What Gives a Twin Reverb Its Sound?

[TJStone]

I rehearse and practice with a Princeton Reverb, but my Twin Reverb is a workhorse that I perform live with, I love the amp I just wish it wasn't so damn heavy!

 

[ETMusic777]

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!

Good enough for this small quartet.

 

[pippoman]

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’ve owned about 6 different Twins and know exactly what you’re talking about. Even at low volume they just sound awesome. I would say it had something to do with the cab, but I had a pro reverb once that didn’t come close to the regal sound of the TR, and it had twin 12s and dual 6l6 power tubes, so it’s not that either. I took two power tubes out of one of my Twins and I couldn’t tell any difference. I think whoever mentioned the massive transformers was correct. The preamp circuit is the same as other Fender amps. Regardless, nothing sounds as lush as a Twin, except a Quad Reverb which is just a Twin mounted in a 4x12 cab, but I can’t lug those beasts around anymore. I’d love to own another one, but it would never be played out. Still, I haven’t forgotten how good they sound. The SF Twins like you have sound better to me than the BF Twins, but that’s just my opinion. I’ve owned both.

 

[DukeOrel]

A twin 12” moves a lot of air. That and volume/ gain is the main ingredient. No small watt single speaker amp Will give that sound.

 

[ETMusic777]

I don't know as much about amps as the tech guys on this forum, but I feel the same way about my Super Reverb as you do - should be roughly the same as your Twin but different speaker setup. A few things I have realized about why is sounds so great:

- To get big bottom you need a fair amount of power, especially noticeable in clean tones, even at home volumes. I tried a modern Champ before the Super and it didn't have enough power for clean lows even in my living room.
- As someone else said, the power and the size of the transformer (especially with large, fresh filter caps) allow the amp to 'pop' a huge amount of power in low frequencies in fast transients. I guess this is the Fender 'bounce' sound, aka responsiveness.
- The sag of the tube rectifier (yours might be solid state?) is part of the wonderful soft sponginess.
- The negative feedback circuit helps with the squeaky clean headroom.
- The mid scoop of the preamp tone stack is Leo Fender's stroke of genius, making the electric guitar a full-frequency range instrument like a piano, instead of the nasal and honky thing it had been.

The Champ can't compare to a Twin on all these points. The Super Reverb is my home practice amp. For bassaholic guitarists, it is the holy grail. I don't even want to hear about any other amps, and my gear acquisition syndrome is fully cured. Enjoy!

I totally agree on the Super Reverb. I have both a 67 blackface Super Reverb and a 67 blackface Pro Reverb and both are outstanding. Recently I put a P Bass through the Super to see how it would sound at low volumes and it was glorious. I may start recording with it at low volumes so I dont blow out the speakers. It had that P Bass sound from all the classic records. I'll have to try it in the Pro 2x12 too.

 

[trber]

re: What gives a Twin it's sound?

Here's some thoughts on that. Some are the road less travelled. Haters can fire away. I can take it.

1. Big power supply - Robust iron, silicon based rectifier, pretty big filter cap section = deep current well to handle transients without crapping out
2. Conservative gain structure in each of the pre-amp and recovery stages, to avoid preamp distortion
3. Characteristic Fender tone stack, with lots of shelving in midrange, and relatively high negative feedback to clean up things
4. A robust phase inverter with some current reserve on the tail
5. Big output iron, the better not to saturate when driven by paired beam tetrodes like the 6L6 in Class AB1
6. A big enough cabinet and speaker area to move adequate air - and enough amp/cabinet MASS to give the speakers something to work against...because a loudspeaker can only move as much air as you will brace it to move. (Think about it)

Thanks for the technical detail about the amp construction and components. Appreciated!

 

[trber]

I see how it is

He did specifically say he's using it at low volume - "around 2-2.5" so he might be pushing a watt or two, maybe. Fine, maybe even three.

I know this has been posted a bazillion times already, but it really shows what every tech already knew - every amp, of any brand, is exactly the same:



He systematically takes his solid state preamp that he made, runs it through a clean power amp, and into the speakers of the amp he's demoing against, and they sound like the same amp. No tubes, no phase inverter/large iron magic, no high voltage or low voltage or bias points.

There's only so many ways you can wire up a 12A$7 and actually get decent audio to come out. This is why every guitar amp schematic looks like the same one from the radiotron designers handbook on page 1 of chapter 12, from the 1930s.

"BUT I NEED EL34S TO SOUND LIKE A MARSHALL"

No, you need your preamp to clip. Lotsa hi-fi guys are out there using EL34s and those people wouldn't tolerate any distortion.

The Twin sounds like a Twin because the preamp is amazing and Fender (and lots of other people) still uses it 59 years later, and sound coming out of well-used 2x12 speakers typically will sound pretty alright.

It really comes down to "buy what you want." I'd also more specifically say "buy what you want that makes you play more and think less about your gear."

Ive watched that video before! Left me seriously scratching my head, as did his guitar one. Man!

