>Hi Rich
>
>OK about the fan speed and, yes, the black baffle was in place. The amp
>has not been used on RTTY
>but I suspect it has been pushed to the limit in CW and SSB contests.
thanks. A DC brushless fan operated from a rectifier/dc-filter connected
to the 11Vrms fil winding would give more cooling for berserko
contesting.
cheerz
>
>
>----- Original Message -----
>From: Rich <2@vc.net>
>To: Brian Miller <brianmiller@xtra.co.nz>; AMPS <amps@contesting.com>
>Sent: Wednesday, October 09, 2002 12:07 AM
>Subject: Re: [Amps] TL922 AMP PROBLEMS
>
>
>>Hi all
>>
>>The ZL6QH team is using a TL922 amplifier which has developed some
>>problems over the past 9 months.
>>
>>Here is a chronological summary of the events. Note that I have not
>>personally observed all of the
>>events - the following is a combination of what I have been told and what
>>I have seen.
>>
>>Jan 2002 - New RF Parts tubes installed and then one of the grid chokes
>>burnt out on start-up. The
>>choke was repaired and the amplifier appeared to work normally again.
>>
>>Sep 2002 - One of the new tubes failed with an open circuit filament half
>>way through a contest. An
>>old "used" tube was installed as a temporary replacement.
>>
>>Oct 2002 - The second new tube failed, again with an open filament. This
>>time it failed on start-up,
>>along with several "popping" noises. At this stage I also noted that the
>>enamel wire on the L3
>>filament choke was discoloured - indicating that it may have been
>>overheating.
>>
>>Oct 2002 - Installed two good "used" Eimac tubes. The amplifier now
>>appears to work normally in the
>>CW 2 KV position but is not stable in the SSB 3 KV "Operate" position.
>>After switching to "Operate",
>>the IP current (indicated on the front panel meter) gradually increases
>>and then suddenly starts to
>>intermittently jump to full scale - along with "popping"noises.
>>
>>It is likely that parasitic oscillations are contributing to the above
>>situation. We will have
>>careful look at the relevant components in the anode, grid and bias circuits.
>>
>>I understand that the amplifier does NOT have a history of instability -
>>the above problems are a
>>recent development. So something has changed!
>>
>>Two questions
>>
>>1. Have other owners of TL922 amplifiers observed a similar sequence of
>>events. If so, then what was
>>the root cause and how was it fixed?
>>
>>2. Any thoughts on why the filaments in both tubes should go open circuit?
>
>50Hz reduces the fan speed compared to 60Hz. Was the perforated black
>baffle next to the tubes in place? Was the 922 used on RTTY?
>
>>
>>I did notice that the
>>filament voltage was running around 5% high. We have fixed this by
>>changing the line voltage setting
>>from 220V to 240V and reducing the external line voltage to the amplifier.
>>
>>Note. I HAVE read the earlier threads about parasitic suppression -
>>including Richard's web pages.
>>No
>>need to repeat this information please.
>>
>>Thanks and 73
>>
>>Brian Miller ZL1AZE
>>Registered Electrical Engineer
>>67 Hornsey Rd
>>Melrose
>>Wellington
>>New Zealand
>>
>>Tel 027 4446614
>>Email: brianmiller@xtra.co.nz
>>
>>
>>_______________________________________________
>>Amps mailing list
>>Amps@contesting.com
>>http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
>
>
>**
>
>
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