preamp tubes 12ax7 vs. 12at7

[JohnnyCrash]

Originally Posted by Silverface

Sorry to have to explain the obvious, but given some of what I've seen posted lately I guess I need to go to fully expanded and verbose answers most threads to avoid being corrected about irrelevant infomation.

Ouch.

As far as my statements... he should still be getting plenty of Clean at very loud Volumes... thats all I meant. Later on, he discovered a tube was unseated and it "improved" things.

The site I criticized also recommended clipping cathode bias caps "one by one" until satisfied - this is a ridiculous statement and it is worthy of criticism.

Earlier in this thread it appeared that I was being a jerk, I apologized and explained it was not my intentions, are you likewise misunderstood, or is it intentional? We all need to play nice.

[sjhusting]

Alright, educate me. I don't want to be an irrelevant jerk. I'm looking at the schematic. I'm interested because I own one of these and I may have been labouring under false information all these years.

Correct me where I'm wrong, I probably haven't been doing this as long as you, and still have a lot to learn:

K1A selects whether the "volume" or "drive" pot attenuates the output of V1a.

K1B defeats the bright switch when the drive channel is selected.

K2a routs the signal to V2b in drive mode.

K2b selects either the output from v2a in clean mode or from the master in drive mode.

That looks to me like V1a -> V1b -> V2a, with V2b being popped in optionally when in drive mode. => V1 remains the decisive tube, regardless of mode.

You're right, V1 will have the most effect. It's been this way on every amp I've ever played through. I even said so in an earlier post. Make sure the power tubes are properly biased, then concentrate on V1, is the way I see it.
But Johnny is right, this amp does loud clean well. Not BF sparkle, but it has headroom out the wingwang if you want it that way.


steven

[JohnnyCrash]

Originally Posted by sjhusting

You're right, V1 will have the most effect. It's been this way on every amp I've ever played through. I even said so in an earlier post. Make sure the power tubes are properly biased, then concentrate on V1, is the way I see it.

But Johnny is right, this amp does loud clean well. Not BF sparkle, but it has headroom out the wingwang if you want it that way.

Here, scoots is trying to do a certain thing. He's new to tube amps and isn't sure what to do, or technically inclined yet (we all have to start our path to learning somehow).

sjhusting and myself have been trying to be friendly and help out a fellow TDPRI'er.

sjhusting and myself have been qualifying our statments with context were possible/practical. sjhusting even already mentioned his thoughts on V1 in a previous post! Likewise my critiques of that site were not "willy nilly" and had proper context.

We're just trying to help scoots out... we're not trying to dump a bunch of over-the-head tech info, or turn anything into a pissing context.

This amp should be plenty loud and plenty clean - its not exactly a "modders dream" either. I really suspect there is a disconnect in communcation and/or a problem with the amp itself...

But at the least, we can avoid being dogmatic, critical, and hostile... and stick to trying to be helpful in solving this particular problem. LEts play nice.

[scoots]

the inverter, what exactly does this tube do? how much effect does this have on your overall sound/headroom. this deville came with a 12ax7 in this spot, but it seems not too many people use them here. is this amp "set up" to use a 12ax7 here. what would a 12ay7 do here? i'm new to tube amps, i appreciate this obvious info!

[sjhusting]

The phase inverter takes the output of the preamp and splits it, sending the "negative" half of the wave to one side of the output stage, and the "positive" to the other half. This is what makes push-pull amps work; each output tube (in a 2-tube power configuration) works on half of the wave. For a variety of reasons this lets you get more power out of a tube when it only has to work on half the signal. The range where it crosses over from one tube to the next is critical though, and the bias has a lot to do with it. If you bias too cold (current too low) you will get "crossover distortion" which sounds nasty.

I wouldn't go with a 12AY7 in the PI slot, personally. You can try it if you want. As a matter of fact, I went back to a 12AX7 last week as a result of this discussion. My ears don't hear much difference there, so I'm going with what was designed for.

its not exactly a "modders dream" either.

Sure it is. Nightmares are dreams too, aren't they?
steven

[JohnnyCrash]

Originally Posted by scoots

the inverter, what exactly does this tube do? how much effect does this have on your overall sound/headroom. this deville came with a 12ax7 in this spot, but it seems not too many people use them here. is this amp "set up" to use a 12ax7 here. what would a 12ay7 do here? i'm new to tube amps, i appreciate this obvious info!

In a very basic way caveman way of saying it - the Phase Inverter sends two copies of the signal in opposite phases to the output section. Each side of the waveform goes to a power tube or side of power tubes.

Class AB is a tube amp that is powered by a tube, pair, or even quad of tubes on either side of the waveforms phase - they require a PI.

Class A works differently - but that's a different story altogether.

Tweaking how your preamp tubes drive a circuit is one way of going about things, but the entire circuit isn't as simple as just Preamp and Power Tubes, and there's many ways to tweak an amp.

For instance, (some as briefly discussed here by others) there are things like insertion loss, tonestacks, preamp component value swap-outs, etc.

Like I said, there are many ways you can tweak an amp for sound. For beginners, its probably best to stick to preamp tube swapouts, different pickups, and swapping speakers.

Power tubes can sound best when biased and bias adjustment is definitely not for beginners as most amps need to be open and running with high voltages for adjustment (not all amps require bias adjustment though), and swapping out output transformers and resistors/caps can be very dangerous as high voltages are present in electrolytic capacitors - even when the amp is off and/or unplugged.

Generally, amps don't require ANY modifications to sound good. Most times, this kind of stuff is for extreme fine-tuning, or to compensate for design flaws in older amps.

[JohnnyCrash]

Originally Posted by sjhusting

Sure it is. Nightmares are dreams too, aren't they?
steven

HAHA, that is true.

[Silverface]

Scots, what is apparent is you want toknow a lot of information about tube amps (yours in particular isn't as critical at first - you have to get the basicsdown) and you could ask individual questions like this for years. It might be much more beneficial to get two or three books about tube amp technology (especially tube guitar amps), read them, and THEN ask questions. The way this is going (and I'm not trying to be harsh) this could end up the longest thread in history.

I'd suggest looking for books by Dave Funk, Kevin Mitchell, and Gerald Weber. They all have good and bad points, but combined give you get a decent working knowledge of tube amps.

I don't think anyone minds answering questions, but it takes a lot of time to answer in the extremely complete way that is apparently necessary to absolutely ensure the reader makes no assumptins (correct or incorrect). And if someone leaves out a small point thought to be fairly common knowledge, it can be misinterpreted or corrected and more confusion ensures.

Just my thoughts on the matter.