[Harp-L] Happy Thanksgiving, and the amazing VHT Special 6 amp
Rick Davis
today in whatever way makes sense to you (eating turkey, watching football,
etc) I invite you to give thanks also for the VHT Special 6 amp. It is
truly remarkable.
Essentially, it is a blackface Fender Champ with a 10-inch speaker for
$200. It is beautifully hand wired point-to-point on an eyelet board with
good quality components. Right out of the box it sounds GREAT for blues
harp. Seriously, you would expect an amp with these features and this tone
to cost closer to $800.
The 6V6 power tube gives a warm crunchy tone that just can't be matched by
the EL84 tubes in other low-priced tube amps. As soon as you plug in your
mic and blow though this amp you recognize it is something special. There
is a slight tearing on the leading edge off the notes, with nice
overtones in the body of the notes. The amp responds well to the pressure
you put on the mic. It just has a natural relaxed blues harp tone I have
never found in modern low-priced amps meant for guitar players.
At the Blues Harp Amps blog I have photos and videos, and descriptions of
the mods I've made to the amp to improve it's tone. Mike Fugazzi has been
enthusiastic about this amp and he is exactly right! It is an amazing amp,
and an amazing value. It should be at the very top of your Christmas list.
Happy Holidays!
--
-Rick Davis
The Blues Harp Amps Blog
http://www.bluesharpamps.blogspot.com/
Jim Rossen
price.
Rick D- I am interested in the circuit mods, particularly done in
conjunction with a master harp amp builder like Bruce. Can you post
the specifics, perhaps referring to the published schematic, which is
at-.
http://www.vhtamp.com/avsp16.html
I have done some mods myself and reported my observations on the Weber
harp board. I reproduce my post about this below. Since that post,
I made additional mods of change the tone control R12 to .01 mfd and
replace the original speaker with an Eminence blue frame Bassman RI
speaker.
Jim
Prior Weber board post:
I can't keep a soldering iron away from an eyelet board, so I had at
my Spec 6. I used the amp at a low volume gig last night and thought
it needed more low-mids. This could probably be accomplished with a
speaker swap, but I decided to make some circuit changes. I was
guided by in part by an excerpt from an interview with the designer
where he encouraged mods. He said-
http://www.frugalguitarist.com/Frugal.aspx?Issue=19&Page=Terry%20Buddingh%20Interview
If you want to re-voice the clean mode�s sound (non-boost mode),
resistors R10 and R12 form the clean mode�s �Treble pot;� decrease R10
for more treble, increase R12 for less treble. R13 is the �Bass pot;�
increase R13 for more bass, decrease it for less bass. R15 is the
�Middle control;� increase R15 for more mids, decrease it for less
mids. R22 controls the amount of boost you get in boost mode; increase
it for more boost, decrease in for less boost. For a cleaner tone,
change R3 and R4 to 100k ohms
Schem is at-
http://www.vhtamp.com/avsp16.html
My read of the schem is that the amp has a Fender TMB tone stack with
fixed values for the three pots, plus an adjustable tweed Princeton
type tone control. The changes described above are changing the fixed
values for the TMB pots. My changes include this and other typical
harp stuff, as below, referring to the schem. I listened after each
change. One of the last changes was the slope resistor, which had the
biggest benefit. One might try this first, but effect is uncertain in
the absence of the other changes.
TMB values-
R10- 1.5K
R12- 100K
R13- 100K
Slope resistor
R9- 56K
Cathode bypass caps
C8, C13- 25 mf
Coupling cap
C14- .047 mfd Mallory 150
Princeton tone control
C11- lift
Input grid resistor
R7- 5 meg
As expected from the eyelet board construction, the changes were
pretty easy to do. Some of the hookup wire lengths were short enough
to make insertion into the eyelets a little tricky.
The changes did bring up the low mids, and preserved the feedback
resistant quality of the amp. It also reduced the strength of the
pull boost control, a good thing, I think.
Your mileage may vary........ I am not an amp tech.
Jim
Mike Fugazzi
If you're not into mods, mine, which will continually be featured on
my YouTube and mp3 from live shows, cost me a total of $275...which
includes the amp, used Eminence Ramrod, Tung Sol RI 12ax7, and JJ
6V6. I have not messed with the guts yet as I wouldn't even know
where to begin.
The stock speaker isn't all that loud, and the EQ is VERY flat...the
Ramrod puts this amp in Double Trouble/Pro Jr volumes, IMO.
