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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 20th Apr 2024, 2:08 pm   #1
deliverance
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Default AR88 LF mains transformer info.

Hi all . I picked a AR88 LF up yesterday and it is in a bit of a state but all there the mains transformer is toast I have a spare D transformer but the secondary

HT on the D is 690ac and on the LF one it's 660ac will the higher voltage cause any issues cheers Chris.
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Old 20th Apr 2024, 2:16 pm   #2
Silicon
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Default Re: AR88 LF mains transformer info.

The difference is 15V on each anode winding and this may translate to a 20V increase in the DC HT.

You might be able to drop that 20V across a high wattage 200 Ohm resistor in series with each rectifier anode.
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Old 20th Apr 2024, 4:37 pm   #3
turretslug
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Default Re: AR88 LF mains transformer info.

Quote:
Originally Posted by Silicon View Post
The difference is 15V on each anode winding and this may translate to a 20V increase in the DC HT.

You might be able to drop that 20V across a high wattage 200 Ohm resistor in series with each rectifier anode.
I found that using 5Z4-type indirectly-heated rectifiers in place of the original directly-heated 5Y3-types (I'm not a fan of directly-heated types from both the initial rapid HT voltage stress and fractured-filament-to-anode-short hazard liabilities) resulted in a HT increase of around 20V and did exactly that with a pair of fusible flameproof resistors. The spacing between two of the transformer securing screws adjacent to the AC HT tags neatly matches a popular tagstrip type, making it a neat and simple matter to fit the resistors between transformer and tagstrip without having to drill the chassis.
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Old 20th Apr 2024, 5:15 pm   #4
G6Tanuki
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Default Re: AR88 LF mains transformer info.

I did something similar to my AR88, but using a single 20W metalclad wirewound resistor from the transformer centre tap, resistor is bolted to the chassis for heatsinking. I was happy to drill the holes..

The mains goes up to 255V here on occasions so calming the upper excursions of the HT line seemed a wise move when dealing with a radio that could be powered on for many hours at a stretch.
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Old 24th Apr 2024, 4:50 pm   #5
deliverance
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Default Re: AR88 LF mains transformer info.

Hi thanks for the advice I will will go the centre tap route cheers Chris.
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