Rootbeer Audio

hi all,
a winter update >>> I closed up shop in October so that we could prepare for the arrival of a baby >>> well/well/well/well >>> about two months ago we welcomed a small human by the name of Oliver into our house & lives >>> happy to report that everyone (humans & critters alike) is/are healthy, happy, and staying warm ~ >>> with that being said…
R O O T B E E R A U D I O reopens this week for repairs, restorations, custom amps, kit builds, foot switches, cables, and so on and so on and so on >>> for more service & ordering info/procedures, take a look at the SERVICES section of the site (link in bio).
education >>> want to learn how to make a pedal or simple oscillator (bleep blip boop)? or about ohm’s Law, signal-flow, & why that microphone shocked you on stage? I’m currently accepting online & in-person lessons >>> more info in the EDU section on the site (LiNK in gOT dang BIO )))
in closing >>> due to some life changes, Rootbeer Audio is more of a full-time gig than it has been in the past >>> I had to restrict the work and projects I took on as I became busier throughout the past few years, but it’s a new dawn >>> have an idea? want me to fix all of your amps at your recording studio in the Catskills? want to host a pedal workshop at your office? want to build a 10,000 watt KT88 public address system? let’s talk.
>>> thanks for reading, Matt

This 1965 Fender Deluxe Reverb came into the shop for intermittent reverb and a general check-over before some recording sessions. While it was mostly original (or at least had almost entirely old American tubes), it already had new filter/cathode caps, and a reverb-on-both-channels mod. Aside from that, it hadn’t seen much work and had been toured heavily for a few years.
It received a new fresh set of Eurotubes 6V6’s (I reused the OG American ones for their other amp I will post soon) for longevity and reliability, new carbon comp plate resistors for most of the preamp (there were some frying bacon sounds), three new coupling caps (3 were leaking), and a few tube swaps. Sometimes an old tube still works relatively well, but it may be a bit too rattly/noisy for a V1 (first preamp tube) position, so I can swap it for say the tremolo oscillator, and repurpose the trem tube (also OG // American) for the V1. I did end up needing to replace the phase inverter and V4 with new 12ax7’s from Eurotubes.

The reverb issue was due to a bad pan (more specifically, the output transducer was intermittent), so it had to be replaced. While I have seen some different pans in these amps, this one had what I believe was a “1” which is short decay. I had a few in stock, but I purchased some options I didn’t already have (3-spring and 2-spring long, medium, and short decays). When the amp was ready for pickup, we compared the various pans and the “2” (2-spring medium decay) pan was the favorite. Enjoy the amp Kurt!

This Marshall handwired 18watt reissue (1974x) amp came in with a weird//troubling noise.
At first it sounded like a bad tube noise, but then started to sound/feel like a bad connection. Upon opening it up (and after some quick tests like swapping preamp tubes, etc) I noticed the first issue... one of the screws that holds the back plate on was either touching a resistor on the volume pot OR it had pushed it at some point and had made the solder joint intermittent. I resoldered it, patted myself on the back for finding it and moved on (see last photo).
But the sound was still there. I ended up spotting some cold solder joints (especially on the tube sockets), so I ended up resoldering the majority of the preamp. I thought I fixed it --- but the issue persisted. The issue seemed to be caused by mostly physical poking and prodding (which was sorta different than what the initial tests suggested). After using the scope I was able to determine the issue was right before the phase inverter. I tested every resistor, cap, and resoldered everything. Around this time I noticed the underboard connections were pretty suspect, so I ended up removing a few and resoldering them to the top of the turrets.
After all of this work, the issue sorta persisted. I say, "sorta", because it became apparent I was chasing two sounds --> one which was an intermittent connection, and another which was a bad power tube.
After a ton of investigating, resoldering, and tube swapping, I ended up replacing the two gold lion powertubes with trusty el84s and the amp was fine ever since. I also serviced it (cleaned/tightened everything) and installed a bracket to hold the attenuator in place.
The amp did have two compounding issues -- and while I initially thought power tubes could be at play (but at one time the volume control seemed to help the issue which would negate that), I never would have considered there could be two problems at once.
I'm reading zen & the art of motorcycle maintenance so I'm one step away from getting too big-picture//deep with this one and my assumptions, but most importantly, the amp lives again! Enjoy the amp Nick!

A 1964 or 1965 Vox AC-30 Super Twin (the Woden transformer code dates to 1964). After enduring a beating in transit, the amp’s transformers broke loose and smashed the tubes. I forget if the transformers were known to be faulty, or if that was a result of the shipping, but the choke and power transformer had to be replaced by Mercury. The owner performed all of the initial work and retubed it before bringing it in. It would have worked as is had he not received a faulty JJ GZ34 rectifier tube. After swapping the tube, we discussed long-term repairs/maintenance and got to work.

