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eHam Forums / Misc / RE: AND YOU THOUGHT THE "RAT SHACK" WAS BAD!!!
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on: September 01, 2012, 02:47:23 PM
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A lot of businesses want info that they don't really need to make the sale. With ID theft so rampant I just tell them I'll go somewhere else to buy my stuff or do without if they insist on collecting personal data that they don't need.
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eHam Forums / Amplifiers / RE: AL-811H HV
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on: May 19, 2012, 09:13:16 AM
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Thanks. I'll have to see about ordering one before something goes pop. But, I'm surprised that Ameritron didn't put in higher voltage power supply capacitors in this amp. I was under the impression that the design rule is to rate the capacitors 1.5 times the working voltage. In this case the capacitors should've been rated at least 600 volts each (instead of 450 V) - since the 4 caps are in series this would allow for voltages as high as 2400 VDC across the capacitor string. However, from what I've read on an 811A spec sheet the maximum plate voltage should be 1500 volts for class AB2 but Ameritron says the HV should be a nominal voltage of 1700V. Oh well, I'm not a design engineer so I don't know what the engineer was thinking when the amp was designed. I should just go buy 572B's and eliminate this issue also. Looks like the 572B can handle 2400V plate voltage - plus I could run RTTY at max amp power with this tube. But, I'm going to leave things pretty much the same as original - otherwise by the time I get done redesigning/improving the amp I might as well as go buy another amplifier that's "properly" designed. |
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eHam Forums / Amplifiers / RE: AL-811H HV
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on: May 19, 2012, 08:48:55 AM
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4WS: Wade, no offense meant, but a screwdrivers isn't a chicken stick! According to everything I've read for decades shorting HV to ground with a screwdriver or similar device can potentially overstress components in the power supply. When I was in the military, we were provided with sticks that were tied directly to ground. Anyway, I discussed this issue with a friend that worked on FM broadcast transmitters and he said it's better that you destroy a transmitter component than risk getting yourself killed. Having a resistor between the stick rod and ground isn't the safest course to take. And if you're working with others it's best to use a shorting stick tied directly to ground in case some moron turns on the power to the transmitter while you're working on it. I suppose the best solution is to have 2 sticks, one for discharge and another for a safety stick that's tied directly to ground. But, I plan to use just a stick that's tied directly to ground. |
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eHam Forums / Amplifiers / RE: AL-811H HV
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on: May 18, 2012, 03:59:43 PM
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The bucking transformer would be placed external to the amp in a metal box. It reduces 264 VAC to somewhere around 240 VAC. I would post a schematic here if eham had such a feature. Here is a schematic that might work. The transformer 240 volt winding is connected across the 240 VAC line. The two fuses use the ~ symbol. The transformer 10 volt winding is connected in series with the AC LINE in a direction such that it bucks, or subtracts from the line voltage. Hooked up the other way it would add to the line voltage.
The fuse in series with the 10 volt winding is the same type and amperage that the AL-811 uses or 10 amps. The fuse in series with the 240 volt winding is a 1 amp SLO-BLO. The transformer is now protected from over current. And the wiring to the bucking box is protected if the transformer fails shorted. It can be used without an ON/OFF switch and it will probably burn just a few watts when the AL-811 is not drawing power. The metal box should be connnected to the AC power GREEN wire (GND).
10V winding
LINE-------------~----------mmm--------AMP
~
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)
) 240 V winding
)
NEUT---------------------------------------AMP
I think that you're missing something on the schematic that you drew. 240 VAC is picked up across Line1 (L1) and Line2 (L2) - not across Line and Neutral. That said, shouldn't there be a buck winding on both L1 and L2 where identical voltage would be dropped on each leg? And I did a little research on buck and boost transformers. It seems that a buck/boost transformer is ideal since there might be substantial swings in voltage if my wife is running the dryer and/or oven while I'm operating. I didn't look at cost, though, but it would probably be more expensive for a buck/boost transformer. |
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eHam Forums / Amplifiers / RE: AL-811H HV
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on: May 18, 2012, 10:08:15 AM
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It looks like you need a bucking transformer to reduce the voltage.
The Triad VPS20-8800 ($40.79 at Digikey and in stock) can be configured to transform 230 VAC to 10.0 VAC at 17.6 A. This is more than large enough for your AL-811H.
With 246 VAC in it will provide a bucking voltage of 10.7 volts (actually more due to this being a bit of a "soft" transformer). The 246 VAC will be reduced to 235 volts and the AL-811H HV will drop from 1850 to 1770 V. This is calculated for an ideal transformer.
I would place a 1 amp SLO-BLO fuse in series with the transformer input.
I'm assuming that this transformer would replace the existing transformer so I'm wondering why I would need an additional fuse for the new transformer. |
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eHam Forums / Amplifiers / RE: AL-811H plate and load capacitors
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on: May 18, 2012, 09:53:58 AM
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IMHO, Just grounding the grids was the wrong thing to do. What if a tube flashes over? Now that could be some interesting Fireworks. If, I were really determined to make a Mod of that type, maybe a fast blow fuse rated at around 25-30% greater than the Maximum rated Plate Current? In my days I have seen lots of Blown Plate Chokes, Rectifier Bridges, and Power Transformers just because of the Mod described here. Also, what good is the extra 30 to 50 watts going to do for you anyway? Just turn the drive up a bit and be done with it. With 600 Watts, and it is the first 500 to 600 that really counts. Figure what the difference to a receiving station would be to add just that little bit extra. In quick summary, those resistors were placed there for a reason. The Al-811 is known for arcing Plate and Load Bread Slicers. And if I were going to do any kind of mod on one at all, it would be 2 things. 1. Better Plate and Load Caps in the Pi Network and 2. Replace those 811's with 572B's ......
