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What tube amp to build next?

9/24/2004 2:15 PM
Munk	What tube amp to build next? Well I have a Marshall 30 watt SS 1x12 combo 80's amp That I'm thinking about maybe gutting and doing a tube amp into. The chassis and cab are perfect platform to use. I wanted to do a different amp build from what I've done in the past (Many Fender style amps, Soldano SLO100 and Marshall JCM800 stuff) and was thinking about a marshall style preamp but maybe a 4xEL84 amp that was class A design sorta like an VOX AC30. Any suggestions on this would be appreciated. Ive never done Class A design and suggestions on transformers available would be great. Also not sure if maybe just building a AC30 clone may be the best route as I hear people rave on the class A sound. Comments welcome Thanks Munk

9/24/2004 2:15 PM

Munk

What tube amp to build next?

Well I have a Marshall 30 watt SS 1x12 combo 80's amp That I'm thinking about maybe gutting and doing a tube amp into. The chassis and cab are perfect platform to use.
I wanted to do a different amp build from what I've done in the past (Many Fender style amps, Soldano SLO100 and Marshall JCM800 stuff) and was thinking about a marshall style preamp but maybe a 4xEL84 amp that was class A design sorta like an VOX AC30.

Any suggestions on this would be appreciated. Ive never done Class A design and suggestions on transformers available would be great. Also not sure if maybe just building a AC30 clone may be the best route as I hear people rave on the class A sound. Comments welcome

Thanks

Munk

9/24/2004 2:39 PM
rooster	AC30's aren't class A. They are hot-biased, class AB1 amps with cathode bias and no NFB. For an explanation of this, check out Aikenamps.com. He has a nice paper on this under "tech info." FWIW, if you go for the AC30, get the OEI OT, and an Alnico speaker, Webers are quite reasonable. The raving about the class A sound is a mystery to me. All my favorite amp tones come from class AB1 push-pull amps. The only class A's I build are SE. YMMV. rooster.

9/24/2004 2:39 PM

rooster

AC30's aren't class A. They are hot-biased, class AB1 amps with cathode bias and no NFB. For an explanation of this, check out Aikenamps.com. He has a nice paper on this under "tech info." FWIW, if you go for the AC30, get the OEI OT, and an Alnico speaker, Webers are quite reasonable.

The raving about the class A sound is a mystery to me. All my favorite amp tones come from class AB1 push-pull amps. The only class A's I build are SE.

YMMV.

rooster.

9/26/2004 3:56 PM
Munk	Thanks for the info Rooster. I am not real up on class A design but could easily build one. Im just wanting to do something different from my last projects. Ive turned Fender mid 60's bassmans into different designs, done Soldanos and Marsall non master amps, many fender amps and other cool designs but needing a new cool project but am stumped on what to do next. I have been thinking about a humble clone but then again I'm not really into the Carlton sound, more good rock tones and good clean tones. Maybe a killer Queen guitar sound would be cool. Ive always liked Brain Mays tone and distortion and those vox amps sound great. I found out that Ritchie Blackmore used Vox ac30s on the machine head album and he got a cool tone even though he used marshall Majors later on in his career. I guess I'm just jonezing on doing another amp build Munk

9/26/2004 3:56 PM

Munk

Thanks for the info Rooster. I am not real up on class A design but could easily build one. Im just wanting to do something different from my last projects. Ive turned Fender mid 60's bassmans into different designs, done Soldanos and Marsall non master amps, many fender amps and other cool designs but needing a new cool project but am stumped on what to do next. I have been thinking about a humble clone but then again I'm not really into the Carlton sound, more good rock tones and good clean tones.

Maybe a killer Queen guitar sound would be cool. Ive always liked Brain Mays tone and distortion and those vox amps sound great. I found out that Ritchie Blackmore used Vox ac30s on the machine head album and he got a cool tone even though he used marshall Majors later on in his career.

I guess I'm just jonezing on doing another amp build

Munk

9/26/2004 8:18 PM
Greg Simon	If you decide to build an AC30 clone, make sure to get the Vox Blue speakers, or the Weber equivilants. It is VERY important to getting the "VOX" sound. I've read in interviews that Ritchie Blackmore only used an AC30 when he was using a Gibson 335, which would have been the first couple Deep Purple albums in the late 60's. Most of his well known stuff like Highway Star, Burn, Smoke on the Water, etc were all a Strat and the Matshall Major. Brian May's sound owes a lot to the pickups he has in his guitar, and the fact the he uses the normal channel of an AC30 with a booster pedal instead of the Top Boost channel as most people use. I know I can get pretty close to May's sound using a Treble Boost Rangemaster type pedal and the normal channel of my AC30. One thing you may consider is to build the Top Boost as one channel and build another channel with the EF86 pentode channel. The first AC30/4 used the EF86 and many people say that it sounds better than the AC30/6 Top Boost channel. I haven't played one with the Pentode but plan to build it into a couple amp projects in the future. I would probably build your AC30 project as a head and build a seperate speaker cabinet. no matter what you build, make sure to allow plenty of ventilation. Old AC30's are known to burst into flames due to heat! And Rooster is right...an AC30, and most of the supposedly Class A amps are not really Class A. They are just Class AB amps that are biased hot and are cathode biased. One of the main things for the AC30 sound is the lack of negative feedback, and also the EL84 tubes as they have a bright and chimey sound. Greg

9/26/2004 8:18 PM

Greg Simon

If you decide to build an AC30 clone, make sure to get the Vox Blue speakers, or the Weber equivilants. It is VERY important to getting the "VOX" sound.

