Thanks Alek, That advice lines up with what I have seen on VKC, and I
wondered why re; 4CX1000 tubes used on DX2, DX3 (2x).
On 24/6/22 14:57, Aleksandar Petkovic wrote:
The main one is that you cannot get a good new tube in this country.
Horror stories abound of people spending hundreds of dollars again and
again, only to have tubes fail in very short order. Even ones that
they bought from OM Power.
All FU728F tubes that you see advertised on Ebay are factory rejects.
They should never have found their way onto the market.
I friend of mine went through 2 tubes in 2 months. He now uses the
4CX1000A in his DX-2SP and we know he'll never have another tube fault
in that amplifier. Thankfully Rudi built that model such that
4CX1000A tubes can easily be substituted. He had the socket modified
and had a 6V tap on the transformer for the heater. A quick tickle of
the pre-bias and bias and you are on the air with a proper tube that
will last forever.
I bought 10 x FU728F tubes ten years ago. They all failed very
quickly, except for one, which has been in daily use for the past
couple of months now. That was when the tubes were US$100 each landed
here in VK. I sold them for virtual cost price. I lost a lot of money
on them. I still have 2 of the failed/returned tubes left. Each year,
I manage to give one or two away as ornaments at our local hamfest.
So, as I said, don't ever go anywhere near a FU728F amplifier unless
it has already been retrofitted with the 4CX1000A.
73, Alek, VK6APK
On 24/06/2022 10:00 am, Adrian wrote:
Alek, What faults / problems did you find or hear about with the 728 ?
On 24/6/22 10:14, Alek Petkovic wrote:
And those FU728F tubes are junk. It is all but impossible to get a
good one these days. The supply has completely dried up.
I would not touch an amplifier that uses that tube.
73, Alek, VK6APK
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