Repairing a 1964 Gibson Skylark GA 5T Tremolo Tube Amplifier

“Adopt a son,” was the tagline under the Instagram photo. A local music shop had a vintage Gibson amplifier listed for sale in remarkably good cosmetic shape — except for the logo.

1964 Gibson Crestline GA 5T Skylark Tremolo

I had a quick chat with Mary about the rising value of vintage instruments that veered into a promise to sell the large Line6 AX2-212 amplifier sitting in my study, and I was off to retrieve the Gibson.

The amplifier had the original speaker, the original leather handle, no tears in the tolex or cloth, and very minimal rust on the faceplate. Unfortunately, the amp didn’t play quite as good as it looked. We still brokered a deal, and I brought it home. That’s when I took the week long deep dive into vintage radio and amplifier repair.

Yes, we have gone way beyond banana bread.

The Death Cap

It wasn’t until 1969 that Underwriters Laboratories mandated three-prong plugs on appliances. Amplifiers from the 1950s and 1960s came with a two prong power cord, which could be plugged in either way. The lack of earth ground made those amplifiers susceptible to RF noise. To combat this, designers added a capacitor between the negative terminal of the power cable and the chassis ground of the amplifiers. It was well-known and accepted at the time that if a musician was touching the guitar strings and touched another reverse grounded object such as a microphone, he or she would receive a noticeable shock. The problem with having a capacitor coming from the cable to ground was that if it failed open, it would deliver the full 120 volts AC to the musician.

The “paper caps” and the “death cap” on the unmolested board.

While I wanted to keep the amplifier as original as possible, I decided removing the “death cap” and adding a three-prong power cable with ground to earth was the way to go. I also relocated the positive cable lead to run through the fuse before the switch for a little added protection of the amplifier internals.

Three strand power cable with earth ground installed.

120hz Hum

The most noticeable issue with the amplifier was a very loud hum coming through the speakers even with the volume turned to zero. A lower 60hz hum can be an indicator of poor shielding, but a 120hz hum is usually an indicator of bad filter capacitors.

From what I could tell, the amplifier internals had never been touched, so the circuit was sporting two paper-wrapped electrolytic capacitors — a Maximite and a Minimite. I didn’t have a way to test those capacitors, but it’s generally accepted that the lifespan for a paper-wrapped electrolytic capacitor is 6 – 10 years. Being 56 years old, it was a pretty solid bet that both of them needed to be replaced.

I replaced the Maximite with two modern 22mf 450volt capacitors, and the Minimite was swapped for one of the same. I flipped the amplifier back on, and the hum was gone.

A pair of 22mf 400Volt capacitors in place of the Maximite.

As a side note, if someone is selling you a tube amp and says, “It has a hum, but it still plays great,” walk away. You can’t play great battling that hum. You can’t record with that hum. You can’t perform with that hum. Also, it’s just a matter of time before the leaking capacitors fry the power transformer and cause more damage to the amplifier.

The Mysterious Disappearing Tremolo

This amplifier has a built-in tremolo circuit powered by the oscillations of a vacuum tube. When I purchased the amplifier, it wasn’t working at all. Later at home you could hear the oscillations in the 120hz hum, but it wasn’t evident in the actual guitar sound. Then I tapped on a few connections and spread some crowded wires apart, and the tremolo disappeared completely.

My online searches turned up conflicting diagrams, some indicating a 6EU7 tube and some indicating a 6C4. As I researched both, the 6C4 was noted for it’s oscillations, so I ordered one thinking I had the wrong tube. Turns out a 6C4 isn’t even the right size for the plug. I tried a new 6EU7, and the tremolo was back.

Matched Power Tubes

When I purchased the amplifier, the dates and makes of the tubes varied greatly. The schematic called for two 6AQ5 power tubes, but one was a much more recent 6005. Power tubes are supposed to be electrically matched, so that they have the same plate current and amplification characteristics. The performance of vacuum tubes can vary wildly, so matched tubes were allegedly manufactured at the same time and more rigorously tested to meet the same specifications. When I ordered replacements from Amplified Parts, they sent me a pair of matched new old stock 6AQ5 tubes that were manufactured together in France in 1963. It kind of blows my mind that there’s still parts for these amplifiers sitting in warehouses.

