What Gives a Twin Reverb Its Sound?

trber

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Did the grunt work of moving my equipment…to get to & open the cabinet. Drove a long screw into the rear panel to keep it open about 2”, cuz it goes right smack against a wall. Good thing my neighbor right next door is 1/2 deaf…
Worth the effort as it did what I hoped it would do. Took away the boominess of the bass response.
Was doing the same thing when I use a ‘65 BFPR (also hooked-up to cabinet). Cured that as well. All is good & it really kicks A$$ in conjunction with a Klon Horsey pedal.

also trber: A Tungsol 12ax7 was in the V2 vibrato channel socket that I swiped from the Princeton Rvb, but have put it back & put a Sovtek back in its place.

Thx all 😉

View attachment 1052491
That's great! Glad it worked out, for sure. Take a look at this page to see if there's anything of interest. Non-intrusive mods to control volume, though from what I've read, mixed results. My error on the tube swap for volume control. It is more specifically seen as a "gain" treatment; you'll get gain at lower volumes, if I have it correct. Anyhow, glad to hear the results, and take a look at this link, if you're interested!
 
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colchar

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Agreed, on both.

I am thinking it's the sum...but I am not much of an expert so defer to experts.

I love my champs, but the smaller speakers seem to set off the hearing problems. Something about the frequency and concentration of the sound that doesn't work for me. Much prefer larger speaker formats. 👍👍


My current amps are a Marshall SV20 (the baby Plexi), an Orange AD30 (insanely loud for 30 watts), and a vintage Traynor YGM3 (their version of the Twin and beyond insanely loud). I wouldn't trade the fullness of their sound for any smaller amp.
 

enorbet2

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Hello. I really don't want to toot my own horn but it is probably somewhat relevant to note that I dabbled in electronics since I was around 8 years old, took Electronics Shop in High School, where I repaired TVs and the school's tube PA system, and worked much of my 76 years repairing, modding, designing and building amps (mostly tube amps) some for a few global stars. What's far more important in my view is I see guitar amps as NOT being mere reproduction devices (like a PA or HiFi) but as musical instruments in their own right.

Comparing a Twin to your Champ, obviously the major differences are power and speaker complement, but what matters most is comparing a Twin to other high powered gear. There, the output transformer is very important to tone and other potent factors are in the Power Supply (especially filter caps and decoupling) and also the level of both Bias and Negative Feedback.

The preamp design is less important to tone than it is to feel. For example Tweeds and their clones like Marshall, Vox, some HiWatts, Sound City, etc., have the Volume control preceding the Tone Stack while post Tweed Fenders (especially Black and Silverface) have the Tone Stack preceding Volume. This means the Q of the tone stack changes a LOT with Volume settings, creating a tonal touch sensitivity in Tweed and clones at the cost of sounding more similar (but less "vocal") at a wider range of signal levels, including guitar volume setting, pedals, and how hard you hit which is what Tweeds, Vox-es and Marshalls etc respond much more dynamically to, either to your ecstacy or chagrin depending on your style.

You can drastically change the respionse of the Twin (or really, any amp) by changing the value of the filter caps, the Bias and/or the Negative feedback. Both the Bias in most amps and certainly the Twin, and with a minor, easy to return to stock, mod (adding a temporary potentiomerter) alter Negative Feedback for more or less headroom and change the position of Edge-of-Breakup. Obviously trying different filter caps to affect headroom and "stiffness" is a bigger job and can't easily be done on-the-fly but all 3 are very instructive if not revelatory.

For a bit of reference regarding headroom and "feel" consider EVH tone achieved by starving mainly the outputs but also all tubes by using a Variac, It should be obvious what comes out, in tone and feel, is most controlled by what goes in as power supply capability and how much the amp is "reined in" by negative feedback..
 

otto jackson

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Minneapolis
Background: I recently bought a 1969 Twin from the original owner and IDd it as an AC568 circuit with the help of responders on this forum. I replaced the filter and bypass capacitors and a 2.2k resistor in the dog house that had drifted. Someone previously removed the large cathode resistors on the power tubes and the capacitors and wiring that were part of the bias circuit on the chassis side wall. Otherwise, it's stock with Oxford speakers and RCA 6l6gc that may be on their way out. I am hoping to get them tested this weekend. Preamp tubes are a mix of vintage and Groove Tube 12ax7s, I believe.

