I was browsing on Craigslist and ran into an ad for a Kustom V Lead. It looked like exactly what I wanted, but I couldn’t find much information on the Internet. Several indecisions later, I ended up purchasing a Kustom I Lead off of Reverb. I’m writing up some details on the amp here as well as a tutorial on upgrading the reverb tank.
Note: Please send me corrections and additions so I can make this more complete. Thanks!
The Kustom I Lead was built in the USA some time in the late 70s. It has one 10” speaker (8ohms) and probably around 35W (I couldn’t find any solid info on that). There are two inputs and they appear to be identical. I looked at the circuit board and it seemed they each went through resistors of the same value and then into the same signal path. There is a master volume and preamp volume which allows you to control the amount of gain while keeping the volume low. The amp also has treble and bass tone controls and spring reverb. Mine came with a three prong power plug, I’m not sure if that’s standard. Almost forgot, there’s a “line out” on the back… but it’s a worthless addition. The tip off the speaker jack is connected to the tip on the “line out” jack by a resistor. That’s it. No thanks.
The amp is solidly built. I’m not sure the exact weight, but it feels rather heavy for it’s size (15” x 19” x 9”). Maybe 35-40lbs. It’s relatively easy to disassemble. If you take all the screws out, the front grill comes off (with speaker attached). There is a back panel access as well. The amp chassis slides out with a little wiggling and the speaker connections slide off. The PCB is a little tough to get out, but if you take all the knobs off, unscrew the pots, unscrew the audio jacks (front and back) and unscrew the bolt on the bottom of the chassis it can be worked into a position where it’s not too awkward to access both sides of the board.
This amp has a fair amount of clean volume. Certainly enough to blow out a bedroom. Probably not enough to compete with loud drums. The sound has a lot of character. I wonder if this comes from the aging parts. The highs seems a little more relaxed. It has a very thick, mid-rangey sound. But not in a bad telephony way. It’s full. If you crank the preamp volume, you get a boomy, ugly, sputtering hard to control distortion. For now the only sound demo I have is the video below, but I’ll post here if I get around to making higher quality clips.
Reverb Tank Upgrade
Not mentioned above is the sound of the built in reverb, which I found to be disappointing. At very low settings, it is useful and adds some blur and depth to the sound. But if it’s dialed in enough to hear the tails, they sound like garbage. Or more specifically, like a garbage can, harsh and metallic. After opening up the chassis up and seeing the tiny tank, I have a good idea why the reverb sounds so trashy. I decided to upgrade the tank. This turned out to be a painless process.
I. Choosing the Tank
NOTE: While these instructions are specifically geared towards the Kustom Lead I, they could be adjusted to work with other amplifiers so long as you can access the circuit board and figure out where the reverb tanks connections are
This was perhaps the most difficult part of the process. There is very little information available on this amplifier, let alone on the specs of its reverb and choosing a reverb is surprisingly complicated. There are a whole bunch of confusingly coded options you have to wade through to find the right part number for your tank. Here are the basics… There are three manufactures making spring reverb tanks right now. Accutronics, Belton (they also make a digital version) and MOD. They all use the same conventions and those conventions are spelled out here by Amplified Parts who I bought my tank from. The most important technical aspect to understand is impedance matching. The correct way to determine the impedance of a reverb tank is to use an oscilloscope. However, I don’t have one right now you probably don’t either. Luckily there is a hack method. Put a multimeter across the input leads and then the output leads and measure the resistance in ohms. This gives the DC resistance of the transducers. Using this chart you can convert to approximate impedance and find the matching letters needed for the part number. In my case I measured in the neighborhood of 26 ohms and 200 ohms, so my letters were BB.