Does the amp sound better with the matched tubes? Maybe I’m just a auditory plebeian, but I can’t tell a difference.

With the three-strand cable, new filter capacitors and new tubes, the amp is playing well, and I imagine it should be able to handle another 50 years. However, if I get the chance to upgrade my testing equipment I’d like to take some measurement and see how far off the original values the other capacitors and various resistors have wandered.

I should also probably spend a little time working on my guitar skills, so they do justice to this amplifier.

Remote Working

I literally haven’t worn shoes in 187 days.

That was always the goal, right? A flip-flop lifestyle with cold suds, warm sun, and sandy beaches?

One out of three ain’t bad.

Until March, “remote worker” was sort of a mythical job description, held only by special computer programmers or gifted day traders. One of my previous roles as a social media manager was the closest I came to remote working, and in that role, I still needed to be in the office most days to host events or shoot photos and videos for the social posts. One day a week from home was a long way from wandering the world seeking adventure–jumping on wifi at foreign coffee houses to accomplish my daily tasks.

My first week at home I started writing a piece about how this pandemic was going to bring an unprecedented change to things like sports, movies and concerts, but it felt trite. I left it sitting in the drafts folder so long that now it seems naïve and irrelevant. (By the way, I had predicted it would all be over by July. I was definitely wrong about that.)

Aside from our trip to the hospital at the end of May to deliver the baby, we haven’t been anywhere or done much of anything.

Meet Michael Finley Facker, born May 31, 2020.

We spent five strange days in the hospital. Masks had to be worn at all times. The facility was a ghost town when we arrived. The halls were eerily empty. No visitors. No elective surgeries. However, that first big wave of Covid took hold in Houston while we were there, and by the time we left, there were people everywhere.

Since then it’s only been an occasional weekend trip to the marina, but we’ve been avoiding the pool and the pavilions as part of our social distancing. I don’t know how Covid will affect an infant, but I don’t want to find out.

He doesn’t seem to mind wearing a PFD, so that’s good news.

We had purchased concert tickets at Christmas for a show in April. In April the show was then pushed to August. In August it was canceled. The entire tour was tentatively rescheduled for next year, but I don’t know that next year will be any better.

I think that even if a viable vaccine is found by the end of this year, with all the logistics involved in manufacturing and distribution, it would probably roll out with the annual flu vaccine in September of 2021. Maybe after the election we’ll get some insight into more honest, realistic timelines.

We thought about spending a few weeks on the boat, but Mary’s big dual-monitor workstation has taken over the kitchen table. My large dual-monitor workstation has taken over the study. While her massive spreadsheets and my design work could be done on laptop screens, it would be tedious at best. The Kadey Krogen 38 doesn’t even have a nav station, so the one and only option on that boat to set up monitors would be at the one-way-in one-way-out foldout table — not ideal. Maybe as the weather cools and the cockpit becomes a viable place to work, we can spend a few days there, but between the speed of internet and hardware required, it turns out that our remote working still isn’t nomadic remote working.

There are definitely some advantages to working from home. The lack of commuting adds over an hour back into the day. We’ve cut at least 1,000 miles a month of driving. That’s only about 10 gallons of gas per week, and gas is cheap right now, but every little bit we can save helps.

For the most part work has continued as normal. I write articles, I build powerpoints, I update websites. Unfortunately, all of my photo and video work is completely gone. The added value I brought to the table with corporate portraits, executive videos, project documentaries, etc. is impossible to continue during our current circumstances. We’re running entirely on stock photos and self-shot smartphone or webcam video messages. And to be honest, I don’t think that work is coming back. Everyone has deemed iPhone pictures “good enough” and decided they can live without shallow depth of field, good lighting or high-fidelity audio.

The quality of audio/video in a Zoom or Teams call is now the acceptable business standard for the entire world. Craft your message with care because only the words matter now.

Before the baby was born, we couldn’t sleep at night due to the existential dread of the proliferating pandemic. Now we don’t sleep because the baby doesn’t sleep.

So here we are, sitting at home. Remote working. Hoping we stay employed to keep our healthcare. So far, so good. I hope everyone out there is doing ok.