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Preamp valves / tubes

Mark PMark P Posts: 2,180Member
I was reading an article about amps in general. A section on Preamp valves / tubes caught my attention.

It mentioned the commonly used 12AX7 (ECC83)which it referred to as a "high gain" design. They mentioned earlier Fender amps being fitted with a lower gain 12AY7. My interest was further aroused when it mentions SRV favouring the 5751 (another low gain substitute).

It sounded it would suit me to replace "sizzly compressed distortion" (their words) of hotter preamp valves for what was described as "more punch and clarity" to be experienced with low gain valves.

I've certainly always been impressed by the clarity of SRVs sound even when there appears to be a high level of overdrive. Is that clarity in part due to these valves?

The Fender VibroChamp XD I use has a 12AX7 so it is making me wonder .....

Anyone done a valve change with this sort of resulting tone change in mind or just generally had experience of low gain preamp valves?

Comments

  • LesterLester Posts: 1,503Member, Moderator
    No, but I am likewise interested as I have a 12w Fender '57 reissue amp with 2 x 12AX7s. The paperwork says that one can substituted for a 12AY7 to get the original '57 sound.
  • Mark PMark P Posts: 2,180Member
    Here's a link which gives gain ratings od the various types of tubes / valves:
    Gain factors - preamp valves

    I notice the 5751 (that the Magazine article mentioned in regard to SRV) is not as extreme a change as the others.

    Interested to hear about your situation Lester and what the paperwork mentions. VERY nice amp you have there BTW - excuse me while I drool quietly in envy. \:\)

    I suppose the general use of the higher gain 12AX7 is rather like the abundance of "hot" pickups being stock in so many guitars.

    I believe my little VibroChamp XD is a Cathode bias amplifier and shouldn't require any adjustments and will work with a wide range of tube plate currents, as the circuit is "self adjusting" and is considered plug'n play when it comes to replacing the tubes. BUT - having said that I've never even opened up an amplifier to look inside - so it's a bit of a scary thought at the moment!
  • Ape09090Ape09090 Posts: 2,744Member
    Hello guys,

    I don't think you need to worry about bias adjustment for the pre-amp valves only for the power valves but I could be wrong so don't take that for gospel.

    I have a Jan/Phillips 5751 that I use in my electro harmonix hot tubes pedal and I like the 5751 very much,it's slightly more open and cleaner/clearer but still retains the richness of the harmonic break up but with that break up more as an undertone rather than being the main ingredient.

    I have some 12 au7's here too and they're even more open being lower gain tubes but if you were inclined you could say they can sound thin when it comes to break up but that would depend on your mood and who you've been listening to recently.

    I also have some 12at7's and they're worth looking at too if you're into swopping valves out.

    You can have quite a variation in different 12ax7's coming from different manufacturers too,I have a Brimar 12ax7 here which is a monster for adding gain and keeps the purity of it's flavour all the way through the gain stages it provides too. If I'd known about that one when I was younger I would've been a happy bunny I can tell you.
    I have a Mullard 12ax7 as the pre amp in my vox,all the other tubes/valves I'm talking about here I use in my valve driven foot pedal as it's so much easier to swop them in and out of that and it has 2 tube slots so I can play about quite a bit mixing up different tube types to see how it behaves with the different combinations in it.

    I've been looking for a good 12ay7 for months now and they very rarely come up you do get some RCA 12ay7's coming up for sale now and then in the USA but costs mount up and I don't really want to spend £25 on 1 tube when re-sale may not be guaranteed at a similar value so...

    I don't think you'd want to go below about a 70 gain valve for using as a preamp in an amp so a 5751 or if you're particular amp has a history of using certain tubes/valves say a 12at7 then maybe that's worth a try but I'd do a fair bit of research before I swopped tubes out of an amp myself as I say it's easy for me having a valve pedal and I'd recommend that as a way of learning about valve values and types myself,I think I paid just over 50 quid for mine on ebay.

    Just found the link,

    http://www.ebay.co.uk/itm/Electro-Harmon...cvip=true&rt=nc

    There are a few types of foot pedal about that use valves and have easy access to them too...
  • LesterLester Posts: 1,503Member, Moderator
    edited August 2016
     Originally Posted By: Mark P
    Interested to hear about your situation Lester and what the paperwork mentions. VERY nice amp you have there BTW - excuse me while I drool quietly in envy.

