The Problem & Unit's History:
I bought my 1991 Ampeg VL-502 in March 2020 from the second owner. Chuck told me the first owner was a shredder chick in her 50s that never took it out of the house. He gigged with it for a short while, then it stayed in his home studio. When I found it, it was in absolute perfect cosmetic condition. We demo'd it for thirty minutes, I gave him $400, and I drove two hours home. I played it for twenty minutes and began to notice a sublte volume issue, similar to a slow tremolo. I contacted Chuck, who sounded sincerely frustrated over the news.

VL Mods: My amp appears to have developed this volume fluctuation before April 2015, when Chuck had sent it to Lee Jackson (the amp's designer) to have the standard VL-502/VL-1002 mods done to it.
1) Remove the entirety of the large Molex connections between the main and power tube boards, and solder the eight leads directly to both boards. These Molex connections can melt. You only solder eight because one of the nine connections is a blank place holder.
2) Swap where the main/heater wires from the power transformer and the logo lamp wires plug into the boards. This will give you just barely enough length to reach the logo lamp socket. You might want to add some length to make this connection easier.
3) ...and then remove these quick disconnect terminal tabs on the power tube board and solder the two main/heater wires directly to that board. This is to ensure adequate current can flow to the tubes by preventing resistance at the terminal connections and scorching the wires. My lamp wires are still utilizing quick disconnects.
4) Remove R12 on the power tube board to bypass the hum balancer pot and relocate the previously-unused power transformer's center tap to an available ground tab on the logic board. This prevents tube shorts from damaging the power board.
5) Remove C11 and C12 on the logic board. This eliminates the annoying channel switching delay.
6) Remove two of the three logo bulbs. I think this is done to prevent drawing too much current away from the power tube heaters. This appears to have been done to mine, and although I've seen it talked about on forums, I've not read why it matters after the mains are hard wired.

Chuck said Lee then also cleaned and biased the amplifier before signing it, which he did upon Chuck's request. After a few sessions, Chuck swore the volume fluctuation was still present. It then seems the problem progressively worsened, becoming slightly more obvious and possibly occurring quicker as time went on. He contacted Lee in August 2016. Back then, Lee had never had one fail after the mods were completed. Lee suggested the problem could be in the Marshall-style impedance selector or a bad output transformer. Chuck put the repair on the backburner until May 2017, when he took it to a local repair shop. The techs failed to reproduce the issue in 2017 and 2018, running a radio signal through the amp during business hours. Tubes were replaced and they made a bias adjustment, but Chuck could still hear the intermittent problem, so he let it sit a year.

In 2019, Chuck fired the amp up and found that the volume issue seemed to have vanished! After a few months of occasional play without a hiccup, he listed it on Craigslist - I actually remember seeing it, but it disappeared. Someone had driven a few hours, demo'd it without an issue, returned home, and heard the problem. Embarrassed, Chuck refunded the money and put the amp back on his studio shelf. In 2020, he played it again and didn't notice the problem - the amp was starting to drive Chuck nuts. Confused, he put it back on Craigslist. I didn't let it get away this time. I spent almost one and half hours at his place demo'ing the amp and checking out his studio ...I never felt he was trying to pull a fast one on me.

When I told him about the volume issue, he was again embarrassed, but also frustrated. He offered to refund my money just so he could be the guy to toss the fucking thing in a dumpster. I really liked the amp ...and my girlfriend loved it, too. He shared all of his emails with Lee, the receipt from the tech shop, and any detail he could remember. COVID started to get crazy, so I didn't ask for a refund - I simply decided I was going to save it. I found the correct AFP-2 footswitch for $45.

I watched YouTube videos on tube amp repair for about a month and got a list of equipment I would need. I then started to focus almost entirely on bass playing, so the VL-502 took a backseat to everything else in my life. Every once in a while, I would fire it up, only to find the problem getting worse and happening quicker. It would start to fluctuate, or even fall flat on its face, after ten minutes of play. I decided it was too risky to keep playing it with the problem, and let it sit for a couple months. At the end of November 2020, I decided to clear out the gear I didn't use. This included two heads (the VL and a 1992 Peavey Ultra 120), plus fourteen effects pedals that I had bought in my two year quest to mimic Peter Steele's tone.

