The VHT Special 6 – A little like Clark Kent
The VHT Special 6 can be a bit deceiving. At first glance it looks to be a relatively simple tube amp with one 12AX7 preamp tube and one 6V6 output tube. For controls it has Volume and Tone knobs along with a boost option that can be triggered with a foot switch. Nothing too out of the ordinary there but it all works together to make great tones and lots of them. But beyond all that, hiding underneath it’s mild mannered black exterior, is some clever circuitry along with a ton of potential.
One thing really great about the Special 6 is that VHT has released the schematic. Many companies don’t want their schematic, the efforts of tons of R&D, to get out in the wild for fears their “secrets” will be stolen. Not VHT and I love it when a manufacturer releases the schematic for an amp. In the case of the the Special 6, VHT is specifically appealing to amp modders to tweak this guy and make it just the way the owner wants. The schematic also gives us a chance to see what’s going on under the hood and that’s what we’re going to do.
When a tone control is a bit more.
Looking at the schematic we can see that the tone control in the Special 6 is the same control that Fender used in the 50’s in the Princeton 5F2A and other amps. It’s a simple but effective tone control which is why it has lasted so long.
Looking right before the tone control we can see a bunch of other capacitors and resistors. That is actually a tone stack very similar to what you would find in tons of other amps such as later Fender Blackface amps. The difference here is that it is all fixed values. Why did they do that? A tone stack is not just Treble, Bass and Middle controls. Most tone stacks, including the one in the Special 6, will provide a dip in the mid frequencies known as a mid scoop.
So the Special 6 has a fixed tone stack and a more simple tone control. Most amps have one or the other but not both. What is VHT thinking? Why didn’t they just add the knobs to the tone stack and skip the other tone control? They could have done that but the reason they didn’t might have something to do with the mid boost switch.
With the mid boost engaged it would have reduced the effectiveness of the tone controls in the tone stack. This has to do with the way tone stacks work. Having the separate tone control ensures it will always be effective whether or not the boost is engaged.
So, as it is designed, with a switch you can turn on or off the mid scoop and boost or cut high frequencies with the tone control. It’s a simple arrangement that allows a whole bunch of useful tones.
One great thing the VHT Special 6 has going for it is that if you are not happy with how it comes from the factory you can change it. The eyelet board makes it easier to modify compared to a PCB board so if you like to tweak your gear the Special 6 can be especially appealing.
Lets say, for example you don’t quite like how the mid scoop sounds. Let’s think of the mid scoop in terms of American (Fender) vs British (Vox/Marshall). A Fender Blackface has a fairly big mid scoop at about 500Hz. A Vox Top Boost also has a good sized mid scoop but it’s closer to 700-800Hz.
It might be a bit hard to see in the image but the dip is right around 800Hz so it’s more of a British type of mid cut. Since the Special 6 is built with a eyelet board this can be tweaked by someone who can do a bit of soldering. By increasing the value of R10 from 180k to 330k and R12 from 27k to 100k we can move the scoop over to about 500Hz making it a little more Fender-ish.
This is just one example, there are all sorts of things you could do. For example, the tone stack could also be tweaked for more highs or lows or whatever you think would benefit your tone.
Obviously I can’t cover every possible modification but one other possibility comes to mind. If I wanted more of a Marshall type tone I would try changing the capacitor labeled C8 from 4.7uF to 1uf. A smaller capacitor in this location would cut lows. This will give a more Marshall-like character.
If, after trying the amp after this little mod, I thought I reduced low end too much I would try increasing the capacitor at C13 to 22uF. Using a larger capacitor there would increase to lows.
It’s not that it’s impossible to mod an amp built with a PCB board, I’ve done it but an eyelet board is much easier.
One last note on modding tube amps. Don’t mod a tube amp if you are not aware of, and can follow, the safety precautions. Look here for more info.
There is a lot to like about the VHT but one thing I would have like to see is a bit more room in the chassis and on the panel. Maybe I’m asking for too much but a nice bonus for modders would have been a bit more room to add knobs on the control panel, maybe even some tiny guide holes to drill out if needed.
How it stacks up
While I went on about the modding potential, the VHT Special 6 is a great little amp right from the factory. The Fender Champion is a little cheaper and has the same tube compliment but the VHT has the eyelet board going for it as well as a bigger speaker, or head configuration if you prefer that. Arguably the VHT Special 6 is more comparable to Fender’s much more expensive hand wired Champ that goes for almost a thousand dollars.
Overall the VHT Special 6 is a terrific value in terms of a hand wired amp without the boutique price. At the same time if offers the potential to go beyond the stock configuration to what ever you and your soldering iron can think of.