Lahmantone Amp Labs

09/30/2024

08/24/2024

TONIGHT

08/10/2024

Twenty four years ago, I designed and built a vacuum tube overdrive pedal for guitar. It was reviewed in Vintage Guitar Magazine in April of 2000. Prior to the review, I built 3 units for local guitarist, and one for myself. The article prompted orders from across the country. The units were built by hand, one at a time, so the lead time was getting longer with each order. 2 units went to recording studios in L.A., one went to a Nashville recording studio. About 20 units total were built and distributed worldwide. I received glowing letters from the studios and other purchasers, regarding the versatility and the durability of the units. I just received one of the units back for a refurbish. It’s in remarkable shape for a 20+ year old device. This unit belongs to Johnny Leal.
I used only the best components and construction methods to build these units as I do with my guitar amps. It’s great to see one, that has been in service all these years and still is intact. Here are some pics and the original article from Vintage Guitar Magazine.

02/14/2024

These little “amp boards”, caught my attention, one of my parts suppliers had a sale, so I bought one. I was curious how it would sound with a tube preamp driving it. So I started to design what I would need to make that happen. A power supply for the little amp board and a power supply for the tube preamp. A preamp is necessary because the amp board is a straight power amp with no volume control. The amp board is stereo, 100w per side. A 12AX7 is a dual triode, so I can drive each channel with half of the tube and add a volume control after the tube gain stage. I installed this prototype amp in a 2-10 cabinet to be able to utilize the stereo amp output. There are no tone controls or equalization, just a volume control for each channel. The tube is running at typical voltages, 200vdc for anode, 1 Meg, grid leak resistor, 33k signal load, and a cathode network consisting of a 1.5k resistor and a 25/25 cap. The amp sounded very dark with a guitar plugged straight in. On another note, I have never been a fan of digital modeling amps and preamps. Even the newest, latest, modeling amps sound bad to me. They sound okay for direct recording but playing live, they always sound odd. Even when plugged into an old Fender tube amp, they’re disappointing.
I still own a Line 6 POD 2.0, and a rack mounted POD Pro. I decided to see how theses digital modelers sound through this stereo hybrid amp. To my surprise, they sound pretty good. The dark characteristics of this hybrid amp, tamed the digital harshness of the POD. I have a 100w Marshall plugged into a 2-12 cabinet at the ready, and I was surprised when I was able to dial in a very close approximation of the Marshall with the POD. Even the distortion sounded convincing, which has always been a sore spot with digital modelers, with me anyway, they don’t sound like a guitar overdrive, more like a chainsaw. The POD has a stereo output so the delay and rotary effects are pretty amazing. Of course, I will have to demo this set up at rehearsal. Maybe this hybrid amp is the answer to the digital modeling harshness. Right now, I’m re thinking modeling preamps, but there is still a vacuum tube in the signal chain to smooth out everything. I just thought I would share my latest craziness on this amp page for those interested.

02/11/2024

I installed these Railhammer pickups in my PRS SE. P90 style in a humbucker size. Designed by Joe Naylor of Reverend guitar fame. They are just what I was looking for. I have an older version of these in a Reverend Rocco. I love the tone.

12/02/2023

Just a little amp repair note to those interested. I had a problem with a Marshall 2203 100watt head. After about 30 minutes of use, the amp started to hum loudly, I looked at the power tubes and one pair had their plates glowing red hot. I shut it down immediately to save the tubes. This has been a chronic problem, because the plastic vent on top of the amp was deformed from excess heat given off by those tubes. Usually this condition is caused by tubes that are starting to fail and cannot be biased properly. I opened the amp on my work bench, with voltage meter’s connected, I watched the bias voltage on one side of the power amp, slowly get lower and lower until one pair of the tubes were in runaway mode. I installed new tubes, still the voltage dropped, so it wasn’t a tube problem. The coupling caps that drive the power tubes off of the phase inverter, had been replaced, which is typical of an amp built in the 70s. The old repair was a mess and had several cold solder joints, and one of the capacitors had failed. With the mess cleaned up and 2 new capacitors, everything was copacetic. This problem had been going on for a long time according to the partially melted top vent. The 6550 tubes, that were originally installed, are so robust that they withstood a runaway condition for years before they also failed. I set the current draw to 30ma. per tube with a new quartet of EL34s. I had to change the bias resistor to get it in range for the EL34s. The amp is solid, quiet, and sounds like a Marshall 100watt Master Super Lead head, should. To most people, Marshall amps are epitome of loud raging overdrive and they do that very well. They also can be very clean and lovely at low volume. The 100 watt amps sound especially nice at a low clean volume, better than the 50 watt heads. (I have one of each).My theory is, at low volume the 100 watt is never driven hard enough to be pushed into AB mode. It stays in class A, and in doing so, it has the tonal characteristics of a class A power amp design. In my humble opinion.

03/11/2022

As you may know, Russia and China are where most of the vacuum tube factories are located. Even though American tube companies ”own” the Russian facilities (as much as anyone can own anything in Russia) Russia has stopped shipments. China’s tube are of lesser quality, but they have gotten better. As far as I know, China is still shipping vacuum tubes. Vacuum tubes are a trivial matter compared to this murderous, humanitarian disaster, that Russia has begun, but one that will impact tube amp aficionados.It’s the perfect opportunity for factories to be built elsewhere.

01/01/2022

I don't usually work on solid state amps, but my friend was in need and he loves this amp. The amp has two channels, two separate preamps, and of course the channel that he preferred had failed. Parts are hard to find because this amp is from the late 60s, early 70s. Solid state technology has changed so quickly that some methods and parts have become obsolete. I bought this "parts" donor amp to salvage the parts I needed to repair my friends identical amp. I decided experiment with the donor amp and build a vacuum tube preamp to replace the missing solid state preamp. I found a low noise switching power supply to operate the tube within it's operating parameters. I used a tried and true schematic for a tube gain stage (preamp) with tone controls, using a 12AX7. Now it's a hybrid with a tube preamp paired with the existing solid state power amp. The newly installed tube preamp is a vast sonic improvement, especially compared to the remaining solid state preamp. It was a gamble, but I had nothing to lose if it didn't work and everything to gain if it did. It's nice when a crazy idea works out.