My turn to kick the ball- comparing the 8877 to a GS35b is like
apples vs oranges. The Russian tube has a mu of 13 vs 20 for the 8877. The
tradeoff- durability & max QRG rating. Exceed the published grid current on
an Eimac tube for even a short time & presto, one very expensive shelf
display, and at minimum, another "pull" [read "used"] tube. In contrast, I
don't even measure grid current on my HB GS35b
amps, and I haven't killed one yet.
A decent 8877 will put out well over 2.4kw, whereas I have never seen a
GS35b put out over 1.8kw. On 6m anyway.
If you want to increase the cost of a HB monoband amp with tube
protective circuitry, might as well use an 8877 (which needs the protection)
& get the extra
headroom.
You won't save anything on the power supply side either way, if you
build an amp capable of pushing a tube to its full potential, at least at
VHF. I run 4400 VDC on the plate of my primary 50 MHz monoband GS35b- a
friend's Henry 3006 (8877) runs ~4200 VDC no load, 3.9-4kv keydown. Another
GS35b amp I built runs plate voltage <3kvdc under full load. As it
approaches max output plate current approaches 1 ampere. The higher plate
voltage GS amp draws less plate current, as expected, and is a tad more
efficient.
The 8877 requires a socket- my GS35b mounts directly to the RF deck
divider plate thru a single drilled hole. If you prefer not to cut a
mounting hole, make grid clamp blocks, cathode ring clamps &
drill/enlarge airholes, there are plenty of GS35b HB "sockets" on the web to
spend your money on.
As for air flow & associated noise, my GS amp w/ ~120 cfm blower is
plenty quiet. At about $70.00 new I got what I paid for. The AC unit in
the shack is by far the biggest source of noise, when my kids aren't around
anyway... Another GS35b I built had a 3CX800 sized blower on it- if limited
to ~1kw output it could, and did contest all day w/ no thermal drift. That
4 lb copper anode
cooler provides a lot of room for error. Would anyone care to test an 8877
at a lower than recommended airflow & backpressure rating at full output?
Both tubes are what they are. If one has a personal preference, sobeit.
Trying to ramrod it, however, makes as much sense as those Bart Simpson
window stickers on many Ford & Chevy trucks. Amusing but pointless.
73 Dave N3DB
----- Original Message -----
From: "MIKE DURKIN" <patriot121@msn.com>
To: <amps@contesting.com>
Sent: Tuesday, July 31, 2012 2:41 PM
Subject: Re: [Amps] 3CX1500A7/8877 vs el cheapo GS-35B
> Well shoot .... I hit 94cfm ... and yea, its noisy. Im sure the fan noise
> is lower at 83cfm...
>
>> From: km1h@jeremy.mv.com
>> To: dezrat1242@yahoo.com; amps@contesting.com
>> Date: Tue, 31 Jul 2012 14:14:41 -0400
>> Subject: Re: [Amps] 3CX1500A7/8877 vs el cheapo GS-35B
>>
>> Physical Characteristics
>> Envelope metal-ceramic
>> Cooling forced air
>> Minimum required Air flow 2500 l/min (83.3 cfm)**
>> Diameter 100.2 mm max
>> Length min 173 max 177mm (6.9")
>> Anode Diameter min 99.7 max 100.2 mm (4")
>> Grid diameter min 59.5 max 60.3 mm
>> Cathode indirectly heated, oxide coated
>> Cathode Diameter min 40 max 40.5 mm
>> Heater Diameter min 25.6 max 26.2 mm
>> Weight including copper heatsink 2.8Kg (6.17 lbs)
>>
>> **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 83.3 cubic feet per minute. 90 cfm is still a good
>> target
>> number.
>>
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