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ultrachrome 7th November 2003 04:02 PM

Grounded Grid Trafo question
I'd like to build Rosenblit's grounded grid preamp and am not sure what an acceptable transformer entails.

He specifies a 120V-50MA and 12V-1A. I did a search on Digi-Key and came up with the following:

229A12D misspelled as 229A120



This guy used toroids so I checked Plitron. They don't have 120V-1A but do have 117V-1A. However the price for three transformers is over $120 which is about four times higher than Digi-Key's.

Any recommendations?


Positron 7th November 2003 05:00 PM

Hi Ultrachrome,

Could go with Allied Electronics, part no. 704-9090 isolation transformer. It runs on both 120 and 240 vac. Easy to mount, but must position and place away from the circuit. Cost is $15.42

Separate filament transformer necessary. 227-0016 is 6.3vac at 1 amp or 227-0045 is rated 1.2 amps. Costs are $7.14 and $7.04 respectively.

Another choice is: 704-5715, which is a 190,160,0,160,190 at 70 ma, capacitive input rating and a 6.3 vac at 3 amps. Cost is $29.58.
Simply use the 160 taps, center tapped (seal off the 190 vac leads). Drop the DC voltage from there. Again, have to position from circuit and probably mount core perpendicular to the circuit for minimum hum.

Hope this helps.

agent.5 21st November 2003 03:34 AM

How is the quality of the Allied filament transformer? The price seems good; but is the quality there? Thanks.

Positron 21st November 2003 03:53 AM

Quality doesn't seem bad from my experience. Pretty quiet.

I always put a piece of tough, temp resistant rubber between the tranny and chassis to reduce any hum that might happen to be present. Doesn't take much thickness to help.

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