I built a box to connect two speaker cabinets

[Michael Smith]

After looking at a product online called the "Cab-Link" by Radial Engineering, I decided to repurpose some old parts I had in my closet. I have two 4 ohm speaker cabinets, a 2 x 10 I built for my Vibro Champ, and a 2 x12 from my Super Twin Reverb. I wired the jacks in series so the combined impedance is 8 ohms, which is correct for my Carvin Vintage 16, Sovtek Tube Midget 80h and Fender Deluxe Reverb. Since I already had RCA jacks in the old box I had made for something a long time ago, I wired one up because the cabinet for my Vibro Champ is wired with a RCA plug (since that's what the output jack on the Vibro Champ uses). Of course I would only plug two cabinets into the box at any one time, a quarter inch and a RCA, or two quarter inch.

With room for additional jacks in the box, I thought about also making a parallel circuit, but don't have a need for that right now.

I've yet to test it out, I will measure the DC resistance with two 4ohm cabinets plugged in to double check.

[Bill Moore]

I'll bet it works!
When I built my Twin, I used a 94 Twin OT, 4-8-16 ohm output, plus a balanced line out. I added another jack for a "series" as well as parallel output. Instead of a head as I planned, a friend traded me a Mojo cab for a chassis. I have only used it with 2 8 ohm loads, maybe someday I'll try other possibilities!

[Michael Smith]

I'll bet it works!
When I built my Twin, I used a 94 Twin OT, 4-8-16 ohm output, plus a balanced line out. I added another jack for a "series" as well as parallel output. Instead of a head as I planned, a friend traded me a Mojo cab for a chassis. I have only used it with 2 8 ohm loads, maybe someday I'll try other possibilities!

I "think" it will work Bill. I don't remember what I built the box for originally. I have another identical one with 1/4 inch plugs on cables coming out of the side of the box. Probably for a reel to reel 4 track tape recorder I once had in my studio. I also had a Tascam 4 channel mixer. Traded it in when I bought a Tascam 8 track tape recorder and 20 channel Tascam mixer. The mixer is still used with my Pro Tools recording rig, but I messed up the 8 track tape machine.

[Bill Moore]

I had a friend back in the day with an 8 track "studio" in his basement. I was the drummer for many of his projects, and did most of the wiring. I built an 8 out, 2 in "snake" from the booth. I installed it while he was out of town, surprised him when he got back! He complained that I painted the sheet metal black, instead of the wall color!

[Michael Smith]

I had a friend back in the day with an 8 track "studio" in his basement. I was the drummer for many of his projects, and did most of the wiring. I built an 8 out, 2 in "snake" from the booth. I installed it while he was out of town, surprised him when he got back! He complained that I painted the sheet metal black, instead of the wall color!

Ha ha. Your buddy could have painted the walls black to match your snake. I built a 10 -xlr, 2- 1/4 inch sends snake box for my drum booth. I used stained pine, so it kind of matches the neutral tone of the carpet, lol.

I tested my home made series box this morning with a 2 x10 and 2 x 12 speaker cabinet and it works great!

[Bill Moore]

I like the wood look!

[Michael Smith]

I've always been curious as to why many Fender amps have an "external speaker" jack next to the main speaker jack. If the impedance of the installed speakers match what the output transformer is expecting to see, wouldn't adding an extension speaker drop the total speaker load below the minimum? (I understand Fender wires the jacks in parallel).

Oddly enough my 1968 or 1968 Fender Bassman (AC568) doesn't have any indication on the back panel what speaker load is correct. It just says "speaker 50 Watts" next to the speaker jacks. On the schematic it says "total load 4 Ohms", and that is what I always have used, but only recently have I downloaded the schematic. Perhaps the original owner's manual had that information.

Edit: I did find an owners manual online for a 1972 Bassman 50, and it does have a diagram of the back panel, and under the speaker jacks it says "total load 4 ohms, 50 Watts RMS", but my actual amp has no such wording.

[phantomman]

Back in the day Fender's iron (Triad, Schumacher-Woodward, and Better Coil & Transformer) was as rugged as they come, built to mil-spec in fact. Most of them could safely operate at a 100% impedance mismatch. Fender's then-contemporary literature of the day mentioned that "Fender amplifiers possess tremendous power reserves that allow extension speakers to be connected as the situation demands" but mentioned no specific load information. In the case of a bass amp used for bass guitar (or keyboard) I would not operate the amp in an under-loaded condition as low frequencies decrease a speaker's effective impedance which *may* present a hazard to the O/T, especially under high-power conditions.

[Michael Smith]

Thanks for that Phantomman. I tend to be very "by the book" when it comes to connecting speakers to tube amplifiers, especially old ones. I would hate to kill any of that "old iron", even if they are rugged. And I recognize that a speaker's stated impedance is only accurate for a given frequency range.

