My Centurion 422b amp is sick. With initial application of power, in selected PTT and STANDBY modes (and un-keyed), the 3-500's are drawing 140 ma plate current (and barely perceptible grid current).
Forgot to mention that I also meggered grid-to-cathode, plate-to-grid, plate-to-cathode at 1KV on both 3-500's (cold). Both passed. 73, Allen--W7GIF -- Original Message -- Sent: Sunday, February 21,
Bias transistor? I had one go out on my Centurion when it was only a couple hours old. 73, Duane Duane Calvin, AC5AA Austin, Texas ac5aa@ac5aa.com Forgot to mention that I also meggered grid-to-catho
Yes, I had to replace the bias transistor in my 422b several yrs ago. TT service still had them. I think a 2n3055 will work. Andy, W3LI ________________________________________ Bias transistor? I had
On 2/21/2016 7:42 PM, A R wrote: My Centurion 422b amp is sick. With initial application of power, in selected PTT and STANDBY modes (and un-keyed), the 3-500's are drawing 140 ma plate current (and
Author: Gary J FollettDukes HiFi <dukeshifi@comcast.net>
Date: Sun, 21 Feb 2016 21:17:47 -0600
This transistor sounds like a likely candidate as the amp is acting like it is keyed regardless of the state of the keying line. Question is, why did it fail? A 2N3055 is good for 15 to 20amps so ove
Duane, Andy, and Carter: Wow. Just confirmed that the TO-3 bias transistor (MJ15001) in my 422b is shorted collector-to-emitter. Admittedly, 4 failures isn't a huge sample, but it sure suggests that
Gary, No problem here. I have a built-in autocorrect "uncorrector". I read "overcurrent" despite the autocorrect's corruption. I'm inclined to suspect the failures are due to a device mfg quality iss
Mine was an early life failure - as I mentioned, within the first hour or so of operation. After replacement, it lasted several years until I sold the amp. I don't recall the replacement device - TT
Author: Gary J FollettDukes HiFi <dukeshifi@comcast.net>
Date: Sun, 21 Feb 2016 22:25:14 -0600
I can only imagine that using legacy old inventory would be the best choice if indeed manufacturing issues are the root cause. These are readily available on the worlds largest auction site. However,
The 2N3055 was notorious for being available in cheep / poor quality units. In addition to doping impurities as Alan pointed out, it could also be the physical build inside of the casing. In an earli
The point of looking for the cause is well taken, but you guys may be thinking in the wrong direction. There is a possibility that common mode current is the cause of the breakdown. To be on the safe
Author: Gary J FollettDukes HiFi <dukeshifi@comcast.net>
Date: Mon, 22 Feb 2016 01:46:57 -0600
I wonder what you mean by putting an RF choke on the output of an amp. There already is one, going directly from the center pin of the power output connector to ground. It is there to prevent presenc
Wow Gary, that was a lot of questions. I generally use a 1:1 Maxwell choke in the two places I suggested. Mine are home-brew but similar to the Model 8232 sold by THE WIREMAN. http://thewireman.com/b
Allen, Look for higher collector breakdown voltages to mitigate any transients. The 2n3055 is a bit puny in the voltage breakdown dept. Pick silicon with higher PIV, and similar Beta as the 2N3055. I
Author: Gary J FollettDukes HiFi <dukeshifi@comcast.net>
Date: Mon, 22 Feb 2016 20:43:22 -0600
Thank you for the information. This is a very interesting read and leads one to believe that many things would improve with these chokes in place, especially in noisy settings. As far as a transistor
Just completed an internal visual inspection of the failed MJ15001 using a 20X stereo scope with alternate light sources. Unfortunately my "shade tree" failure analysis/forensic lab doesn't include t
With installation of the JANTX 2N3055 completed, and three full days of on-air operation, the amp is performing beautifully...tube bias problem solved. Pre-test of the '88 date-coded JANTX 2N3055: hf
Allen, have never seen a procedure for calibrating the meters or I would be glad to send it to you. Andy, W3LI ________________________________________ With installation of the JANTX 2N3055 completed