Question: What gives these amps their sound characteristics?

I am a low watt amp, home player. I normally play a Silverface Champ through a 2x12 cab or a Princeton 10" kit thought the cab and a 12" extension cab, so I am familiar with multiple speaker amp set-ups. Because of hearing sensitivity, I can't get on with high wattage, loud amps. So, I am not referring to the sound of an opened-up Twin moving lots of air and getting the amp and tubes in the sweet spot.

I am asking about the full, deep, rich and broad sound that comes from this amp at around 2-2.5 on the volume. It's like no other amp I've heard before. Maybe it's like other large size and wattage Fender amps: Supers, etc. but I have not played those. Once, in a Vintage Guitar and Amp store in LA, I heard someone play what I thought was a Blackface Deluxe or maybe Twin and it was amazing: similar low volume sonic bliss.

So, what is it? Tubes (large 6l6), transformers, speakers, cab, circuit, some combination of these things?

This amp has really reset my expectations and desires for what tube amps can be.

Thanks for any feedback!
I got a '74 TR sliverface for $200 in 1989 and the only reason I have another amp is to have something easier to carry. Part of the amazing sound (even at lower volumes) is tubes, and when you replace them you might need to bend the pin contacts in the sockets back into place for full contact. Another reason is the massive transformer which allows for nearly unlimited headroom. An additional thing I have wondered about is the odd placement of the speakers on the back of the baffle board. I think this is a likely source of the intensity inside the notoriously narrow cone of sound in front of the amp (I have seen old school blues guys like James Cotton run a pair of twins on either side of the stage and not even mic them up for the mains). To experiment with this effect, I built a new cab and put the original speakers (re-coned, probably Jensens) into it outset on the new baffle board. I stacked the amp (with new Ted Weber Chicagos) on this and ran ("speaker out" jack) out to the cabinet (the massive transformer absorbs the impedance without need for a matcher). The resulting stack produces the legendary, intense narrow cone and the extra cab spreads it out. I've had the whole rig running for more than two hours with no sign of overheating. I would rather have this than any re-issue or hipster amp from Orange any seven days of any week. To TR doubters, I say sometimes more is, well, more.
 

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trber

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Hello. I really don't want to toot my own horn but it is probably somewhat relevant to note that I dabbled in electronics since I was around 8 years old, took Electronics Shop in High School, where I repaired TVs and the school's tube PA system, and worked much of my 76 years repairing, modding, designing and building amps (mostly tube amps) some for a few global stars. What's far more important in my view is I see guitar amps as NOT being mere reproduction devices (like a PA or HiFi) but as musical instruments in their own right.

Comparing a Twin to your Champ, obviously the major differences are power and speaker complement, but what matters most is comparing a Twin to other high powered gear. There, the output transformer is very important to tone and other potent factors are in the Power Supply (especially filter caps and decoupling) and also the level of both Bias and Negative Feedback.

The preamp design is less important to tone than it is to feel. For example Tweeds and their clones like Marshall, Vox, some HiWatts, Sound City, etc., have the Volume control preceding the Tone Stack while post Tweed Fenders (especially Black and Silverface) have the Tone Stack preceding Volume. This means the Q of the tone stack changes a LOT with Volume settings, creating a tonal touch sensitivity in Tweed and clones at the cost of sounding more similar (but less "vocal") at a wider range of signal levels, including guitar volume setting, pedals, and how hard you hit which is what Tweeds, Vox-es and Marshalls etc respond much more dynamically to, either to your ecstacy or chagrin depending on your style.

