Hy SSA,
The symptoms that you describe are rather odd; if anything, a resistor between a TRIAC gate and MT1 (alternatively named, anode 1) should inhibit triggering rather than enable it.
Here are a few questions/observations:
(1) I suspect from your other thread about transformers that you are probably driving a transformer with the TRIAC.
https://www.electro-tech-online.com/threads/transformer-theory.149125/#post-1275375 If that is the case, you have a highly inductive load which can cause triggering problems.
(2) I suggest that you try the circuit with a restive load (not a filament lamp as the resistance is only a tenth when cold) just to see what happens.
(3) The T2512MH TRIAC is a fairly old design and is not as well behaved as some of the newer 'Hi Com' TRIACS.
(4) Try putting a capacitor in parallel with the TRIAC gate and MT1. Start with 47p and work up until, hopefully the TRIAC operates normally
(5) It is possible that you have a faulty TRIAC; have you tried another TRIAC
(6) Driving a transformer (inductor) with an SCR/TRIAC is fraught with problems if you do not take adequate precautions. One of the main precautions is to use soft start so that the transformer core does not saturate and blow the SCR/TRIAC due to excess current.
(7) Another danger with driving transformers is that you can exceed the maximum rate of change of voltage which can lead to false triggering or even damage.
(8) Inductive loads can also lead to an excessive rate of current change which can damage the SCR/TRIAC
(9) I suspect that, if you are driving a transformer, you will need a couple of back to back SCRs (which are available in higher power ratings) rather than a TRIAC.
There is another thread, presently open on ETO, about phase control of a welding transformer where some of the problems of driving a transformer with SCRs are discussed:
https://www.electro-tech-online.com/threads/ac-control-circuit-question.147790/
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