VHT Special 6 Project

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VHT Special 6 Project

Post by Slowy »

Disclaimer: What I know about circuitry is how much I don't know. I'm good with a soldering iron however.

Got this amp back from Robthemac after selling it to him a few years ago. I bought it originally with an eye to learning amp modding stuff and that's back on the agenda.
IMG_4786.JPG
IMG_4786.JPG (2.05 MiB) Viewed 533 times
The amp is quite big and bright sounding. Lots of bottom end and heaps of presence when pushed. The sound should work well with a band, (will try Thursday) but it's too strident for happy home use.

It's handwired in China and it's cheap. This suggests cheap components to me.

Question: Would upgrading certain components have an effect on the tone? (Notice I'm not saying 'improve' because I only have a vague idea of what I'm looking for). Let's say a warm, 6V6 clean/ breakup tone for single coils.

There's lots of mods for this amp but I'm more interested in tone than options. I have several pedalboard engine amps; would be cool to have something that did its own thing.

Any thoughts? Here's the schematic:
VHT Special 6 schematic.jpg
VHT Special 6 schematic.jpg (154.84 KiB) Viewed 533 times
"We were playing so loud that just one note on the guitar was sufficient".
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Re: VHT Special 6 Project

Post by Slowy »

Putting this here to keep it all in one place:

Thing about the Special 6: It actually has bass, middle and treble controls. Except instead of pots it has fixed resistors inside on its circuit board. They are: R10, R12, R13 and R15 with R9 setting the slope. It's actually related to the Fender Champion 600 circuit that has the same thing, a tone stack with no controls. I should have called the popular "lift R19" Champion 600 mod "The Much Mod" 'cuz I'm pretty sure I originated it. The boost switch on the Special 6 does the same thing as the Champion R19 lift. Unlike the Champion 600 the Special 6 has a tweed style tone control in series with its internal tone stack. Yup... It has two tone controls in series. Like I said, there are bass, middle and treble controls in there with no knobs.

It's relatively easy to juggle nickel and dime resistors substituting for R10, R12, R13 and R15 rather than buying expensive tubes. Unlike blowing a lotta money on tubes it actually works!

Functionally it's a '60s Fender tone stack.

R10 and R12 function as a bass control. The sum of R10 and R12 should add up to approximately 250k. R13 (33k) functions as a treble control. The treble pot in a Fender tone stack is wired to function as a variable resistor. Fender uses a 250k pot so values from zero to 250k set your treble response.

R15 is a 6.8k resistor, same as the 6.8k tail in larger Fenders. Substitute 15k if you want more mids.

Or rig a couple 250k pots in there so you have real bass and treble controls.


For some real fun you could change C6 to 500p / 400v, C9 to .022uf / 400v, C10 to .022uf / 400v and R9 to 56k. That's a Marshall stack.
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Re: VHT Special 6 Project

Post by H671 »

Slowy wrote: Tue Jan 04, 2022 9:58 am Disclaimer: What I know about circuitry is how much I don't know. I'm good with a soldering iron however.

Got this amp back from Robthemac after selling it to him a few years ago. I bought it originally with an eye to learning amp modding stuff and that's back on the agenda.
IMG_4786.JPG

The amp is quite big and bright sounding. Lots of bottom end and heaps of presence when pushed. The sound should work well with a band, (will try Thursday) but it's too strident for happy home use.

It's handwired in China and it's cheap. This suggests cheap components to me.

Question: Would upgrading certain components have an effect on the tone? (Notice I'm not saying 'improve' because I only have a vague idea of what I'm looking for). Let's say a warm, 6V6 clean/ breakup tone for single coils.

There's lots of mods for this amp but I'm more interested in tone than options. I have several pedalboard engine amps; would be cool to have something that did its own thing.

Any thoughts? Here's the schematic:

VHT Special 6 schematic.jpg
I had one some years ago & they are great little amps. I had Alan from Anvil Amps mod mine according to the info that I found on the telecaster forum. It ended up as a 10 watt amp with a 6L6 power tube.
have a look here: https://www.tdpri.com/threads/vht-speci ... ad.207986/
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Re: VHT Special 6 Project

Post by jeremyb »

I guess it depends what you wanna get out of it tone wise, personally since its a fendery circuit I'd be trying to mod it to be more like a dumble, but then thats not to everyones taste...
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Re: VHT Special 6 Project

Post by Slowy »

H671 wrote: Tue Jan 04, 2022 11:31 am
Slowy wrote: Tue Jan 04, 2022 9:58 am Disclaimer: What I know about circuitry is how much I don't know. I'm good with a soldering iron however.

Got this amp back from Robthemac after selling it to him a few years ago. I bought it originally with an eye to learning amp modding stuff and that's back on the agenda.
IMG_4786.JPG

The amp is quite big and bright sounding. Lots of bottom end and heaps of presence when pushed. The sound should work well with a band, (will try Thursday) but it's too strident for happy home use.

It's handwired in China and it's cheap. This suggests cheap components to me.

Question: Would upgrading certain components have an effect on the tone? (Notice I'm not saying 'improve' because I only have a vague idea of what I'm looking for). Let's say a warm, 6V6 clean/ breakup tone for single coils.

There's lots of mods for this amp but I'm more interested in tone than options. I have several pedalboard engine amps; would be cool to have something that did its own thing.

Any thoughts? Here's the schematic:

VHT Special 6 schematic.jpg
I had one some years ago & they are great little amps. I had Alan from Anvil Amps mod mine according to the info that I found on the telecaster forum. It ended up as a 10 watt amp with a 6L6 power tube.
have a look here: https://www.tdpri.com/threads/vht-speci ... ad.207986/
Great point for helping clarify what I want.....

