2 Channel "H" tube questions

Discussion in 'Amplifiers' started by BMiller, Jun 10, 2016.

  1. BMiller

    BMiller New Member

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    I picked up a used 2 Channel "H" combo a few weeks ago and can't find much info on it and the tubes. My question regards the use of the 12WD7 and it's role. Now I'm assuming that this tube is the phase inverter (it should be considering the physical location). My question would be why they used this tube in this slot and if any damage would be caused by swapping it out for a balanced 12AX7. Also, might anyone know how the tube topology is used in this circuit? Such as, V1A feeds the clean channel which then, after the gain and tone controls, goes directly to the input of the first 12AT7 of the reverb circuit. I have yet to pull the chassis.

    As for the amp....man is it honest! Unlike my other amps, I can clearly hear the differences between the various guitars and pickups that I have. Not that my other amps are shabby at all....they just don't show the huge diffence as this one does. The power tubes have to be swapped out though. The tubes it came with were so far out of match (20+ mV plus) that I couldn't bias it properly. I swapped in a pair of Sovteks that are within 3 mV of each other but they sound rather dull and "cardboard-ish". Nonetheless, this amp has a lot of tonal options and has some great sounds in it.

    Thanks for any tube info!
     
  2. AP515

    AP515 Mostly Normal

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  3. Rider1260

    Rider1260 New Member

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    From Sean at PTC as far as power tubes go you can also put in EL34s using the same bias figure.

    Hi Michael,

    Thanks for contacting PRS Guitars.

    To re install 6L6 tubes in your two channel H we would recommend Ruby 6L6 GCMSTR tubes. The bias would be 30 + /- 5 .
     
  4. BMiller

    BMiller New Member

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    AP515 - thanks for the tube chart and manual....but yes, I've seen this before.

    Rider - Thanks for passing that info along as well! For power tubes, PTC and Doug (Dougs Tubes) both recommended those Rubies. I like the EL34 variants of those for my M style amps. I was leaning towards the JJ 6L6's because I liked them a lot in several Peavey amps I owned over the years (Ultra, Ultra Plus, XXX, and the JSX I still have) but I will need to look into the Rubys. .

    I was finally able to get back to the amp today after having my water tank blow up Friday evening (spent all day yesterday replacing it...I'm an electronics tech and not a plumber by any means) and did some tube rolling. I replaced V1 and V2 with some JJ ECC83 HGs I had on hand, left the Tung Sol in V3, left the JAN 12AT7's in V4 and V5 for the reverb, and swapped in a JJ Balanced ECC83 (again, had on hand) to replace the 12AT7 that was in the PI slot (V6). Holy Cow what a change! Clean channel breaks up sooner but is easy to control via the guitar volume. I might end up pulling this tube and putting in either the standard ECC83 or maybe even a 12AT7 depending on what I need this amp to do. On the gain channel, I'm now hearing the gain that I've read about. The amp is louder, punchier, and just plain out more "tonefull" than earlier. I had to change the tone controls drastically to get control of it. I can only imagine what some good power tubes will do to this amp (ordering today)! I'm posting this in part to talk about my thoughts but more so the next person in my situation might find this info useful (not much info that I could find).

    Out of curiosity, since both of you own this amp, what tubes (pre and power) are you guys using? I'm just playing with what I have on hand right now and would gladly take recommendations on different options.

    Something else, what speakers are you using with the amp? The stock CL80 is a great speaker, but I'm not sure if I like it yet. It seems to me to be rather, well, sterile with this amp.
     
  5. AP515

    AP515 Mostly Normal

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    I have JJ 6L6's in mine. I still have the stock speaker also, but I have a Eminence Texas Heat that I'll drop in sometime to check it out.
     
  6. andy474x

    andy474x Knows the Drill

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    If you want to cut some gain out, try a JJ 5751. 12at7's can sound pretty thin in a gain stage! 5751 has about the same gain as the at7, but with the tonality of the ax7.
     
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  7. Rider1260

    Rider1260 New Member

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    Hey BMiller
    I have JJ EL34s in my H and I think the rest are whatever came stock.
    Please don't get me started tube rolling in this amp also I thought I was past that one I traded my Marshall for the H


     
  8. LSchefman

    LSchefman Hears Tones

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    If you're happy, why roll tubes?

