Pro reverb versus Twin reverb???

[Jalmeida]

Hey folks,

I have a friend wanting a lower wattage single wattage Twin Reverb with reverb only. So would the Pro reverb be the right direction to capture the sound of the twin reverb with 40w? Anyone done a similar build? I appreciate any advice anyone has.

[stratomaster]

The main differentiators between the two are the 2 vs 4 6L6s, the solid state rectifier in the Twin vs the tube for the Pro, the mids cap value (some Pros used 0.022uF), and the transformers. 

There's a reason the two models exist. They sound different.  If I were to attempt to make a half power Twin I'd at something like the Bandmaster Reverb with a solid state rectifier.  The Pro output transformer is pretty small for the amp's size (and part of its charm).  The Twin isn't as restrained in this respect.  Much closer to the Bandmaster

[HotBluePlates]

... I have a friend wanting a lower wattage single wattage Twin Reverb with reverb only. So would the Pro reverb be the right direction to capture the sound of the twin reverb with 40w? ...

Close enough, though the Pro Reverb is somewhat sweeter/softer.

Naturally, you would need to add a Middle control to the Pro's circuit.  And you could use a solid-state rectifier (but I would suggest that just to avoid the risk of a flaky rectifier tube, rather than to be more like the Twin Reverb).

You could pick a stouter output transformer, though I'm pretty sure the blackface Pro Reverb, Bandmaster, Tremolux and Vibrolux Reverb all used the same output transformer.  You would have to move to something like the blackface Bassman's OT to get a bigger transformer for 4kΩ to 4Ω.

[Yeatzee]

I call my '66 Pro Reverb a mini twin all the time. It's imo better in just about every way (for me), enough headroom to be loud but not so much that you can't get it into any breakup at gig volumes. Very stout tone still, big sounding amps (mine has jensens).

I guess it depends what he has in mind when he says a mini twin. Like a 2x12 combo that's got some power = mini twin? Then check on the pro reverb. If he means mini twin like a 1x12 very with infinite headroom, negative.

[Jalmeida]

I call my '66 Pro Reverb a mini twin all the time. It's imo better in just about every way (for me), enough headroom to be loud but not so much that you can't get it into any breakup at gig volumes. Very stout tone still, big sounding amps (mine has jensens).

I guess it depends what he has in mind when he says a mini twin. Like a 2x12 combo that's got some power = mini twin? Then check on the pro reverb. If he means mini twin like a 1x12 very with infinite headroom, negative.

He wants gigable volume clean without back injuries and hernias to move. In 1x12 form. So I definitely see how the inifinte headroom is one of the defining tone attributes of the Twin reverb. My initial plan would be to fit a Pro reverb or Bandmaster circuit without vibrato and single channel into a Princeton chassis. Setup with a TMB tone setup and bright switch. Then reverb and dwell knob. Maybe get Soursound to custom make a bigger core Pro reverb OT.

[DummyLoad]

 Build a Bandmaster Reverb clone with solid state power supply - Use the Hammond 1760K or Mojotone MOJO774 output transformer and 5881/6L6BG to get the output power down under 40W. Using a Super Reverb/Basssman OT is beefier and closer to Twin in tone (power bandwidth mostly) and dynamics.

Super/Bassman OT options.
https://www.mojotone.com/Blackface-Bassman-Super-Reverb-Vibroverb-Output-Transformer

https://www.hammfg.com/files/parts/pdf/1760K.pdf


Bandmaster/Pro/Vibrolux OT options.
https://www.hammfg.com/files/parts/pdf/1760J.pdf


--Pete

[tdvt]

My initial plan would be to fit a Pro reverb or Bandmaster circuit without vibrato and single channel into a Princeton chassis. Setup with a TMB tone setup and bright switch. Then reverb and dwell knob.

The pic below is nearly just what you describe; a single channel AB763, with TMB & dwell, the only differences are this one has trem, but no bright switch. It also has a tube rectifier with a Vibrolux tranny set.


I had planned to put it in a Princeton chassis, but after the initial fitting, I moved up to a Bassman chassis, which is a couple inches longer than a Princeton, but has the added depth of all the big amps. But still shorter than a Deluxe.

I am happy I went that route as it made things way easier to fit, (especially as you plan larger transformers) while keeping a "Princeton" vibe, visually.

No pic of the cabinet yet, but I kept the Princeton height-to-width ratio to that end

[tdvt]

No pic of the cabinet yet

Fixed

Easy to dig them out, need to get busy on the cabinet-side of things...

Pro Reverb, single channel cab & Princeton

[Jalmeida]

My initial plan would be to fit a Pro reverb or Bandmaster circuit without vibrato and single channel into a Princeton chassis. Setup with a TMB tone setup and bright switch. Then reverb and dwell knob.

The pic below is nearly just what you describe; a single channel AB763, with TMB & dwell, the only differences are this one has trem, but no bright switch. It also has a tube rectifier with a Vibrolux tranny set.


