Posts: 1,114
Threads: 14
Joined: Feb 2013
City: Irvington, NY
Here is a copy of a newspaper page from 1940 I ran across, describing the latest features of the 1941 Philco models.
Although it seems like all the writing was done by Philco's marketing department, there are some technical details among the hype. The advantages of the XXL (triode) mixer are discussed, along with the benefit of two IF stages, and the intermodulation problems sometimes caused by an RF amplifier stage. The beam of light phono pickup is also mentioned.
A little hard to read but interesting nonetheless.
http://fultonhistory.com/newspaper%2010/...200628.pdf
Posts: 4,832
Threads: 437
Joined: Jun 2011
City: Boston
State, Province, Country: Massachusetts
I love this kind of stuff, thanks for sharing.
Paul
Tubetalk1
Posts: 52
Threads: 1
Joined: Mar 2013
City: Minneapolis, MN
Posts: 403
Threads: 40
Joined: Feb 2011
City: McPherson, KS
Yep, just like the Philco PR dept. sent them. But that's okay. We wouldn't know it if they hadn't done it.
Posts: 5,650
Threads: 56
Joined: Sep 2008
City: Sandwick, BC, CA
Using twin triodes as a mixer and oscillator seems to work quite well, though I don't have any sets that use the XXL tubes I do have two AC/DC sets that use an XXD/14AF7. What I can't understand is why they decided to use a triode as a mixer, maybe another patent royalty dodge? I also can't figure out why they used a silly designation for a tube like XXL or XXD, that must have been the marketing department's idea just to make them sound mysterious then just calling them 7A4s or 14AF7s.
Regards
Arran
Posts: 1,114
Threads: 14
Joined: Feb 2013
City: Irvington, NY
There is some legitimate technical basis for using a triode as a mixer. In general, the lower the number of grids in a tube, the lower the internally generated noise, called partition noise.
RCA did some research in the late 30's and found that multigrid tubes like hexodes and pentagrid tubes were the noisiest, followed by pentodes, and triodes being the quietest. So using a triode as the converter results in the lowest internally generated noise level. It is interesting that while RCA did the research, Philco actually put it into practice in their 1940's sets.
As to the XXL name, it seems that it was pure marketing. This way
Philco could claim that they were the only one using this particular "special" tube. Anyone could use a 7A4, but no one else had the "XXL".
http://www.radiomuseum.org/forumdata/use...e_TEXT.pdf
Posts: 4,832
Threads: 437
Joined: Jun 2011
City: Boston
State, Province, Country: Massachusetts
I thought the XXL's were for big guys like me!
Paul
Tubetalk1
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
