For those interested....
I have completed the modification to my homebrew 8877 amplifier,
replacing the 8877 with a YC-156.
After some initial testing I have the following to report:
These are the negatives so far.
The amplifier will no longer tune 15 meters. The increased Cout in
the YC-156 is going to require me to retap the inductor for a little
less inductance, thus raising the operating Q of the amp on 15 meters.
I have no idea if I will get it to play on ten meters.
And, I now have to wait 2 more minutes for the tube to warm up.
The YC-156 takes about 4 times the space on a chassis as the 8877.
On the positive side the YC-156 is easier to drive. The following
operating perameters were obtained with the amplifier terminated
into a Bird dummy load;
14.2 Mhz.
50 watts drive
4300 Ep
.93 Ip
3999 watts input
1900 watts output
47.5% efficiency
I notice at higher drive levels the efficiency improves...100 watts
drive
the efficiency went to 58%. I don't know how much of this is because
of my LC tank cicruit ratios versus maybe better operating point of the
tube.
If anyone else has any numbers on their YC-156, including 10 meter
operating values, I would be curious to compare notes. I have not done
any number crunching yet...I hope the needed raise in tank Q for
10 meter operation will not kill the efficiency to the point all is for
not.
Terry - W6RU
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