Search results

Almost 30 years ago RCI changed the 2950 radio's computer from a "two-board" with separate computer and display to a single board. The new 1995 version had the 100uf capacitor in place of the lithium coin cell found in the first versions. When we asked them about this, they said the capacitor...

With any luck the relay has three poles. We adopted the habit of leaving the negative grid bias fixed, and using the center section of the relay to shut off screen voltage to the tube in receive mode. Seems to do a better job of shutting down the tube than switching the grid bias. 73

My money is on D19. No need to pull it. Tends to fail as a short, so checking for a short to ground where R98 and R124 come together would reveal if it's shorted. 73

Good chance the only reason the sidebanders were popping 2SA754s was from turning the ALC too high after they got the radio home. Never bothered with an analysis. Back in the 90s we had callbacks from failure of newly-installed 754s, but only from sideband operators. Simply upgrading a...

Whatever antenna you try, the higher it is the better. Up to around 80 or 90 feet, anyway. 73

Did you try an external DC supply feeding a DC power cord? 73

You'll need to choose between a correct reading on transmit or receive. The PLL jumps 45 and a half channels (I think) down from the receive frequency when you transmit. The transmit offset is 10.695. Pretty sure the receive-mode offset is 11.150 MHz. I think. You'll find most AM-only...

But a larger package with more surface area in contact with the heat sink will exhibit a lower temperature rise. Heat is heat. The heat sink will still get just as hot. The transistor's temperature will always be higher than the heat sink. But the larger package will let the transistor breathe...

Here's a product I never thought I would announce. For years my advice to keying a ham linear from a CB or 10-meter radio was to install a relay inside the radio. A patch cord keys the ham linear as soon as you key the mike, and drops back to receive when the mike does. No chatter, no sideband...

Yeah, one kind of 'norm' is to consult the horse's mouth, so to speak. Last time I spoke to Chris Fallen was six years ago at this conference. Had a special-event ham station on the hotel's top floor. Chris helped us out with rigging antennas on the hotel's roof 20 stories above midtown...

Here's the rundown of a 7-tube version we converted to six. Your specimen has a grounded-grid (cathode-driven) driver stage. Much better than the grid-driven version. You'll need a small radio to match that single driver tube. A Cobra 2000 busting a gut to swing 15 Watts would be about perfect...

Is it filling up the spectrum between channels? Or does the spec-an show a carrier on each 'extra' channel center frequency with sidebands on each channel above and below? That would be different defect from overmodulated "bleedover". RCI built a batch of 2990/Turbo radios in the 90s that had...

When I first heard the "dollar a Watt" a pack of cigarettes was a quarter. A gallon of regular gas wasn't a lot higher. Inflation has hit the price of a linear Watt like everything else. 73

Depends when it was made. The older versions with the single 2SC1969 radio final are fine at 3 Amps. Post-2006 radios with two IRF520 final transistors on the radio board should be okay with a 5 Amp. 73

Sometimes a 'scope is your best friend. 73

A few years back a CB customer got interested in a QST magazine. Found the Ameritron ad for their 600-Watt ham linear and was shocked at the price. Told me he could get a 600-Watt linear for a third that price. I told him the Ameritron had three times as many parts in it. You get what you pay...

Some of them. The capacitors that have the plates stacked onto a shaft with spacer rings can be disassembled. But Heathkit used capacitors that had the rotor and stator plates staked permanently in place in later production. Which version of each air-variable cap your amplifier has is a roll of...

The voltage that's needed to strike an arc across the air gaps in the capacitor is higher when the plate surfaces are smooth. The spot where the arc occurred will now be disrupted and rough with pointy features on the surface. The reason the tip of a lightning rod is sharpened is to make it...

Sounds like a clear case of cause and effect. The only way to pin down how much damage was done involves unsoldering component leads and checking parts with a tester of one kind or another. Never assume that only one thing has failed. 73

Looks like a high-school science-fair project. Might be solid and stable. Maybe. I would place more trust in one of the chinesium counters on fleabay. Many of them have a temperature-compensated time-base oscillator. I'd be surprised to find that feature in the home-brew counter. Biggest...