Mc step-up

[tttubes]

Hi all just installed a pair of Partridge 1:6 step up transformers in my eros they are the perfect size for the eros and you can keep the leads short. They sound better than my silk 220's and and stevens and billington 1003-5 are inexpensive 150 a pair on eday.

How would I calculate the resistance for a resistor across the 47K ohm resistor to get a 200 ohm input independence? 

# Type 977.
# 6 : 1 step up ratio.
# 20 ohms input DC resistance.... 300 ohms impedance.
# 250 ohms output DC resistance.....10k ohms impedance.
# Flat frequency response, across audiable range.
# Mu-metal core.
# Shielded, screened metal can enclosure.

  http://global.ebay.com/PARTRIDGE-MOVING-COIL-MC-STEP-UP-TRANSFORMERS-VINTAGE/380336058264/item

Thanks

Jim

 

[Paul Joppa]

From the specs it is apparently designed for a 10K load, so put 12.7k across the 47k to get a net 10k. This should give the best performance, assuming the spec means what I think it means.

Reflected impedance is then 10k/36 = 278 ohms. Add the primary DCR (20 ohms) plus the reflected secondary DCR (250/36 = 7 ohms) to get 305 ohms primary impedance with this load. Parallel another 582 ohms across the primary to reduce this to 200 ohms.

 

[tttubes]

From the specs it is apparently designed for a 10K load, so put 12.7k across the 47k to get a net 10k. This should give the best performance, assuming the spec means what I think it means.

Reflected impedance is then 10k/36 = 278 ohms. Add the primary DCR (20 ohms) plus the reflected secondary DCR (250/36 = 7 ohms) to get 305 ohms primary impedance with this load. Parallel another 582 ohms across the primary to reduce this to 200 ohms.

Thanks Paul I tied a 13K and wow sound was even better ordered some resistors to play with.

Thanks.

Jim