Back to Index   GE Delta Supplemental Information
Maintained by Kevin Custer W3KKC

The radios that preceeded the Delta and RANGR in the GE product line mostly used push-pull audio power amplifiers and audio output transformers, and drove the speakers as a hot wire to ground. The Delta, and many later radios eliminated the audio transformer and they run the the speaker as the push-pull load directly... both sides floating off of ground. This quirk is significant on your workbench: any audio test equipment that connects to the speaker (such as you would use to make a quieting measurement) must be on the far side of a audio isolation transformer. Motorola has a low-power one as part number SLN6435 in their test equipment catalog (being "test equipment", it's high priced - at about $80), and they also include a cheaper but higher audio power one in every tabletop base station (part number 2580188B01, about $35 in late 2006) since common wireline remote controls expect ground-referenced audio to drive the remote sepakers. You can order either of the transformers separately, or you can get one from a web-based car stereo seller or at a local high-end car stereo shop (many dash-mount radios expect floating speakers, and many trunk mount audio amplifiers have gounded inputs). In a pinch you can connect a 2 watt resistor of any value from 8 to 22 ohms to the radio as a load, and use a 600 ohm to 600 ohm line transformer between the radio and the test equipment. Note that the audio bandpass characteristics of whatever isolation transformer you use will have to be wider than the audio frequencies you hope to pass through the radio.

In short, if you ground one of the Delta or RANGR speaker leads the odds are better than 75-25 that you will let some of the magic smoke out of your radio. So use an audio isolation transformer to prevent this - just put the transformer between the radio and any load that isn't a floating (an ungrounded) stand-alone speaker.

Note from WA6ILQ:
If you are looking to buy a "real" audio isolation transformer, check the car stereo shops in your area - sometimes they are marketed as "audio ground loop eliminators", or as "balanced to unbalanced adapters" - but look at them carefully as some are R-C networks, some are designed to work at millivolt levels - very limited as to the power level, and some are at 600 ohm impedance levels. You really want one that is at 8 ohms both in and out and can handle a watt or two of audio... (the audio level alone precludes using a transformer salvaged from a old modem or PC sound card). Always check the schematic - you want a transformer-based one that has no DC path from either input lead to either of the output leads.
You may already have something that will work - if your junk box includes two identical audio transformers that have an 8 ohm secondary (no matter what the primary is, as long as both transformers are identical) then you can use the pair to make a single substitute 8 ohm to 8 ohm audio isolation transformer. Just tie the primaries together and ignore them, then use the secondaries of the two transformers as if they were one 8 ohm to 8 ohm transformer.
And some times you can recycle something - the most flexible audio isolation transformer I ever found was an aircraft radio power transformer from the 1940s - the two separate 6.3 volt windings worked fine as 8 ohm windings, the primary 110/120 volt winding worked fine as a line level connection (as a source or destination), and the 400 Hz design worked just fine from 250 Hz to over 3500 Hz.
On the other hand, if you are just feeding a test meter (like for SINAD checks) or feeding the input of a repeater controller then you can get away with a non-1:1 transformer. I've had good luck with 600 Ohm-to-600 Ohm transformer (like a Triad TY145 - available from Mouser Electronics (p/n:553-TY145P) under $4 as I write this). I put one side across the radio speaker output leads with a 1 watt 8 ohm resistor as a speaker load with the other side of the transformer feeding the test equipment.

Another caution: The name "Delta" covers three different product lines, and all are different internally. The earliest "Delta" design is a crystal controlled design. Then the geniuses at GE came up with a synthesized design, and it was marketed as "Delta-S" - but it only covers about 2 or 3 MHz from highest to lowest frequency. Then they got a chance at a redesign and came up with the "Delta-SX" which can cover a range of about 37-38 MHz before the VCO falls out of lock - but it was made only for VHF and UHF - it was never made in a low band version. If you want a broad bandwidth radio on low band you need to find a Motorola "Syntor X" or "Syntor X9000" - they can cover from 28 to 54 MHz in one range (but the mobile antenna can't)... more details on those radios (and an antenna bandwidth workaround) on the Motorola pages.
When using the TQ2310 Suitcase Programmer (LBI-31229) to program Delta radios you need to refer to LBI-31263.

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