• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Lafayette KT-250-A

Hi!!!
Tell me how much volt does this winding of the transformer have? How many volts is there? alternating current
I want to order a power transformer need data!
How many volts? How much ampere?
 

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We will need to find a schematic with voltages indicated, at least B+, or a specification for the power transformer. Help anyone? The schematic you found has no voltages shown, so it will only lead to guesses. Here goes! Hope it helps.

Below is a partial schematic that I believe is of the KT-250 which shows voltages, but I don’t know its provenance. Here the kt-250a ran the EL86 at plate and screen voltages at the top of Mullard datasheet specifications of around 250V across the tube. (Other manufacturer datasheets often show lower maxima). If 260 V B+ is correct as shown in the schematic the High Voltage winding on the power transformer you asked about is probable 95-100Vac before it goes to the voltage doubler rectification.

1685282724580.jpeg
 
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Regarding current capacity.

I copied the Mullard sheet for PP class AB1 conditions. That shows you need about 140 ma per channel at maximum signal for a pair of EL86s. Due to voltage doubler action I would guess you need 300 ma at 100Vac for each output pair. Then add some for front tubes and bleeder resistors, a 100V winding with 0.6-0.7 amps will work.

The Mullard operating conditions is different than what you have in your Kt-250, which claims 25 watt output per channel. With the much higher screen voltage your operating condition may be require much higher instantaneous current on musical peaks. However, since music averages at lower levels the 600-700 ma will like be sufficient. (I hope someone has the actual specs of the transformer, so that we could all learn).

1685285027221.jpeg
 
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Radiomuseum has the KT-250A schematic; the Sams folder is for the KT-250. There are differences in the bias and feedback networks, but transformers may be the same. Sams transformer ratings: 100V @ 900 mA (270 mA DC @ 260V), 6,3V @ 4.1 A, 35V @ 390 mA. Lafayette part number 15-19. Biggest problem for replacement is size - fairly small footprint. 200 VAC @ 450 mA would work with full-wave bridge, 200-0-200 @ 270 mA could work, but would likely be larger.
 
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