Then you are going to have to order some parts. This is designed differently than a standard resistor, and will handle a surge current properly, without exploding. That is why Ameritron puts them in their bigger amps. I got this part from one of those Ameritron parts lists. It is not standard on the economy amps in the AL series. I favor using the parts Ameritron and the designer, W8JI, recommend.
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New metering schematic: Meter protection diode D16 is the unlabeled small black diode near C It protects the meters in the event of an arc. If D16 fails from an arc, the grid and plate current meters will track. The grid meter will no longer read grid current and the plate current meter will no longer read plate current. They each will read a combination of plate and grid currents.
This diode can be replaced with any 1 to 5 amp silicon power rectifier diode that physically fits. The original concept by marketing was a cheap, two-tube amplifier, but I convinced marketing that the life of two tubes would be far too short. I talked them into a bare bones minimum three tube amp, and a slightly more refined four-tube amp. Amazingly, the H has become the largest selling amplifier in the world! This is largely due to the limited budget of most Hams, and the large power increase per dollar investment.
I still have a few original prototypes of the Heathkit amplifiers. All of these amps, like the ALH, push the tubes pretty hard. Of the above amplifiers, the Collins 30L1 is actually the least stable design. Heathkit, Gonset, and Ameritron were wise enough to add neutralization but Collins did not. The result is that the Collins 30L1 was plagued with a series of stability mods throughout production, and even the final production units are not unconditionally stable.
The three tube AL, like the Collins 30L1, is not neutralized. Because the AL uses three tubes and directly grounds the grids, the AL with only three tubes and directly grounded grids has less feedback capacitance than the Collins and is not as unstable as the 30L1. The ALH, with neutralization and other necessary additions, is a much more stable and repeatable design. Tube Rating Nearly ALL tube failures are related to excessive dissipation by improper tuning or operating, or by simple tube manufacturing defects.
I have actually seen brand new tubes with fingerprints inside the envelope! Tube quality control is nothing like it was, but at least the tubes are inexpensive. The A tube has a rated dissipation of 65 watts. Please read the link to understand the complexity of dissipation ratings for various modes.
Because anode dissipation limits are greatly exceeded in normal IVS intermittent voice service and CW operation, as they historically have been in every amateur amplifier, the operator has to be very careful with tuning and duty cycle.
Ameritron actually pushes the tube no more than Collins or Heathkit did, both of whom allowed watts dc input on CW. I recommend a TOF circuit to help monitor proper operation. This circuit gives a visual warning of excessive grid current or improper tuning. It eliminates the need to check grid current with a steady carrier, and gives a running warning of tuning and drive conditions that cause splatter.
Amateur use is generally not commercial service, and this is why everyone from Collins to Gonset to Heath, and even ARRL Handbook articles, have pushed tubes. The reasons the tubes can be pushed are low tube cost and, even when pushed, IMD splatter or distortion performance stays well within acceptable limits. It is just a bit more rugged and significantly cleaner than a sweep tube.
On voice emission tests, using peak power taken over long periods of swept peak storage, peak sideband voice IMD is around dB for third-order products with watts PEP output per tube. It is perfectly acceptable to replace the tubes with three or four B tubes in the AL or ALH respectively to increase duty cycle and tube reliability. While you should NOT run more output, duty cycle can be greatly increased without hurting tube life.
Common Failures The single largest problem with the AL amps is tubes. The tube needs short tuning periods with at least equal time, or longer, to cool between carrier periods. Remember it is the plate dissipation averaged over time periods of 15 seconds or longer that cause tube heating failure problems. The most frequent problem with new tubes are tube factory failures to pump tubes down, so they are gassy.
The most frequent failure mode of properly manufactured tubes is over dissipation and resulting heat damage to the anode. This generally shows as a silver looking color at the center of the anode.
When the tubes arc, the arc path is from anode to grid. If the grid resistor opens, the grid no longer provides a grounded barrier that shields the filament from anode voltage. This can allow the filament to pull to a high voltage of volts or more.
This helped protect the exciter and parts inside the AL My suggestion is the grid circuit be reworked to eliminate R and directly ground the grids with the shortest possible leads, and that gas clamp tubes of about volts or slightly less be added. Link to AL mod. If the grid and plate meter track and show similar deflection, D16 is often the cause. D16 is the metering protection diode, and it fails from tube arcs.
If the amplifier shows anode current without being keyed but meters are normal, RL1B has welded. If the amplifier shows anode current without being keyed but the grid meter reads backwards, the most likely cause is a tube shorted from filament to grid.
Use WD40 carefully applied through a spray tube. Carefully and slowly flood the switch from the front panel side with a little WD40 while clicking the switch back and forth many times. This will wet the contact paste inside the switch and wipe the contacts clean.
AMERITRON AL-811H Instruction Manual
Long Tube Life: The A tubes are long life, reliable transmitting tubes. The Grid Current meter provides a continuous reading of the A grid current to indicate proper loading of the Amplifier. Multi-voltage Heavy Duty Transformer: A unique "buck-boost" winding allows adjustment of primary voltages to match a wide range of line voltages centered on and volts. This versatile Ameritron feature allows the user to maintain optimum voltages on the tubes and other components to obtain maximum performance and life. Vernier Plate and Load Adjustments: Both tuning controls have vernier reduction drives for smooth tuning logging scales for accurate and rapid tune-up. Safety interlock: AC input power is removed from the transformer when the cover is removed.
Ameritron Diagrams, Schematics, Service Manuals
Time Owned: more than 12 months. Well, the Ameritron ALH is not as inexpensive as shown at the top of the page eHam really needs to go in and edit some of the review header material , now being over a thousand dollars. But the ALH is still a tremendous bargain for a tube amp capable of around watts or a bit more a realistic figure, though the amp is advertised as having watt capability. I figured sticking with watts would keep relations with the neighbors on a friendly basis.
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