It had resistors in the grid circuit. They burned up so I installed the mod that eliminated the resistors and tied the grids directly to ground. The mod was developed by the original designer of the amp.

It doesn't look like it'll be a simple task to remove the air variable capacitor either. I figured that since it'll be a PITA to replace the cap I might as well add another improvement. But, if it's really that much of a problem I won't bother. A friend had an arcing problem with an air cap and solved it by replacing it with a vacuum variable (he has a different amp, BTW).

Not to mention that it was a PITA to convert my AL-811H amp to a grounded grid amp.

Obviously, it wouldn't be the first time that a mod would be problematic. I run into these issues at work also - I'm an electronic tech with 30+ years experience in communications electronics so I've had my share of issues with electronic equipment.

Why not? It solved a friends problem.

I suppose a cap would be good to keep snow from accumulating but I don't know if you get snow where you're at.

Kinda similar to calling tubes valves. I remember some Americans going to an electronics store in the UK and asking for tubes. The clerks response was "A tube of what?".

I've been told that they are much less likely to arc.

I'd like to replace the air variable capacitors with vacuum variable capacitors. I don't see any capacitance values in the manual so I'm wondering if anyone knows of any vacuum capacitors that'll replace the air capacitors. From looking at some websites it appears that I would need some other method to determine settings, also, since the vacuum capacitors are listed as multi-turn capacitors. I have to replace the plate capacitor so I figured I'd replace the load capacitor also.

I'd like to replace the air variable capacitors with vacuum variable capacitors. I don't see any capacitance values in the manual so I'm wondering if anyone knows of any vacuum capacitors that'll replace the air capacitors. From looking at some websites it appears that I would need some other method to determine settings, also, since the vacuum capacitors are listed as multi-turn capacitors. I have to replace the plate capacitor so I figured I'd replace the load capacitor also.

I bought an ALS600 several years ago and the finals kept blowing. After the fourth repair (the amp still under warranty), I sold it. Ameritron tried to solve the problem. Someone had told me that my Kenwood TS-450 generated spikes which is what caused the amp to eventually die. Maybe, maybe not. I would have liked to have kept the solid state amp but I needed something reliable. As a matter of fact, because of my experience with the ALS600 I'm reluctant to buy any solid state power amplifier. I suppose that an Alpha amplifier would be the way to go but how many hams can afford a new amplifier with an $8000 price tag? Even used Alphas aren't cheap. Oh well, enough of my rant.

Section 8 should be the one to use for your base.

Finally got back to this. Yep, one of the plate capacitor fins shows obvious arcing. I'll see about ordering a replacement tomorrow. Strange that this just started instead of being a problem from "day 1". There must be a way to upload an image but I don't see anything obvious (like a paper clip icon).

The bottom section is #8. Buying a 25G TBD.

Kenwood wrote back and said to do the MARS/CAP mod if I want 60 meters. Too bad they don't make it a firmware upgrade so no one has to open up the radio to remove a resistor. When I go to do that I plan to replace the backlight since I'll have the front opened up anyway.

BTW, N3GX has issued freeware that manipulates the DSP. Anyone have experience with that? Does it substantially improve receiver performance.

According to additional articles that I've read, I believe that you might be right. And, there's a review in eham that supports your post, also. However, when I look at an image of the HDBX tower, I'm not sure if mine is an HDBX tower since there appears to be more cross bracing on the HDBX than what my tower has - I was going to add an image of the bottom section to this  post but I didn't see a way to do it. But, if mine is an HDBX, then it would save me a few thousand dollars. I bought my tower used but my trusted friend said that it's a BX tower.

UPDATE: According to criticaltowers.com, my tower is an HBX-56 but I'm not using the top section. So, essentially I have an HBX-48. According to another source, my tower is actually an HDBX-48 since I'm not using the top section and since the bottom section is #8.

Anyway, this is probably moot since Rohn recommends that the boom length be less than 10 feet for all models even though there is no engineering data for booms greater than 10 feet. But, since I haven't had any problems or evidence of any impending problems I have to assume that Rohn is just being conservative.

But, I'm considering a 25G tower anyway.

I was just reading a post from 2011 where someone was asking about putting a Mosley TA-33SR (aka TA-33M) on a Rohn BX tower. The surface area of the antenna is 5.8 while the tower spec is a maximum of 6. But, the boom length of the TA-33M is about 14 feet while the Rohn spec says the boom should be 10 feet or less. Well, I've had a TA-33SR on my Rohn BX-48 for about 15 years with no problems. We rarely get winds exceeding 50 MPH here. I wonder if there's a torsion bar kit for the BX?

Anyway, I'm considering replacing my BX tower with a Rohn 25G (to be on the safe side) even though I don't like guyed towers (due to aesthetics). I was wondering if there's a way to reuse my existing concrete pad with the 25G? It looks like there's some kind of base plate that can be anchored to the concrete but I'm not certain if this can be done with something like the concrete anchors that I use at work (not for towers). I'm talking about drilling into the concrete and put in a concrete anchor and use something like lag screws to attach the base plate or do bolts have to be encased in the concrete? Anybody want to buy a BX tower?    BTW, I have one more section that would turn it into a BX-56.

Anyway, I might consider installing a 45G instead. Whenever I can come up with the bucks......