I replaced the original filter caps, cathode bypass caps, el84 bias resistor, dropping resistors, and power cable. I also replaced a few leaky coupling caps in the vibrato/tremolo channel and resoldered the grounds and many old cracked solder joints. After completing the service; tightening and cleaning everything (even scraping the scuzz off the chassis with a blade and patience), it fired up! The amp sounded great, but the tremolo and vibrato were still not functioning. After going through everything else involved, I realized the low-frequency-oscillator wasn’t oscillating. I replaced a few way-out-of-spec resistors, the usual suspect capacitors, and found the original pot had a few bad spots where it would go open. It still wouldn’t “fire up”. Slowly I had rebuilt the entire LFO (it sounds like a lot of parts, but it’s more the time testing and systematically replacing each one) and it still wouldn’t work. So I did my usual plea to the forum lords and hoped for something other than the rote, “try replacing a cap”. I stumbled onto the Aiken Amps tech articles and found a section that suggested, for dealing with pesky LFO’s, to try moving the resistor (the 2nd HPF resistor in the oscillator feedback loop) from ground to a small DC potential, such as the cathode bias voltage. A volt or two later and it worked! It works and sounds just like it should. If anyone is still reading and has any rationale for why the LFO wouldn’t oscillate, or has had a similar experience, I’m all ears.

The amp is in great shape (just needs a back plate!) and will sing for years to come. Enjoy the amp Erik!

A Fender Pro Jr. —-> this smaller counterpart to the blues jr came into the shop with its original tubes and some complaints of noise. Upon testing I noticed V1, the first preamp tube, was microphonic as hell, and the original power tubes were nearing the noisey//inconsistent stage of their life. Like many of the modern-ish fender combos, the line in the sand for any repair is whether you “drop”/dismount the PCB (which has the pots, jacks, etc soldered directly to it) or leave “well enough alone”. Often the issue is a broken input jack or something that makes the decision for you. But in this specific case, since it has its original nearly-20-year-old filter caps, a wonky input jack (but functioning), and the owner plans to keep it for the long haul, we decided to go all-in.
After the usual cleaning//tightening of everything (especially the baffle —- if you have an amp that remotely resembles this, check those screws in the corners that hold the baffle in!!), the amp received new F&T filter caps, new JJ el84s, a new preamp tube (V1), a new metal switchcraft input jack, and bias. This small (but deceptively loud with two power tubes) amp is ri ri ri ri rippin!¡!¡!Enjoy the amp George and Julian!

A Fender Pro Jr. —-> this smaller counterpart to the blues jr came into the shop with its original tubes and some complaints of noise. Upon testing I noticed V1, the first preamp tube, was microphonic as hell, and the original power tubes were nearing the noisey//inconsistent stage of their life. Like many of the modern-ish fender combos, the line in the sand for any repair is whether you “drop”/dismount the PCB (which has the pots, jacks, etc soldered directly to it) or leave “well enough alone”. Often the issue is a broken input jack or something that makes the decision for you. But in this specific case, since it has its original nearly-20-year-old filter caps, a wonky input jack (but functioning), and the owner plans to keep it for the long haul, we decided to go all-in.
After the usual cleaning//tightening of everything (especially the baffle —- if you have an amp that remotely resembles this, check those screws in the corners that hold the baffle in!!), the amp received new F&T filter caps, new JJ el84s, a new preamp tube (V1), a new metal switchcraft input jack, and bias. This small (but deceptively loud with two power tubes) amp is ri ri ri ri rippin!¡!¡!Enjoy the amp George and Julian!

This ~1968 drip edge Twin Reverb came in for a spruce-up before some recording sessions. The amp was last serviced around 10 years ago (or according to one date scribbled inside, maybe the aughts) at which point all of the electrolytics were replaced. Aside from a sketchy, ground-plug-missing power cable and a baffle that was falling out, the amp worked well! But like many of these jobs, once they're under the knife and you get to testing, you find some worthwhile small repairs.
The amp received the usual servicing//tightening//cleaning, a new fuseholder (the original was stripped), a new standby switch, a new pilot light bulb (I rarely need to replace these), a new power cable (and removed the death cap), new power tubes and bias, and a thorough reflowing/tightening of all the chassis grounds. After that I fired it up and it was working mostly great! However after some testing and scratchy pots I realized the majority of the blue coupling caps were leaking a relatively large amount of DC. After that, I added a cap to tame the "tick" of the tremolo, added an RCA "dummy jack" so it works without a foot switch, and got to work on the cab. I drilled some new fresh holes to hold the baffle, added two small L-brackets, and tightened it all up. 10 or so hours of burning-in new tubes and a loud stress-test and it's good to go for recording! Enjoy the amp Brian!

