can you substitue 12At or AU7s in a Trainwreck?

[aaronz28]

I know i'm playing with fire here, so no offense, but I now own a Liverpool clone, and while it really does the over the top hi-gain thing really well, it i uncontrollable to me if I have the volume above 12:00... and I really don't need the kind of gain it offeres even at that point.. so I find myself in the happyspot with the guitar volume at about 80%....

I have no interest in modding a perfectly functioning amp, so i'm wondering if this amp will accept a 12au7 or 12at7 just to experiment with.

i'd also be curious to know if anyone else has tried this and what the results were, before I go buying up tubes.

Thanks

Aaron

[dartanion]

Yes, you can swap those in either preamp position or in the PI. I have setup a few guys amps like this: V1 12AU7, V2 12AX7, V3 12AT7 with great results. You can mix them around until you find something that suits your tastes. The brightness may not change so much though as Wrecks are voiced bright to cut through the mix. To round off some of the brightness, try Saratov EL84s and a darker speaker/cab setup.

[paulster]

12AY7s are a good option as well depending on the gain level you want.

[aaronz28]

thanks guys,
what does putting a lower gain tube in the p.i do?

i put a 12AT in both the 1st Pre, and the P.I. and the gain is much more controllable now... however the amp sound buzzy or fizzy to me... it actually does with the 12ax7 but with the added gain, it isn't bad.

is this a characteristic of the EL84? if so... then i need to move on to an express LOL..

A

[dave g]

The Express and Liverpool have too much gain for my taste as well. I tried several different combinations of preamp tubes, and eventually settled on a 12AY7 in V1 and 12AX7s in V2 and V3.

[aaronz28]

the gain is one thing... it might be the fizzy ness of the EL84.. if that is in fact what I am hearing?

my other two amps are a Komet K60 and a 1968 50watt Plexi... both very similiar and I love the EL34 crunch... they have plenty of gain for me, but the Liverpool definately has more in that dept, but it gets unusable for me.

i push both my K60 and Plexi with a 1979 tube screamer for over the top gain when I need it... which isn't needed or even possible really on the Liverpool...

i thought the amp was just overly bright, but that wasn't really it.
when I dropped the gain with the 12at7. i hear more of that fizzy thing that i'm not really fond of.

is this just the nature of the Liverpool circuit, or the EL84 valve?

A

[sliberty]

I use a 12AT7 in several of my amps as the PI, including my Express. Love the results.

[dave g]

If you are getting some of that characteristic EL84 "fizz" then I can see why an AT7 would accentuate the problem. The bias voltage on those tubes is low enough as it is, making them a bit too easy to push into grid conduction. Combine that with the low output impedance of the AT7 and they'll be able to draw even more current than an AX7 PI would allow them to, resulting in an even greater negative bias shift due to the coupling capacitor charging, resulting in crossover distortion.

I would probably try changing the 220k bias feed resistors to 100k. You can also try a split plate load arrangement in the PI, using something like two 47k resistors for each side of the PI rather than a single 100k, then taking the output in between them.

[aaronz28]

that is a little beyond my amp knowledge...
are you referring to the Fizz just when using an AT7 in the PI spot?

i kinda like the usable gain that the AT7 has in V1.... but i don't like the added fizzyness....

i'm going to play it now with an AT in v1, and AX7 in V2 and PI and see how that works...


i wish someone made a reverse Yellowjacket so I could see if it really was the EL84 sound that I don't like, or if there are other things... oh well.

[dave g]

Yes, I was referring to an AT7 in the PI.

Seriously, try reducing the bias splitters from 220k down to 100k and see if it takes you in the right direction.

[aaronz28]

i will...

i just spent the last 20 minutes tracking down a bad 12ax7.. that I had in all three positions at some point this evening...

i've now got 12ax7s in the V2 and PI and a 12AT7 in V1... and its better... but still has a charachter to it that i'm not crazy about yet... but I have my 2.5 year old running around upstairs so i really can't crank the amp to see if I like it.


the only other 12At i have now is really microphonic so i need to get a few tubes to play with and I can make those changes... i'm sure I don't have those other resistors in stock either as i don't build or mod amps... but i am willing to toy with this.

what could I expect differently from a 12at to a 12au in V1?

Thanks

Aaron

[dartanion]

Wrecks are super picky about tubes, so make sure you find ones that work well in your amp. I normally go through every tube I have in stock to see what works well in a particular amp. V1 is the major problem area, followed by getting the right power tubes. The Saratov and other 7189 types seem to round of some of the sharpness of an EL84 and are a lot less bright and less fizzy.

My setup is a bit different in the PI as well, so it doesn't fizz as much in general.

[aaronz28]

i'm also curious...

about changing the 220k to 100k

looking at the layout drawn by Ron Worley,

looks like those bias feeds are R17 and R18???

sorry for the noobness here...

if i swap those to 100ks... does that only impact the bias on the the PI?


and in the end... what does a lower gain tube in the PI actually do for the tone of an amp?

thanks

Aaron

[geetarpicker]

Somtimes I'll use my wreck in a situation where I need the gain down to almost Fender levels. A good combo for me is a 12au7 in v1, a 12ay7 in v2, and a 12ax7 in v3. GK

[aaronz28]

i'll have to try that... i'm going to see if I can find some AU and AYs tomorrow. i dont know of any local place that has the less common tubes.

thanks

Aaron