>> Hold it down to 600 watts RF output and you can run it all day long.
600W output is close to the safe CW output! Eimac's data sheet gives
600W CW or PEP as the "useful power output" for a single 3-500Z with
2500V on the plate.
Considering that it is the continuous current in the plate transformer
that causes the overheating and both power/heat are current squared
effects, reducing the current by 30% would reduce the heat by 50%.
A 30% reduction in current (to ~280 mA) would be roughly 1/3 reduction
in power out (if the plate tank can be adjusted to maintain efficiency)
or around 400 watts.
Even at 400 W, I would look for ways to add auxiliary cooling.
73,
... Joe, W4TV
On 9/24/2012 1:07 PM, Don AA5AU wrote:
Bill is correct, the weak point in this amp is the transformer. I blew mine up
on RTTY twice and no longer have it. The trick is to replace the transformer
with a Peter Dahl transformer if you can find one at a reasonable price.
I ran mine at 500 watts on RTTY until the transformer went out.
73, Don AA5AU
________________________________
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
To: RTTY Reflector <rtty@contesting.com>
Sent: Monday, September 24, 2012 11:46 AM
Subject: Re: [RTTY] Heathkit SB-1000 On RTTY
IGINAL MESSAGE:
On Mon, 24 Sep 2012 11:07:56 -0400, NZ4O wrote:
I have a Heathkit SB-1000 amplifier with the single 3-500Z. The manual for
the Heathkit SB-1000 says a maximum plate current of 400 mA for CW and 550
mA on SSB.
What would be a safe maximum plate current for RTTY operation, which is
obviously 100% duty cycle like AM operation?
REPLY:
I ran an SB-1000 on RTTY for several years. The weak point in that amp is not
the tube or tank circuit, it's the power transformer. At 1kW RF output during
RTTY contesting you will soon start to smell the transformer overheating.
Not a good smell.
Hold it down to 600 watts RF output and you can run it all day long.
73, Bill W6WRT
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