Hi
I am stuck here with a blown out toroidal transformer for this amp. I think this transformer cannot be rewound. Thinking about replacing an EI transformer, I do not know the secondary voltages. Can this transformer be bought online. If anyone has information or know of an alternative , please assist me.
Thanks
I am stuck here with a blown out toroidal transformer for this amp. I think this transformer cannot be rewound. Thinking about replacing an EI transformer, I do not know the secondary voltages. Can this transformer be bought online. If anyone has information or know of an alternative , please assist me.
Thanks
You can look at the voltage rating on the rail caps. The peak transformer voltage is 80% of that on conservatively built amps. 100% on consumer grade. Transformers are sold by average voltage so that is 70% of the peak voltage.
So if 2 rail caps are 80 v , .7*.8*80 is 44.8. So if there are two rail caps for two different rails, you need a 90 v CT transformer. CT stands for center tap. That is for EI transformer. Toroids have two different windings that you have to put together to make the center tap. So in a toroid you need one with two 45 v windings.
VA size (toroids) has to do with how many output transistors you have. For post 1990 amps, In 45 v an output transistor pair can handle about 1.6 A so that is a 90*1.6 is 140 va. Two pairs would be 280 VA. EI transformers are sold by output amps so 1 pair would be 2 amp transformer. 2 pairs would be 3 or 4.
Old 1970's equipment can handle about an amp per output transistor pair.
Derate output current for undersized heat sinks in consumer equipment.
Read the dimensions on the datasheet before buying. I find usually line frequency toroids will not fit in the box where an EI transformer was, not in the same VA (amp) rating. Forces me to buy EI from salvage houses, or consider a switcher supply. Switcher supplies have their own curse, they require shielding on both box and lines out to keep the RF away from the amplfier circuits. These Peavey & Allen amps with switcher supplies I work on always have a perforated steel box. The switchers for sale on e-bay always come as a naked PCB,usually also without the necessary heat sink.
So if 2 rail caps are 80 v , .7*.8*80 is 44.8. So if there are two rail caps for two different rails, you need a 90 v CT transformer. CT stands for center tap. That is for EI transformer. Toroids have two different windings that you have to put together to make the center tap. So in a toroid you need one with two 45 v windings.
VA size (toroids) has to do with how many output transistors you have. For post 1990 amps, In 45 v an output transistor pair can handle about 1.6 A so that is a 90*1.6 is 140 va. Two pairs would be 280 VA. EI transformers are sold by output amps so 1 pair would be 2 amp transformer. 2 pairs would be 3 or 4.
Old 1970's equipment can handle about an amp per output transistor pair.
Derate output current for undersized heat sinks in consumer equipment.
Read the dimensions on the datasheet before buying. I find usually line frequency toroids will not fit in the box where an EI transformer was, not in the same VA (amp) rating. Forces me to buy EI from salvage houses, or consider a switcher supply. Switcher supplies have their own curse, they require shielding on both box and lines out to keep the RF away from the amplfier circuits. These Peavey & Allen amps with switcher supplies I work on always have a perforated steel box. The switchers for sale on e-bay always come as a naked PCB,usually also without the necessary heat sink.
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