Hi,
I have a friend who has problems with his AL-811 and the anode
parasitic chokes on 28 mhz. He doesn't have Internet access so I'll
have to mail any answers to England. I sold my AL-811 to fund a bigger
amp purchase so I can't even help him with the resistor values. His
letter:
" All works very well on all bands except on 28 MHz (10m). On this band
alone I find that if I tune up to produce even around 300 watts out,
the resistors in the anode parasitic chokes overheat. I burnt out the
first set, George. I have installed a second set made by a guy over
here who is marketing a linear amp somewhat similar to the Ameritron
linear using four 811 tubes. However even with this guy's parasitic
chokes the resistors get to hot and I smell burning unless I limit power
out to around 200w on 28 MHz. His chokes consist of three 220 ohm 1
watt resistors in parallel with about 5 or 6 turns of say 16swg wire
around them.
I wonder if you have had this problem on 28 MHz with your Ameritron,
George? (I never had any problem with mine, George) Perhaps you know of
a solution. One old friend over here who runs a home-brew linear with a
pair of 813 tubes became so fed up with the parsitic choke resisotrs
burning out (similarily only on 28 MHz) that he removed them altogether
and simply makes the connection with lengths of coax shield wire.
Apart from this one frustaration in having to keep the power down to
about 200w on 28 MHz only, I am very pleased with the Ameritron. I do
find the manual very basdic and would welcome on with more information.
For instance what value are these resistors in the anode parasitic
chokes? My original ones were so beaten up that I cannot be sure but
thy look like 200 ohm 2 watt. If so, then 200 ohm seems quite a high
value to me for this job. Perhaps you would let me know the value of
these resistors if you can, George.
PS I had no such problem with my previous linear running two 3-5000z
tubes."
Thanks in advance for any help, I won't be able to check for any answers
until Sunday, so won't be able to supply any additional information
until then.
73, George / KF9YR
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