[R-390] Mouser 600 Ohm to 8 Ohm transformer

[Roy Morgan]

(Subject changed from original thread.)

On Aug 4, 2014, at 4:35 PM, Richard Wojnar via R-390 <r-390 at mailman.qth.net> wrote:

> On a separate note, has anyone tried the Mouser 600 Ohm to 8 Ohm transformer?  I just required a very nice rebuilt R-390 from K1QAR and am getting ready to set it up.

Gary,

I am not familiar with that particular transformer, but others of the sort, including line to voice coil transformers, all work well.  Hammond makes the best one commonly available. Radio Shack and other sources also have ones likely to perform just as well for our uses, though with lesser actual specifications and performance.  An ebay search with “line matching transformer” brings many choices.

One reason these work well is that *most* such transformers are rated at 5 watts and up.  The power output from your R-390x is on the order of half a watt max.  So any such transformer will be loafing and not ever get near it’s power limit.  Further, the line to voice coil transformers are meant to handle a moderately wide audio bandwidth.  The R-390x actual bandwidth is quite a bit less by comparison.

Line transformers often show input (line) windings by power to be delivered to the speaker. Conversion from the normal 70 volt line voltage yields useful impedances.  The 10 watt tap for 70 volt units (and the 1-watt tap for the less common 25 volt units) give nearly 600 ohms impedance (500 and 625 ohms respectively).

Note that an audio amplifier transformer from ages ago that has multiple output taps may have a 600 ohm tap along with a variety of voice coil taps.  Used as an auto transformer with the primary open, these will do the job very well indeed.

I attempt to attach a page from the informative document:
https://adn.harmanpro.com/site.../Guide_to_constant_Voltage_systems_original.pdf
(The mail system may not forward it - I’m glad to send it to anyone in that case.)

Happy audio matching to all.




Roy

Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958