A pair of 812As should get you about max 360 watts out with 65 watt PD
in intermittent service (CW not AM). I can't see the T55 doing better
with a lower plate dissipation limit.
For those that don't readily have the specs--
812A Class C Plate Modulated (CCS) 45 watt PD
Plate Voltage . 1250
VGrid No. 1 Voltage -115
VGrid No. 1 Current 35 mA
Plate Current . 140 mA
Driving Power . 7.6 W
Power Output (approx) . 130 W
Grid leak resistor 3286 ohms
That is 175 watts input on a single tube with 130 watts output.
Plate dissipation in this service is only 45 watts of the 65 watts
rated, so this should be a continuous duty service.
Push pull specs for Class C should yield about 350 Watts input and 230
watts output, an efficiency of 75 percent.
Grid current and plate current doubles for push pull service as does
output and driving power. Grid leak resistance should be one half or
about 1643 ohms
The two most common cause of poor efficiency is improper drive/bias and
improper Q in plate tank circuit Ratio of (C to L).
These tubes are easy to drive, rugged, good efficiency, modulation
characteristics fantastic, low filament power, uses common components
for construction.
In my opinion this service and tube line up is the best choice for a
conservatively rated light weight legal rig.
John, WA5BXO
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Brett gazdzinski
Sent: Tuesday, February 21, 2006 9:44 PM
To: 'Discussion of AM Radio'
Subject: RE: [AMRadio] 1930's Old Buzzard Open Rack
TransmitterFinallySeestheAirwaves! (Long)
The T55 has 55 watts of plate dis, and gives 170 watts out?
The 812A has 65 watts of plate dis and gives 130 to 150 watts out?
I get about 275 watts out at 1500 volts, no color on the plates,
maybe I should try the T55's, they will give me 340 watts out?
I never even plugged the T55's in or tested them.
Filaments are no problem, I have a panel mount variac
to adjust the voltage between 0 and 12 volts.
I did try a set of 572b tubes, but they seem to work hard and not
give a lot more power output.
Brett
N2DTS
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of crawfish
Sent: Tuesday, February 21, 2006 10:07 PM
To: Discussion of AM Radio
Subject: Re: [AMRadio] 1930's Old Buzzard Open Rack
Transmitter FinallySeestheAirwaves! (Long)
My 1937 Jone Radio handbook says that a T-55 has 55 watt
plate dissipation,
typical 1500 vdc plate voltage with -180 vdc grid bias, max.
Ip is 150 mA,
max. Ig is 30 mA.10 watts RF in, 170 watts RF out for 225
in.7.5 VAC @3.25
on filament. The 811A is 65 watts plate dissipation, the
difference in the
811A and the 812 is that the 811A is zero bias and the 812A
needs -110 vdc
bias. Power out of the 811/812 is 130 to 150 watts.
811A/812A info from 1970 ARRL Handbook.
Joe W4AAB
- Original Message -
From: John E. Coleman (ARS WA5BXO) [EMAIL PROTECTED]
To: 'Discussion of AM Radio' amradio@mailman.qth.net
Sent: Tuesday, February 21, 2006 8:33 PM
Subject: RE: [AMRadio] 1930's Old Buzzard Open Rack
Transmitter Finally
SeestheAirwaves! (Long)
CONGRADULATIONS A JOB WELL DONE!
I really like the choice of tubes. I don't know what a T55 is but
probably one of the special Taylor triodes with 55 watts
plate dissipation.
Probably not a lot different than the 812s but I know that
the 812s are very
good tubes to use in a class C plate modulated rig especially
if used with
100% grid leak bias or the configuration that Don, K4KYV,
uses where there
is a safety bias supplied thru a diode and the diode becomes
reversed biased
when RF drive causes grid leak bias. The 100% Grid leak bias
DOES make a
difference in the modulation characteristics of the rig.
John, WA5BXO
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of ne1s
Sent: Tuesday, February 21, 2006 2:27 PM
To: AM Radio Reflector; [EMAIL PROTECTED];
[EMAIL PROTECTED]
Subject: [AMRadio] 1930's Old Buzzard Open Rack Transmitter
Finally Sees
theAirwaves! (Long)
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