Fender Twin Reverb to Dual Showman Cabinet conversion

[t_byrd]

Hey ya'll, first post here.

I have a 76 SF Twin Reverb with MV that I'd like to put in a Dual Showman cabinet along with some 8" speakers to have a smaller and lighter combo unit. This may seem like a backwards idea but I already have a Twin that I'd like to keep at home and use this one for some gigging since I don't need a lot of volume. I mainly do solo performances in small rooms so I don't need to compete with a band.

The Twin has been sitting in a garage for a while and sounds good since I've replaced a few tubes in it but there are a few things that are confusing me about it. It has 2 25w speakers which I know is too low for a Twin, it seems to be running ok at low volumes but I don't want to push it.

My plan is to remove 2 of the power tubes to make it run at 50w (I know this is its own subject to debate) and install 2 25w speakers in the Showman cabinet. The goal of removing the power tubes is simply to have it run at the right wattage for the smaller speakers and I don't intend to crank the amp for tone/breakup purposes. I've also read that I'll need to double the speaker output impedance if I do this, its a 4ohm output so I would need 2 4ohm speakers wired in series to achieve 8ohms.

Will running the 2 25w 8" speakers cause problems if I remove 2 of the power tubes? I know its better to have higher wattage speakers than the amp output wattage but the amp seems to have been doing ok with 50w of speaker with a 100w output and I'm pretty sure it had been gigged like this with a full live band.

Just looking for some input on this project since I already have this Twin as a spare and I have an empty Showman cabinet ready to go.
Ideally I'd like the end result to be something like this - https://www.youtube.com/watch?v=8oXcSt3prVg

Thanks!

[The Dude]

Welcome to the place!

It seems you've already done most of the research. In short, your idea seems fine to me. Normally, speakers are rated at RMS power and can handle more peak power. A pair of 25W speakers on a 50W guitar amp should be just fine.

[olddawg]

Frankly.. I would sell it, save yourself the trouble, and get a smaller, lighter, more appropriate amp for what you are doing.

[t_byrd]

Thanks for the warm welcome Dude!

[t_byrd]

Frankly.. I would sell it, save yourself the trouble, and get a smaller, lighter, more appropriate amp for what you are doing.

I see where your coming from, but it honestly isn't too much trouble for me to make the conversion and I like having this one as a project amp.

I like the size of the Bandmaster/Showman cabs with 8" speakers but I'd be paying more to buy one of these and it seems that they're not too far from a Twin besides the output power.

Mainly just looking for some input as to whether or not the Twin will operate ok with removing 2 tubes and using 50w of speakers.

[bob p]

I'm probably the king of buying dead or dysfunctional twin reverbs to hack them into something else, so I'm with you on the idea of reworking a Twin chassis. Where else are you going to get midrange controls in a Fender chassis? There aren't many options.

But I'm not sure that I'm on board with the idea of using a 50W amp with a pair of 8" speakers, or turning a working TR into a full-time 50W amp. It's still going to be a heavyweight amp masquerading in a lightweight application. I'm with dawg on this -- there are better starting points than a working Twin for what you want. If the twin were DOA, needed iron, etc, then I'd be all over rebuilding it as a 50W or 20W. Still not on-board with the 8" speakers though.

[eschertron]

Recently we had a thread about that here. I think you'll find the consensus matches what you're contemplating.

[t_byrd]

I'm probably the king of buying dead or dysfunctional twin reverbs to hack them into something else, so I'm with you on the idea of reworking a Twin chassis. Where else are you going to get midrange controls in a Fender chassis? There aren't many options.

But I'm not sure that I'm on board with the idea of using a 50W amp with a pair of 8" speakers, or turning a working TR into a full-time 50W amp. It's still going to be a heavyweight amp masquerading in a lightweight application. I'm with dawg on this -- there are better starting points than a working Twin for what you want. If the twin were DOA, needed iron, etc, then I'd be all over rebuilding it as a 50W or 20W. Still not on-board with the 8" speakers though.

Hey thanks for the input! In regards to not liking the idea of using 8" speakers with a 50w amp is that simply because I'll be using a heavyweight amp in a lightweight application or do you think it could cause issues?