You can drastically change the respionse of the Twin (or really, any amp) by changing the value of the filter caps, the Bias and/or the Negative feedback. Both the Bias in most amps and certainly the Twin, and with a minor, easy to return to stock, mod (adding a temporary potentiomerter) alter Negative Feedback for more or less headroom and change the position of Edge-of-Breakup. Obviously trying different filter caps to affect headroom and "stiffness" is a bigger job and can't easily be done on-the-fly but all 3 are very instructive if not revelatory.

For a bit of reference regarding headroom and "feel" consider EVH tone achieved by starving mainly the outputs but also all tubes by using a Variac, It should be obvious what comes out, in tone and feel, is most controlled by what goes in as power supply capability and how much the amp is "reined in" by negative feedback..
Brown sound!

I'm working on my technical understanding of amps, and your response is helpful and appreciated. I have the basics and am entering into a more detailed understanding of the nuance involved. Right now, as I play the twin, I have the chassis on top of the cab and am reminded of the behemoth transformers every time I look at it, so that part is sinking in from the visuals. Lol

I'm also going to install a Bias pot so I can adjust it so the huge 6l6s are at their best. I'll be interested to hear how it affects the tone, and I know from adjusting my Princeton kit amp it is quite audible. I'm curious if the tech who worked on it last got it mostly right.

I've also been considering adding a variable Negative bias to the ground switch. If I do, I'll be able to explore a most/all of the variables you mentioned. I did just pick up an inexpensive variac but don't really know if it's sufficient to explore varied input voltage, but I could try it to see.

Many thanks. I appreciate that you shared your expertise.
 

trber

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Posts
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Location
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I got a '74 TR sliverface for $200 in 1989 and the only reason I have another amp is to have something easier to carry. Part of the amazing sound (even at lower volumes) is tubes, and when you replace them you might need to bend the pin contacts in the sockets back into place for full contact. Another reason is the massive transformer which allows for nearly unlimited headroom. An additional thing I have wondered about is the odd placement of the speakers on the back of the baffle board. I think this is a likely source of the intensity inside the notoriously narrow cone of sound in front of the amp (I have seen old school blues guys like James Cotton run a pair of twins on either side of the stage and not even mic them up for the mains). To experiment with this effect, I built a new cab and put the original speakers (re-coned, probably Jensens) into it outset on the new baffle board. I stacked the amp (with new Ted Weber Chicagos) on this and ran ("speaker out" jack) out to the cabinet (the massive transformer absorbs the impedance without need for a matcher). The resulting stack produces the legendary, intense narrow cone and the extra cab spreads it out. I've had the whole rig running for more than two hours with no sign of overheating. I would rather have this than any re-issue or hipster amp from Orange any seven days of any week. To TR doubters, I say sometimes more is, well, more.
That's awesome! What a great find and story. I'd never have thought about speaker mounting location, although the celestions in my 2x12 for the Champ are externally mounted. I just figured each maker had a reason for how they're mounted and never questioned it beyond that. Good info!

Regarding the tube pins, is that just to ensure good contact, rather than there being something about new tubes and how their pins align? I did retention the sockets... would that do the trick?

Thanks for the response!
 

TromNek

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I've got my '74 TRSF for sale. But after reading all these posts, I think I might keep it !

I bought it back in '74 (when I was 14) for $200. It was a floor model at a music store.
It was my first 'real' amp and it's one of my best friends.
I keep it up at my mom's house in Upstate NY and rock out on it when I go up there to visit.
rocknRosemary.jpg

My Mom must be getting hard of hearing. She said;
"Turn it up !"

Really thinking now that I should keep it.
But it's probably better to sell it to someone who will actually play it more.
 

misterdontmove

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Don't forget the legs! Tilting any amp gives it a great deal of definition.

Except when your outdoors. I tilt my Super Reverb for the very reason you stated, but on an outdoor gig, with no ceiling, or mic on the amp, you're the only one who can hear you. I was ATOMIC BOMB loud, but people kept asking me to turn up. Just an FYI.
 