    This advert has description, specification and reviews tabs half way down the page. That's the same text I have about swapping one 12AX7.

    I don't think you need to to drool as I think we both have 12AX7 and 6V6 valves in a Fender amp so they will not sound so very different.

    Have you seen this video which compares 12AX7, 12AY7 and 5751 valves? It's probably of more interest to me as it is the same 5E3 circuit my amp has and he even has the identical Tele to me, so it's a pretty interesting test for me - and I like the 12AY7 sound best. I don't know what circuit the VibroChamp XD has but as I say, it's a Fender and with the same valves so these are most definitely family!

    Thanks for the link, that is most helpful. I have just ordered an Electro-Harmonix 12AY7 from Watford Valves.
  • Mark PMark P Posts: 2,180Member
    Thanks for your link to that comparison video Lester. Interesting listening. After a couple of goes I'm not 100% sure between the 12AY7 and the 5751 ... but I'm pretty sure i like the 12AX7 less than the other two as it's sound definitely seems just a bit compressed and clipped to my ears. I'll listen some more later - I'll try playing it through the hi-fi sytem.

    Thanks for the information in your post Andrew. The thought occurs having seen what you've said there about the pedal that I've got a Vox Tonelab LE with a 12AX7 in it (assuming the previous owner didn't change it).

    Oddly enough I went into the newsagent today - and found guitar and bass magazine have just released a special issue - DIY on pedals and amps. So I've got some reading to do to try to understand this topic better.

    Thanks for the help guys. \:\)
  • LesterLester Posts: 1,503Member, Moderator
    My 12AY7 valve arrived yesterday and this evening I put it in my Fender amp. The 12AY7 has 45% of the output of the 12AX7 so it was pleasantly quieter. Before, the volume does nothing until I get to 2.5 and then it kicks in. By 4 distortion was starting to be noticeable if my guitars are turned up to 10. Now, it is still the same at the bottom end, kicking in from nothing to plenty at 2.5 but the sound is now clean all the way up to 7. I didn't go higher than 7 as it was unbearably loud yet still clean. From weaker to stronger signals: Strat, Tele, Burny with P90s, Burny Archtop (single humbucker).

    I cannot describe it better than you can hear it in the YouTube video comparison but the 12AY7 sounds more natural to me, a little less honky which sounds better, less artificial. I love the Fender sound, especially with the Tele for country but the sound before was a bit OTT, as though the mid was too high and overly compressed (without a compressor being used). It now sounds gorgeous and clean. I'd even say a bit thicker, maybe it accentuates lower mids more than the 12AX7. And it is a lovely clean valve sound, ready for any pedals to do the dirty work should it be required. I was so enjoying clean and natural I played without any pedals all evening.

    In short, the 12AY7 is staying in there.
  • Ape09090Ape09090 Posts: 2,744Member
    Nice report Lester,thanks.

    What brand is the 12AY7 please?

    I took delivery of 2 Brimar ECC83's today and I had a good old play about with them in the pedal along with a Mullard ECC81 and an E.I. (Yugoslavian brand) 12AX7.

    I really enjoyed the extra head-room the ECC81 (12AT7) was giving me and mixing that valve up with a higher gain 12AX7 and a lower gain one passed a few nice hours here this afternoon.
  • LesterLester Posts: 1,503Member, Moderator
    It's an Electro-Harmonix 12AY7 from Watford Valves.
  • Mark PMark P Posts: 2,180Member
    That is a report of great interest to me Lester. Very clear and detailed and tells a great deal - many thanks to you for that. \:\)

     Originally Posted By: Lester
    And it is a lovely clean valve sound, ready for any pedals to do the dirty work should it be required. I was so enjoying clean and natural I played without any pedals all evening.

    In short, the 12AY7 is staying in there.

    "Natural and less artificial" - that sounds great to me! I'd have to call that a very successful outcome - congrats on the upgrade.
  • Ape09090Ape09090 Posts: 2,744Member
    Thanks Lester
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