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AL-811H Low/no grid current on some bands

FatHam

FatHam

Well-Known Member
Staff member
Apr 15, 2011
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Sorry, this is a long one. I'll start with the issue before I get in to the back story...

Current situation - Just got my AL-811H back from Ameritron repair. All good on 15/17/20 & 40m. On 10/12/30 & 80m, I can't get the grid current above 10mA and if I increase input power, grid will actually drop BELOW "0". On 160m I can't get the grid current above 20mA.

Co-ax is routed radio>amp>SWR meter>dummy load. Basically same results to the antenna.

Pre-repair situation - Keyed up and heard a "crack". Opened it up and found a blown bleeder resistor. Without the means to check the tubes or other circuits to find the cause, I opted to send it to Ameritron for diagnosis and repair. They had advised me to pull the tubes and ship it without tubes as they had "test" tubes that they could use.

3 months later, I got a call from an Ameritron Tech stating that they had replaced the resistor and everything seemed "okay" other than 4 "swollen" 450v capacitors. He went on to say that their may have been an issue with one or more of the tubes that were still in my possession. I opted for all new tubes, capacitors and bleeder resistors. They also changed a diode.

Now I'm wondering if the "new" tubes that they installed after my approval weren't tested across the bands, or maybe something was damaged in shipping? Shipping it back and forth again would cost almost as a new set of tubes, but I'd hate to roll the dice on either of those two options if I'm missing something obvious here.

Any help/insight here would be appreciated!
 
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FatHam said:
Sorry, this is a long one. I'll start with the issue before I get in to the back story...

Current situation - Just got my AL-811H back from Ameritron repair. All good on 15/17/20 & 40m. On 10/12/30 & 80m, I can't get the grid current above 10mA and if I increase input power, grid will actually drop BELOW "0". On 160m I can't get the grid current above 20mA.

Co-ax is routed radio>amp>SWR meter>dummy load. Basically same results to the antenna.

Pre-repair situation - Keyed up and heard a "crack". Opened it up and found a blown bleeder resistor. Without the means to check the tubes or other circuits to find the cause, I opted to send it to Ameritron for diagnosis and repair. They had advised me to pull the tubes and ship it without tubes as they had "test" tubes that they could use.

3 months later, I got a call from an Ameritron Tech stating that they had replaced the resistor and everything seemed "okay" other than 4 "swollen" 450v capacitors. He went on to say that their may have been an issue with one or more of the tubes that were still in my possession. I opted for all new tubes, capacitors and bleeder resistors. They also changed a diode.

Now I'm wondering if the "new" tubes that they installed after my approval weren't tested across the bands, or maybe something was damaged in shipping? Shipping it back and forth again would cost almost as a new set of tubes, but I'd hate to roll the dice on either of those two options if I'm missing something obvious here.

Any help/insight here would be appreciated!
Click to expand...
My personal experiences with Ameritron tech support, has been more challenging that dealing with pre-schoolers. They don't know their ass from their elbow. You may need to re-adjust the tuned inputs on the affected bands. Also, inspect the plate choke. Look inside and see of any tank parts shifted during shipping.

I should have asked, if the tubes were shipped back to you separately from the amp?
SuperLid
 
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SuperLid said:
My personal experiences with Ameritron tech support, has been more challenging that dealing with pre-schoolers. They don't know their ass from their elbow. You may need to re-adjust the tuned inputs on the affected bands. Also, inspect the plate choke. Look inside and see of any tank parts shifted during shipping.

I should have asked, if the tubes were shipped back to you separately from the amp?
SuperLid
Click to expand...
They were shipped back installed, but seriously wrapped in foam and taped
 
You can tell if you need to adjust the input tuning slugs based on the SWR your radio sees into the amp. If the radio is folding back the input power, that would be a tell-tale sign.

For grins, you could always swap the old tubes back in and see if the same thing happens.
 
Oh yeah, I should have added >tuner> in to the coax run noted above.

Any time this IC-7100 folds the power back, it shows on it's meter and it's not showing any reduction.

Oddly, it's putting out as much or more power on the above mentioned "problem bands" as it did pre-Ameritron, just not showing any (or negative) grid current.

For a $500 repair bill, I was expecting plug and play. Crap. I may try the old tubes when I get time.