I want a 6V6 amp. Don't have one. So I want this to be the best 6V6 amp it can be.
"We were playing so loud that just one note on the guitar was sufficient".
Ritchie Blackmore.

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Re: VHT Special 6 Project

Post by Mattallica »

Lots of 6V6 amp options out there. List some examples you like?
Is it for band use or home use? or both?
I don't think the components will be any cheaper than what the major manufacturers are using.
Changing component values >> changing component quality. Tubes excluded.
What are your "pedalboard engine amps"?
Based on what you've said so far, I would change V1A to typical Fender values. Change R3 to 100k and C8 to 22uF. See how that tickles your fancy and report back.

Rob Robinette's amp voicing page is trove of goodness. Get some learning and inspiration there:
https://robrobinette.com/Voicing_an_Amp.htm

If you follow stuff about the tone stack works, I suggest having a play with the Duncan Tone Stack Calculator:
https://www.guitarscience.net/tsc/info.htm
It's so much more comprehensible once you can see a graph and how the changes shape things (the options are at the top of the page).

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Re: VHT Special 6 Project

Post by RectifiedAmps »

You could try swapping out the speaker before you do anything else. It could get you closer to the sound you want more than some simple mods and it’s easier to reverse if you don’t like it.

After that, I’d look at the weird dual tone stack design - having a fixed TMB-style tone stack, then the volume control, then a variable tone control - it’s a strange recipe for a ‘low-gain’ amp. It might sound more ‘open’ if you removed one of them. If you disconnect one end of R15, that’d basically disable the TMB so you could hear how it sounds with just the variable tone control.

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Re: VHT Special 6 Project

Post by Slowy »

RectifiedAmps wrote: Tue Jan 04, 2022 7:45 pm You could try swapping out the speaker before you do anything else. It could get you closer to the sound you want more than some simple mods and it’s easier to reverse if you don’t like it.

After that, I’d look at the weird dual tone stack design - having a fixed TMB-style tone stack, then the volume control, then a variable tone control - it’s a strange recipe for a ‘low-gain’ amp. It might sound more ‘open’ if you removed one of them. If you disconnect one end of R15, that’d basically disable the TMB so you could hear how it sounds with just the variable tone control.
It's a head. I have a G12H30, Blue and Alnico Fane to play with.
Thanks for the TMB tip!
"We were playing so loud that just one note on the guitar was sufficient".
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Re: VHT Special 6 Project

Post by RectifiedAmps »

Slowy wrote: Tue Jan 04, 2022 7:50 pm It's a head. I have a G12H30, Blue and Alnico Fane to play with.
Sorry - Looked like a combo in the photo.

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Re: VHT Special 6 Project

Post by Slowy »

RectifiedAmps wrote: Tue Jan 04, 2022 7:53 pm
Slowy wrote: Tue Jan 04, 2022 7:50 pm It's a head. I have a G12H30, Blue and Alnico Fane to play with.
Sorry - Looked like a combo in the photo.
You're right; it does.
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Re: VHT Special 6 Project

Post by Slowy »

Gave it a Tung Sol 12AX7 and an old Philips 6V6. There's definitely some sweet spots to be found. Does a crystalline clean tone with a thumpy bottom and the fairly maxed out tone is still well defined but with a tweedy grit.

It's all upper mids and presence; insists it wants to be a gig amp so I'll give it a workout with the band tomorrow.
"We were playing so loud that just one note on the guitar was sufficient".
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Re: VHT Special 6 Project

Post by Slowy »

Played this with the band on Thursday; an educational experience...

It's a single 6V6 putting out 6 watts max. Even with the volume at 4, tone at 3 it was so searingly bright that the whole band turned up way too loud to be heard over it. It was plugged into my Fane; my most mellow and hifi speaker.

So it's unusable in a band. I reckon it would actually work on a stage with 500 people in front; it cuts through that well!

If you think of the presence knob on a Marshall, this is like winding it up to 30.

So first circuit change is going to be teaching it some manners. Any suggestions?
"We were playing so loud that just one note on the guitar was sufficient".
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Re: VHT Special 6 Project

Post by robthemac »

Slowy wrote: Sat Jan 08, 2022 8:51 am Played this with the band on Thursday; an educational experience...

It's a single 6V6 putting out 6 watts max. Even with the volume at 4, tone at 3 it was so searingly bright that the whole band turned up way too loud to be heard over it. It was plugged into my Fane; my most mellow and hifi speaker.

So it's unusable in a band. I reckon it would actually work on a stage with 500 people in front; it cuts through that well!

If you think of the presence knob on a Marshall, this is like winding it up to 30.

So first circuit change is going to be teaching it some manners. Any suggestions?
The

Half-power mode takes away a lot of that presence, if it's loud enough.

Or buy Strummer's Bandmaster cab. That thing is warmer than my crotch will be after 90 overs of cricket today.

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Re: VHT Special 6 Project

Post by Slowy »

robthemac wrote: Sat Jan 08, 2022 9:13 am Half-power mode takes away a lot of that presence, if it's loud enough.
Half power takes away a lot of the body and harmonics too. Not desirable.

I don't want to dwell on why Cricket makes your crutch hot.
"We were playing so loud that just one note on the guitar was sufficient".
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Re: VHT Special 6 Project

Post by NippleWrestler »

Is it too bright even with the tone knob at 0? One thing that jumped out would be changing the cap hooked up to the tone pot for something bigger. That's rolling off high frequencies to ground so looking there might be an idea.

If you can access that capacitor, crocodile clipping other caps in parallel with it would allow testing different values until you're happy since capacitors in parallel combine their values.

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