[phantomman]

Yes. A speaker's static impedance (ie: the DCR measurement) is generally determined by injecting a 1kHz into the voice coil and noting the resistance with a VTVM.

[Michael Smith]

Funny how my Vibro Champ calls for a 3.2 ohm speaker load. I currently use two 10 inch 8 ohms wired in parallel.

[phantomman]

I've wired up a Vibro Champ to a Dual Showman cabinet. Sounds absolutely outrageous driving a pair of 15-inch JBL's!

[Michael Smith]

I've wired up a Vibro Champ to a Dual Showman cabinet. Sounds absolutely outrageous driving a pair of 15-inch JBL's!

I will try my Vibro Champ thru a Peavey 2 x 15" speaker cab. For now the Vibro Champ is on the sidelines, as I discovered the idle plate dissipation was 135% of the 6V6 maximum, and that was with the original 40 year old tube. Even higher with a fresh 6V6. I need to buy a 1K or 1.2K ohm resistor for the cathode bias to replace the resistor that was installed at the factory.

[Michael Smith]

I just looked at the rear panel of my 1969 Super Reverb. There is nothing to indicate the minimum speaker load. (2 ohms per the schematic). There is a speaker jack and an external speaker jack and it just says "speaker 40 watts" beneath the main speaker jack. I imagine over the years some unsuspecting person hooked up a 4 ohm external cabinet with the built in 4 x 10" 2 ohm speaker load, yielding a total speaker load of 1.33 ohms. Although this would still be within the 100% impedance tolerance as mentioned above. On the other hand the Super Reverb is so loud with it's built in speakers, I don't see the need for an external cabinet, but with the external speaker jack sitting there "just waiting" for something to plug into it, I'm sure the temptation has been too much for someone.

I played my Deluxe Reverb through the 2 cabinets on the right, using my newly built series speaker cabinet combiner box in the photo below, and the sound was rich and full, AND LOUD!, even at volume level just below 4. The cabinet on top normally houses my Vibro Champ chassis, but I am working on it at the moment.

[phantomman]

The Deluxe Reverb is a wonderful platform with a lot of untapped potential. I've built several of these 1 x 15 upgrades for clients plus a number of 2 x 10 conversions......

[DanTheBluesMan]

dang, dude

you got me drooling. DR with a 15"? 2x10"

I'll take one of each, please

[phantomman]

The 2 x 10 conversion is easy, requiring only a new baffle board and a pair of 16-ohm speakers. You could probably build it yourself.

The 1 x 15 "Spankmaster Reverb" needs an all-new enclosure.

[Bill Moore]

Roger, try your 5E3 through a 15, when I started it up on the bench, I had my extension with the K130 under the table.
Oh boy!

[Michael Smith]

The 2 x 10 conversion is easy, requiring only a new baffle board and a pair of 16-ohm speakers. You could probably build it yourself.

The 1 x 15 "Spankmaster Reverb" needs an all-new enclosure.

Interesting, I would like to get a couple of 10" alnico's and try them out in the Deluxe. But if I'm not mistaken, my 1977 Deluxe has the baffle board that is not removable. I will have to check it tomorrow.

[phantomman]

Yes, all CBS-era Fender cabinets from 1971 onward have the glued-in baffle board and lap-joint construction. It's possible to reconfigure those enclosures to accept a screw-in board but very time consuming. Most folks just buy a new box.

[Michael Smith]

Yes, all CBS-era Fender cabinets from 1971 onward have the glued-in baffle board and lap-joint construction. It's possible to reconfigure those enclosures to accept a screw-in board but very time consuming. Most folks just buy a new box.

Ya, I just confirmed my Deluxe Reverb has the glued in baffle board. I guess I could cut it flush with the sides of the cabinet and glue in some cleats to attach a new baffle board to, but that would kind of destroy the cabinet. It would be better to just construct a new external cabinet that would accept a 2 x 10 or 2 x 12 baffle (interchangeable). I've begun to sketch out some dimensions based on my Super Twin Reverb cabinet, which "barely" holds two 12 inch speakers side by side. I think if I designed an offset baffle so one speaker is higher than the other, it would give me a little more room for some cleats on the sides. Like I did with my vibro champ 2 x 10 cabinet (although I had to notch out part of the cleats to fit the speakers).

[Bill Moore]

I have fixed a couple of cabs by cutting the baffle and prying the old baffle out of the cab. Cut and install strips to make the grooves flush, then either installing a "Blackface" type baffle, or "Silverface" style.
An amp tech friend steams the tolex from one side around the corners, and the cab joints on one side. Remove old, and install new baffle re glue the cab and reinstall tolex, looks original!