Hi and welcome to this listing for my Alnicomagnet "5F2A" mod kit for the VHT Special 6 Combo or Head amp.
This kit is suitable for all territories and mains voltages.
This kit is designed to re-configure the circuit similar to a mid-to-late fifties Fender “Tweed” 5F2A Princeton.
The stock Special 6 circuit is loosely based on the classic Fender AA764 (mid-sixties Blackface) circuit, (also used in the Champion 600), but biases the preamp tube to sound dirtier. My mods revert it back to the simpler, late fifties Princeton design. As such, the sound of the amp has no “mid scoop”, has less preamp distortion, and has more internal gain.
The Tweed Princeton had a negative feedback loop. The stock Special 6 does not. The kit includes the components for adding a switchable feedback loop. You can leave the amp permanently with no negative feedback, or configure it permanently with negative feedback, or, have the feedback loop switchable.
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 higher quality Alpha 24mm pots, copying the simple Tweed Princeton tone and volume controls, but using modern high quality silver mica and Sprague Orange Drop capacitors.
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. My personal favourite is current production JJ Electronic.
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 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. With the head amp there are no such space restrictions, and it is reasonably well ventilated. My suggestion would be the JJ 6L6S which draws 900mA, 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 10watts 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 will void the manufacturer’s warranty and that this kit and the procedures described are neither affiliated with nor endorsed by VHT.
You can choose black or white chickenhead knobs. Both colours look good against the black control face. The default choice is black. If you prefer white, tell me during the checkout procedure, or message me when paying through PayPal.
Tools needed
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
• 8mm HSS bit (for the new volume pot)
• 6.5mm HSS bit (for the feedback switch)
• Various screwdrivers, including a set of small jeweller’s screwdrivers
• Small side-cutters
• Small needle-nosed (radio) pliers
• Flat file
• Masking tape or sticky tape
• Heat gun or hot hair dryer
• A desk-mounted light or 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
Instructions and pictures are kept in a folder. The folder is stored on a download site (dropbox). You will receive a download link via email which will be sent to you at
the same time as you receive confirmation from eBay that the kit has been shipped.
I will use your PayPal registered email address unless you inform me of an alternative preferred email address.
Important! Dropbox has recently changed and now requires you to open an account with them before you can access the files.
You will need a pdf
reader to access the instructions. You will need a picture viewer to view the pictures.
Here's an email I recently received from Charlie who had his amplifier modified by me to my 5F2A spec:
Hi Nigel
Picked up the amp this morning and haven't stopped playing it all day.
It sounds really really good, another amp entirely. Very pleased with
it and no background noise at all. My Gibson nighthawk and home made
Strat have never sounded better. Tried it through a Weber Alnico and a
Celestion greenback and although they sound very different the amp
works well with both. Still not entirely sure either is the best match
for the amp. I'm glad I kept the low input as I quite like the sound
through that as well now. The negative feedback switch is interesting
I'm guessing the higher gain setting is with it on? I like the variety
it gives the amp.
Thanks again. Looking forward to many happy hours of playing. Charlie
Nigel,