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Post subject: Tube Question
Posted: Mon Mar 22, 2010 6:12 pm
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What tonal differences should I expect if I change my V3 (phase inverter) tube from a 12AX7 to a 12AT7? Also, I currently have a high gain 12AX7 in V2, what should I expect if a change to a regular 12AX7, tone wise? Would it just be a little less gain, or would there be tonal differences? Anyone have any experience with these types of tube switches? The amp is a HRDLx, so it is a two power tube and 3 preamp tube configuration.

I'm always fiddling with my tube configuration, just hoping to get some opinions before I spend the money.



Thanks!

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Posted: Mon Mar 22, 2010 6:55 pm
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Usually you should try and use tubes with a balanced current for phase inverter use. Generally speaking, putting an 12AT7 in place of the 12AX7 will increase headroom among other things. Going from a high gain 12AX7 to a standard should yield a similar type of effect (Since it's in V2 the change will be only noticeable in the drive channels.) Myself, I used JJs I bought from Eurotubes, but there are many options if you're looking for a swap.

https://ssl.eurotubes.com/cart/index.php?page=view_products&category_id=2&sub_category_id=12

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Posted: Mon Mar 22, 2010 11:23 pm
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For $30-ish, try a Mullard CV4024 - very nice stuff.

I've found the JJ's harsh as V1/V2 tubes compared to the NOS, which isn't that much more expensive, and yes, I A/B'd it and my amp tech was surprised as well.

Mike K at kcanostubes.com is a great guy - tell him your amp, music style/tonal goals, and budget, and he'll recommend a mix of new and/or NOS tubes for you. I've bought tubes for all 3 of my Fenders and he's been great.

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Posted: Tue Mar 23, 2010 5:14 am
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In order for the JJs to sound good you have to crank up the bias pot til the tubes are running around 70-90 mv. That'll eliminate the harshness among other things, they definitely sounded better in my Deville (My stock tubes were running at 48 mV >_>). NOS tubes are awesome too, anything's better than the stock tubes ^^

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Posted: Tue Mar 23, 2010 7:54 am
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I changed V3 in my Hot Rod Deluxe to a 12AT7. It made the volume controls a little less sensitive, and since V3 is pushing close to 1.5 milliamps through it, it was actually more than the 12AX7 is rated for. Might last longer with a 12AT7 in there. I can't tell that it changed the tone dramatically.

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Posted: Tue Mar 23, 2010 1:12 pm
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Thanks for the feedback. I put an old Sovtek AT7, that I had forgot I have, in V3 to give it a try. I'm not sure if it was balanced or not. It gave the amp a little more headroom, seemed to slightly warm up the clean channel, but it made the OD channel sound brittle and harsh . The small improvement in the clean channel isn't worth the loss in the OD channels. I had read somewhere that using a 12AT7 in the phase inverter as opposed to a 12AX7 would generate more sag, but I didn't hear it. I use JJ tubes already, and like them. I don't have a standard 12AX7 to put in V2. I wouldn't mind "warming-up" the tone a little and was hoping a regular 12AX7 might take a little of the edge off, but if there is no tone difference I'll just save the money.

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Posted: Thu Mar 25, 2010 11:12 am
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Try a good 12au7 in V1. Allows you to crank up the volume to a sweeter spot. I use one in my HRDx.

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Posted: Mon Mar 29, 2010 2:54 pm
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I have a HRDLX.
So is there any recomendations for tube(s) that won't break up as soon?
Cleaner sound at higher volume.


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Posted: Mon Mar 29, 2010 3:51 pm
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Try JJ 6L6 power tubes. You can use a variety of 12AX7, 12AT7, and 12AU7 tubes in the preamp to get more clean headroom, I like JJ's but Tung Sol's are popular as well as the NOS stuff out there. Maybe try a balanced 12AT7 in V3, a 12AX7 in V2, and a 12AU7 in V1. That should maximize your clean headroom and give you a nice warm tone. You can turn the bias down to around 60 mv as well, but you will want to experiment with the bias to find the bias point that works best for you. You won't have as much gain this way, but it doesn't sound like you are concerned about that anyway.

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