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I removed the ATU after identifying bands each antenna works alone w/ analyzer. This was part of my effort to have amp work on antenna with cover attached instead of on bench into DL without any cover attached. It's progress albeit baby steps as it's still into DL. I did not expect the cover...

That sums up my situation spot-on. Thank you for the added insights. I will replace my coax (>3 decades) and reassess the ATU afterwards. I find it hard to replace coax because it looks OK from the outside lol. HF is so quiet lately, low noise level just not hearing any activity.

I've been using a Dentron T-Match that's inefficient and it's increasingly noticeable. It appears that an L-Network is more efficient and very do-able using the same Dentron case. So it prompts the question, 'Why Dentron or other manufacturers always made T-Matches instead of L's given the...

"Cathedral" that's the best descriptive word for it that I've ever seen or heard.

I’ve had the bottom sealed up for a few days now so it’s starting to look reliable, fingers crossed. Marking the Load cap and Roller settings for 10 - 15 - 40 & 80 so there’s less tuning guesswork (picture). Little more than half a turn of Roller causes serious decrease in output from...

Was too beat yesterday to make it online. Nomad you were right about my Screen voltage causing of high zsac. I must apologize apparently, I forgot I had left the Screen V at 400 when I swapped the 300Y tubes for the 300A's which run at 350v. A senior moment already? I just turned 65. Yet...

I removed old pics because of the part swaps above and below chassis. This is top pic showing new Roller, Tune & Load air variable. Progressively shorting rotary panel switch adds 120pF caps as needed for lower bands. Tune cap needs almost nothing. I'm seeing 300 mA zsac (2 NOS 4cx300a) while...

SBE base units had the fine walnut case, like furniture. Console was real pretty. The Sierra was my first base rig in 1974. They had a pcb mounted fuse that could only be accessed if radio removed from case. Console is real classic from that period. Miss that radio.

Yeah, I got it going now. :giggle: Apparently that protection diode made it impossible to set zsac/bias. 500 PO from 5w drive on 15mtrs AM from a pair of 4cx300a. That's enough to make me happy. Now I can finish setting the pi values for 40 & 80. neil

My 2nd post on this, I deleted the first, poorly written late at night. I'm chasing my tail lately on Tetrode project. It stopped amplifying despite correct voltages at tube pins and a reasonable zsac but in retrospect (below) I recognize the bias voltage was nowhere close to datasheet values...

I'm so tempted it's cross town so pick-up no problem. https://www.ebay.com/itm/395045335841?mkcid=1&mkrid=711-53200-19255-0&siteid=0&customid=link&campid=5336136228&toolid=20001&mkevt=1

True dat, but a tower that rotates got me all excited.

Entire tower rotates.

Thanks for posting those diagrams Nomad. Never a dull minute here it seems.

Been busy. In addition to the snubber diode, my inclination to use regular 12v zeners in place of BZX79C12 zeners was a bad idea. The BZX zeners (D-6 and D-118) control the mosfets that take the Screen & Plate offline when triggered. Also found BZX D-6, to be open/nc. After removing boards...

How did it go? I watched the YT vids and it looks useful. Cost is reasonable. Problem is, I've never used a real Spectrum Analyzer, so I have no experience to compare it to. Is it possible to use to view harmonic output from the freq of interest? For amps it would need a large attenuator but...

Thread was a great read. Kenrich Golden Eagle 750 was my first base amp early '90's.

Found the problem (ha I’ve written that before) : The diode across the coax relay (N4006) shorted. Keying amp repeatedly tripped the 3 relays upstream on the G2 board. Never saw an ordinary axial type diode go short. Removed G2 board and teste on table where it worked fine. I was oblivious...

Last Post for awhile. Relay repeatedly switch from On to Off fast when activated. I suspect the k-3 relay on the G-2 board is defective. I realize relays rarely fail ... don't think I've ever seen such a fail ... contacts get ruined but the coil armature mechanism? The G3SEK description for...

So I fell prey to NXP's fancy wording? It had me chasing my tail and I almost ordered another BZX out of reflex despite having a strip of 12v 1w zeners. Today I removed the relay board and found the problem, I think. It was mechanical: A torn pcb foil trace feeding the relay electrolytic...