[Boatanchors] SX25 Hallicrafters

[Richard Knoppow]

----- Original Message ----- 
From: "Joe Connor" <joeconnor53 at yahoo.com>
To: "David Knepper" <collinsradio at comcast.net>; 
<wq9e at btsnetworks.net>; <rbethman at comcast.net>; 
<boatanchors at mailman.qth.net>
Sent: Friday, March 07, 2014 3:21 PM
Subject: Re: [Boatanchors] SX25 Hallicrafters


Was the PM-23 the correct speaker for the SX-25? The PM-23 
has an impedance of 5K Ohms. I'm curious if there is any 
reason why Hallicrafters chose 5K as one of the two output 
impedances on the SX-25 and SX-28. Was it a marketing 
decision to help sell PM-23 speakers? It seems to be pretty 
unusual to find one of these receivers with the original 
speaker.

Joe Connor

     I answered this in another post.  I think the 5K is a 
carry over from speakers that were intended to be connected 
directly to the output tube or which had the output 
transformer in the speaker cabinet.  About 5K is a good 
match for many single-ended tubes.  500 ohms was very common 
for feeding phone lines or other long lines but also many 
speakers of the 1930s had 500 ohm windings, for instance all 
the Jensen high quality speakers did right up to the late 
1940s. Many James Lansing speakers did also such as the old 
Iconic two-way system and the original 604 with 
electro-dyamic magnets.  I am not sure why such a high 
impedance was chosen except that it may have made it easier 
to make the cross-over networks since the coils could have 
much lower inductance than at 8 or 16 ohms.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com