Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: candletears7 on November 22, 2018, 08:29:43 pm
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I want to add a 16/8 ohm impedence selector switch to my old '64 AC30 Top Boost.
The reason is so I can use it at 16 ohms as per usual as a combo, or switch to 8ohms to run into a Radial Cab Link and then one out to the amp's Blues and also to another old 16 ohm Marshall Greenback cab.
I thought a simple solution would be simply leave it as 16ohm, then when I want to use the extra cab it would mean the Blues (wired at 16ohm) in the Vox would get 8ohm and the same for the Marshall cab.
I always thought that lower impedence from the amp into higher impedence at the cab was fine, but I'm reading about "flyback voltage" from correctly mismatched setups?
Is everything ok as long as the amp's load is less than or equal to the cab? If not, what's the least invasive impedence switch setup for one of these old amps?
Thanks.
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It's not a transistor amp. 8 Ohm load on 16 ohm tap will do no harm. The Watts will be reduced, but the increased cone-area and more complex sound field may trick the ear. So just add an external jack and run both 16s in parallel as 8 Ohms, see how it sounds.
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Your speaker connection to the chassis should be made via a screw terminal block like the attached photo. If so, just put your selector switch and 8Ω, 16Ω speaker jacks in a small metal box and run 3 wires from the box up to the chassis terminal block. Use Velcro tape to attach the box to the side of your cab. Totally non invasive.
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Thanks guys - I just wanted to run this past other people. Appreciate the help!