Ameritron AL-811H shows about 40 mA of grid current with no drive

[CT1EHM]

I bought an Ameritron AL-811H to a colleague and he warned me that the amplifier had a problem, the problem is even with no drive it shows about 40 mA of grid current. Please help me, thanks.

 

[wavrider]

How is the plate current ?
How is the high voltage?
Does the amplifier draw any plate current unkeyed?
Keyed?
Tubes or faulty metering circuit but hard to suggest what it could be without knowing more information.

 

[linearone]

I bought an Ameritron AL-811H to a colleague and he warned me that the amplifier had a problem, the problem is even with no drive it shows about 40 mA of grid current. Please help me, thanks.

Does it show grid current when keyed only without RF drive?

 

[nomadradio]

Step 1, make sure the resistor from each tube socket's grid lug to ground is not open. When a tube fails, that resistor can be damaged.

Step 2, key it with just one tube installed, no drive. Should narrow down which tube to blame if that's the cause.

73

 

[CT1EHM]

How is the plate current ?
How is the high voltage?
Does the amplifier draw any plate current unkeyed?
Keyed?
Tubes or faulty metering circuit but hard to suggest what it could be without knowing more information.

Thanks for the answer.
Plate currente a litle more than 625mA
Plate voltage 1700V (1.7KV)
Plate current 75mA

 

[CT1EHM]

Step 1, make sure the resistor from each tube socket's grid lug to ground is not open. When a tube fails, that resistor can be damaged.

Step 2, key it with just one tube installed, no drive. Should narrow down which tube to blame if that's the cause.

73

Thanks for the answer. I will do it.

 

[CT1EHM]

Thanks for the answer. I will do it.

When I went to remove 3 valves, leaving only one connected, I noticed that the RX TX relay was glued to TX. I think I found the fault. There didn't seem to be any burnt resistances. Now that I've bought new tubes, I'm afraid to test the amp.

 

[nomadradio]

If contact points have welded themselves together this means you need a new relay. That one can't be fixed by filing the contact surfaces flat again.

Here's the solution we used for a AL811 https://www.worldwidedx.com/threads/ameritron-al811-relay-headache-solved-my-way.265840/

The enclosed relay is still made and sold by a variety of sources. Obtaining the original from Ameritron may or may not go smoothly.

73

 

[CT1EHM]

If contact points have welded themselves together this means you need a new relay. That one can't be fixed by filing the contact surfaces flat again.

Here's the solution we used for a AL811 https://www.worldwidedx.com/threads/ameritron-al811-relay-headache-solved-my-way.265840/

The enclosed relay is still made and sold by a variety of sources. Obtaining the original from Ameritron may or may not go smoothly.

73

Many thanks for the reply. I understand that this relay has to be replaced, because of it my IC-7300 had to take one of the transistors from the final stage, but in Portugal it will be impossible to buy it, I'll do a search on the internet. Thank you again.
73!

I found a site where they sell the KUP14D15 12V relay. Thanks, 73!

 

[CT1EHM]

Many thanks for the reply. I understand that this relay has to be replaced, because of it my IC-7300 had to take one of the transistors from the final stage, but in Portugal it will be impossible to buy it, I'll do a search on the internet. Thank you again.
73!

I found a site where they sell the KUP14D15 12V relay. Thanks, 73!

Unfortunately the KUP14D15 it's not in stock, but I found another 8-pin relay for 20Amp 12V, I think it's pretty good.

 

[linearone]

You switch tubes and key this thing yet,?

 

[CT1EHM]

Step 1, make sure the resistor from each tube socket's grid lug to ground is not open. When a tube fails, that resistor can be damaged.

Step 2, key it with just one tube installed, no drive. Should narrow down which tube to blame if that's the cause.

73

 

[CT1EHM]

Yes, there was a resistance that did not make contact.

 

[nomadradio]

Just because you located a fault, don't take that to mean you have found ALL faults. And if this fixes it, be grateful it wasn't a failed tube. Consider that failed tubes are usually what damage that resistor.

73

 

[CT1EHM]

Just because you located a fault, don't take that to mean you have found ALL faults. And if this fixes it, be grateful it wasn't a failed tube. Consider that failed tubes are usually what damage that resistor.

73

Yes, you are completly sure, it was indeed a failed tube that damaged the resistance. Thanks and 73!