Have you very closely inspected the input band switch contacts? Maybe spray them with deoxit and move them around some? The contacts always fail
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
-
A Winner has been selected for the 2025 Radioddity Cyber Monday giveaway! Click Here to see who won!
AL-811H problem/ question
- Thread starter Crambone
- Start date
Something is blocking the tracks. This is where a 'scope is your friend.
Pulling the plug makes it safe to poke inside. A handy bench-type 12-Volt DC supply is used to energize only the amplifier's relay circuits. A current limit if 1 Amp or other protection is a good idea.
Putting the amplifier on "operate" and keying the radio will now feed drive into the tube's cathodes. They won't care since the filaments are cold.
Turn down the radio's CW output to 5 Watts or so. Should make life safer for the radio. Key the radio and probe the output of the relay's input side. Comparing the RF voltage you get to what's on the center pin of the radio's coax socket will reveal loss of driver power.
The tuned-input circuit will show (I think) a slightly-higher signal level at its output than at the input. Finally, seeing the drive level on each side of the blocking capacitor that feeds the tubes' cathodes. Is the last link in this chain.
Something is blocking the tracks. Since your DC continuity tests eliminate the relay as the culprit. Tells us this is a fault in some AC component that can't be tested with a DC meter.
We know the tracks are being blocked somewhere between the relay and the tubes' cathodes. Question is where?
73
Pulling the plug makes it safe to poke inside. A handy bench-type 12-Volt DC supply is used to energize only the amplifier's relay circuits. A current limit if 1 Amp or other protection is a good idea.
Putting the amplifier on "operate" and keying the radio will now feed drive into the tube's cathodes. They won't care since the filaments are cold.
Turn down the radio's CW output to 5 Watts or so. Should make life safer for the radio. Key the radio and probe the output of the relay's input side. Comparing the RF voltage you get to what's on the center pin of the radio's coax socket will reveal loss of driver power.
The tuned-input circuit will show (I think) a slightly-higher signal level at its output than at the input. Finally, seeing the drive level on each side of the blocking capacitor that feeds the tubes' cathodes. Is the last link in this chain.
Something is blocking the tracks. Since your DC continuity tests eliminate the relay as the culprit. Tells us this is a fault in some AC component that can't be tested with a DC meter.
We know the tracks are being blocked somewhere between the relay and the tubes' cathodes. Question is where?
73
I have been using my Rig Expert AA-55 Zoom " antenna Analyzer for the signal input. It reads 2.2 vac on my simpson 260 meter. That way I can put the amp on my side bench to work in it.
Um, okay. Wouldn't have thought of that. If you don't have a scope handy, my advice isn't so useful. I'm surprised the Simpson will read RF voltage on the AC scales. Following it downstream from the radio socket to the tube cathodes is still what needs to be done.
73
73
With my RigExpert connected to RF IN, I can read the RF current All the way to the tube plate. I was closing the 12 vdc external power supply.
I am at a loss as to why when I put this amp in service, I have high SWR back to my transmitter. That causes the transmitter to roll back its output power due to seeing the high SWR.
Can anyone see what can cause this problem?
Bob K9HOU
I am at a loss as to why when I put this amp in service, I have high SWR back to my transmitter. That causes the transmitter to roll back its output power due to seeing the high SWR.
Can anyone see what can cause this problem?
Bob K9HOU
I've asked about the input rotary switch, you haven't said much about it. It's a huge pita to get to I know.
Could the input tune just be off? There are adjustments I think ... Unless I'm mistaken. You will need to figure out what the cathode impedance is for your tubes in total. Then put the same value resistor to ground from the cathode . Manually key the relay with no HV. Leave the box off. Connect rig expert to the input connector, make adjustments so you have suitable input swr, then remove the resistor and try it out.
Could the input tune just be off? There are adjustments I think ... Unless I'm mistaken. You will need to figure out what the cathode impedance is for your tubes in total. Then put the same value resistor to ground from the cathode . Manually key the relay with no HV. Leave the box off. Connect rig expert to the input connector, make adjustments so you have suitable input swr, then remove the resistor and try it out.
Hmm. I've been thinking open circuit between the relay and tube cathodes. Clearly not so. Maybe what's causing the mismatch is a leaky part with one side grounded?
If it's not a problem in series with the drive signal, maybe it's a fault in parallel with the signal input?
73
If it's not a problem in series with the drive signal, maybe it's a fault in parallel with the signal input?
73