If I had the money, I would go with the VHT Classic 6 and a Cannabis
Rex speaker.
Splash!
pull/volume knob which activates an additional gain stage. The push/pull
switch also can be used with a foot pedal. I don't remember the tweed champ
having THAT! Also has diodes instead of the GZ3Y or 5AR4.
Having not completely removed the eyelet board to draw out a schematic yet,
I suppose the additional gain stage might be coming from the second half of
the 12A*7. Or a germanium transistor somewhere? I did remove the chassis
for a quick inspection.
Also, swapping tubes for American Vintage 6V6GT & 12A*7's is an adventure
into warm creamy tones that boutique amp makers strive to achieve. That
russian 12AX7 is kinda harsh! (Good for guitar)
Currently running a metal 6V6GT from an old 1959 Cadillac car radio and
aWWII US Navy JAN 12AU7.
This amp absolutely LOVES the Shure 545SD. Not too shabby either with
vintage hot bullets, but there must be some kind of DNA match with the 545.
I can dime the Special 6 with the high-gain stage on and it just honks like
a cool horn. This is definitely the mic for this amp.
On my list of things to do: Create and install a line-out with adjustable
line level pot. It's really not loud enough to stand alone with a bunch of
guitar stacks on stage =8^D.
I repeat, "Thanks, Mike!"
Splash!
Splash!
Oh, and thanks for the links to schematic &c.
Splash!
----- Original Message -----
J. Scott Ball
mess with it, just the tubes some, love it, I was wondering does anybody get
a hum in thiers when the volume is turned up a quarter or more with even
more when the boost is pulled, I need to get it out of my house and plug it
in to a different circuit, but if the volume is at 12 oclock or more I can
still hear a hum ten feet away....thanks....Scott
Arthur Jennings
interview<http://www.frugalguitarist.com/Frugal.aspx?Issue=19&Page=Terry%20Buddingh%20Interview>with
Terry Buddingh, the designer of the VHT Special 6:
While it had to be as minimal as possible, it also had to have some unique
> features to set it apart from the pack. So I designed a unique preamp
> circuit using a classic tone stack, but with resistors in place of pots, and
> combined this circuit with a single-pot tone circuit that’s essentially in
> parallel with the Volume control, and thusly isolated from the tone stack.
> The trick is the fixed tone stack can be defeated/bypassed with a footswitch
> (or the push/pot switch on the Volume pot), while the separate Tone control
> remains functional.
>
So, apparently the "Boost" switch doesn't actually add any gain; rather, it
increases *apparent* gain by removing the passive bass-mid-treble control
stack from the circuit. Clever.
Also some interesting stuff in the interview about how you can tune the tone
stack to taste by swapping resistors.
Arthur Jennings
http://www.timeistight.com
Rick Davis
I agree... Great little amp!
A couple of things:
The Pull Boost doesn't activate an additional gain stage. It lifts the
ground on some components in the tone stack, thereby increasing apparent
gain.
The harshness you heard in the amp may not have been from the 12AX7 tube. I
heard the same reedy harshness, and in my case it was cured by a change in
the cathode bybass cap. Running a low-gain tube like the 12AU7 may mask the
hashness, but it will be at the expense of much of the amp's gain. With a
6-watt Class A amp you don't have a lot of power to waste, and a 12AU7 tube
has a different impedance than the tube you replaced, which affects
components downstream of the tube.
You're absolutely right about the line out. The amp is not loud enough for
most gigs, and would get buried at your average blues jam. But the tone is
glorious, so a line out is a must. There is room on the back of the chassis
for the line out jack and a LO Level pot (both standard features on the
Mission Chicago 32-20 amp, btw). Or, you could use the 4-ohm speaker tap as
the line out, it the amp owner does not anticipate the need to drive a 4-ohm
cab.
--
-Rick Davis
The Blues Harp Amps Blog
http://www.bluesharpamps.blogspot.com/
Rick Davis
louder. That may be at least partly due to the speaker breaking in. It
sounds great.
Also, one of the best features of the amp is this: A big comfortable
leather handle!
This amp is very thoughtfully designed. Even clever. When poking around in
it we could tell it was designed by musicians who actually listened to it at
every step of the process, something not always evident in low-priced
amps.. Even Bruce Collins was impressed.
But it is still a guitar amp, and nearly all guitar amps have design
elements that make them less than ideal for harp. Fortunately the circuit
of the Special 6 just begs to be modded.