5eN2pq8ksi=nrSebqrij0q80PT2

[@bryanst.martin7134]

Sometimes Liquid electric tape is the best answer...

[@GIBKEL]

These are infamously poorly designed amps. I’m gonna watch to see what you can do with this train wreck. I’m rooting for you as then there might be some deals to be had.

[@learnelectronics]

Thanks