A ~1970 Oliver Sound B120 came in with inconsistent volume (cutting out). While issues like this can often take a lot of patience to find/recreate, luckily this amp “broke” almost immediately after I plugged in; out of nowhere the volume would drop low enough that you’d notice, but would otherwise be fine. I started methodically (lightly) pounding the cabinet & noticed that the signal level would change accordingly which led me to assume a bad connection or power tubes. Once inside the chassis I resoldered the entire amp (two PCB’s), replaced all filter caps, & I rebuilt the bias supply. After servicing it (cleaning & tightening everything & scraping/cleaning the chassis), I tested it & it was fine! The power tubes weren’t new & had drifted a bit, so for a total clean bill of health we decided to throw in new power tubes & a fresh bias. After the amp was running strong, I noticed some noise coming from the phase inverter, so I replaced the plate resistors & coupling caps. After completing the electronics work, I made three small tolex repairs on the cabinet, shielded the amp cavity, & tightened up all of the cabinet & speaker hardware. After a few days of testing & burning-in, the amp was good to go!
Personally, I love all-tube bass amps & Ampeg-derived designs, & this nails both. It sounds “loud” for only using two power tubes (roughly 60w), & the baxendall-esque tonestack along with the ultra low & ultra high (usually switches on ampegs, but here they’re variable controls) features work well on bass. The cabinet is a closed-back, ported (bass reflex) design with a massive vintage Electro-Voice speaker, so it sounds great, but humbled me every time I had to lift it for the workbench/photos.
On a more personal note, I first came into contact with Oliver Sound amps when I was working for Jess in his Long Island shop ~ 2008 (see 22 y/o dork in last pic). I’m always reluctant to name drop Jess in these posts – however, most rock n’ roll // “music industry” articles name drop Leo Fender, Les Paul, and Bob Moog’s, but leave out Jess and his contributions (along with the work of many women & BIPOC), so here’s one for Jess. Look ‘em up!
Enjoy the amp Jesse!

This is (what I believe to be) a ~ 1954 or 1955 Ampeg 815 “Bass Amp” (or 822 – read on). Based on the control panel and the OC3 voltage regulator, it would be the 3rd and final variation of the 815. However, the grillcloth cut-outs do not resemble any other 815s that I can find online or in the Ampeg book. Additionally, most of the components with EIA codes have already been replaced. The only code I can find is on the output transformer which has an “A-410”. Additionally, a 2011 forum post describes a similar amp and suggests a rare 822 model (which has little to no information online, but the forum points to a 2008 vintage guitar magazine). If anyone has any info or may be able to help ID this amp, get in touch! On to the work…
This amp came in working but with a bad rattle/rendering it almost unplayable. After checking out the amp rattle, along with the state of the components), I got to work. The amp received new power tubes, one new filter cap can, a few resistors, and the usual cleaning and tightening of everything. The amp has a bottom poweramp/power-supply chassis that connects to the upper preamp via two plug-in connectors. The one carries the filament voltage and the mains voltage (for the power switch) was deteriorated, so I ordered shielded power cable and rebuilt the connector.

Since the initial rattle seemed related to both old power tubes/electronics and cabinet resonances, I glued up the entire cab (including some failing joints) including every interior seam/joint. After all of this work, it sounded great, but I still found some noise (but a different, lesser noise). I found the OC3 voltage regulator to be rattly (especially on F # related frequencies). After replacing that and adding some dampeners on a few select tubes, I made the final modification… adding some small pieces of dampening material behind parts of the grillcloth/baffle. While the basic design will always be an issue --- a large powerful speaker mounted directly next to a sensitive preamp and a bunch of vacuum tubes -- the amp is sounding great and is about as rattle-free and quiet as an early 50’s bass amp can be. Enjoy the amp Ian!

This mostly original Ampeg Jet came in with a two-prong power cable, leaky caps, and a non-functioning tremolo. It received the usual cleaning//tightening of everything, all new electrolytic capacitors, grounded power cable, and some small tolex repairs. At that point I fired it up and tested it for a few days. I heard some intermittent sounds and noticed that the original 6V6’s were getting weak and really rattly. Additionally, the tremolo still didn’t work. After digging back in, I realized that most of the coupling caps were leaking (the one or two that weren’t were still replaced since they’d probably go soon). After it received all new caps it’s sounding strong/consistent, and the trem works again. I installed some fresh eurotubes 6V6’s and let it burn-in. It’s sounding strong and ready to go for another 60 years.

On a personal note, I love these early Ampeg Jets. The tremolo, while lacking an intensity/depth control, seems perfectly dialed in and the overdriven sound of the amp cranked up, with its worn-in alnico speaker, is kinda perfect. Maybe I’ll build a few 🤓🤫🤓🤫
Anyhoo, goodbye for now. Enjoy the amp Gershon!