Notes on Alpha 78 Linear

History

Moved from W8AV to PJ2T in February 2002 and used at run station in ARRL CW contest.

October 2002

Removed from service due to apparently severe TVI generation and second harmonic birdies (160 signal was heard S9 + on 3.6 MHz in the US). 

November 2002

Had one tube (8874) and R11 HV metering resistor 25 ohm 25 watt wirewound with screw lugs cannibalized to fix the Alpha 76. New front panel on hand at W0CG. Needs assessment and decision about whether to ship to States for repair at Alpha.

January 2003

Amp brought back to US and shipped to Alpha factory by W0CG.

March 2003

Linear came back from factory totally rebuilt, with new panel and case. W8TK added two new 8874s to the one medical pull already at QTH. Photo

July 2003

Returned to service at PJ2T. Used at Station # 1 in IARU contest. Worked great!

December 2004

Failed -- would not turn on -- blowing primary main fuses.

March 2005

Replaced one 8874 which showed a near short from plate to ground. Tests OK 3 March 2005 by W0CG. (The new tube was taken out of the "Arizona" linear.)

February 2006

After increasingly showing problems of high input SWR (as seen from the transceiver), intermittently, this amp hard-failed in November 2005 prior to the CQWW CW contest. Installed new K4 (input reed relay) in February 2006. We made an error and shorted the DC coil to ground, so when the amp was first turned on it blew the step start (1.75 amp slow blow) fuse and the step start resistors overheated. N1ZZ scabbed in two diodes from the PJ9JT old parts supply and linear started OK. Reconnected K4 coil leads and tested OK 24 February 2006 (W0CG).

July 2007

Used at Station 1 by WI9WI for WPX CW. Occasional keying drops but got through the contest OK. Prior to IARU 2007 it kept turning itself off. Moved to closet.  

November 2008

Moved out of closet for backup in CQWW CW. Kept turning itself off and once blew the step start 1.25 amp slow blow fuse.

13 December 2008

In troubleshooting in December, it came up OK but turned itself off after about 20 seconds without blowing any fuses. After pulling the QSK board and removing HV board and doing a lot of blowing and wiggling, it came up and stayed on. After one minute of time delay the lights turned green as they are supposed to. Came up OK after about 15 minutes when pushed CW button. Swapped into position at Station 1 after power tests good and the amp stopped turning itself off, but will not make RF. I can hear the relay keying inside but there is no output. No RF is getting to the tubes. All is good in standby and TX and RX through the amp work fine. K4 must not be keying.

15 March 2009

Retested at Station # 1 and still getting no RF to the tube cathodes. Found that K4 is getting 24 vdc properly applied when the amp goes key down, but there is still no evidence of RF getting to the cathodes. Also noticed the sealed vacuum relay sticking now and then in TX. There would be value in replacing both of these relays.

21 March 2009

Replaced the sealed vacuum relay K5. Noticed that it shows about 500K from one of the coil pins to ground. Also noticed that the K4 reed relay is continuously receiving 24 VDC to the coil. Further, amp presents SWR of 4:1 at all times to the XCVR. I give up. Time to return to States. Packed for return to States 27 March 2009 in a Cabbage case. Will also transport the transformer.

30 April 2009

Amp arrived at W8TK (Ohio) following Alpha repair. Transformer is at W0CG and good tubes in Curacao. Tom will retain it now that the period of loan to PJ2T is ended. Club and W8TK split the $1066 repair charge.