VHT Special 6 Ultra - Getting Ultra Channel cleaner/brighter

Discussion in 'Amp Tech Center' started by jdpas29, Sep 30, 2019.

  1. jdpas29

    jdpas29 TDPRI Member

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    Hello, all! I love this forum. I mostly lurk but have run into a situation where I hoped that a consultation with the Tele gods would be of value.

    I have used a VHT Special 6 ultra for years and I really love it. It was the head only version that I modded with a little 6" speaker which works great for worship music mic'd up at low volume. But in order to achieve the low volume that I am getting I have to use the JHS little black amp box in the effects send/return loop which acts somewhat like a master volume (I understand that it isn't LOL). I use pedals for very light distortion and I prefer to have headroom on demand with slight breakup by pick sensitivity as opposed to always on distortion/overdrive. My question has a few parts...

    1) Can the Ultra channel be modded to not have such a dark, muddy character and essentially be another clean so that i could crank it to the point of breakup and then knock that volume down using V1B (clean side) like a master. Would this make sonic sense to do? I'm not that tech savvy so...

    2) Could the pinout of a 12DW7 help with this if the 12ax7 side was V1A and the 12AU7 side was V1B?

    3) Would it just be better to do the master volume mod and use the clean channel like I'm already doing?

    Thanks ahead for any help. Peace and brass barrels to you...
     
  2. Wally

    Wally Telefied Ad Free Member

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  3. jdpas29

    jdpas29 TDPRI Member

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    I have read through that page and will be doing the master volume mod. I would like to gain stack a bit with the ultra channel. I just want that channel to not be so dark and muddy right off the bat. It has to be some capacitor values and such that are doing this. Just wondering what may be an acceptable method to make the freq response and character of the ultra channel a bit more Champish or at least flatter in response. —-I don’t see anything on his page for this. —- it’s possible that the master volume mod alone will accomplish what I would like tonally. Thanks for responding
     
  4. Obsessed

    Obsessed Telefied Ad Free Member

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    Have you considered a larger speaker? My S6U has fairly good headroom through a 10". Also, what about going to a 6L6 power tube? I am not sure what happens, but you will find some discussion in the VHT thread in the Amp owner's section.

    Good luck and it will be interesting to know what you do.
     
  5. Wally

    Wally Telefied Ad Free Member

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    This is a single channel amp with a tube stage cascaded in front of the clean mode preamp stage in order to achieve the higher gain Ultra mode. If one were happy with the clean mode and wanted to change the Ultra mode, one might want to deal with the bypass on V1A cathode....reduce or eliminate the capacitance on that bypass??? If one wanted to address the overall voicing, one might change the tone Stack cap values.
    And actually the little black box you are using is a type of master volume. IF you can get a usable sound from the clean mode when running that little black box to knock down the volume, then the ’true’ in-circuit MV might be all you need to do. However, if you want to use the gain mode, I suppose you are looking at doing some deeper mods.
     
  6. jdpas29

    jdpas29 TDPRI Member

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    Thanks for the reply, Wally. Just did the Master volume mod and WOW!! I don't know why this isn't stock on these amps as many are trying to use smaller amps like this for worship settings or low volume playing. I actually removed the jack for the ultra channel since it was useless to me and placed my new MV pot in the ultra channel jack spot. worked out very well.. just had to solder the old channels' grounds to the new pot pin 1. I will say that the pinout labeling on the tube socket is NOT what the tube actually does. not sure why it is this way but i had to just trace the white wire from C23 to where it contacted and figure out that it actually mounts to an unused pin and jumps over to pin 5 through the R38 resistor. That took a minute.

    Even on the low power setting you want to be able to smack the PI tube with enough signal from the preamp tube to get breakup. The little black amp box helped with volume but the degradation in tone, particularly loss of bass response with the low level signal at that stage didn't work well at all. Now I can get that touch sensitive breakup with this amp into a 6" speaker that I mounted in the head cabinet and it is perfect for what I'm trying to use it for.

    On a side note, GE 5751 in the PI is glorious. RCA 6V6 ftw.

    thanks for the help and replies.
     
  7. jdpas29

    jdpas29 TDPRI Member

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    anyone have a favorite cap value/type for the master volume mod? I used a single 100pF. sounds well enough.
     
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