Kris -
The PA in the Drake transmitters is a linear amplifier. So
theoretically, any input from "0" to "MAX" should be amplified
linearly! :-)
However ....
There is always a certain amount of dissipation going on any time the
transceiver is in transmit mode. 650 VDC X 0.1A = 65 watts with NO
input signal or OUTPUT signal at all. This is above the maximum 52.5 W
dissipation rating of three 6JB6 tubes. This 'maximum' rating (17.5W /
tube) is for 'CCS' operation, inside a closed up TV set with 30 other
tubes, running continuously for a week, so 'part-time' operation in a
TR-4 (hopefully with a small fan) is MUCH less strenuous. But, right
away, operating at reduced power gets very inefficient very fast. Throw
in another ~60W of filament power and you're eating up 110W with NO RF
output!! When input IS applied, this current (and power) only go UP.
What all this means is that a TR-4 is NOT a "green" QRP transceiver!
:-) The TR-4 is designed to operate at full power (~200W output) in
'ICAS' (intermittent) operation. It does NOT do well in RTTY or other
continuous duty modes, although with a fan the PA tubes will last quite
a while under these conditions.
What you do NOT want to do is to LOAD up to a lower output power by
reducing the LOAD control. This is easier on the plates of the tubes,
but VERY damaging to the screens. This is why you sometimes see PA
tubes that seem to be fine, but won't even draw idle current. Their
screens are gone, melted/vaporized or just "open" from over dissipation.
Bottom line, QRP transmitters are cheap! And a LOT more efficient at
low power than a TR-4!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Kris Merschrod wrote:
Good morning, Ron,
Good points all around - tune up of the air, excellent watt meter, etc.
I just never gave a thought to a low drive detuning or adding stress
to tubes. Does anyone have some facts on those questions, i.e.,
detuning or tube stress for low driving?
Kris KM2KM
Merschrod
123 Warren Road
Ithaca, NY 14850
www.merschrod.net <http://www.merschrod.net>
----- Original Message -----
*From:* Ronald Erickson <mailto:[email protected]>
*To:* Kris Merschrod <mailto:[email protected]>
*Cc:* Drakelist <mailto:[email protected]>
*Sent:* Saturday, August 14, 2010 12:19 AM
*Subject:* Re: [Drakelist] Low power tuning
It is the tuning and drive that heats up tubes. When you turn
down the drive the power you are using is determined by accuracy
of your meters or Bird watt meter into load. You can use a dummy
load that is 50 ohms or so to figure your power off the air. I
like using noise bridges when I can.
73,
Ron, K0IC
On Fri, Aug 13, 2010 at 9:36 PM, Kris Merschrod
<[email protected] <mailto:[email protected]>> wrote:
Good evening All,
Well, for years I was a QRP "nut" and all I had was my
TR-4CW. I tuned it up as per the manula and then, with key
down backed off the xmtr gain to QRP levels and operated that
way. I did that with CW and also SSB. How accurate was it?
I am not sure. The finals seem to hold up after all of these
years.
73,
Kris (KM2KM)
Merschrod
123 Warren Road
Ithaca, NY 14850
www.merschrod.net <http://www.merschrod.net>
----- Original Message -----
*From:* Ron <mailto:[email protected]>
*To:* Drakelist <mailto:[email protected]> ; Richard
Palmer <mailto:[email protected]>
*Sent:* Friday, August 13, 2010 8:28 PM
*Subject:* Re: [Drakelist] Low power tuning
Well there might be better ways, but I always tune for
max, then reduce the drive (xmtr gain). I think
technically the tubes are not actually perfectly tuned
when you "just back off the drive" but I don't think the
tubes will care. I also think the vox setting might need
some tweaking when you do this.
73,
Ron WD8SBB
--- On *Fri, 8/13/10, Richard Palmer /<[email protected]
<mailto:[email protected]>>/* wrote:
From: Richard Palmer <[email protected]
<mailto:[email protected]>>
Subject: [Drakelist] Low power tuning
To: "Drakelist" <[email protected]
<mailto:[email protected]>>
Date: Friday, August 13, 2010, 10:46 AM
Rookie tube radio guy here Hi Hi. How do I tune my
TR-4 to less than maximum power?
Thanks,
KB8NXO
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