Thx
 
To be clear, take the tuner out of line, radio>meter>amp>dummy load and check/adjust SWR at the amp's input tuning? You'd think they'd have tuned it into a dummy load as well to be "all good" before they shipped it. Like I said on the radio's meter though, it's showing power out as expected rather than folded back.

Easier to start there than switching the tubes I guess...
 
FatHam said:
To be clear, take the tuner out of line, radio>meter>amp>dummy load and check/adjust SWR at the amp's input tuning? You'd think they'd have tuned it into a dummy load as well to be "all good" before they shipped it. Like I said on the radio's meter though, it's showing power out as expected rather than folded back.

Easier to start there than switching the tubes I guess.
Click to expand...
Beware of the old tubes. I would not try them, unless you can bring up the line voltage slowly on a variac. The fault is most likely not tubes, because you have output on some bands. I would be looking at the bandswitch and tuned inputs.

Ameritron should pay the freight on the return and fix it promptly. The problem is, the people there are brain dead and have no concept of time and reality. I just had to unleash some frustration with them this week. I have a 1500 that should not have left the factory. Whoever assembled it, was drunk, hungover or blind. I am fixing it on my time and they are taking their sweet time sending me parts.

Anyone here remember the V31BB MFJ junk net? It was a result of his AL-1500 constantly failing. I just wonder how some of these people got the jobs they do there. The conversations I have had with Ameritron techs, were like I was talking to a toddler. They seem to know everything about nothing.

Good luck.
 
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FatHam said:
4 "swollen" 450v capacitors.
Click to expand...
And they didn't get replaced immediately? "Swollen" equals trouble, and soon.

Just the same, I feel their pain. I have given up finding qualified help, and run my shop solo now. Unless Martin starts a technical school, he won't find people with the needed skills. Hardware is not taught in vocational education. Hardware is obsolete. Everything is firmware now.

Except the stuff MJF sells.

73
 
nomadradio said:
And they didn't get replaced immediately? "Swollen" equals trouble, and soon.

Just the same, I feel their pain. I have given up finding qualified help, and run my shop solo now. Unless Martin starts a technical school, he won't find people with the needed skills. Hardware is not taught in vocational education. Hardware is obsolete. Everything is firmware now.

Except the stuff MJF sells.

73
Click to expand...
The person I spoke to claims to have been there over 20 years. Good employees cost money. I highly doubt they could pay me enough to work there, I don't feel sorry for them. I know they use students with no electronics/soldering skills to assemble their junk, cheap labor.

My parts are out for delivery today. Maybe I will be able to get the AL-1500 working.
 
Well, they did get replaced (eventually), but I hadn't even noticed their condition when I took the cover off. I'm scratching my head here wondering if that was from the old tubes, or if there's still an unidentified problem.

Oddly it's still putting out power on the problem bands, just with no grid current. I haven't played with it very hard for fear of smoking it, but discovered last night that 30 in gave me 200 out on 30m just like before the repair, but it's doing it with no (or next to no) grid current.
 
FatHam said:
Well, they did get replaced (eventually), but I hadn't even noticed their condition when I took the cover off. I'm scratching my head here wondering if that was from the old tubes, or if there's still an unidentified problem.

Oddly it's still putting out power on the problem bands, just with no grid current. I haven't played with it very hard for fear of smoking it, but discovered last night that 30 in gave me 200 out on 30m just like before the repair, but it's doing it with no (or next to no) grid current.
Click to expand...
I received my parts today. 2 of 4 are wrong...I sent a photo of what I needed.

You didn't answer my question about the EBS board. Is it in there? There is a diode that can short, that will cause what you describe. I don't know the component designation, but it is a single diode at the far edge of the filter board, close to where the HV connects to it. Check it for short. If it is shorted, replace with 1N5408.
 
SuperLid said:
I received my parts today. 2 of 4 are wrong...I sent a photo of what I needed.

You didn't answer my question about the EBS board. Is it in there? There is a diode that can short, that will cause what you describe. I don't know the component designation, but it is a single diode at the far edge of the filter board, close to where the HV connects to it. Check it for short. If it is shorted, replace with 1N5408.
Click to expand...
Sorry, I'm on the road but will check it when I get back later this week
 

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