TCBA founder, Harry Goldman and the TCBA logo

TCBA - Tesla Coil Builders Association

Devoted to the construction, operation and theoretical analysis of the Tesla coil

TCBA Volume 11 - Issue 1

Page 13 of 18

The magnifier is an amazing tool and we have learned a lot from our work but much, much more work lies ahead. A key point is that the primary and secondary do not function as a normal Tesla coil but act as a high power low impedance signal generator used to base feed the extra coil which can be thought of as a 1/4 wave helical resonator which is “free resonant” or unfettered by a primary. The VSWR of this coil seems to determine the voltage gain over and above the base voltage fed to it. We have found that only a “hands on imperative” will help the amateur get a feel for the construction of these interesting R.F. power machines.

The Method for Assembling Your Own Magnifier

Start any magnifier work by reading what the Corums have to say! Next choose a transformer. If it is a neon sign or magnetically shunted type then you will need a large, heavy duty, air blown, multiple series gap (8-10 gaps is just barely enough). If you are operating above 2KW then a rotary might be in order but make sure and use series gaps in with the rotary to assist quenching. If you choose a non-shunted type transformer (pole pig) you must use proper ballasting in the primary to limit line current and you must use a rotary with mulitple series gaps as well! The large transformer systems above 2kw can use coupling values of K>.4 with good quenching gaps. To start construction of the coil system you should do the following:

  1. Wind a secondary on a large coil form using large insulated wire. The primary should be movable (for variable coupling) and in very close proximity to the secondary. Special techniques may be needed to insulate this setup to avoid flash over. Place the primary/secondary in its firing position with all primary connections in place and characterize the secondary from the top with its base lead loose. The measured frequency we will call “F”. It should be stated that placing the primary/secondary system too close to the ground level may result in large capacitive losses or, in the case of a concrete reinforced floor, both inductive and capacitive losses. We have found that in almost all cases 3 feet above such a floor reduces these losses to almost zero.
  2. Now wind the extra coil. This is a simple 1/4 wave coil on a coil form of moderate diameter with the wire lightly spaced or tight wound with insulated wire. The wire gauge for this coil may be small in a lower power system but remember, the larger the wire the more power and voltage gain you will have. Wind the wire on a form that is too long for the coil you wish to make so that wire can be added or subtracted later. The finished coil should characterize (in place) at a frequency somewhat above that of the secondary frequency “F”, say 10% higher.
  3. Use a very heavy duty series static gap that is fan blown in series with a very fast break rotary gap. At K values above .4 it is recommended that the tell-tale rotary “follow around” flare be watched for as a sign of bad quenching. Adjust your ballasting or change your coupling or gap to correct this condition, as you are not operating efficiently if this occurs. Above K values of .5 the gap is the most critical part of a magnifier!

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