Bob M

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I once had a Dual Showman Reverb in the seventies. 2 15” JBLS. Big ass cabinet. At any volume it was incredible sounding. These days if I had one I would have to hire a cartage company to move it for me. There is something about 4 6l6s moving air that is exhilarating.
 

studio

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I once had a Dual Showman Reverb in the seventies. 2 15” JBLS. Big ass cabinet. At any volume it was incredible sounding. These days if I had one I would have to hire a cartage company to move it for me. There is something about 4 6l6s moving air that is exhilarating.
Steve Howe was famous for using Dual Showmans back in the day, with a Gibson ES175! Craaaazy!

Now I think he uses all Line6 stuff.
 

Cosmic Cowboy

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Background: I recently bought a 1969 Twin from the original owner and IDd it as an AC568 circuit with the help of responders on this forum. I replaced the filter and bypass capacitors and a 2.2k resistor in the dog house that had drifted. Someone previously removed the large cathode resistors on the power tubes and the capacitors and wiring that were part of the bias circuit on the chassis side wall. Otherwise, it's stock with Oxford speakers and RCA 6l6gc that may be on their way out. I am hoping to get them tested this weekend. Preamp tubes are a mix of vintage and Groove Tube 12ax7s, I believe.

Question: What gives these amps their sound characteristics?

I am a low watt amp, home player. I normally play a Silverface Champ through a 2x12 cab or a Princeton 10" kit thought the cab and a 12" extension cab, so I am familiar with multiple speaker amp set-ups. Because of hearing sensitivity, I can't get on with high wattage, loud amps. So, I am not referring to the sound of an opened-up Twin moving lots of air and getting the amp and tubes in the sweet spot.

I am asking about the full, deep, rich and broad sound that comes from this amp at around 2-2.5 on the volume. It's like no other amp I've heard before. Maybe it's like other large size and wattage Fender amps: Supers, etc. but I have not played those. Once, in a Vintage Guitar and Amp store in LA, I heard someone play what I thought was a Blackface Deluxe or maybe Twin and it was amazing: similar low volume sonic bliss.

So, what is it? Tubes (large 6l6), transformers, speakers, cab, circuit, some combination of these things?

This amp has really reset my expectations and desires for what tube amps can be.

Thanks for any feedback!
Coming at the question as a player, and not being an amp tech in even the slightest, its a combination of big, powerful amplification...the negative feedback circuitry and the bassy response of the OT and speakers.

The sound you are describing is why the Jazz cats love those things (twin reverbs). When I was studying in school, every guest guitarist either opted to play through the school's twin reverb, or brought their own.

They are warm, big and organic-sounding amps.

Yeah you dont have to crank em to hard rock stage volume to get a steller sound.

Guess I am saying I dont know, but I agree.
 

Cosmic Cowboy

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Damn those are right at ear level…. Nirvana until you can’t hear anymore
I really dont think that many guys understand just what kind of big sounds these stage setups are.

We get told to turn down our Deluxes to the point of not being able to hear it without monitoring. Correct me if Im wrong but I didnt see Carlos leaning into a wedge to hear his guitar.

In order to get a big sound, you need to have big poweful sound pressure.

Live music should hit you in the gut, and if you have powerful amps and good music...mixed right, its not really that 'loud'. Just clear and powerful...puches you in the heart and lungs and guts with pressure.
 
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misterdontmove

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Steve Howe was famous for using Dual Showmans back in the day, with a Gibson ES175! Craaaazy!

Now I think he uses all Line6 stuff.

Check out Clapton on an ES335 plugged directly into a Blackface Showman (I think it's a "Dual" you can see it in one of the shots) in this clip from The Rolling Stones Rock and Roll Circus. Listen through to the solo at 2:48. He looks like he's all geeked out on blow, but WHAT GREAT TONE!!!!!!!

 
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