 

[FlatAffectCamper]

I totally agree on the Super Reverb. I have both a 67 blackface Super Reverb and a 67 blackface Pro Reverb and both are outstanding. Recently I put a P Bass through the Super to see how it would sound at low volumes and it was glorious. I may start recording with it at low volumes so I dont blow out the speakers. It had that P Bass sound from all the classic records. I'll have to try it in the Pro 2x12 too.

Totally. For bass it's magnificent, especially for a punk/grunge kind of sound. I think it sounds as good or better than an SVT by the time you get it on tape. Definitely can't do much volume with those speakers, better to use an external cab, I sometimes use a 4ohm load bass 210 cab and I think it's okay to do, but don't hold me to that. In fact I installed Robinette's line out for the purpose of recording bass with it.

I modded my Normal channel with the mid resistor removed so it's like Mid on zero.

If I knew then what I know now, I would have bought a AB763 Twin, for the additional power for bass, although I think the Super's cab sounds bassier for guitar.

 

[SJerseyDevil]

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 have had a 66 Twin, a later one and the Randall that is similar. The sound,to me, was the absolute best for Country and Classic Rock. The downfall is the weight and when I gave up having a Band I just did not want to lug those beautiful sounding amps around to Jams and open mikes and did not need an amp that large in the house. I still have a 1966 Princton Reverb that I purchased new for about $150 and recently retubed and it does all that I need,but it will never sound like a Twin. Over the years I have had the opportunity to play through most of Fender's large amps and I still prefer the sound of the Twin.

 

[trber]

This is what's known as a 'loaded question'!!! To some extent, 'almost' everyone that's posted on this subject is right to some degree. The exception might be corliss1, who claims it's all in the preamp and speakers. Not so! RMS Output power is a HUGE factor in sound definition. It's 'power' that provides headroom, and headroom is what keeps notes from distorting at the power amp stage. In the Twin Reverb, it's the RMS Output power that rather defines that amp. At 80 watts for an old blackface or early silver face version, this is LOADS of power by today's standards. With guys now turning to 'flea' amps...... those that operate at 10 watts or under (or there abouts), the 'trend' has been to abandon these mega-amps, buy something smaller or even a modeling amp, or buy no amp at all and go 'direct' into the PA board.....vs lugging around some beast like a Twin Reverb or a Super Reverb. But, the reality is that ALL the things mentioned will contribute to sound quality and 'tonality'. Even the type of tubes can make a HUGE difference. As corliss1 somewhat alluded to, tubes in the preamp can make a difference that can be audible. But, so can power amp section tubes. If you were made of money and didn't have a SPL sensitivity issue I'd suggest trying to find an NOS set of US made GE Short Bottle Black Plate 6L6 tubes for that amp. Peg the controls, run it WIDE OPEN, and 'feel it' with what's in it now. Then sub the GE tubes in and you'll find an incredible difference in the way the amp reacts, feeds back, and inter-acts with your guitar. This is why a set of 4 of these can cost upwards of $500 or more. I honestly haven't checked lately. But go from them to a set of Sovteks in that amp and you'll think something broke.

That amp should be pretty much 'blue-printed' (as we say in the car engine world) in order to really get the best performance out of it. And when everything is right, it can be 'amp heaven' for some guys. Maybe too 'clean' for others, but certainly a perfect pedal-platform. I guess if it had any problem it might be that, like an old Chevy, Ford, or Chrysler, you can have a bunch of problems with it and it can still get you where you want to go. The iron in that amp is spectacular!! The old Oxford speakers.......really kinda Ho-Hum....but easily replaced. You're doing the right thing by addressing the power supply filters, the bias level, and then coupling caps (which you may be doing and referencing them as 'bypass' caps..... not sure. They're also referred to as 'blocking' caps....read on). The coupling caps can get 'leaky' and no longer block the DC in the signal path. As such, they can also cause problems with bias levels, particularly in fixed bias amps like the TR. Frankly, all the resistors on the grids and plates should get checked too, as those affect operating voltage levels of the signal and power tubes. If not right, again, 'sound quality' is affected (though like the old Fords, Chevs, and Mopars, you may not really notice it).

Anyway, that's my 2 cents worth.....almost. I also believe that, like 'guitars', each amp has a character of it's own. Try 10 Les Pauls hanging on a Guitar Center rack and of the 10, one or two might stand out as being wonderful, while another one or two might actually be immediate 'put-backs'. Likewise with a Strat, Tele, SG, etc. And, I believe the same is true with amps. Sometimes the moons and stars just line up in an amp and it has the tone, the feel, the 'mojo' that you're looking for. Go find another one like it, and you can try 10 or 20 and NEVER find one that's quite the same. I'm sure I'll get some disagreement on that, but I don't really care. At 70 and having been doing this now since I was 10, I think I'm entitled to my opinion.

OK, now I'm done!! Good luck....Sorry about that 'ear' affliction, but I feel your pain. Sadly, I'm starting to suffer from arthritis, and 'playing' has become more difficult and actually painful. ARG!! Growing old is hell, but it beats the alternative!!! I'm out........... Tom D.

