Hi and welcome to my listing for this newly updated (February 2018) Alnicomagnet "Blues Harp" mod kit for the VHT Special 6 Combo or Head amp.

I've been asked to come up with a decent sounding mod kit specifically for Harp players, so, after many many hours of research and development, tweaking and listening, here is the result.

New kit (V2.5) now includes 3-position toggle switch which replaces the stock "LO" input jack.

Switch selects:

• Middle position = Very High Impedance (5 megohms) for crystal mics
  
• Up position = High Impedance (1 megohm) for most other types
  
• Down position = Low Impedance (500 ohms) for Shure SM57, SM58 etc.   
  

The instructions also cover the fitment of the very popular Eminence Lil' Buddy driver.

Check out Mat Walklate playing a crystal mic through a newly modded amp, (switched to 5 megohms). He was so impressed that he asked me to update his own amplifier to the latest spec:

https://youtu.be/6s0RLnPrN08

This kit is suitable for all territories and mains voltages.

This kit is designed to change the voicing of the amp to give a thick, ballsy, Chicago Blues tone, suitable for Blues Harp microphones only. After the amplifier has been modified, you may still use it for guitar, but there will be virtually no clean sound, and it will sound too thick especially with humbucker equipped guitars. The “boost” pot and footswitch are no longer used, so I’ve taken this opportunity to use the boost footswitch jack as a line-out jack, suitable for feeding to a larger amplifier, P.A. mixing desk etc. The line-out jack signal comes after the output transformer so is rich in output valve as well as preamp valve distortion. I’ve also taken this opportunity to replace the poor quality pull switch volume pot and tone pot with high quality Alpha 24mm pots, together with a simple gentle “Treble Cut” control, which is much better suited to Harp microphones to help tune out feedback.

You will probably know that the current stock output valve is a generic Chinese no-name item. It is the same as which is supplied with the Fender Champion 600, which I have had problems with in the past. I therefore recommend you change it to a higher quality name brand.

The amp uses a 6V6GT 8-pin international octal type which apparently can be substituted with a 6L6GT, 5881, EL34, KT66, KT77, KT88 etc. However, before doing so, please understand that these valves draw a lot more heater current, compared to the 450mA of a 6V6GT. The mains (power) transformer is identical to the unit fitted in the Fender Champion 600, and I know from experience that this transformer already runs very warm (in both amps) so caution will be required if considering a valve type swap. (Don’t forget that the preamp valve will draw 300mA heater current all the time irrespective of which output valve is fitted).

If you have the combo, I would keep it running a 6V6GT, as there is no room for anything larger, unless you remove the speaker, or fit a driver with a smaller magnet (not recommended).

With the head amp there are no such space restrictions, and it is reasonably well ventilated. My suggestion would be the JJ 6L6GC which draws 900mA heater current, and has a very safe (well over 400V) anode and screen max working voltage. Fitting this valve, and increasing the B+ voltage, changing the cathode resistor, and loading the valve harder will produce around 10 watts audio output power. I have included in the kit, various resistors so that you can adjust the B+ to suit the valve type fitted, and your local mains voltage.

Please be aware that installing these modifications may void the manufacturer’s warranty and that this kit and the procedures described are neither affiliated with nor endorsed by VHT.

Installation of the modifications requires only basic soldering tools and a few other items available from your local hardware or electronics store. You will need:

• Paper and a pen
• A good quality general purpose soldering iron with stand (rated at about 25W)
• Solder and a good desoldering pump
• Safety glasses or goggles.
• A multimeter, preferably with a digital screen, and a couple of alligator clips to attach the probes to component leads
• An electric drill with 8mm and 12mm HSS bits
• Various screwdrivers, including a set of small jeweller’s screwdrivers
• Small side-cutters
• Small pliers
• Flat file
• Round file
  
• Masking tape or sticky tape
• Heat gun or hot hair dryer
• A desk-mounted illuminated magnifying glass (useful but not essential)
•  A ¼” or 3/8” drive metric socket set and/or a set of small metric spanners (wrenches)
• A calculator