Help! Fried my VHT Valvulator with + ground pedal

[deke99]

Hi all,

I recently built the Tone Bender Mark II Pro positive ground pedal.  My Valvulator is supposed to have isolated power supplies, so I tried hooking they pedal up for power from that using a separate power output for that one pedal.  Everything else (negative ground) was powered off my TU-2 on a separate Valvulator output.  Here is what happened:

I got a crazy noise out of my rig and immediately shut it down. . . it was then that I realized my mistake.  I had the 'Ground Lift' switch on the valvulator on, so I "think" this basically connected the grounds together.

Now when I try to use the valvulator (without the TB in the chain at all) it works fine with the ground lift in the 'off' position.  If I try and engage the ground lift, I get the same screaching howl that I had before that almost completely drowns out any guitar signal to the amp.

I tried contacting VHT directly about 1 week or so ago and haven't heard back from them.  Is anyone familiar enough with this circuit to know what I can do to try and fix this problem?  Personally, I'm a full fledged hack and can etch and build pedals, even do a layout now and again.  But I don't really understand how everything works together to alter signal etc.

Thanks in advance for all replies!

Derek

[cockaroacha]

I've searched for the schematic online before, & I've never seen it. I suspect that it's just a single 12A_7 low-gain input stage using one triode & a cathode follower (buffer) using the other triode. Pretty standard amp stuff.

As to your problem, I'm thinking that maybe the voltage regulator or rectifier on that 9v power circuit is now shorted to chassis ground. They're probably fairly common parts, so replacing them wouldn't be a problem. Worst case would be that the transformer winding is shorted, but I doubt it, the regulator or rectifier would probably blow first. Good thing, as a shorted tranny winding would probably make it a total loss.

Since the Valvulator runs on high voltage, read through the safety tips at Aiken Amps (in the Tech Info/Introductory section) before poking around inside. If you've never worked with tube amps before, do the reading first! It'll save you from getting zapped, maybe even dead.

http://www.aikenamps.com/

Looks like the Valvulator is supposed to be compatible with positive ground effects, just by swapping polarity in your cable. I'm not crazy about the way that they explain it, looks like it's WAY too easy to get things mixed up. You know how us musicians are! 

From the Valvulator FAQs

14) How can I power "positive ground" effects with the Valvulator 1?
Top

        Positive ground or reverse polarity effects can be powered from the DC outputs of the V1 three ways. If the effect has barrel type jack you can cut the plug from one end of the dual barrel cable provided and reconnect it with the leads reversed, or you can connect a new barrel plug to the raw wire ended cable provided. If the effect uses a mini phone jack, you can obtain a reverse polarity mini phone cable available from your Authorized VHT Dealer.

[deke99]

Thanks for your input I'll take a look at the regulator and/or rectifier and will definitely read up before attempting any sort of repair.

Thanks again %^&*aroacha!