I've read in interviews that Ritchie Blackmore only used an AC30 when he was using a Gibson 335, which would have been the first couple Deep Purple albums in the late 60's. Most of his well known stuff like Highway Star, Burn, Smoke on the Water, etc were all a Strat and the Matshall Major.

Brian May's sound owes a lot to the pickups he has in his guitar, and the fact the he uses the normal channel of an AC30 with a booster pedal instead of the Top Boost channel as most people use. I know I can get pretty close to May's sound using a Treble Boost Rangemaster type pedal and the normal channel of my AC30.

One thing you may consider is to build the Top Boost as one channel and build another channel with the EF86 pentode channel. The first AC30/4 used the EF86 and many people say that it sounds better than the AC30/6 Top Boost channel. I haven't played one with the Pentode but plan to build it into a couple amp projects in the future. I would probably build your AC30 project as a head and build a seperate speaker cabinet. no matter what you build, make sure to allow plenty of ventilation. Old AC30's are known to burst into flames due to heat!

And Rooster is right...an AC30, and most of the supposedly Class A amps are not really Class A. They are just Class AB amps that are biased hot and are cathode biased. One of the main things for the AC30 sound is the lack of negative feedback, and also the EL84 tubes as they have a bright and chimey sound.

Greg

9/28/2004 8:45 PM
Munk	Thanks for the good info Greg, Any others care to inject any comments? Munk

9/29/2004 4:59 AM
Steve L.	Here's my two cents- First, consider the sounds you want. I know that seems obvious, but I know that at least I for one have become too excited over the idea of the building part and lost sight about what I was trying to acheive. For instance, you mentioned not liking Carlton's tone- cool, but just what DO you like? Then, search out designs that look good to you. As for something complementary to the high gain amps you mention, Vox AC30 TB's are cool, but maybe a Matchless type of variation or the EF86 preamp would indeed suit you. Happy building!

9/29/2004 4:59 AM

Steve L.

Here's my two cents-
First, consider the sounds you want. I know that seems obvious, but I know that at least I for one have become too excited over the idea of the building part and lost sight about what I was trying to acheive. For instance, you mentioned not liking Carlton's tone- cool, but just what DO you like? Then, search out designs that look good to you.

As for something complementary to the high gain amps you mention, Vox AC30 TB's are cool, but maybe a Matchless type of variation or the EF86 preamp would indeed suit you.

Happy building!

10/3/2004 5:00 PM
Brutus	You can easily hear how class A sounds by taking any of your current amplifiers and reducing the bias into class A territory. I've done this many times and in general this happens: - The sound gets noticeably thicker. - The sound has less headroom and distorts quicker but in a pleasing way. - The midrange becomes more pronounced. - The highs roll off noticeably. - The tone gets smoother. - The tubes get noticeably hotter. You have to ask yourself if this is the tone you really want because class A amps in general are warmer and sound a little less agressive than class AB. If you like class A then I would recommend trying class A with a cathode biased final output section. To my ears cathode biased class A is smoother and sings better than fixed bias class A. Also, cathode biased output sections actually distort less than fixed bias (see RCA Radiotron Designers Handbook for details on why this is true). In other words, using cathode bias in the output stage will make the amp even warmer and a bit less aggressive. The VOX AC-30 and the Matchless Chieftain are two popular amps that use cathode biased class A operation. I believe that the fender 5e3 is pretty much of a class A amp cathode biased amp as well. Brutus

10/3/2004 5:00 PM

Brutus

You can easily hear how class A sounds by taking any of your current amplifiers and reducing the bias into class A territory. I've done this many times and in general this happens:

- The sound gets noticeably thicker.
- The sound has less headroom and distorts quicker but in a pleasing way.
- The midrange becomes more pronounced.
- The highs roll off noticeably.
- The tone gets smoother.
- The tubes get noticeably hotter.

You have to ask yourself if this is the tone you really want because class A amps in general are warmer and sound a little less agressive than class AB.

If you like class A then I would recommend trying class A with a cathode biased final output section. To my ears cathode biased class A is smoother and sings better than fixed bias class A. Also, cathode biased output sections actually distort less than fixed bias (see RCA Radiotron Designers Handbook for details on why this is true). In other words, using cathode bias in the output stage will make the amp even warmer and a bit less aggressive.

The VOX AC-30 and the Matchless Chieftain are two popular amps that use cathode biased class A operation. I believe that the fender 5e3 is pretty much of a class A amp cathode biased amp as well.

Brutus

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