The rest of the choices are mostly maters of tastes. The Accutronics guide makes it seem like the mounting position is very important, but I talked to a tech who said as long as you mount your tank the way it’s intended, you’ll be fine. I picked the least desirable configuration, laying across the bottom of the cabinet (i.e. B, open side down). There are four tank types you can pick from based on two variables, the size of the tank and the number of springs. I chose Type 8, which is a three spring smaller tank. I’d have gone for a big one, but couldn’t fit it in the cabinet. For my situation and probably for most, it seemed better to with grounded connectors. That means that the RCA connections will have their shields directly connected to the chassis of the tank. The tank’s chassis needs to be grounded somehow (to reduce noise). If you go with insulated connectors that means you’ll have to run a separate ground wire and connect it to the chassis of the tank. When it came time to choose a decay time, medium was the only option available. Good enough. If you’re trying to find a tank for a different amp, I recommend deciding on a tank type and determining the impedance. Then you can search on just that (in my case 8BB) and pick from the available option.
Ultimately, I bought a MOD 8BB2A1B Tank and it works wonderfully with this amp.
II. Accessing the Circuit Board
Up above under the “Construction” heading I described how to take the Kustom I Lead apart. Do that first. The tricky part is maneuvering the circuit board into good position for working on it. You’ll also need to clip the leads coming from the reverb tank. Make sure to note which lead goes where (i.e. which is positive, which is ground, which is input, which is output). On my amp green=ground, black=hot. I found that tilting the board so the front panel comes up first is easier. I needed to pull the chassis apart a little to get the pots to fit past the edges. I’m not very spatially inclined, maybe there’s a less ugly way.
III. Installing RCA Jacks
Simple… drill a couple of holes in the chassis and screw the RCA jacks into the holes. Done. I recommend getting the nicer individual ones. They don’t cost much, they’re easy to install and they look nice. The only thing is, take a moment to think about how you want your wires to run and where the jacks won’t be in the way. I put mine close to the speaker connection.
IV. Modifying the Circuit Board
Once you can get at both side of the board, desolder the remaining leads from the reverb tank and clean up the holes. Most likely you can get away with only doing the hot leads since the jacks will be grounded to the chassis. Solder new wires into the holes leaving enough slack to reach wherever you want to mount the RCA jacks.
IV. Removing the Old Tank
Technically you could leave the tank in there… but it’s now useless, so might as well pull it out. It’s adhered to the chassis using foam tape. It’s easy enough to pull off once you get a corner up. I used a screwdriver to wedge under it. There aren’t any screws.
V. Wiring the Jacks
As mentioned above, your jacks should be grounded to the metal of the chassis. If this isn’t the case (what the hell is wrong with your amp?) then run a ground wire to the board (for example to one of the holes from the reverb). Take those wires you soldered to the board and solder them to the tip of your jacks… You can now reassemble the chassis!
VI. Installing the Tank
I put my tank inside the cabinet of the amp lying across the bottom behind the speaker. You can do whatever you like, but that’s the most convenient spot for it. I originally bought a custom bag to put the tank in, but I couldn’t think of any good reason to use it and it wouldn’t fit over the RCA jacks I used, so I returned it. Instead I put some sticky tack on the feet of the tank. If you’ll be moving your amp around a lot, you’ll want to come up with a more stable system. But you have to be smart about it because it’s best not to have the tank rigidly connected to the vibrating walls of the cabinet.
VII. Routing the RCA Cable
There’s already a hole that the speaker wire runs though underneath the chassis. I put a new hole right next to it using a stepped drill bit. I don’t recommend using a stepped bit because the cabinet walls are too thick and I ended up with a heavily tapered hole. I didn’t have a big enough drill bit to do the job right. Maybe I should pay more attention to the ads in my SPAM folder… Once that business is done, run the RCA wire from the back of the chassis through the new hole and plug it into the tank. Make sure you have it connected the right way. You did keep track of which jack was in and which was out, right?
VIII. Finishing Up
Put everything back the way you found it, just like Ma always used to tell you to do. If everything went well, you are now soaked in sweet reverb. If not, go sit in the corner and think about what you’ve done.