Jet City Picovalve mod thread

Discussion in 'The Squawk Box' started by Dr.Distortion, Aug 27, 2013.

  1. wagdog

    wagdog Member

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    Trying to get my web page updated - it's mostly done. Just a little cramped for time right now. The 10k/3.3k on a switch is a nice boost.
     
  2. kfowler8

    kfowler8 Senior Member

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    Tone report:

    I took the Pico to rehearsal tonight for the first time. I play at a contemporary church service. Very rockin. The service is in a gym with sound dampening to help with the reverb. I was using a 12AT7 in V1, 12AX7 in V2, and KT66. The speaker cab was an 8 ohm 2x12 Mesa cab. Not sure if it had Black Widows or Celestions.

    First comment is related to how loud the Pico was. We mic all our speakers but the sound guy asked me to turn it down some when I was on 6.5. He said it was screaming. I ended up at 5.5 for Master Volume. Makes me think about all that wasted wattage in my Marshall and Mesa.

    As a whole I was really pleased with the tone. I thought it really sounded good. It had the right balance of dirt without sounding fuzzy or too "gainy". I was using one of my LP builds with a reverb pedal and Sparkle Drive in the FX loop.

    I think it's no secret that you can't ever evaluate how something really sounds until you put it in a live setting. This certainly was the case as well. What sounded great in the basement only sounded so so live. An example is the cathode bypass switch. At home I preferred the 22uf Cap vs. the .22uf Cap. Live the .22uf cap sounded the best. The 22uf sounded like it was just making the amp louder which makes sense given the graph curve. After this weekend I think I'll change it to a .47 or 1uf.

    The boost switch was a nice option. I pretty much kept it on.

    Loved having the FX loop. Can't imagine not having it.

    I was getting some really weird interference every now and then. It would go away after a minute. Not sure what that was about.

    So really please with everything. Very functional amp.
     
  3. duhvoodooman

    duhvoodooman Member

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    What exactly do you mean by "weird interference"? Can you describe it?
     
  4. kfowler8

    kfowler8 Senior Member

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    So I don't know if this is something local to Michigan since I've never heard it anywhere else. Anything with a speaker up here seems to get a ghost noise every now and then. It's like a buzzing sound that lasts between 10 sec and a minute and then it goes away. Sometimes you won't here it for weeks.

    Last night for the most part the amp acted as normal. Every now and then I would get this buzzing sound that would last up to a minute and then it would go away. It would happen about every 20-30 minutes or so. Almost sounds like when you have a live amp and the cable is not plugged into the guitar. It could be picking up interference from lights on stage. I've noticed similar issues noise issues with my strat.

    Note that it doesn't matter if I have my volume rolled down on my guitar or I have the mute switch engaged on the amp.

    Hopefully it was just a one time nuisance and it'll be gone by Sunday. I'm going to try a gate pedal just in case.
     
  5. duhvoodooman

    duhvoodooman Member

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    If it does it with the amp input muted, a noise gate won't help any. You'd be better off trying some kind of filter on your incoming power.
     
  6. duhvoodooman

    duhvoodooman Member

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    Last (I promise!) tube change:

    I bought a second ECC823 hybrid preamp tube (first triode = 12AX7, second = 12AU7) to try running my Picovlave with this tube type in both V1 and V2. (Special thanks to Wagdog, who was good enough to buy one for me along with an order he was placing with Eurotubes, so that I could avoid paying $9 shipping for a $13 tube! :thumb:)

    The amp sounded very good with both ECC823's in, but when I tried the 12AY7 back in V1, it was a tad brighter & livelier sounding to me, so that's what I'm going to leave in there. The two tube types have virtually identical overall gain (100*20 vs. 45*45), so the sweep response of the Gain control was exactly the same, to my ear. But a bit more brightness is a good thing with this amp, so I consider this my "final" tube compliment:

    V1 = EH 12AY7
    V2 = JJ ECC823
    V3 = JJ KT66
     
  7. kfowler8

    kfowler8 Senior Member

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    I'm really liking the KT66. I assume you are too.

    Good idea on the power conditioner. Haven't thought about that.
     
  8. wagdog

    wagdog Member

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    Hey there...

    Updated my page on the picovalve a bit: PicoValve Mods

    sorry it took so long, but I was pretty busy this past week or so.

    kfowler: thanks for that tone report. Sounds like the amp will be usable for ya, so that's cool.

    I was wondering if you folks found your bass control pretty much an on/off kind of thing? Mine is off at < 1.5 and sounds like it pretty much switches on > 1.5 with not much in the way of an audible change after that.
     
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  9. kfowler8

    kfowler8 Senior Member

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    Looking forward to reading your site.

    I'll have to look at the bass closer but that sounds about right.
     
  10. kfowler8

    kfowler8 Senior Member

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    Really nice update to your website. Really helped on a lot of questions I had.
     
  11. wagdog

    wagdog Member

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    I wonder if it's the circuit, or the taper of the pot? It's really noticeable on mine.
     
  12. tol

    tol Junior Member

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    RE: 2/5 watt switch. I have a few 6g6's and 6k6's. They are used in the Emery Sound MicroBaby. I think at least the 6g6 have lower voltage tolerance and was wondering if it would be worth keeping/repurposing the 2/5 watt switch for that?

    Rather than switching pentode/triode it would lower the voltage so the 6g6 will have a longer life? I tried using these in my Groove Tubes Soul O Single and I may have caused it harm. I know the Soul O Single and the UniValve were marketed as capable of sensing the needs of the power tube but Aspen Pittman discouraged me from using 6g6's and 6k6's.

    I just really like the idea of 2 watts. I tried both the Blackstar Ht1 and the Randall Diavlo 1. I felt like they pushed the speaker almost but not quite enough.
     
  13. duhvoodooman

    duhvoodooman Member

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    Should work. You'd need to determine what size dropping resistor you'd need on one side of the switch to get the plate voltage down to the recommended range for the 6G6 type, which looks to be 180V max. from the datasheets I could find. I doubt you'd need to do anything to run the 6K6 (315V recommended max. plate voltage), because the B+ voltage on the Picovalve is already pretty low, in the 300V range.
     
  14. tol

    tol Junior Member

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    nice! Thanks duhvoodooman!
     
  15. tol

    tol Junior Member

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    My bass is like yours but I didn't swap C10 yet.

    I performed the mods you detailed on your page. Thanks for that! My amp sounds great but it's very bright. I'm tempted to replace C1 and c3(on your site it says c2 but on my pcb it's labelled c3).
     
  16. wagdog

    wagdog Member

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    Yeah, those do cancel out some highs. I suspect it's speaker dependent. I thought it sounded better with them out... but I've probably got high freq hearing loss after 35+ years of amplified guitar playing.
     
  17. tol

    tol Junior Member

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    hey guys! Did I connect r22 to the screen supply node correctly or did I make it permanently 2 watts? I'm turned all around in my brain!
    [​IMG]
     
  18. wagdog

    wagdog Member

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    You're good.
     
  19. tol

    tol Junior Member

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    thanks a ton! It sounds fantastic with the amp set clean and my byoc RAT in overdrive mode(2nd to last setting on the rotary clipping dial)!
     
  20. wagdog

    wagdog Member

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    Cool. Glad to hear you like the mods you put in too.
     

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