Lectradio

10/29/2009 12:52:37 PMTerry Decker

I recently returned to the repair and restoration of old radios. From eBay I acquired an Electronix AM/Police/Wireless intercom. I've finally got it up and running, but I am DESPERATELY seeking ANY information about this item. It was probably manufactured in the 40's as it uses type 14 tubes, (14A7, 14Q7, etc., and a 117Z6 rectifier) It has a buzz that sounds like the open input of an intercom, yet the intercom is wireless and seems to transmit to the middle of the broadcast band. So, anybody got any ideas? By the way, I'm glad I found a forum that's actually current!!

10/29/2009 1:13:24 PMWarren

Florescent lighting and light dimmers can cause that. Electrical interference can sometimes be helped by the use of an EMI filter on the AC line cord.

10/29/2009 1:17:31 PMTerry Decker

:Florescent lighting and light dimmers can cause that. Electrical interference can sometimes be helped by the use of an EMI filter on the AC line cord.
:

10/29/2009 1:28:37 PMTerry Decker

::Florescent lighting and light dimmers can cause that. Electrical interference can sometimes be helped by the use of an EMI filter on the AC line cord.
::
:

10/29/2009 5:44:22 PMEdd

Sir Terry . . . . .

There are two 35A5 output tubes, one of which goes through a cap to a binding post, the on/off switch is on the intercom input control instead of the volume control,
There are shielded wires going everywhere, two output type transformers in addition to the speaker transformer,

My thoughts from the sole information that you supplied, would be the unit having one moderate powered RF transmit section,
far above the peanut power status of a simple phono oscillator. That being, in order to get any decent range in its intercom function to another unit.

That just might account for the second 35A5 function , as RF power output, and it feeding over to the "binding post ?" type of termination, to then connect to a wire aerial to further enhance the units range.

Your date frame suggests the time era before the FCC was so clamped down on RF emissions levels. Also, it was well before the common use of "carrier current mode" which pumped low frequency RF into the AC wiring to be used as the interconnect medium, if the units were used on a shared AC transformer out at the pole.

The logic for the units better than normal shielding was the somewhat moderate RF level that would be floating around
on the chassis in its "intercom" transmit mode.
You might confirm the aforementioned tubes function , by the placing of a "host" AM receiver close enough to the unit to be your "Ears" for the transmitted intercom signal and then tune in to get the best of the best in reception and then go to the plate of the suspected "RF 35A5" and touch the leads of a ceramic .01 @ 1kv from ground to its plate and see if the transmitted signal doesn't stop dead.

As per the mention of the two extra transformers, I would expect one of then to be tied into the speaker in its intercom function such that its low Z winding is switched into the speaker and the secondary ups the Z to 1st grid input impedance for the 1 or two stages needed to up it to the audio level needed for end modulating that 35A5 RF tube. With the second transformer mentioned being the modulation transformer used by the normal AF output 35A5 tube..

As far as the "trimmers" mentioned, at least two on the units chassis would probably be associated with the intercoms RF
power portions oscillator function. One being to trim in the oscillating frequency that the unit is desired to operate on.

You could pinpoint that one by the having of the unit operating on the present frequency and tuning in on the host radio receiver and then the finger touching of a trimmer that would be associated with the osc circuit should skew the unit off from that frequency as it is (was) being heard on the receiver . . .HUH . .WHAT. .where did it go . .where did it go ?

OR . .the same is true of the oscillator coil inductance associated with that trimmer. Touching its winding should also skew its frequency off.

The other probable trimmer use (or two . . if in an RF output pi network matching situation) would be relevant to optimizing the output of the unit in use with that added aerial wire.
No positive idea on the "hum / noise" being transmitted by the unit, with only one thought in the respect of the other 35A5
which is probably the AF modulator in the transmit mode.

You might take that AF 35A5 units(NOT the RF 35A5 unit) 1st grid and connect a 100 ufd @ 25 VDC electrolytic from ground to that 1st grid with the 1st grid receiving the - polarized lead.

