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10-09-2018, 02:57 PM
Hi Guys
In the above examples of MI use of hifi OT designs, the extended power use is not great. The Fender PS-400 uses six 6550s to generate 450W continuous. The OT has three secondaries to match the 2x15" cabinets Fender designed for this amp - one amp + three cabinets as a standard rig. Modern players want to use their own modern cabinets which are usually 8-ohms or 4-ohms, but in any case, the player wants ALL the power available in one output. The Hammond 1650W is the exact same size and primary impedance as Fender's OT, but has secondary that matches the player's needs. 1650W is rated for 280W, so here we have an extended use by a factor of 450/280=1.6 which is still small enough to allow massive low-end output.
Most people including "amp designers" tend to view the applications listed in the tube data sheets as "limiting cases" or "optimums", which leads to the idea that a given tube MUST work into a GIVEN primary load and can ONLY produce this much power. For many tubes, the plate curves are not available and/or the plots are at quite low screen voltages for tetrode/pentodes. We know from TUT2 and TUT4 how to scale these graphs to acquire full power from the tube and do it safely. If we read the data sheets carefully, we can see the real capabilities of the tubes we use and that there is much more overlap than difference. The important difference is their TONE.
In the above examples of MI use of hifi OT designs, the extended power use is not great. The Fender PS-400 uses six 6550s to generate 450W continuous. The OT has three secondaries to match the 2x15" cabinets Fender designed for this amp - one amp + three cabinets as a standard rig. Modern players want to use their own modern cabinets which are usually 8-ohms or 4-ohms, but in any case, the player wants ALL the power available in one output. The Hammond 1650W is the exact same size and primary impedance as Fender's OT, but has secondary that matches the player's needs. 1650W is rated for 280W, so here we have an extended use by a factor of 450/280=1.6 which is still small enough to allow massive low-end output.
Most people including "amp designers" tend to view the applications listed in the tube data sheets as "limiting cases" or "optimums", which leads to the idea that a given tube MUST work into a GIVEN primary load and can ONLY produce this much power. For many tubes, the plate curves are not available and/or the plots are at quite low screen voltages for tetrode/pentodes. We know from TUT2 and TUT4 how to scale these graphs to acquire full power from the tube and do it safely. If we read the data sheets carefully, we can see the real capabilities of the tubes we use and that there is much more overlap than difference. The important difference is their TONE.
