Yes and maybe, Carl. I had been using the amp for some time on 12M without problems. But I recently moved my 12M antenna to a different location where it is unfortunately interacting with something e
On a suggestion I checked the oscillation with a scope. It agrees with my frequency counter - oscillation around 400 - 450 kHz. I failed to add in my first post... when this problem occurred during "
Recently I asked about an instability problem after my 10 year old HB 4CX1500B amp suddenly started destroying vacuum relays. Thanks for all the advice! I discovered under certain conditions it was g
The problem is occurring with several different antennas. However, there is on thing I have not yet taken apart for inspection: an antenna switch. What makes me think oscillation is: Suppose I have t
What makes me think oscillation is: Suppose I have the amp tuned for maximum output at 28 MHz. Indicated antenna SWR is low, output is 1500 watts. Now assume that for the following procedures I maint
Once again I would like to thank everyone for your input on my amp woes. There was a massive pile of private responses, which I have not fully worked through in terms of replies. Each and every one i
It is a 4CX1500B, cathode driven. Screen: direct to chassis. Grid: RF grounded, 6000 pF (3 x 2000 pF). Bias currently fed through 150 ohm resistor with bypass/feedthrough cap The 50 ohm RF load resis
The regulator supplies power for switching transistors Q1, Q2 and the opto-isolator U2 (which handles bias switching). The relay coils are powered directly from the ~35V supply (before the regulator)
Today I did three things: 1.) Added a safety choke to ground on output side of pi network. Of course it should have been there all along. 2.) Added a .01 uF cap across the filament pins. 3.) Upgraded
I will no doubt say at least one incorrect/stupid thing in my response to Bill. I trust and hope someone will point it out so I can learn from it! That is my present theory, based partly on the fact
Tube ceramic looks OK, no sign of arcs. Some discoloration/dirt typical of a tube that has been in service more than 10 years but nothing that looks like it would cause trouble. Tube tabs have no vis
On 08/03/2013 01:13 PM, donroden@hiwaay.net wrote: The FCC sold the public a bill of goods when they were promoting digital TV. They told TV stations that their coverage area would double in area. Ov
I still make most of my holes that way. The (rare) exception would be when I happen to have a hole saw the correct size - or slightly under size and finish with the half round file. If I had to take
This brings up something I have been wondering about. I agree the maximum surge current would be limited by resistance in transformer windings and primary wiring. But I believe the surge current rati
Several months ago I inquired about a problem with my 4CX1500B 160-10m amplifier. The initial symptom was a welded vacuum relay while operating on 12 meters. I replaced the relay and subsequently dis
That is what worries me. I wonder it it was on the edge of instability all along until a minor change in the plate choke pushed it over the edge. I wonder if I should think about upgrading the by-pas
Manfred, Thanks for the reply. Could it be that your plate choke was arcing over between those turns where the insulation flaked off? Or perhaps those turns tended to get shorted via creepage over th
Manfred, Thanks for the work and reply on analyzing my problem! Sorry I got behind on correspondence this week. Now I'm catching up. From the number of turns, length of the winding, and the dimension
I would like to thank Peter, Jim, Carl, and others in addition to Manfred for input on my amplifier issues. I now have a plan to improve the by-passing. I wish it were reasonably possible to add the
I have a question related to recent discussion of my amplifier oscillation problem and need for better by-passing. I am not particularly knowledgeable about the relative merits of various capacitor t