That would shut down ALL incoming low level audio to the modulator. Thereby, if you STILL hear the "hum / noise" floor on the companion receiver the possible source would most likely be the power supply filtering.

My only thoughts to date.

73's de Edd

:::Florescent lighting and light dimmers can cause that. Electrical interference can sometimes be helped by the use of an EMI filter on the AC line cord.
:::
::
:
:True, but not the case here- no florescent bulbs, (don't believe in them), and the radio is only tested with an isolation transformer. I suspect a leaky coupling cap somewhere, but this radio has such a crazy circuit that I'm kind of lost. there are 4 trimmer caps on the back of the chassis, 5 oscillator coils in addition to the IF cans, two 35A5 output tubes, one of which goes through a cap to a binding post, the on/off switch is on the intercom input control instead of the volume control, There are shielded wires going everywhere, two output type transformers in addition to the speaker transformer, PLUS- I think there's a problem with the AVC. I know how a superhet works, I repair them all the time; but this bugger has got me stumped. I've left messages with every site I can find, but so far this item is an enigma.
:

10/29/2009 8:18:36 PMTerry Decker

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I've found that the intercom broadcasts in the middle of the AM band. If what you say about the output level is true, that would be great, since I've recently become interested in micropower AM transmitting, and just built the Antique Electronics K-488 transmitter. I believe that some of the trimmers might be associated with the extended AM frequencies for the old AM police band. One thing that I need to do is get down to some voltage measurements and signal tracing. I admit that I've just been too intimidated. I keep hoping for a schematic. Maybe just some encouragement from this forum will get me off my butt.
Right now I'm in the middle of repairing a neat RCA C5X1. Some goober has been in there changing parts, like hanging extra resistors on the VC, and it's going to be fun cleaning up his bad work. Hint: I purchased a CD with 58K schematic diagrams, plus 50 Riders volumes. So far I have found a schematic for every radio I've worked on, including a Stromberg-Carlson 1A Neutrodyne. I love this forum, I'm afraid I'll get addicted. Terry
:
:
:
:Sir Terry . . . . .
:
:
:
:
:
:
:There are two 35A5 output tubes, one of which goes through a cap to a binding post, the on/off switch is on the intercom input control instead of the volume control,
:There are shielded wires going everywhere, two output type transformers in addition to the speaker transformer,
:
:
:
:
:My thoughts from the sole information that you supplied, would be the unit having one moderate powered RF transmit section,
:far above the peanut power status of a simple phono oscillator. That being, in order to get any decent range in its intercom function to another unit.
:
:
:That just might account for the second 35A5 function , as RF power output, and it feeding over to the "binding post ?" type of termination, to then connect to a wire aerial to further enhance the units range.
:
:
:Your date frame suggests the time era before the FCC was so clamped down on RF emissions levels. Also, it was well before the common use of "carrier current mode" which pumped low frequency RF into the AC wiring to be used as the interconnect medium, if the units were used on a shared AC transformer out at the pole.
:
:
:The logic for the units better than normal shielding was the somewhat moderate RF level that would be floating around
:on the chassis in its "intercom" transmit mode.
:
:You might confirm the aforementioned tubes function , by the placing of a "host" AM receiver close enough to the unit to be your "Ears" for the transmitted intercom signal and then tune in to get the best of the best in reception and then go to the plate of the suspected "RF 35A5" and touch the leads of a ceramic .01 @ 1kv from ground to its plate and see if the transmitted signal doesn't stop dead.
:
:
:As per the mention of the two extra transformers, I would expect one of then to be tied into the speaker in its intercom function such that its low Z winding is switched into the speaker and the secondary ups the Z to 1st grid input impedance for the 1 or two stages needed to up it to the audio level needed for end modulating that 35A5 RF tube. With the second transformer mentioned being the modulation transformer used by the normal AF output 35A5 tube..
:
:
:As far as the "trimmers" mentioned, at least two on the units chassis would probably be associated with the intercoms RF
:power portions oscillator function. One being to trim in the oscillating frequency that the unit is desired to operate on.
:
:
:You could pinpoint that one by the having of the unit operating on the present frequency and tuning in on the host radio receiver and then the finger touching of a trimmer that would be associated with the osc circuit should skew the unit off from that frequency as it is (was) being heard on the receiver . . .HUH . .WHAT. .where did it go . .where did it go ?
:
:
:OR . .the same is true of the oscillator coil inductance associated with that trimmer. Touching its winding should also skew its frequency off.
:
:
:The other probable trimmer use (or two . . if in an RF output pi network matching situation) would be relevant to optimizing the output of the unit in use with that added aerial wire.
:
:
:
:No positive idea on the "hum / noise" being transmitted by the unit, with only one thought in the respect of the other 35A5
:which is probably the AF modulator in the transmit mode.
:
:
:You might take that AF 35A5 units(NOT the RF 35A5 unit) 1st grid and connect a 100 ufd @ 25 VDC electrolytic from ground to that 1st grid with the 1st grid receiving the - polarized lead.
:
:
:That would shut down ALL incoming low level audio to the modulator. Thereby, if you STILL hear the "hum / noise" floor on the companion receiver the possible source would most likely be the power supply filtering.
:
:
:
:
:My only thoughts to date.
:
:
:
:
:
:
:
:
:73's de Edd
:
:
:

