[AMPS] Dumb directly heated cathode amp operational questions

Wed, 7 Jun 2000 15:27:21 -0400

Ok, I'll offer a comment... I own two TL-922s.  I think that the RF deck cooling is excellent, and is fairly quiet.  Following Rich's suggested mods, the amps operate very quietly and the only noise I hear from my amps is the sound of the fan...

I suspect that the reason these amps aren't popular with contesters is that the HV section (specifically the transformer) is perhaps not robust enough for serious contesting ops.  

The '922' has a thermostat built into the HV transformer that opens when the transformer gets sufficiently hot - never happened to me, but I'm a ragchewer, and not a contester, and the amp does get a chance to cool down a bit more than during contesting ops... 

When the thermostat opens due to high transformer temp, the keying line is de-activated and the amp can't be keyed until the transformer cools down.  However, the amp remains fully powered regardless of the state of the thermostat.

Even after some very lengthy ragchews, the vented air fairly quickly cools from "rather warm" to "about" room temp.  After the three-minute fan timer times-out following shutdown, the RF deck area is never "hot", although the HV transformer usually is hot, and the core tends to retain the heat.  I could probably quantify these temps with a temp probe  

73 de Don (ki6sz)

-----Original Message-----
From: Chris Tran GM3WOJ [mailto:gm3woj@talk21.com]
Sent: Wednesday, June 07, 2000 10:28 AM
To: billp@wwpc.com
Cc: amps@contesting.com
Subject: Re: [AMPS] Dumb directly heated cathode amp operational
questions

Hi Bill et al

>>2) After I've been running the limit in an SSB QSO what's the recommended
>>cool down period before I shut the power off?
>
>My guess is c. ten-seconds cooldown for unprocessed SSB and 30-seconds
>for RTTY.  .

I would suggest more like 3 - 4 minutes, Bill. The 3-500z is a
radiation-cooled
tube i.e.  most of the heat is infra-red radiated by the plate structure,
and
absorbed by the surrounding metalwork, circuitry, glass envelope, etc -
the blower/fan should keep the tube glass seals at the right temperature,
but usually does a POOR job of cooling the surroundings.
You'll find that it takes anything up to 2 minutes for the orange/red colour
of
a hot 3-500z plate to die away.
I've rewired all blowers/fans here so that they remain 'on' even after the
filaments are switched 'off', then switch everything off once I'm sure it
has
properly cooled down.

>>That would allow me to not cycle the filaments just for the sake of
>>getting the noise level down. I could even set up this blower control
circuit
>>to run the blower the cool down period after I turn the power switch off.
>
>3-500Z amplifiers with superior cooling to the Henrys are the TL-922 and
>the SB-220.  The 220 is definitely the quietest.   ''Air system'' sockets
>cause the tubes to operate at elevated temps.

I'm feeling brave today and I'm going to disagree with you again, Rich !
The standard Kenwood TL-922 has one of the worst cooling systems
I've seen - far too little air movement, etc.. !
Consequently, 922s are not very popular with contesters who like
high duty cycles with loads of processing !

73
Chris    GM3WOJ
www.gm7v.com      www.qsl.net/gm3woj/

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