Rootbeer Audio

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!

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!