Speaker swapout 8" Champ Combo

[212Mavguy]

This particular 70's silverface Fender Champ has almost no Fender parts left in it. It's a home made Blackface type circuit with top end parts stuffed into a nice turret board, it's modded from experimenting to much more agressive in output than from the original circuit and build, to say it's a beast is an understatement.

 

The 8 ohm CTS speaker that was in it had been salvaged from an Allen Gyrophonic organ speaker cab. It had a square ceramic magnet, the snowflake type basket, a small (1" or less) VC and paper dust cap. It was loud and sounded surprisingly fat and warm for its size.

 

I had an interesting one of a kind boutique 8 inch guitar speaker on my fleabay list, but I wanted to try something I already had before spending any more money, already spent lots for that new Leslie cab...

 

So I had this 16 ohm JBL/Ampex 8 incher with a much bigger (1 1/2"- 1 3/4") VC, paper dust cap, a huge 4 inch diameter round alnico magnet, a curvilinear cone profile and doped cloth surround. The mounting holes were spaced father apart than most other 8 inchers, so new holes were drilled and t-nuts were installed in the baffle board.

 

After mounting it and soldering the wires to the terminals, I fired it up. The amp's OT was running the 16 ohm tap to the speaker jack. I noticed louder volume, more definition, better musicality/harmonic content, great cone control at high volume and distortion levels, and better compression/sustain at higher volume settings than the speaker formerly mounted. This long out of production speaker can be found on eBay for 80 to 120 bucks apiece. The high gain tones were simply huge, and the cleans were full and sweet. It is really, really hard to believe that this much volume and sound quality come out of an amp runnning a single 6v6 for 7-8 watts and having only an 8 inch speaker in it. The JBL is staying in it!

[bolero]

cool tip, got any pics?

 

thx!

[212Mavguy]

Don't have a working camera that can easily get pics to computer right now. These baby monster alnicos are found in early 60's vintage Ampex powered speakers. They have a tube amp inside the cab, and those tube amps are really good. Ampex was serious top, top shelf item in their prime.

[Hfan]

Sounds like a fun tinker. So the original 8 ohm speaker was just swapped out for the 16ohm or did the OT have dedicated taps for each? I've heard you can go from 8 to 16 ohms on fenders but I'm fuzzy on that aspect.

[212Mavguy]

The original output transformer was the size of a walnut and the output was 3.2 ohms. I had long ago donated that tranny to my amp tech/mentor. The OT currently in the amp is so massive that it had to be mounted to the bottom of the cabinet with bolts and t-nuts. The ebay seller claimed that it was a Schumacher SE 30w, 5000 primary, 4/8/16 secondaries. It is bigger than the oversized power transformer. All the Fender iron was junked long ago.

 

The 16 ohm tap was the one connected all along, so the CTS was operating at mismatched impedance, which usually indicates a louder, punchier sound then a proper impedance match. So some of the improved sustain with the JBL/Ampex is directly attributed to the increased loading to the output tubes from proper speaker impedance matching instead of being under loaded as is the case with the CTS. You can be off in impedance match one setting up or down. So from the 16 ohm tap that would be 8 and 32 ohms, for an 8 ohm tap that would be 4 and 16 ohms. Mismatch down in loading is more loud and punchy, mismatch up is more compressed, sustain-y.