The VL went on Craigslist for $250 and Reverb for $270 in December 2020, local pickup only. I was very explicit in explaining the volume issue at the top of the ad. I continue to be shocked by people who want to buy something, but can't be bothered to read about condition. "Does it have any issues?" I also had several requests to ship it, but they apparently thought I would ship 50lbs+ of delicate electronics on my own dime. Fed up, I decided to finally open the amplifier up a week later to see if I could find a problem.

The Repair:
With the chassis flipped over on my table top, the output board's solder connections are the only ones visible, so I focused on that. This is also the board that gets the majority of mods. I immediately took note of Lee's solder job on the two relocated main/heater leads. There was way too much solder on them, the wire jackets were burnt into the joint, there was crust around the solder edge, and neither wire had a full-circumference joint. This didn't surprise me because I have watched Lee's VL mod video - he is kind of ham-fisted with this stuff. He may be an incredible engineer, but he is no craftsman.

Then I noticed two factory joints that appeared to be cold, like the wire was either dirty or didn't warm up enough. These were connected to each tube's #7 pin at the board. These are JW1 and JW2. I fixed those and took it back to the bedroom for testing. It failed in about five minutes, just like it had been. I decided to clean up the mains by removing a mountain of solder, scraping off the crud with my fingernail, and cutting the nasty ends off the wires. Exposing the ends, I noticed some very light corrosion disperse from the strands. That's not good! I clipped an additional inch off and they appeared to be better. I reattached the leads, and play-tested it with the pre and post gain maxed. Again, it failed before I hit five minutes.

Time to get serious. I removed the power transformer and cut all but three inches off of the mains. I had some yellow marine-grade 16AWG wire on hand, which was perfect. I soldered the new wire to the old wire, remounted the transformer, and resoldered the leads to the power tube board. Back to testing, this time with a TS9 to occasionally push the suspect circuit even harder. At least twenty minutes went by and I never noticed anything other than perfectly consistent volume output! The corrosion makes sense as to why the problem worsened as the years went on. Whether or not I got all of the bad wire out or not, remains to be heard. I may try to replace the entire run of wire from the transformer. Otherwise, Mercury Magnetics has replacements for these if it acts up again.

Pre Repairs and Post Repairs

Now, Lee mentions in his mod video that these main/heater wires are either green or yellow. Mine were green with a white stripe and it is an earlier unit. I was wondering if there was a manufacturing defect, and the update brought in transformers that have yellow wires? However, Lee had stated in 2016 that it could have been the output transformer and never said anything about the power transformer. I initially blamed the dirty wire jacket melting into the joints, but the issue predates the modifications.

If you have one, I have read a few forum posts by Voodoo Amps in NY. It sounds like they specialize in VL repair and they swear the amps are reliable once Lee's modifications are done. You might want to contact them if you're closer to them than Lee in Texas.

The VL and Stealth Series:
In 1986, SLM (formerly St Louis Music) acquired Ampeg after MTI had filed for bankruptcy. SLM were already known for starting Crate in 1978. They immediately set out to offer a new line of amplifiers to guitarists with the Ampeg branding. In 1987, the SS (Solid State) series was released. The company went headlong in 1991, upgrading the SS to the VH series and introducing the monstrous VL. They brought on Lee Jackson, already known for modding the Marshall JCM800, to build a head to melt everyone's face off: a JCM800 killer. According to Lee, Ampeg requested a few changes to his design to lower the costs, which he blames for some of the problems. Eventually, Lee graciously posted his repair video to YouTube on how to correct those shortcuts yourself. In any case, what came from the Ampeg-Lee endeavor was a shredder's dream. The amp is sick and nasty, in all the good ways ...and loud as all hell. Rumor has it that the VL stands for Very Loud.

Unfortunately, Ampeg was pigeon-holed as a bass company and the marketing failed. Even with Zakk Wylde and Paul Gilbert using them, shops had VLs sitting on shelves long after the guitar lines were discontinued. From my understanding, Russ Parrish (Satchel of Steel Panther) used a VL-502 for every song on Fight's 1992 album, War of Words. I guess I should also mention that Tom DeLonge used them on tour. No one cares? Moving on... The VL-501, VL-502, VL-1001, and VL-1002 heads were notoriously problematic, but supposedly didn't hold a candle to the nightmarish VL-503 combo. SLM and Lee also released a somewhat similar, but seemingly even more troubled (cheaper components), version of the VL under the Crate name. These were the Stealth GT-50 and GT-100. The guy I bought my VH-140C from had a Stealth 50 that was flawless and it was one of his all-time favorite amps - coincidently, it was also his girlfriend's favorite. I've read of a few people owning both, and the Stealth might be the slightly more-preferred model. The VLs and Stealths seem to have all but vanished, though. Is it because they've been tossed into dumpsters out of frustration, or because anyone who has one refuses to let the unicorn go? I wager it's both since once I fixed mine, I immediately could not bring myself to sell the infamous rarity ...but I ultimately did a month later since I was more into bass. When I first posted what is a Holy Grail to some collectors on Reverb, it had 100+ views within fifteen minutes. Players are obviously still looking for them. I sold it the second time around for $625 within ten days (January 2021).