:
:

:
:
:
:
:
:
:
::::Florescent lighting and light dimmers can cause that. Electrical interference can sometimes be helped by the use of an EMI filter on the AC line cord.
::::
:::
::
::True, but not the case here- no florescent bulbs, (don't believe in them), and the radio is only tested with an isolation transformer. I suspect a leaky coupling cap somewhere, but this radio has such a crazy circuit that I'm kind of lost. there are 4 trimmer caps on the back of the chassis, 5 oscillator coils in addition to the IF cans, two 35A5 output tubes, one of which goes through a cap to a binding post, the on/off switch is on the intercom input control instead of the volume control, There are shielded wires going everywhere, two output type transformers in addition to the speaker transformer, PLUS- I think there's a problem with the AVC. I know how a superhet works, I repair them all the time; but this bugger has got me stumped. I've left messages with every site I can find, but so far this item is an enigma.
::
:

11/4/2009 1:54:50 PMTerry Decker

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I finally got around to testing this thing. Yeah, it splatters all over the AM band. Don't want to dither the dittos. The intercom switch makes it very difficult to trace. I tried the cap- no change. I might sell this back on eBay as the rarest radio ever!!!
Thanks for the advice.
Terry
:
:I've found that the intercom broadcasts in the middle of the AM band. If what you say about the output level is true, that would be great, since I've recently become interested in micropower AM transmitting, and just built the Antique Electronics K-488 transmitter. I believe that some of the trimmers might be associated with the extended AM frequencies for the old AM police band. One thing that I need to do is get down to some voltage measurements and signal tracing. I admit that I've just been too intimidated. I keep hoping for a schematic. Maybe just some encouragement from this forum will get me off my butt.
:Right now I'm in the middle of repairing a neat RCA C5X1. Some goober has been in there changing parts, like hanging extra resistors on the VC, and it's going to be fun cleaning up his bad work. Hint: I purchased a CD with 58K schematic diagrams, plus 50 Riders volumes. So far I have found a schematic for every radio I've worked on, including a Stromberg-Carlson 1A Neutrodyne. I love this forum, I'm afraid I'll get addicted. Terry
::
::
::
::Sir Terry . . . . .
::
::
::
::
::
::
::There are two 35A5 output tubes, one of which goes through a cap to a binding post, the on/off switch is on the intercom input control instead of the volume control,
::There are shielded wires going everywhere, two output type transformers in addition to the speaker transformer,
::
::
::
::
::My thoughts from the sole information that you supplied, would be the unit having one moderate powered RF transmit section,
::far above the peanut power status of a simple phono oscillator. That being, in order to get any decent range in its intercom function to another unit.
::
::
::That just might account for the second 35A5 function , as RF power output, and it feeding over to the "binding post ?" type of termination, to then connect to a wire aerial to further enhance the units range.
::
::
::Your date frame suggests the time era before the FCC was so clamped down on RF emissions levels. Also, it was well before the common use of "carrier current mode" which pumped low frequency RF into the AC wiring to be used as the interconnect medium, if the units were used on a shared AC transformer out at the pole.
::
::
::The logic for the units better than normal shielding was the somewhat moderate RF level that would be floating around