I've seen the 8" speakers on a few different Bandmasters and I like the idea, here's a youtube video of someone who has done it - https://www.youtube.com/watch?v=nC3maq9MeNc

I understand that the whole idea of this project is a bit backwards but I like the sound + reverb and vibrato on the Twin and I'm not really investing too much into this conversion, also everything would be reversible.

[bob p]

My only amp that uses an 8" speaker is a champ. I've never found an 8 that I think sounds good. 10, 12, 15 can sound great, but 8 just sound bad to me. it's a personal preference.

[olddawg]

Like everything else... speaker tech has changed. I see people using small(ish) speakers with a long cone throw and giant magnets for bass application. But again, honestly for the application you are describing a single 12" 60 watt speaker would be better and you would probably also be fine with a solid state amp. Both would reduce the weight, cost, reliability and footprint. I just can't see chopping up a good working Twin to make a lackluster boat anchor that will probably disappoint you.

[bob p]

I talked to Bob Carver about his subwoofer patent after he lost the patent defense case in court. The reason that he was able to get away with "cheating" to create his high power long throw mini subwoofer design is that he realized that people are not very good at identifying IM distortion at LF. that made him free to break several speaker design rules by creating a speaker that had high IMD figures. He got away with this because it was being used in a passband where people couldn't identify the IMD problem.

Those long throw drivers suffer from horrible IMD, but you can get away with using them in a sub application because it's hard for people to notice it. At guitar frequencies the IMD would be pretty bad, and noticeable too. The IMD would probably dwarf the 5% distortion of the power tubes, and it would occur in a passband that our ears are sensitive to as far as IMD is concerned. But if you're someone who likes a distorted guitar tone the IMD might not bother you.

[t_byrd]

I talked to Bob Carver about his subwoofer patent after he lost the patent defense case in court. The reason that he was able to get away with "cheating" to create his high power long throw mini subwoofer design is that he realized that people are not very good at identifying IM distortion at LF. that made him free to break several speaker design rules by creating a speaker that had high IMD figures. He got away with this because it was being used in a passband where people couldn't identify the IMD problem.

Those long throw drivers suffer from horrible IMD, but you can get away with using them in a sub application because it's hard for people to notice it. At guitar frequencies the IMD would be pretty bad, and noticeable too. The IMD would probably dwarf the 5% distortion of the power tubes, and it would occur in a passband that our ears are sensitive to as far as IMD is concerned. But if you're someone who likes a distorted guitar tone the IMD might not bother you.

Thanks for the info!

I'm wasn't familiar with IMD before you mentioned it but I sort of understand it after doing a bit of research.
Not sure what your referring to with Bob Carver's subwoofers, but are you saying that this would be a common problem for any 8" speaker?
I was planning on getting a pair of Jensen CR8's which seem to have pretty good reviews all around. Also basing this off of Rob Robinette's website where he's shown a pair of CR8's in his Bandmaster Reverb - https://robrobinette.com/Silverface_Amp_Mods.htm

[bob p]

it's a common problem for all inefficient speakers that are driven to large excursion with high power to provide big sound in a small cabinet. most any modern bass rig, for example.

[Tqi]

a single 12" 60 watt speaker would be better and you would probably also be fine with a solid state amp.

This is also more appropriate for the 'Showman', semantically - as there were several Showman combinations with 1x12" cabs, as early as 1960.

A silverface Twin is a 2x12 Showman combo with something like one resistor value changed, so building a 'mini-twin' in a Showman head kinda makes sense still. Weber do some 30W 8" guitar speakers that would give you plenty of power for either a two tube Showman or one switched into Triode operation, whatever suits.

That said, 8" speakers tend to work better in sealed cabs... Why not build a head and cab? The head and cab together would be about the same size as your Twin, but you should still save some weight from the small speakers. If you really wanted to build a speaker inside your head; one thing I've been considering is using a power soak with 50W resistors, with something like a 6", 10W speaker you could get a 1/2W to 1W output for practice use, then just unplug the jack and hook it up to the 60W 2x8 cab for proper use. In your place, I'd even be lazy with the cab and use a fixed speaker cable, rather than a socket and separate cable.

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[Tqi]

you would probably also be fine with a solid state amp.

On that subject... Ever heard of Quilter? They make a solid state, 50W blackface copy called the 101 Reverb, which is $400 and under 1Kg.

101 Reverb | Quilter Performance Amplification

https://www.ebay.com/p/Quilter-101-M...ead/2256100480