Critical Meter Test Tuning Ameritron Amplifiers
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- Опубликовано: 28 дек 2023
- The grid current is the single most authentic and important tuning indicator in any grounded grid amplifier.
In the 1980s and earlier FCC rules required watching power input, this mandated we watch plate current. Additionally, our transmitters were generally grid-driven tetrode or pentode stages with only the plate current monitored. Older hams are just trained to "dip the plate" even though that is passe'.
In grounded grid AB2 amplifiers, we should really focus on grid current. No matter what any instruction, video, or Elmer tells us the grid current is key to proper tuning.
In the spring of 1983, the FCC changed rules. Instead of the plate input power of 1000 watts, amateurs could run 1500 watts PEP output. This meant we had to know the peak envelope power output to the antenna, which is forward peak power minus reflected peak power.
Because of this, all amplifiers I designed had a dedicated grid current meter. I installed a negative rail clamping diode to protect the meters. That diode conducts and sometimes shorts if the tube or anything on the high-voltage lead from the power supply to the tube should arc to the chassis. If you have a shorted rail clamp (aka meter protection diode), it is likely from a tube arc. It could also be from any arc to chassis in the HV system.
This video shows how to safely test the meter protection diode without removing the amplifier cover.
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Tom, I can't thank you for posting this video. I found out my diode was bad. I replaced the diode and it seems to tune up better now than it ever has. Thanks again.
Nice job Tom. You explained the process very clearly. Thanks
Thank you so much.
I have been looking ing for this clip in short form.
Thank you!
My Amp is 25 years old. I have no clue how long both of my needles have been moving in unison!
My output has dropped to just almost 400 watts and I thought it was just weak tubes ( probably still is) but I have ordered a 1N4007. Thanks for the insight.
How do I tell if the filter cap. board is the better board on the AL-1500?
Thank You so much Tom!!
Excellent!!
Hi Tom, in the event the diode is open would it be possible to have a trigger circuit that turns on an led using the votlage ir current level present when open? It would only indicate an open diode while doing your test scenario, not used or pay attention to while in normal operarion?
Jim WB8ZLK
Honestly, in over 50 years of doing this and using that form of protection, I have not ever seen a diode open.
The only common diode failure is a short. We use a 1N540x or a 6Ax diode to improve immunity to shorts. Mostly we use a 1N5408 (because we stock them by thousands) or a 6A10 (because we stock them) in real big amplifiers
@@Jerrythenerdful ah ok, could think of a way to use the potential difference that is present when diode is ok but then adding anything into this pathway adds more potential for shorting failures, where the simple test you suggest just needs to become SOP.
How are you going to test the amplifier and I assume radio is on and the relay connection is in place without depressing the key what you say is not even plugged in unless of course you're going to use the send on the radio but on the other hand my ts2000 does not allow a zero watt out. The minimum power on my ts2000 is 5 Watts.
I would love your response and also I need a link to a web page if you have it on anything you have on neutralization particularly for the AL 8118 H and I understand you had a method for that did not require power because I would like to read more details on that then your video showed and in addition to that I want to check that before I put in a new 572 B's I just bought and I would also like to know that if the neutralization was correct for an 811 whether or not it would also be correct for a 572B. I realized this supposed to be one for one Replacements but there are some differences including the fact that the 572b has a much more robust plate dissipation level.
Thank you very much sir
Put it on CW, do not plug in a key or close a key if one is plugged in, and push the MOX or Send button. If your radio does not support that (almost all do) you can go to SSB, use PTT with mic gain at zero or just do not say anything into the mic.
@goinghomesomeday1 Thank you. I'm actually Tom W8JI, that Jerry thing is just the name of an anti-spam sign-up like your @ going home someday.
U@@Jerrythenerdful