
Compare
the
GS35B
With the 3CX1500A7/8877
(See photographs below)

This
is a basic comparison of the GS35B and the 3CX1500A7/8877. This information
is to be used for making up your own mind about which tube is for you .
I don't make any claims about the accuracy or source of any of this data. 
Specification

GS35B
medium mu


Length 
6.9
inches (177 mm) 
3.51 inches (89.15 mm) 
Diameter 
4
inches (100 mm) 
3.38
inches (85.85 mm) 
Weight 
6.17
lbs (2.8 kg) Anode cooler alone is 3 lb 7 oz (more than two complete 8877s) 
1
lb 9 oz (708 gm) 
Operating
Position 
Any 
Any 
Base 
Concentric
Rings (use simple clamps) 
Special
7 pin base 
Internal Construction 
Planar 
Conical 
Heater
Voltage/Current (Watts) 
12.6
Volts / 3 Amps (37.8 Watts) 
5
Volts / 10 Amps (50 Watts) 
Warmup
Time 
Greater
than 90 Seconds 
Greater
than 90 Seconds 
Maximum
Frequency Rating 
1000
MHz 
250
MHz 
Gain** 
13
dB (900 MHz) 
15.1
dB (< 30 MHz)
14.3 dB (220 MHz) 
Maximum
Output Power 
3000+
Watts 
2075
Watts 
Cin
(grounded grid) 
1824
pf 
42
pf 
Cout
(grounded grid) 
3.85.0
pf 
10
pf 
Cpk
(Transfer ca) 
<0.12
pf 
0.1pf 
Cathode 
Indirectly
heated oxide coated 
Indirectly
heated oxide coated 
Plate
Voltage Absolute Maximum 
6000
V (pulse) 4000 V SSB/CW 
4000
V 
Plate
Current Absolute Maximum 
1.4
Amps 
1.0
Amp 
Plate
Dissipation 
1500
Watts (>2500 Watts) 
1500
Watts 
Grid
Dissipation 
26
Watts 
25
Watts 
Forced
Air Cooling Minimum Volume 
88.3
cfm (2500 lpm)* (150 cmh) >10,000' 
38
cfm (1076 lpm) (65 cmh) sea level 
Approximate
Least Cost (Jan, 2006) 
US
$110.00 each 
More
than US $900.00 each 

*Commonly
published data shows 1500 liters/min as 90 cfm but that conversion is WRONG.
The correct data is 2500 liters/min or 150 cubic meters per hour which is
88.3 cubic feet per minute. 
** Let's work this gain and max output thing backwards:
Plate dissipation 
Maximum power input
based on 60% efficiency 
Maximum power
Output 
Tube Gain 
Required Drive 
1000 Watts 
2500 Watts 
1500 Watts 
15.1 dB 
46 Watts 
1000 Watts 
2500 Watts 
1500 Watts 
13 dB 
75 Watts 
1500 Watts 
3750 Watts 
2250 Watts 
15.1 dB 
70 Watts 
1383 Watts 
3458 Watts 
2075 Watts 
15.1 dB 
64 Watts 
1500 Watts 
3750 Watts 
2250 Watts 
13 dB 
113 Watts 
2500 Watts 
6250 Watts 
3750 Watts 
13 dB 
188 Watts 
1333 Watts 
3333 Watts 
2000 Watts 
13 dB 
100 Watts 
2000 Watts 
5000 Watts 
3000 Watts 
13 dB 
150 Watts 
2667 Watts 
6667 Watts 
4000 Watts 
13 dB 
200 Watts 

What does all this mean?
It means that if you run an 8877 in class AB Grounded Grid with a maximum of 60% efficiency, and with the maximum rated power output of 2075 Watts, the dissipation of the tube will be 1383 Watts and the required drive would be 64 Watts. It means if you drive the 8877 with 70 Watts to get to the 1500 Watts maximum plate dissipation, you've exceeded the rated maximum power output by 175 Watts.
It means that if you use a 100 Watt transceiver, you can drive the GS35B with 75 Watts, get 1500 Watts output and have headroom to spare. 100 Watts drive should yield 2000 Watts output with a plate dissipation of only 1333 Watts.
Using these examples you should be able to figure out the rest of the numbers in the chart above. 

GS35B
Planar Domed Grid
This one has been through the BIG BANG 
8877
Conical Grid
Rich, AG6K, shows gold sputtering. Thanks to him and his wife Susan who took the photo. 




GS35B Planar Anode
This one has had the BIG BANG 
8877 Conical Anode 

I'm looking for a photo of the innards of the 8877 anode. It is nothing more than a copper tube. 


