VHT Special 6 Combo Amp >>> AX84 P1 Extreme

[MAO]

Thought I'd share my experience modding a VHT Special 6 combo...so far :0)

I wanted a small tube amp for home use and for testing pedals.  Most reviewers said the Special 6 is well made and easy to modify. I have to agree.

I found one used, excellent condition for $140.

It sounded pretty good stock, better with clean tones at lower volumes, had to crank it up pretty loud to get good overdriven/distorted tones.  

Even cranked there wasn't a lot of sustain and I wasn't crazy about the low power setting (triode mode), plus there was a bit of hum in triode mode.

In all fairness, the tubes may have been part to blame for not being thrilled with the amp as is.

I started modding it before replacing the tubes.

Mods:
1. Replaced the fixed tone stack with an adjustable Fender tone stack, Treble/Mids/Bass controls and replaced the original tone control with a Master Volume as described here
2. Replaced 6v6 with EL34 and rebiased with 280ohm cathode resistor.
(no holes drilled, used existing external speaker jack holes for tone controls)

Better, but still not crazy about the overdriven/distortion tones. And I didn't want to have to crank the amp all the way up to sound good...although it did. Good crunch, but sustain still lacking.

Decided to try moving the tone stack.

3. Moved the tone stack after the 2nd gain stage and tweaked the preamp slightly based on the Ampeg Reverberocket R212  as the 1st 2 stages and tone stack were pretty similar. Replaced 4 caps and changed 2 pots.

Also replaced the tubes with a Svetlana EL34 and a 12AX7A I had.

Sounded a bit fizzy. 20 minutes later I was back at it, modding away.  

Decided to go for Marshall tones instead.

4. For about $5, I rebuilt the preamp and power supply based on the AX84 P1 Extreme Still using the original transformers.  

Wow, much better! And finally some sustain.

Almost there.

Next mods up:

5. I may use the original push/pull volume control (and footswitch) to add Marshall-style diode clipping. Or, may use those switches to add headroom by adjusting the 604R. Not sure yet, as I haven't played it enough with pedals to see if headroom is an issue. Probably will go with the clipping switch.  

6. Considering adding a Watts control like VHT uses in the Special Ultra.

7. Also, considering replacing the 16 ohm speaker with an 8 ohm Eminence RamRod to better match the output transformer to the EL34...and for more British tone :0)  

Conclusion...so far:

I highly recommend this amp if your looking for an inexpensive, small wattage, quality built tube amp that's easy to mod.

If you like a Fender Champ type sound, the stock amp is probably fine as is. No mods necessary.  

If you prefer Marshall-like tones, for another $5 or so, and an EL34, convert it to an AX84 P1 Extreme!  
 


 

 

[Stymie13]

Cool, thanks a lot for sharing. I use a small 5W Blackheart Little Giant into a 4x12 for home practice and had very a very similar experience. I modded the tone stack and output stages and installed a Classic Tone OT which improved it but the natural overdriven sound is still awful. Great pedal platform at low volumes but harsh and unmusical with the volume cranked. I'll try to apply some of the principles you shared although I'll have to change the tube socket to swap it to 6V6/EL34. Thanks!

[Travis]

Instead of changing the socket you could use an adapter like this

http://m.ebay.com/itm/320960131594?_mwBanner=1

Sounds like fun stuff guys! How bout some pics?



Edit: I thought you were talking about changing 6V6 to EL84. If you're switching to EL34 the octal socket is fine

[Stymie13]

Thanks Travis, hadn't thought to look for an adapter. I'm not sure changing the power tube will make much difference but will photos if/when I get around  to tinkering again.