Don´t mix things up with highµ grounded grid designs!
The 4CX5000A in that 2m amp is used with 1.2KV screen voltage and -300V grid
voltage.
The 4CX1000A with its zero watts grid dissipation works flawless in the Collins
30S1 either.
73
Peter
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Fuqua, Bill L
Sent: Dienstag, 18. März 2014 19:07
To: Hsu
Cc: amps@contesting.com
Subject: Re: [Amps] 4CX5000A in grounded-grid
Yes, most of the drive power is fed thru to the output.
However, one problem with these tetrodes is that if both grids have he
same applied voltage the control grid will dissipate more power than the
screen grid rather than the other way around. Since there is no way to
tell how much current each is drawing you can't tell when you are getting
into trouble.
However, it does look like the amp builder will be operating at a lower
power level.
There was an article in QST, the first I believe, where 4x150A tubes were
operated in grounded grid with both grids grounded. However, they were
operated an reduce power.
A month or two later it was followed up by an article by Bill Orr where
he stated that this was not a good idea for the 4x and 4cx series tubes.
I did know a guy, he is SK now was experimenting with different tubes in
grounded grid and he tried four 4cx250A in grounded grid, both grids at zero
bias,
and fried them. He tried a lot of other tubes. The most impressive was four
4-65A tubes. The plates were glowing red orange and then even hotter. As
he increased the drive.
73
Bill wa4lav
________________________________________
From: Hsu [hsu4qro@gmail.com]
Sent: Tuesday, March 18, 2014 7:05 AM
To: Fuqua, Bill L
Cc: amps@contesting.com
Subject: Re: [Amps] 4CX5000A in grounded-grid
4CX5000A's grid dissipation is 75W, not too weak.8877's grid dissipation
only 25W, but often handle over 100W driving power.
If the grid rigged enough, many tentrode can work in GG well , like 813,
GU-81M ,4-400 etc.
-----原始邮件-----
From: Fuqua, Bill L
Sent: Tuesday, March 18, 2014 1:58 PM
To: Hsu ; amps@contesting.com ; ham_amplifiers@yahoogroups.com
Subject: RE: [Amps] 4CX5000A in grounded-grid
This type of tube usually doesn't do well in zero bias grounded grid.
Usually the control grid is fried due to excessive control grid current.
But if he is only turning out 1kW then the drive must be low. Also, his
plate voltage for this tube is low compared to normal operation.
The high Q tank, 130kHz bandwidth, must be unloaded during test. That
is a Q of 100. The plate resistance will drop that.
I have 2 old MRI 200MHz 4CX5000a amplifiers in the garage.
Could not resist them at a UK auction.
73
Bill wa4lav
________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Hsu
[hsu4qro@gmail.com]
Sent: Tuesday, March 18, 2014 1:32 AM
To: amps@contesting.com; ham_amplifiers@yahoogroups.com
Subject: [Amps] 4CX5000A in grounded-grid
Found a interesting web about 4CX5000A(8170) 2m VHF GG power amplifier,
http://www.g4ftc.co.uk/amplifiers/8170_2m/home.htm Anyone use this
configurtion in HF ?how many power gain？
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