73 de Wade/KJ4WS
Maybe you should take the time to read the details about the mod. This mod is recommended by the designer of the amp. http://www.w8ji.com/al811_important_modifications_changes.htmWhat do you mean by better plate and load caps? Do you have a recommendation? Next time I need to replace the tubes I'll consider buying the 572's. |
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eHam Forums / Amplifiers / RE: AL-811H plate and load capacitors
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on: May 16, 2012, 05:06:56 PM
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The capacitor has been replaced with the original type from Ameritron. It's working great. No more arcs and sparks.
I guess I might have tuned incorrectly at least once to trigger the problem since the capacitor has worked fine since I bought the amp until now.
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eHam Forums / Amplifiers / RE: AL-811H HV
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on: May 16, 2012, 05:01:53 PM
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Measure your line voltage with a volt meter and then read page 4 of your owners manual to determine the correct buck boost connections. I measured 246 VAC. The amplifier is strapped for 240 VAC. |
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eHam Forums / Amplifiers / AL-811H HV
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on: May 15, 2012, 11:25:18 AM
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Since restrapping my amp for 240VAC my HV has been as high as 1850V. Is there a way to strap the amp to get the voltage down to the nominal 1.7 KV? It was around 1.7 KV when strapped for 120 VAC. I could go back to 120 VAC but since I went to the time and expense to install 240 VAC to the shack I'd like to use it. Or is 1850V HV a non-issue? I suppose another option would be to replace the 811A's with 572B's.
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eHam Forums / Amplifiers / RE: 811A tube to replace 572B?
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on: May 07, 2012, 04:58:20 PM
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The voltage rating difference (1500 for the 811, 2000+ for the 572B) may seem slight, but it's not.
Are you sure about those voltage ratings for the 811A? I have an AL-811H and according to the manual the HV should be 1700 volts. According to the manual the voltage can be as high as 1800 volts. Since re-strapping my AL-811H for 240 VAC, the HV is showing as 1.8 kV. So far, no problem. This is pushing it for a 811. The 572's idle at 2700 volts in my Dentron and have for 18 years now. I guess my next set of tubes will be 572's even though they're more expensive. |
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eHam Forums / Amplifiers / RE: AL-811H plate and load capacitors
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on: May 07, 2012, 04:55:15 PM
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If you increase the plate spacing then you will probably shift the problem to the next vulnerable component like the bandswitch. Smoke that one and "you in a heapa trouble boy!"
It can be replaced. Anyway, I ordered the original plate capacitor. I don't know why it arced because I followed Ameritons instructions. I've tried tuning the amp by using a keyer running at 60 WPM (to keep duty cycle low) also. After reading what I felt like reading about amplifiers, I wonder why anyone would want an amplifier. They're too easily damaged. It seems that it's tricky to get the drive and loading set right. And if you're a contester, re-tuning after each band change is a hassle and undesireable. I have thought about buying an auto-tune amp like an Alpha but I've read negative comments about them also. I once had an ALS-600 but kept blowing up the finals. The ALS-600 would have been nice since you didn't have to tune it after changing bands but it couldn't handle the repeated, initial transceiver key up. So, what is a ham to do? |
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eHam Forums / Amplifiers / RE: 811A tube to replace 572B?
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on: May 07, 2012, 03:31:06 PM
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The voltage rating difference (1500 for the 811, 2000+ for the 572B) may seem slight, but it's not.
Are you sure about those voltage ratings for the 811A? I have an AL-811H and according to the manual the HV should be 1700 volts. According to the manual the voltage can be as high as 1800 volts. Since re-strapping my AL-811H for 240 VAC, the HV is showing as 1.8 kV. So far, no problem. |
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eHam Forums / Mods And Repairs / My TS-450 is back from repair
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on: May 02, 2012, 07:41:16 PM
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Just back from FTH. Just under $300 to replace just a tunable coil & lithium battery!!!!! The labor rate is $70 an hour but I doubt that it took them that long to replace the coil and definitely not long to replace the battery.   I don't know what happened to that coil or what part of the receiver circuit that it was located. But,to put a positive spin on this, the radio is working great again. |
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eHam Forums / Amplifiers / RE: AL-811H plate and load capacitors
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on: April 30, 2012, 05:24:57 PM
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First off you didn't "change" your amp to grounded grid by just grounding the grids instead of using a resistor. The amp was still grounded grid with the resistors. What? That statement flies in the face of logic. But, I'm not going to argue the point. I'm done with this thread, anyway, since I didn't get any positive responses. |
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eHam Forums / Amplifiers / RE: AL-811H plate and load capacitors
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on: April 29, 2012, 05:08:53 PM
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I can see the merit of vacuum variables in a harsh or hostile environments but in a amp in shack? As far as concerns of possible arc over this can easily be addressed through the use a air variable with larger plate spacing.
Well, I'd welcome a recommendation for an air cap with greater spacing. It'll probably be much cheaper than a vacuum cap. |
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