I'm currently playing around with a YC156 and have and have discovered an interesting phenomena which I'm having difficultly explaining. On previous amps I have never really bothered tuning the i/p m
Neil, As the cathode in an indirectly heated cathode circuit heats up, or a directly heated cathode, the resistance or impedance changes. This is why you get a different SWR until it heats up to wher
As the cathode heats up, a cloud of electrons build up around it - I'm guessing that this changes the capacitance to ground. The usual form of biassing in gg amps won't prevent the cloud forming and
Neil Carr G0JHC wrote: I set my input matching up for 1:0 SWR with the MFJ, at this time the heaters are not on. Soon as I switch them on SWR shoots up to 2:1, then over a 6 minute period gradually t
Neil I can't imagine that this has gone on all day and no one has told you. I may get a little heavy handed here. Sorry in advance. Applying drive power without pre-heating the filaments is not allow
Well, perhaps he merely tickled the input of the YC156 through the MFJ with a tiny amount of drive. All the same, there is nothing to be gained in doing this without the filaments preheated and plate
Thanks to all last 24hr who have commented on the YC156 and my i/p findings. All noted. Leigh, KR6X, thanks, ..I think you may have misunderstood what I was doing. Your rules are of course excellent
On Sep 16, 2004, at 9:54 PM, Leigh S. Jones wrote: Neil I can't imagine that this has gone on all day and no one has told you. I may get a little heavy handed here. Sorry in advance. Applying drive p
_________________________________________________________ Is this true even when the tube is biased into cutoff? I've owned four commercially-made amps and all of them apply HV as soon as the power s
To observe how much warmup time a heater-type cathode requires, connect a DMM between the cathode and the grid, apply heater power (only) and measure the potential as the cathode warms up. When the V
On Thu, 16 Sep 2004 21:54:56 -0700, Leigh S. Jones wrote: rule 1: never apply plate voltage to the tube nor apply drive power until after the prescribed filament warm-up period has elapsed __________
Bill, In any amps I've made, I did kill the B- lead for the HV until the antenna relay pulled in even though it was biased to cutoff on idle. The reason being is that if the bias ever failed while th
Gentlemen, In reading the posts below do I detect a tendency to use a HV relay to switch the HV on and off every time the amplifier is keyed? Using the 3CPX5000 scenario posted before, would then the
Hal, The plate and a screen voltage if needed was killed the same time as the antenna relay opened. It was then applied as the antenna relay closed. Now this was using a smaller tube type (4CX250B) t
Peter, Yes your correct. I mentioned doing this because I had success with it using 4CX250B's. But, when you get up into the big tubes, there's a lot of current with the anode voltage to deal with. I
Sirs, One of the phenomena about amplifiers that concerns me is the precipitation of VHF parasitic oscillations by transient-pulse type events much akin to hitting a bell with a clapper. The proponen
it lot voltage to this tube have this problem every list. another toast voltage think turning pretty Yes, it depends on the kind of tube. I run several different homebrew amps: Two with glass envelop
It`s my common practice to have a 50k (Or so) resistor in the negative lead shorted by a relay during transmit...I find this to be less tramatic to tube stability in my amps as opposed to totaly open
This is a requirement that is specific to oxide coated cathodes such as the YC-156. Read your tube's data sheet for information like this. Thoriated cathodes generally heat more quickly than oxide co
Peter, On the bias circuits of most amps I've done had a relay that switched full negative supply voltage on G1 when the amp was idle. When it was keyed, it applied an adjustable regulated supply. Fo