Tube Options:
In his correspondence to Chuck in 2015, Lee explained the differences to expect when choosing output tubes. Though the amps were originally spec'd with GE 6550 tubes, Ampeg started shipping them with EL34s when GE ceased production of the 6550. At the time, Lee preferred the "British" sound of an EL34 over the "American" sound of a 6550 because the EL34s break up earlier. The owners manual states that the EL34s provide a more controllable and less penetrating distortion effect when overdriven. Lee told Chuck that the Svetlanas were his favorite 6550 tube, which the manual claims 6550s are more suited for heavy metal players. He went on to say that if playing the upper limits of the amp, the 6550s will produce more volume and dynamic headroom, but I've also read of users doing the swap with no notable difference in output. Lee said the 6L6 tubes also sound great, providing more low end than the EL34. The bias fine adjustment pot is located on the logic board, directly behind Channel 1's high frequency potentiometer.

Bias selector set at 6550: 6550, 6L6, KT88
Bias selector set at EL34: EL34, 6CA7, KT77

A common complaint among VL owners a weak clean channel, which many attribute to the EL34 tubes. I can attest that the clean channel on my VL-502 with EL34s is very lackluster. I have read owners saying the 6550 tubes produce a better bottom end, giving the amp a much improved clean channel along with a more modern type of distortion. Users describe the EL34 as producing a style of gain typical for the 1980s, being very mids-minded like a Marshall. I felt my EL34-loaded VL would sound much better to me when I cut the mids with an EQ pedal on both channels. I play metal, so purchased a pair of matched Svetlana 6550C tubes for $100 to try after the repair. After five minutes, I was pretty certain I preferred the 6550s for both channels, even though I'm not getting as much break up. I don't think I gained any volume, though the 6550s actually might have made the treble a little less harsh, allowing me to turn it up a bit before killing my ears. I have read a comment by Tim Stanley (appears to be a VL guru on YouTube) that mixing 12AX7 preamp tubes is the key to a livelier and thicker gain. He recommends a setup of long plate Mullards in V1, V2, V3, and V7. Then some Tung Sol reissues in V4, V5, and V6. He advises that generic Chinese tubes can make a VL sound dull and bland. He goes on to say that with his preamp tube combination, along with 6550s, it should give the amp the exact same sound as Zakk Wylde's Metaltronix on the No Rest For The Wicked album.

According to Lee's emails from 2016, a single pair of KT88 tubes are only useable in the 100watt heads. He says to use the outer sockets, due to their larger diameter. However, I ran across a picture on Reverb showing a pair from Groove Tubes installed in a VL-502. I then searched and found a few people that have managed this without mention of any issue. Looking at mine with 6550 tubes installed, there appears to be enough room between them. From my understanding, the KT88 tubes are more likely to require an adjustment to the internal bias pot.

Noise Gate Notes:
I doubt noise is only a problem with my amp due to the very high-gain nature of the circuits. It can get very noisy and overly feedback-prone, especially with the addition of the on-board reverb engaged. I tested an ISP Decimator G-String and a Boss NS-2. I know the ISP is a favorite among metal players and I don't like how the NS-2 seems to color the tone, but the NS-2 easily wins with this amp. I first placed these between the guitar and the input, and the maxed ISP still let a shocking amount of noise through. However, the NS-2 (Threshold: Max; Decay: Noon) was able to clamp the signal to total silence, yet still remain completely responsive to the entire signal. Placing the ISP in the VL's loop definitely helped the pedal get the job done. However, without a decay knob, the ISP would start clamping my weaker tails down too early due to the higher settings that it required to adequately gate the background noise.

Ampeg VL FAQ & Links:
Lee's answers to common problems can be found here.
Pics of the mod can be found here. Right-click "open image in new tab" to see the broken links.

CrankyGypsy (established 2001)