    If you're not, it's a different story.
     
  9. DreamTheaterRules

    DreamTheaterRules New and improved member

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    BMiller, I'd be interested in hearing how much change the 12AX7 in the PI slot made alone.
     
    #9 DreamTheaterRules, Jun 13, 2016
    Last edited: Jun 17, 2016
  10. BMiller

    BMiller New Member

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    AP - when you try the Texas Heat I'd be interested to know how it sounds in the amp! I am looking into it now.

    DreamTheaterRules - You know, since I don't want to do the gymnastics to swap V1 and V2 back, I will take the time to A/B the AX and AT PI drivers as I'm curious as well. I have some thoughts about how it will sound but I'll give it a shot. I have a feeling that I know exactly how it will sound, but I will do it and document my thoughts.
     
  11. DreamTheaterRules

    DreamTheaterRules New and improved member

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    Much appreciated! I was initially surprised when I saw that, and my first thought was that it could turn the clean channel into a smokin' blues channel. But the OD channel already has a lot of gain so interested to see how that pans out. You let me know when you can, and I'm tempted to get my nice balance JJ or my lowly Sovtek LPS (which is a really popular PI tube!) and see what happens. You've definitely got me interested in something I hadn't thought about since I first got the amp.

    Oh, we get a new brother in the C50 club today so I imagine he'll be watching this too. Wonder if PRS has an official stance on this change. I might shoot them an email...
     
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  12. BMiller

    BMiller New Member

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    Brother, with the way my amp is currently tubed up you can get that smokin' blues channel all day long depending on the guitar, pickups, pickup selection and how you ride the volume knob! Cranking the clean channel gain and using the bridge humbucker setting of my 91 CU24, I set the amp up for a heavt ACDC sound. Roll off the volume and then you have Malcom. Switch the rotary up a notch and you have some serious Texas heat! Roll the rotary up to the neck humbucker, back off the volume, and you have some great cleans.....or crank the guitar the volume for some killer blues solo tones.

    For the two tubes you have (neither of which are bad!) I would say to give them both a run and see how you like it. I would also recommend an HG version of the ECC83 for V1 if you're wanting something with with more gain on the clean channel (it certainly worked for me!) Talk to the guys at Eurotubes and explain what you want....they will give you solid advice. Doug at Dougs Tubes is also great to deal with!

    I will try to do my test tomorrow or Saturday and will let you know my opinions.
     
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  13. bodia

    bodia Authorities said.....best leave it.....unsolved

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    In the club! Watching with interest!
     
  14. DreamTheaterRules

    DreamTheaterRules New and improved member

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    I have other tubes, just mentioned those as I bought both specifically because they were supposed to be good (for new stuff) PI tubes. The JJ came from Bob at Euro and is balanced, the LPS has a great rep as a PI especially with the Marshall guys. I have a few NOS as well, but my main first interest before I try that, is just how much difference the 12ax7 Makes in the PI slot because it would be a whole lot hotter than the stock tube. I can't stand it. I'm going to try one this weekend! :)
     
  15. DreamTheaterRules

    DreamTheaterRules New and improved member

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    I'm curious, because in theory this wouldn't add "gain" to the amp such as more gain in the pre-amp stages, but it would push the power stage much harder at any given setting on the master. Meaning, 10:00 now might be like turning it up to 1:00 was. I'm thinking it should be much louder earlier on the master, and only push more gain when it gets really loud because it's pushing the power stage harder, not the pre- obviously.

    Does this go with your thoughts so far? It sounded more like you felt it had additional gain, such as more gain in the pre-stage would add. Just food for thought as you try this out this weekend. Meantime, if I get home in time tonight, I'm going to try it.
     
  16. BMiller

    BMiller New Member

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    So I was able to take the time yesterday and do a non-scientific A/B of the AX and AT tubes in the PI slot. My assumptions going into it were confirmed - the AX makes the amp sound and feel so much better! Much more open and responsive.

