If I may recommend some additional steps. Either purchase a used older edition of the ARRL handbook or go to your local library and check one out. Study the basics starting with resistors,
Originally Posted by VA3WPN
how to calculate resistance in series, parallel, and series/parallel and how to use ohms law formulas to calculate current, resistance, and voltage in simple circuits. Don't move on to the next
topic until you have a firm understanding of the section you are studying.
As for the other adjustments referring to high current in the final tubes, take the time to read the alignment section in the assembly manual before you attempt any of the adjustments.
Don't try to circumvent/side step any of the adjustments, you'll run into trouble every time doing that. You should have at least an analog VTVM, an RF probe, and maybe a DVM for
testing and aligning the HW-100. You can find these items on ebay or, in the case of an RF probe, you can build one yourself for a few dollars. There are websites that will show you
how simple it is to build an RF Probe so take some time and research the web for instructions on building a simple RF probe. You should also have a solid understanding of safety
and how to work around high voltage, 375VDC, 825VDC, etc. There are voltages in the HW-100 and the power supply that are lethal. The ARRL handbook has a section on safety,
Thank you. I am familiar with ohms law, and the safty of voltages. Im new, but not unfamiliar. I did find an old ARRL handbook in my collection. Ill go threw it andsee what it says about alignment if anything. Iv got an oscilliscope, DVM and will build an RF probe to use as well. Im always lookng to add tools to my tool box.
Iv ordered the tubes, they should be here in a week or two. Until then i will read over the alignment portion again to make sure im not skipping steps. Im a soldier, so i know what it is to follow procedure. Thank you again for the RF probe suggestion.
I fully support what Mike is telling you. However, I suggested a week ago in Post #2 that you measure the bias voltage at the final tubes and to clean the bias adjust pot. I would add measuring the screen grid voltage. You can do this with the tubes removed and mic gain turned down and key rig in SSB mode. Measure these voltages directly at the tube socket pins 4 and 5 and no where else. Report back these two voltages.
Just make sure 6146 plate caps are in the clear so not to short B+ supply to ground.
Also you can measure R917 2.2 ohm ( with rig turned off) cathode meter shunt resistor. Typically this resistor would drift high causing lower plate current (actually cathode but not important to know that now) readings so not likely it is the problem but may need to replace it to ensure accurate plate current readings.
Until you measure grid bias voltage and screen grid voltage directly at 6146 tube socket pins you have no prayer of figuring out reason for high resting plate current indication. This is so simple and bemuses me why you have apparently not taken these simple readings at the tube socket pins as suggested. I am moving on as you are in good hands. Wish you success. 73s Terry K9TW
I am not trying to be a jerk. I am simply trying to help you avoid destroying your "new" NOS finals the first time you key the rig and attempt to set the resting plate current by adjusting the bias voltage pot. In your original post you reported that on two occasions the plate current was maximum while attempting to set the resting plate current and you saw blue sparks. I do not see where you have identified the root cause of this condition. I would hate to see you destroy the new tubes.
I am trying to give you some simple steps to perform to minimize the likelyhood that you will destroy your new finals. Here are some suggestions. You can perform none or all:
1. Measure the bias voltage at 6146 tube socket in receive mode to ensure you have spec bias voltage and there is no problem with any of the bias supply components.
2. Measure the bias voltage at 6146 tube socket with rig keyed in SSB mode. It should be approx -65vdc and you should have smooth control of it with the bias voltage adjust pot.
3. Measure the Screen Grid voltage at 6146 tube socket in receive and transmit mode to ensure no excessive high screen grid voltage. With no finals installed the voltage should not drop much in transmit mode.
4. Measure the 2.2 ohm cathode meter shunt resistor (least important but good idea to check it)
5. Conduct all measurements and testing on 40 meters until you can get the NOS finals neutralized. It is less likely that tubes will take off and oscillate on 7 mhz. Once you can get resting plate current set on 40 meter then go ahead and neutralize on 10 meters. Your O-scope is good tool to do this. If you do not know how to neutralize come back and ask.
Possible causes of 6146 tube failures include:
1. Loss of bias voltage due to problems with bias supply components (bad filter cap) or bad/dirty bias pot causing thermal run away.
2. Tube arc over from anode to cathode due to aging and off-gassing and air ingress around tube pin seals. This usually will blow cathode meter shunt resistor and/or blow rig fuse.
3. Exceeding Screen Grid dissipation due to excessive high screen grid voltage.
4. Excessive off resonance key down time during testing due to operator error.
5. Tube breaking into oscillation due to neutralization problem (we know you had dissimilar type tubes. Dont need matched set but should not run with mixed types)
So again not trying to be mean spirited with my comments. Just trying to help you. I will leave you in the good and very capable hands of Mike and Glenn. 73s Terry K9TW
I got my rigs mixed up. You should not have any screen grid voltage at the final tube socket in RX mode. Just measure it in TX mode. Sorry about that. I have owned and built HW-101, SB-101, SB-102 but many years have past and going kind of off memory. I work on Kenwoods now and much more familiar with how they work and design voltage levels. I also forgot that Heath shows the schematic in TX mode which can throw you off if not aware of that when looking at relay contacts.
Originally Posted by VA3WPN
My response about learning the basics, about safety, ohms law and resistors was based solely on your statement:
I never meant to sound disrespectful, only to point out some reference material and subjects you should study, based on your initial statement about your skill level. If you have any questions about what you are reviewing/reading,
Im new to Tubes, and really Ham radio and its electronics. So This is all a learning curve for me.
come and ask.
DVMs are not good to use when performing alignment where you have to adjust for a peak indication. I recommend using an analog VTVM (look on eBay) since they display a smooth peak indication during the alignment adjustments.
I agree with Terry and Glen, you should measure the final amplifier bias and screen voltage with the final tubes removed from their sockets FIRST. Putting new (NOS) tubes in the final amplifier without ensuring the voltages are
correct, and adjustable as Terry said, can only lead to possible destruction of the NOS final tubes you just bought.
As for the alignment, it is a good idea to read the alignment section in the manual so you have a good understanding of what the alignment steps are telling you. Don't start the alignment process until you have located the source
of and made repairs to the arcing and full scale plate current indication.