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Post subject: Preamp tube question?
Posted: Tue Sep 22, 2015 6:41 am
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The hot rod deluxe has three preamp tubes. What all do the pre amp tubes do? Is it one tube for each channel. The amp has a clean, drive, and more drive. I know the first tube will affect the clean tone just not sure about the second and third. Are the second and third tubes just for the drive channels? And how much will power tubes affect the tone?


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Post subject: Re: Preamp tube question?
Posted: Tue Sep 22, 2015 6:53 am
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Each of those pre-amp tubes is a dual triode, ie: two independent tubes within a single glass envelope. The first of them (V1) provides the first and second gain stages for the basic clean mode. V2 provides a cascaded third and fourth gain stage, each of which is accessed sequentially via the "drive" and "more drive" switch. The V3 tube is a phase inverter which splits the incoming signal into two halves then feeds each of them to one power tube.

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Post subject: Re: Preamp tube question?
Posted: Tue Sep 22, 2015 11:35 pm
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Just adding to Retroverbial's great explanation. All tubes are used for all channels, with the second half of V2 being used only when Drive and More Drive are selected.

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Post subject: Re: Preamp tube question?
Posted: Wed Sep 23, 2015 7:07 am
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That's the info I was looking for. Thanks


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Post subject: Re: Preamp tube question?
Posted: Thu Sep 24, 2015 5:20 pm
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So besides tone is there a reason to put tubes such as 12at7 or 5751 in any certain order.


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Post subject: Re: Preamp tube question?
Posted: Thu Sep 24, 2015 11:16 pm
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Generally speaking, V1 will have the most impact on tone for all channels, and is the first gain stage, so a lower gain tube here can really set the stage. V2 will have the most impact on the drive and More Drive channels, and a lesser affect for the clean channel. V3 (PI) will mainly affect how much the output tubes are driven, less gain here for a cleaner output section.

Basically, your best tube for tone and the amount of desired preamp gain for V1, a 12AX7 for normal/high gain, and a 5751 or even a 12AY7 for lower gain. For V3, using a lower gain tube, such as a 12AT7 will give you more headroom, and make it harder to push the output section into distortion.

My favored tube lineup for my HRDlx is a JJ 5751 in V1, practically any 12AX7 for V2 (I think I have a GT which is a Sovtek), and a GT 12AT7 for V3 (the GT 12AT7 is Chinese). This lineup gives more clean headroom, and tames the drive channels just a bit, while still having plenty of drive when selected. To tame the drive channels even more, you can put a 5751 in V2.

I have had good results with the JJ 5751, while the Sovtek 5751 seems to be hit or miss on performance. I have used several US made NOS 5751s, and none were any better than the JJ 5751.

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Post subject: Re: Preamp tube question?
Posted: Fri Sep 25, 2015 6:30 am
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I have seen where some people say the 12AT7 is a driver tube for reverbs and phase inverters. Is this correct?


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Post subject: Re: Preamp tube question?
Posted: Fri Sep 25, 2015 7:03 am
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thunderfan1979 wrote:
I have seen where some people say the 12AT7 is a driver tube for reverbs and phase inverters. Is this correct?


Yes -- principally in Fender's brownface, blackface, and silverface designs. The 12AT7 draws significantly more heater current than the other common dual-triodes (12AX7, 12AY7, 7025, etc) so its use in certain amps with marginally-engineered power supplies may not be appropriate.

Arjay

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