I've just fired up a Dentron Clipperton V modified for 6M operation per Dentron instructions. It uses a single 4CX250B in Class AB2. The bias is adjustable, and the factory recommends 50mA plate curr
Jim, I'm pretty familiar with this amp and have repaired/modified a few of them. The 4CX250B plate current isn't very important at all...what's important is grid current and screen current, and the D
Tune it for maximum output while using the screen grid current as the indicator; provide another meter as tetrodes are best tuned using Isg. The tube likes to be heavily loaded and will find its own
Remember the filament is 6.000 not 6.3. Keep an eye out for a 4X250R. Supposed to be more better for linear service. -- This message has been scanned for viruses and dangerous content by MailScanner,
I am not sure about using screen current as an indicator. The 4CX250B tubes can have under certain conditions a negative screen current. This has to do with the fact that the screen grid elements are
Negative screen current can happen to many tetrodes during tuning and loading but the operational current in the 4CX250 and 8122 family ones we use is always positive. Screen current is always the be
Most of the Tetrodes you will see in ham service including some pretty hefty QRO setups can show negative screen current, particularly at lower power settings. All of the ones with which I'm, familia
So if I watch the screen current, am I tuning for minimum? Do I need to watch grid current, or will that take care of itself if the screen current is right? Many thanks for all the great responses, b
No. In the final stages of tuning a Tetrode amp you are peaking the screen current with the loading control. This peak coincides with maximum output, or should and is a sharper peak than the output.
Your tuning for a peak BUT not exceeding the tubes screen current rating. The Load cap controls the amount of Isg once the Tune control is set for a resonance indication on the screen meter. They int
Don't you peak the screen current with the TUNING control? Isn't the LOAD control set to produce the desired screen current at a particular level of drive? Dave Hachadorian, K6LL Yuma, AZ . ________
Never having had a tetrode amp, I feel compelled to ask: Should you always tune such an amp for a peak reading (within the acceptable range for screen current) and not add a tad bit of loading for li
All these points are well and good about screen peaks, within the limits of the screen dissipation etc. Heck, we could even add a grid current meter to make things really interesting, and pray never
ORIGINAL MESSAGE: REPLY: Don't you mean the tune control? You should adjust the tune control for a peak, while the load control sets the value of the peak. Same as with a triode, only screen grid ins
Loading a bit heavier than the peak works with any tube or configuration. Since you are decreasing the loading capacity you are also decreasing screen current. Good tetrodes will also have their powe
Good points Dick. The 4CX250R/7580W and 8930 can push the IMD into the high 20's and then add another 5-6dB using G3SEK's tetrode boards. Add NFB and you are at -40dB 3rd. Ive measured -35dB from my
Thanks Carl, This is what I've been trying to say, but my allergies are kicking up to the point of it being like a cheap drunk. Want to go flying? It'd certainly be interesting<:-)) That was said in
ORIGINAL MESSAGE: REPLY: The first time you tune either a triode or tetrode, you should start with a very small amount of drive, adjust both tune and load for maximum power out, increase the drive a
At output levels of about 250W PEP per tube, the 4CX250B is capable of IMD3 figures around -35dB (referenced to PEP). It is Eimac's marketing claims, inciting users to drive the tubes to a much highe
Author: jonathan white <jonathan.white20@btinternet.com>
Date: Sun, 23 May 2010 12:05:01 +0100
I agree with you Ian, 25yrs back,there was some outrageous signals on 2mtrs with overdriven `250b`s poor regulation of screen supply, poor anode supply and zenner diode stacks feeding screen. Also th