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Ameritron AL-811HXCE - Input tuning

EI6DP

EI6DP

New Member
Feb 12, 2024
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Hello - I have an ongoing problem with my AL-811HXCE.
My problem is that on 160m I have a reflected VSWR of 3.5:1 showing on my IC-7200, even when tuning the amp into my test load (Bird 1kw load).
When running my IC-7200 into the test load I have zero VSWR i.e. 1:1.
I have tried peaking the input stage on 160m but the lowest VSWR I can achieve is 3.5:1.
Any ideas

Gerald EI6DP
villiers@hotmail.com
 

EI6DP said:
Hello - I have an ongoing problem with my AL-811HXCE.
My problem is that on 160m I have a reflected VSWR of 3.5:1 showing on my IC-7200, even when tuning the amp into my test load (Bird 1kw load).
When running my IC-7200 into the test load I have zero VSWR i.e. 1:1.
I have tried peaking the input stage on 160m but the lowest VSWR I can achieve is 3.5:1.
Any ideas

Gerald EI6DP
villiers@hotmail.com
Click to expand...
Id be curious if a visual inspection of the input network would show you something. Sometimes they forget to solder stuff at ameritron.
 
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I got no business getting involved in tube gear threads, but I have at least one suggestion I feel comfortable making. With the amp unhooked/unpowered, you could ohm between C27 and C8 to see if the band switch is making good contact.
811.png
 
Our go-to tool for this has been an air variable cap with a foot-long coax and gator clips on the cable's far end.

When the tuning slug won't get you where you want to go, the two fixed caps, one on either side of the input coil become the next suspects. Clipping the variable to one, then the other side of the input coil may bring the input match down to an acceptable level.

Simply tack-soldering an additional 150 or 220pf cap across one or the other of those two caps will either make the mismatch worse or better. What we usually find is the some capacitance needs to be added to the input side of the 16-meter input coil.

But this is a by-gum and by-gosh procedure, and incredibly awkward. That coil and its two hookup terminals are clumsy to reach.

Ameritron did not make it easy to tweak this part of the design.

73
 
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nomadradio said:
Our go-to tool for this has been an air variable cap with a foot-long coax and gator clips on the cable's far end.

When the tuning slug won't get you where you want to go, the two fixed caps, one on either side of the input coil become the next suspects. Clipping the variable to one, then the other side of the input coil may bring the input match down to an acceptable level.

Simply tack-soldering an additional 150 or 220pf cap across one or the other of those two caps will either make the mismatch worse or better. What we usually find is the some capacitance needs to be added to the input side of the 16-meter input coil.

But this is a by-gum and by-gosh procedure, and incredibly awkward. That coil and its two hookup terminals are clumsy to reach.

Ameritron did not make it easy to tweak this part of the design.

73
Click to expand...
Hello - That a great idea - deffo going to try that. What I have done in the mean-time is to put my Dentron Jr ATU on the drive input and it works great. I can tune the VSWR down to around 2:1. When convenient I will investigate the problem further. The Ameritron tuning system leaves a lot to be desired, it is worse than useless.
73 de EI6DP
 

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