I had planned to put it in a Princeton chassis, but after the initial fitting, I moved up to a Bassman chassis, which is a couple inches longer than a Princeton, but has the added depth of all the big amps. But still shorter than a Deluxe.

I am happy I went that route as it made things way easier to fit, (especially as you plan larger transformers) while keeping a "Princeton" vibe, visually.

No pic of the cabinet yet, but I kept the Princeton height-to-width ratio to that end

I can definitely see with that vibrato circuit how fitting it into a princeton chassis would be tough. My hope which may not be the case is that with out the vibrato controls and components I may have an easier time fitting into a princeton chassis. Perhaps a princeton(non-reverb) chassis and omit the dwell.

[HotBluePlates]

He wants gigable volume clean without back injuries and hernias to move. In 1x12 form. ... My initial plan would be to fit a Pro reverb ... single channel into a Princeton chassis. ...

Does your friend know that Fender already makes the amp you're contemplating building?
'68 Custom Pro Reverb

It weighs about as much as a Princeton Reverb, but partly because the Neo Creamback speaker is 6 pounds less than a comparable ceramic magnet speaker.  The cabinet size is a little larger than a Princeton Reverb, and I strongly suspect it's about as-small as the amp can comfortably shrink.

Doing the same but with a normal speaker will weigh in around 41-42 pounds.  Will that be enough weight reduction compared to the 64 lb Twin Reverb?

This is part of the impetus for the 35lb Tonemaster Twin Reverb, that ditches an output transformer & large power transformer, and uses neodymium speakers.  Some folks also use Quilter solid-state power amps with a carefully chosen preamp and/or pedals with speaker cabs to solve this problem.

[Jalmeida]

He wants gigable volume clean without back injuries and hernias to move. In 1x12 form. ... My initial plan would be to fit a Pro reverb ... single channel into a Princeton chassis. ...

Does your friend know that Fender already makes the amp you're contemplating building?
'68 Custom Pro Reverb

It weighs about as much as a Princeton Reverb, but partly because the Neo Creamback speaker is 6 pounds less than a comparable ceramic magnet speaker.  The cabinet size is a little larger than a Princeton Reverb, and I strongly suspect it's about as-small as the amp can comfortably shrink.

Doing the same but with a normal speaker will weigh in around 41-42 pounds.  Will that be enough weight reduction compared to the 64 lb Twin Reverb?

This is part of the impetus for the 35lb Tonemaster Twin Reverb, that ditches an output transformer & large power transformer, and uses neodymium speakers.  Some folks also use Quilter solid-state power amps with a carefully chosen preamp and/or pedals with speaker cabs to solve this problem.

He has played through them and was looking at them. He doesn’t want vibrato and he wants to go all out on iron, speaker and components.

He also played a show with the new tonemaster twin. I got the impression it didn’t blow his socks off. And he is a bit old school too. Likes the tube sound. 

[tdvt]

He wants gigable volume clean without back injuries and hernias to move. In 1x12 form. ... My initial plan would be to fit a Pro reverb ... single channel into a Princeton chassis. ...

Does your friend know that Fender already makes the amp you're contemplating building?
'68 Custom Pro Reverb

I thought about mentioning that new single-channel Pro, pretty close to the end-goal in a turn-key package.

Never heard one in person. But also a PCB if that is an issue. Probably not my first choice.

I strongly suspect it's about as-small as the amp can comfortably shrink.

Thankfully, I never cut up my Princeton to use a 12" speaker but will confess to thinking about it decades ago. A friend just sold his SF Princeton which had a 12" installed & I know that it was a very tight fit in the stock Princeton cab with stock PR transformers.

Addendum:
I am thinking about putting a 15" in the UL Pro cab in the pic above. A 15" just fits top-to-bottom, but dodging the transformers might not work out. This era has the dado-ed in baffle & this particular amp got wet so the baffle needs to be replaced anyway. We'll see...

[passaloutre]

I can attest the Neo Creamback sounds great in my 1x12 Bassman/Plexi thing. Not a very efficient speaker though, if headroom is your goal, but extremely light.

[SoundmasterG]

Another thing your friend could try is to get an early 6L6 Traynor head with a custom 1x12 cabinet. With the big Hammond transformers in those, they are sort of Twin like in that they don't give up the goods as easily. Those amps are based of the 5F6A Bassman though so it is a slightly different sound. It could easily be modified into a more blackface circuit if desired, and the cost would likely be less than building something from scratch.

Greg

[Platefire]

My Allen Accomplice is my little twin. It's really a one channel DR AB763 (with Middle and Raw pots, no trem) with a hotter PT biased for 6L6GC's.  With the MV at 10 and using the Pre volume set as needed, you can get medium or really loud solid backbone clean tones. It's got an Eminence Red Coat Private Jack that also lends itself to bright tones.

On the other hand if you want darker distorted main sound, you can dial that in too. Here is the prescription: