Ameritron AL-811HXCE - Input tuning

[EI6DP]

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

 

[linearone]

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

Id be curious if a visual inspection of the input network would show you something. Sometimes they forget to solder stuff at ameritron.

 

[brandon7861]

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.

 

[nomadradio]

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

 

[EI6DP]

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

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

 

[GlocknSpiel]

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

I'm planning to integrate one of those cheap N7DDC ATU's (called an "ATU-100") tuners to the input of an old Gonset GSB-201 amplifier I'm currently rebuilding.... And some other mods. Believe it, or not, these early 60's vintage amps were made without ANY input tuning network whatsoever.
At only around $80 from ebay, I'm not breaking the bank to take a gamble that I think is going to work anyhow.

 

[nomadradio]

Believe it, or not, these early 60's vintage amps were made without ANY input tuning network whatsoever.

When it was designed, every ham transmitter/transceiver had a Tune and Load knob on the front. This served as the matching method. The radio would just tune differently when driving the amplifier than it tuned driving the antenna.

There are other good reasons for having a tuned matching circuit on the amplifier's input, but this was the excuse for leaving it out.

I have seen the SWR protection on a modern solid-state ham transceiver turn down the power to a safe level, such that the amplifier barely puts out double what the radio drives into it. The Dentron 160-10L amplifier is very similar, and lacks any tuned input. Not a good choice for a modern transceiver.

Just be sure the input band and the output band selectors are set to the same band. A mismatch between them will make the amplifier into an aggressive oscillator, most likely.

73

 

[GlocknSpiel]

Just be sure the input band and the output band selectors are set to the same band. A mismatch between them will make the amplifier into an aggressive oscillator, most likely.

73

True, and this was the main reason why I opted for this cheapo auto tuner, as opposed to a WD7S TU-7B input board that I already had for a different future project; No band-switching required, and it can handle 100W (according to claims).
I'm still undecided on the exact mounting location inside the Gonset, or what to do with the externals (three buttons and a 1"x1" OLED display). There isn't much spare real estate inside for it and the ready-made soft-start module, but the ATU-100 is a good bit smaller than the TU-7B anyway..