[Top] [All Lists]

Re: [Amps] Failure of a pair of FU728F

Subject: Re: [Amps] Failure of a pair of FU728F
From: "Roger (K8RI)" <>
Date: Mon, 23 Sep 2019 04:55:17 -0400
List-post: <>
As I have an Emtron manual tune amp I can only comment on the FU728F Tetrode. I would not run a single one of these tubes at 200-330W output, let alone a pair. There are at least 3 versions of the FU728F.  The earlier versions tend to have some problems and the later ones say they have a 1200W plate dissipation, they really are 1500 watts.  Other tubes have had this change on paper as well. The FU728F is a relatively  inexpensive tube for its power capabilities as "were" the Chinese 8877s Like many Tetrodes, when run much below 75% output they may exhibit a negative screen current.  The tubes should be operated in the normal screen current and tuned for a peak in screen (G2) current, for best efficiency and linearity keeping at less than the maximum ratings . IOW, the tube should be tuned for a peak in screen current, NOT for max output, or max plate current

73., Roger (K8RI)

On 9/15/2019 6:40 PM, Guido Tedeschi wrote:
Thanks Joe,

   but the manual says that the amp protection is activated from Grid current too high...

73 de Guido, ik2bcp

Il 16/09/2019 00:20, Joe Subich, W4TV ha scritto:
On 2019-09-15 4:40 PM, wrote:
I was running the OM4000a at 200-300w out (with around 3-4w of
drive), and tuning it as normal to the "carrot" on the tuning

Roger (K8RI)

Amps mailing list
<Prev in Thread] Current Thread [Next in Thread>