Great read, here! I appreciate the comments on output power and sound definition. My current take is that is a big factor in the equation. The other contributors discussed in the post are also very important, but I think the big one is the transformers, as often mentioned.

I attempted to "blueprint" my Ford 260 for my Tiger many years ago, so that is a familiar concept. Porting, polishing, and balancing... In an amp, I will be even less capable than I was with that motor, but will give it a go!

To start, I checked resistor values and replaced a one or two. The coupling capacitors, or fondly Brown Turds, have not been checked for DC leakage yet, but I definitely will. After I got the filter and "bypass"caps (using a term from a layout I followed, but they are the white 25/25 Mallory caps) replaced, I was excited to see if that helped with the volume drop that was happening on the Vibrato channel before the recap. So, I fired it up and played it for a long time enjoying what I was hearing! I'll get back to measuring voltages and looking for DC resistance on the Turds asap. Thanks for the comment about it affecting bias. Checking it will be downstream of the coupling cap checks. More blueprinting to be done.

I am still not sure I'll keep the amp, but if I do, I'll change the screen resistors, though I checked both them and the grids, already. They were still in spec. I just don't want to go crazy pulling components without them having failed. People get touchy with too many non-stock parts, me thinks.

I've owned a number of Champs, and they all were different. I didn't keep the best sounding ones, but that's another story! I agree with you on amps and guitars.

Tubes: I am crossing my fingers that the RCAs are OK, but intuition says no, at least one or two need replacing. If that's the case, I have to decide what to replace them with. One answer if I keep it, another if not.

Arthritis sucks. My mom has it bad. I am hoping I am not headed the same direction, but I sympathize.

Thanks for your comments, Tom!

 

[trber]

I have had a 66 Twin, a later one and the Randall that is similar. The sound,to me, was the absolute best for Country and Classic Rock. The downfall is the weight and when I gave up having a Band I just did not want to lug those beautiful sounding amps around to Jams and open mikes and did not need an amp that large in the house. I still have a 1966 Princton Reverb that I purchased new for about $150 and recently retubed and it does all that I need,but it will never sound like a Twin. Over the years I have had the opportunity to play through most of Fender's large amps and I still prefer the sound of the Twin.

They sure are heavy!

So cool...enjoy that Princeton!

 

[trber]

Nothing sounds like big iron.

I'm learning that, now!

 

[trber]

mine doesn't get moved around much any more. back in the day I could carry it with one arm. it's gotten a lot heavier in the last 20-25 years.
I have a 1966 Deluxe reverb and I just throw a mic on it. we aren't as loud as we used to be either, but still pretty loud.

I'm wondering if a Black or Silverface Deluxe may be the best compromise for me. Gotta find a Silverface for the pocketbook, or build a Blackface kit. Cool you have an original!

 

[trber]

I rehearse and practice with a Princeton Reverb, but my Twin Reverb is a workhorse that I perform live with, I love the amp I just wish it wasn't so damn heavy!

Right? Hernia waiting to happen! When I bought it, the owner kept offering to bring me a hand truck. I probably should have accepted.

 

[Ian T]

Check out these Twins, have to be the same year as yours.

 

[trber]

Good enough for this small quartet.

Before I bought this a few weeks ago, Get Back was my greatest association with the Twin. Love it!

 

[trber]

I’ve owned about 6 different Twins and know exactly what you’re talking about. Even at low volume they just sound awesome. I would say it had something to do with the cab, but I had a pro reverb once that didn’t come close to the regal sound of the TR, and it had twin 12s and dual 6l6 power tubes, so it’s not that either. I took two power tubes out of one of my Twins and I couldn’t tell any difference. I think whoever mentioned the massive transformers was correct. The preamp circuit is the same as other Fender amps. Regardless, nothing sounds as lush as a Twin, except a Quad Reverb which is just a Twin mounted in a 4x12 cab, but I can’t lug those beasts around anymore. I’d love to own another one, but it would never be played out. Still, I haven’t forgotten how good they sound. The SF Twins like you have sound better to me than the BF Twins, but that’s just my opinion. I’ve owned both.

Love it! At least I know I am not imagining things. Lol. It's a really special sounding amp, I think. Fascinating comment about your preference for the SF versions. I hope to be able to compare the two some day. I just need to find some knowledgable amp collector guru who wants to educate a novice enthusiast.

Anyone!??

 

[trber]

Check out these Twins, have to be the same year as yours.

That's awesome! Love Santana, and I'm impressed...no one's ears were bleeding with multiple Twins. Sounded great, too!

 

[Jay Jernigan]

Back when everyone else had Marshall half stacks, I had a SFTR that would keep up and sound glorious with a Gibson guitar. Any Gibson. For most gigging I used a Princeton reverb to drive the speakers. It wasn't the same, of course, but the two twelves (don't even know, for sure, but I think they were CTS) made a huge difference.
Short answer to the OP's question, though, is: All of the Above.

 

[Maguchi]

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!

The big output transformer and the pair of clear, tight 12" speakers