Randy or Sherry Guttery wrote:
Dave Burson wrote:

S-W model R-1822 has a "reactance dimmer" (item 2) with a 6.3 v lamp
that illuminates the band indicators. The bandswitch physically moves
the nameplates over the lamp. The transformer primary appears to be
open, and a 10K resistor across it does provide a little signal to the
speaker. C21 & C14 are listed as 10 mfd, 25 v and 0.1 mfd, 150 v, and
both are absent. I am suspicious that C21 of that value doesn't
belong, since the schematic has misidentified a C22 elsewhere.
Schematic is from Nostalgia Air.
This radio had been severely hacked, but the beautiful cabinet has
kept me picking away at it for a long time.
I've found a little about reactance dimmers but nothing about use in a
tube radio, mostly fluorescent dimmers. I'd really appreciate any
explanation of the function here and especially thoughts about the
caps that parallel the primary.

What this appears to be is a saturable reactor who's input is the B+
current to the RF/IF stages - which means the less signal strength - the
higher the B+ current - due to AGC bias action.

This is the same idea that "drives" the Philco shadow meter. Low signal
- high current - since the AGC is low - and biases the tube more "on".
Signal strength comes up (as a station is tuned in) AGC goes negative,
turning the RF & IF tubes "down" (less current). As the current through
the primary rises and falls - so does the saturation - effecting the
transformer's coupling.

Now notice the two secondary windings- If the transformer's "coupling"
is working well - the two windings "buck" - the lamp is dim. However -
if the transformer's coupling isn't - the two windings "interaction" is
reduced - and the lamp is brighter.

Oh, the two caps - well the last thing you want is for the AC signal on
the secondary to be "coupled" through to the B+ - so the two caps act as
bypasses to keep the 60 cycle out of the B+.

(shooting from the hip - again - (sigh) - OK guys - what'd I miss?

best regards...
So with high B+ current, the xfmr is saturated, less bucking, lamp is
bright? That means the bulb dims when on station? Ken

"Ken" wrote in message
...
Randy or Sherry Guttery wrote:
Dave Burson wrote:
best regards...
So with high B+ current, the xfmr is saturated, less bucking, lamp is
bright? That means the bulb dims when on station? Ken

Core saturates, and windings lose their inductance, basically becoming
purely resistive (only the wire winding DC resistance with no reactance),
the light would be brighter.

Pee

In article ,
"Uncle Peter" wrote:

"Ken" wrote in message
...
Randy or Sherry Guttery wrote:
Dave Burson wrote:
best regards...
So with high B+ current, the xfmr is saturated, less bucking, lamp is
bright? That means the bulb dims when on station? Ken

Core saturates, and windings lose their inductance, basically becoming
purely resistive (only the wire winding DC resistance with no reactance),
the light would be brighter.

The problem with this explanation is that the two secondaries appear to
be connected so that they "buck" one another. If that is the actual
case then the reactance of the two series connected secondary windings
wouldn't change much with transformer saturation.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

John Byrns wrote:

The problem with this explanation is that the two secondaries appear to
be connected so that they "buck" one another. If that is the actual
case then the reactance of the two series connected secondary windings
wouldn't change much with transformer saturation.

Yes, I agree - I think its more of the coupling increasing and
decreasing causing more or less bucking between the windings. The
decrease in inductance (at 60 cycle) would not be near as influential as
the loss of coupling... Then again - as you noted - physical layout
could have very significant impact on both / either... hmmmm...

It is an interesting application. Didn't GE have something like this in
some of their consoles? I've never had one in for service - but it seems
I recall reading something about them.

best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com

Uncle Peter wrote:
"Ken" wrote in message
...
Randy or Sherry Guttery wrote:
Dave Burson wrote:
best regards...
So with high B+ current, the xfmr is saturated, less bucking, lamp is
bright? That means the bulb dims when on station? Ken

Core saturates, and windings lose their inductance, basically becoming
purely resistive (only the wire winding DC resistance with no reactance),
the light would be brighter.

Pee


But the core saturates on high current, that's off station. So the light
is bright off station and dim on. It would make sense to have the lamp
brighten on station, but I have seen other schemes work like this. Ken