::on the chassis in its "intercom" transmit mode.
::
::You might confirm the aforementioned tubes function , by the placing of a "host" AM receiver close enough to the unit to be your "Ears" for the transmitted intercom signal and then tune in to get the best of the best in reception and then go to the plate of the suspected "RF 35A5" and touch the leads of a ceramic .01 @ 1kv from ground to its plate and see if the transmitted signal doesn't stop dead.
::
::
::As per the mention of the two extra transformers, I would expect one of then to be tied into the speaker in its intercom function such that its low Z winding is switched into the speaker and the secondary ups the Z to 1st grid input impedance for the 1 or two stages needed to up it to the audio level needed for end modulating that 35A5 RF tube. With the second transformer mentioned being the modulation transformer used by the normal AF output 35A5 tube..
::
::
::As far as the "trimmers" mentioned, at least two on the units chassis would probably be associated with the intercoms RF
::power portions oscillator function. One being to trim in the oscillating frequency that the unit is desired to operate on.
::
::
::You could pinpoint that one by the having of the unit operating on the present frequency and tuning in on the host radio receiver and then the finger touching of a trimmer that would be associated with the osc circuit should skew the unit off from that frequency as it is (was) being heard on the receiver . . .HUH . .WHAT. .where did it go . .where did it go ?
::
::
::OR . .the same is true of the oscillator coil inductance associated with that trimmer. Touching its winding should also skew its frequency off.
::
::
::The other probable trimmer use (or two . . if in an RF output pi network matching situation) would be relevant to optimizing the output of the unit in use with that added aerial wire.
::
::
::
::No positive idea on the "hum / noise" being transmitted by the unit, with only one thought in the respect of the other 35A5
::which is probably the AF modulator in the transmit mode.
::
::
::You might take that AF 35A5 units(NOT the RF 35A5 unit) 1st grid and connect a 100 ufd @ 25 VDC electrolytic from ground to that 1st grid with the 1st grid receiving the - polarized lead.
::
::
::That would shut down ALL incoming low level audio to the modulator. Thereby, if you STILL hear the "hum / noise" floor on the companion receiver the possible source would most likely be the power supply filtering.
::
::
::
::
::My only thoughts to date.
::
::
::
::
::
::
::
::
::73's de Edd
::
::
::

::
::

::
::
::
::
::
::
::
:::::Florescent lighting and light dimmers can cause that. Electrical interference can sometimes be helped by the use of an EMI filter on the AC line cord.
:::::
::::
:::
:::True, but not the case here- no florescent bulbs, (don't believe in them), and the radio is only tested with an isolation transformer. I suspect a leaky coupling cap somewhere, but this radio has such a crazy circuit that I'm kind of lost. there are 4 trimmer caps on the back of the chassis, 5 oscillator coils in addition to the IF cans, two 35A5 output tubes, one of which goes through a cap to a binding post, the on/off switch is on the intercom input control instead of the volume control, There are shielded wires going everywhere, two output type transformers in addition to the speaker transformer, PLUS- I think there's a problem with the AVC. I know how a superhet works, I repair them all the time; but this bugger has got me stumped. I've left messages with every site I can find, but so far this item is an enigma.
:::
::
: