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Please email me or sign the guestbook if you have any suggestions on the site or for the Download of the Week -- I'll be looking for your input, thanks!
If you don't know already, I'm kind of a gearhead when it comes to musical instruments and equipment. This area of my website is where I talk about technical matters for those who share the passion. Suggestions and questions are welcome via email.
Tube Substitution In A Leslie
Here's a hot tip if you own a Leslie 122 or a Leslie 147 rotating speaker. (For those who are wondering, Leslie rotating speakers are used to give electric organs that classic woo-woo sound.) The 122 and 147 Leslie amps are designed to run 12AU7 tubes in the preamp section and 6550 tubes in the power section. You can change the sound of your Leslie by substituting tubes. Try a 12AT7 or 12AX7 instead of the 12AU7. (On the 122, I believe there are two of these tubes, one is for controlling the speed, but you want the preamp. You can do the replacement and listen for changes to see if you get the right one.
Incidentally, you may find that the higher power consumption of the 12AX7 taps the amp so much that the speed control no longer works properly, it may stick on the high speed, which corresponds to a low voltage signal to the speed switch.
KT66 or KT88 tubes will work instead of 6550's. KT66's are now being made again, they were very hard to get for awhile. A 7581 is the same as a KT66, it's a military version of the same tube.
Technically, the amp should be re-biased after changing the power tubes, but I never did when I had a Leslie. The 7581 tubes I used sounded fantastic near the end of their usable lives, then they went downhill. Tubes can be like that, they sometimes sound best right before they fail...
Don't come to me if you blow your amp doing this, by the way. Mine handled it fine tho...
Loudness Wars
The music you listen to is messed up! Did you know that? In general terms, it's because record companies don't know how far you plan on turning up the volume to listen to the music they sell you. So they optimize it for stronger sales. It's our fault as consumers, really. Click Here to get an introduction to the subject...
Swapping Speakers
Guitar amps can vary in tone greatly just by changing the speakers. The difference can be dramatic. Unfortunately, it is often not possible to audition the results without installing the speakers first. A rough approximation is possible if you (or a technician) wire up an adapter to drive other speakers installed in other amps. For my 1966 Fender Champ, this was just a speaker cable I soldered with a male RCA plug on one end (to come out of the Champ) to a 1/4 inch female, which can either plug directly to the speakers of most Fender amps, or to a 1/4' speaker cable, commonly used with PA speakers.
In addition to auditioning possible replacement speakers (which will also depend on the cabinet configuration), this rig allows me to use my little 5 watt Champ to drive some large speakers, rather than the built-in 8 inch one. It turns out the amp produces some mightly lows which are not audible with the small speaker. The amp is also capable of playing very loud when hooked up to a couple of efficient 12" speakers mounted solidly in a cabinet. Hard to believe it's five watts at that point...
Some attention should be paid to the ohmage... My Champ is meant to drive 4 ohms. Varying the output too much (or leaving the amp unconnected to speakers) can blow the output transformer, so do your homework and test at your own risk. Usually however, driving 2 or 8 ohms instead of 4 isn't the end of the world. An amp intended for 8 ohms that is allowed to go nuts on a 2 ohm load is asking for trouble.
I made another adapter with a male 1/4" instead of the RCA which I used to audition some speakers for my 1965 Fender Twin. The experiment was a success and I was able to find speakers I like without spending a lot of money trying out ones I wouldn't have liked so much...
Tweeding a Blackface Champ
The Fender Champ is a classic 5 watt amplifier that has evolved over the years, and has played various roles in rock history...
Eric Clapton used one when he was in the Yardbirds, Pete Townshend used one with the Who. Frank Zappa mentions the Champ in his song "Joe's Garage."
Why does a 5 watt amplifier get so much attention from these heavy hitters? Generally, low wattage vacuum tube amps are easier to distort, and they distort at low volumes. This makes them great for recording because you can put a mic up close to them and they end up sounding monstrously huge.
Early Champs were brown, with a "Tweed" type of covering on the amp. They were first made in the 1950's. In the 60's Fender changed the design to black styling, with a black faceplate and tone knobs added. These are the classic "Blackface" Champs. The late 60's brought a change of direction, as CBS bought Fender. Over the next few years, CBS started changing the designs to Fender's various amps. Most of their changes do not stand the test of time. It is widely accepted that CBS screwed up the amps gradually, so that the later you bought one, the worse it sounded. Fortunately, the Champ didn't experience a drastic change over most of the early 70's, perhaps because there were so few parts to cut corners on. Eventually, vacuum tubes were no longer used in the amps, which increased their desirability among interior designers, as they now made the perfect doorstop.
Luckily, CBS changed the styling when they took over, making them readily identifiable. The black faceplates were replaced with silver ones for the entire line of Fender amps. These are known as "Silverface" amps. The rest of the amp exteriors retained the same grill cloth and black tolex covering of the 60's versions.
So with the exception of a fuzzy time period around 1968 or so, vintage Champs (and other Fender amps) can readily be categorized by three distinct eras: Tweed, Blackface and Silverface.
Tweed Champs are very hard to come by. They typically sell for $700 to $1000 and are sought after for their creamy distortion and they make outstanding harmonica amps. Blackface champs have a cleaner sound and often run $350 to $500 these days. The Silverface champs are slightly cheaper and sound similar to the Blackface, but may vary especially depending on the speaker inside, which is easily replaced.
I own a Blackface Champ which I rewired to make it more like the Tweed version. Any modification can seriously diminish the value of a vintage amp, but I don't plan on selling mine and I would prefer a Tweed sound.
CLICK HERE for the instructions I used, which are reprinted widely on the internet. When I was done, I stapled a copy of the instructions inside the amp so that the changes can be undone after I kick.
Anyway, speaking of kicking, the amp kicks ass! I like it! I have not been able to compare it directly to a tweed, though. Also, the Champ is somewhat of a one-trick pony, regardless of era... The tonal qualities of Champ are delicious, but limited in range and versatility.
Twenty Dollar Tube Bass Amp
I converted one side of my Fender Twin Reverb to a bass amp for just $20! Check out the kit at AntiqueRadioSupply.com. By replacing some components of the tone stack on the Twin's "Clean" channel (the one that no one ever uses), the amp's eq becomes more suited to amplifying a bass guitar's signal. I don't want to blow the 50 watt speakers, so I run the speaker line to a high wattage 15" bass bin I already had lying around. Connecting the bass bin requires a speaker cable with a 1/4" female plug for the Twin to plug into. SOUNDS EXCELLENT! ...and the amp (a 1971 Silverface) still works great as a guitar or organ amplifier using the reverb channel, which wasn't altered.
Modding vintage gear is discouraged by the purists... I folded the instructions that came with the kit and stuck them inside the amp in case any future owner wants to return it to original specs.