I really enjoy your column in Premier Guitar – it has helped me understand a lot about amps. I have three questions relating to my Fender Super 60 combo amp. I have replaced my preamp and power tubes with 12AX7s and 6L6GCs from Ruby Tubes. Changing the preamp tubes smoothed out the raspy distortion (now similar to Santana smoothness) and got rid of the hum. What would I need to do to get a modern rock sound?
Also, this is a very loud amp. I understand that removing certain tubes can cut the power in half. Which ones would I remove? And finally, when I bought the amp, it had an EV 12L speaker, which weighs more by itself then the amp does without it. I love the tone with the EV, but need something lighter. What speaker options are there to replace the heavy EV with something lighter that will have a similar or the same tonal characteristics? The help is appreciated.
Thanks for reading Premier Guitar. I’m glad you enjoy my column and I’m happy to hear that it has helped you.
For its time in the eighties, your amp probably had a “modern rock sound,” but as we all know, times change. I’ll try to answer your power and speaker concerns and since this is a DIY-themed issue, I’ll go one step further and give you a few small circuit modifications to try.
Let’s first discuss the possibility of removing tubes to reduce the output power. While removing output tubes is a possible option in some amps (consult the manufacturer prior to attempting this), it is not an option for your amp. Output stages which use four output tubes can generally have two removed in order to reduce the output power; since your Super 60 only uses two output tubes, the removal of one would leave half of the output transformer unloaded. In short, this is not a happy situation for the transformer.
There are a couple of other options you could explore, the first being the use of an external attenuator. Numerous companies produce attenuators which can be inserted between your amp and speaker. This will allow you to reduce the amount of power being sent from your amp to the speaker.
Another option would be to install power reducers in the output tube sockets. THD makes a unit called a Yellow Jacket, and they can be installed in the output sockets of your amp, enabling the amp to utilize EL84 tubes in place of the stock 6L6 tubes. This will effectively place the output in the 15 to 20 watt range, a more-than-manageable power for most situations.
As for the EV speaker, you have the typical EV love/hate relationship – love the tone, hate the weight. Since corporations and guitar players seem to be downsizing nowadays, speaker companies are answering the call with a few choices. Jensen, Eminence and Celestion all offer models utilizing neodymium magnets, a lightweight magnetic material, cutting some heft from the design. After reviewing the selections from the three companies, I would choose the Tonkerlite by Eminence. In my opinion, it stands to be potentially closer to the EV than any of the others. You simply won’t find anything that sounds the same, but unfortunately that’s the price to be paid for making weight the more important parameter.
As I mentioned earlier, here are a few internal tweaks that I would try in order to give the amp a more “modern” sound. These will in no way effect a huge change in the amp, as that would require much more extensive modification. I have not previously attempted these modifications – they were simply developed after reviewing the schematic of your amp. If you like them, great. If not, you can simply return the amp to stock with no harm done.
Please note: any involvement inside the chassis of a tube amp can result in contact with some potentially lethal voltages! Do not attempt to perform any type of servicing unless you first turn the amp off and discharge the filter capacitors. If you do not know how, find someone who does. Neither Premier Guitar nor I will assume any responsibility for damages suffered by you or your equipment.
But enough with the scary disclaimers – now for the mods.
- Replace the .0047ìf coupling capacitors in the first and second gain stage (C102 & 105) with 0.01ìf 600V caps. This will provide a slightly fuller signal range in the signal path.
- Replace both the 0.047ìf and 0.1ìf caps in the tone stack (C6 & 7) with 0.022ìf 600V capacitors. While the prior values are great for the “traditional” type of Fender tone, I feel the .022 caps sound better in higher gain circuits.
- Replace the 120K resistor in the power supply (R167) with a 100K resistor. This should raise the plate voltage in the first couple gain stages by approximately 30 volts.
- If it’s not already a part of your amp, install the bias control. The schematic actually lists the 5K bias potentiometer (R171) and 8.2K series resistor (R178) as “optional,” so install them if necessary. If you do so, remove the 10K bias set resistor (R158).
Now hopefully you’ll love your amp enough to buy it a Valentine’s Day card! Until next time.
Co-Founder and Senior Design Engineer – Budda Amplification
©2007 Jeff Bober