    I can go into the technical details if you want but I'll keep it simple - the phase inverter has the most impact on tone, feel, and output than any other tube in the amp. This is the tube that connects the input section to the output section and its output level, gain characteristics, and tonally qualities dictate how the output tubes work. This tube is also responsible for what many refer to as "power tube distortion". With this amp, the "Master Volumes" control how much signal hits the PI input (it's called a Pre Phase Inverter Master Volume). This type of circuit tends to be thin and buzzy as you are hearing preamp distortion until you get the volume up high enough to start driving the PI (think about the early JCM800s that had a Master Volume). Truth be said, Sewells design on this works very nicely and sounds great at many levels and I would really like to see the schematic!

    So why is this important and what impact does it have on PI tube selection? Well, you need a tube that can stand on its own with a high enough gain factor to account for lower incoming signal levels. The AX can do this nicely while the AT will struggle and tap out. The AT will work mind you, but the power tubes will never get to work as much as they are capable of and you won't have the joy of "feeling" the amp as you play at higher levels. Also, your output tubes might as well be cheap Chinese white boxed seconds because you will never hear the difference between them and some nice NOS tubes.

    Now all of the talk on tone and feel is subjective and what you need from any given amp might be very different from what I need. However, it won't matter how nice of a tube you put in V1 (the first tube that your signal sees in any amp) or how nice your output tubes are, if the PI can't provide the needed gain for the circuit in a tonefull way, your expensive guitar running through expensive pedals into an expensive amp through expensive speakers in an expensive box will sound dull and lifeless.

    And with that said, I'm stepping off of the soap box for now.
     
  17. DreamTheaterRules

    DreamTheaterRules New and improved member

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    So, I got majorly sidetracked this weekend and didn't get to try it. I'd be interested to hear more about the post swap tone though.
     
  18. DreamTheaterRules

    DreamTheaterRules New and improved member

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    Here is the response from PRS... "There should not be a problem using a 12ax7 in the PI slot. Compared to the AT the AX should add a little gain and warmth with less definition and clarity. If you try it let me know how the swap works out for you. "

    BM, I read what you said above. I know what you mean, but feel that in general I'd agree, but it's not necessarily that simple. I'm no amp designer. But from what I know, if the amp was designed to run on AX7, then an AT might make it weak or anemic or thin. But if it was designed to run wide open with the gain provided by an AT, then it won't sound anemic with one. So I agree that if you took some amps that do run AX7 in PI, and replace it with an AT, you might get exactly what you said. But this amp was designed for AT7. So, I'd guess it will change it, and anxious to try it, but it may not transform it. I may LOVE it. I hope so.

    The response above curbed my initial wild enthusiasm a bit. The definition and clarify is what I love about this amp. One of the things that sets it apart and makes it more "high end" IMHO. So, here's to hoping I get about 3 times as much gain and warmth as I lose definition and clarity. If so, I have a nice old 5751 to try. :D
     
  19. BMiller

    BMiller New Member

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    DreamTheaterRules - Thanks for posting the feedback from PRS. I agree with the "add a little gain and warmth" but not so much with the loss of "definition and clarity". The definition and clarity is still there....just back off the guitar a bit, but when you do, the warmth and tone remains.

    Yeah, my post was rather simplified. And I agree with you, whatever the amp was designed to run with probably sounds the best with that tube and gain factor. There are components that are picked due to differences in the tubes. As far as the "H" goes, the only thing that makes me think that the amp might have been designed with an AT in the PI is that both you and I have them in that slot. The layout in the manual calls for a 12DW7 which is half AX and half AU and when I researched getting a replacement, I found quite a few references to this amp as well as how harp players loved them in their tweeds. I need to add one to my 6L6 order just to hear the difference that it can make to the power section.

    I still highly recommend trying out the AX and letting us know what your thoughts are. I find that the AX opens up the output section and allows it to "breathe" and work. That 5751 might sound really good as well.....I need to dig one or three out and give it a shot as well! Oh the joys of tube substitutions!
     
  20. lv4rock

    lv4rock New Member

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    Actually, the 12DW7 is for the effects loop but mine came with a 12AT7 (ECC81). I tried a 12DW7 in the effects loop but found that the amp sounded better with the 12AT7. Also, I noticed that 12AT7 tubes which have longer plates act microphonic in the reverb and effects loop slots as opposed to the ECC81 versions which have shorter plates. No problems in the PI slot though.
     
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