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Thanks for the reply Carl. I am confused as to your suggestion to use -13 volts. I am using -39 now and its still 225 MA at 4000 volts.? The Sheet lists -100 to be Class C bias.

C

?

My experience with the Alpha and a few later EBS circuits is that the
switching transient spike goes out over the air.

Several have commented the same about the AL-80B circuit and they have
removed it, but I havent had one in here recently to test.

The 3-1000Z is fine with 100 ma idle at 5000V in Class B and ~ -13V bias.

Carl

----- Original Message -----
From: Clark Turner clark@... [ham_amplifiers]
To: ham_amplifiers@...
Sent: Sunday, April 07, 2019 12:54 PM
Subject: [ham_amplifiers] Bias Boards

I have a BTI LK2000(single 3-1000Z) that I have rebuilt a few years ago.
The Power supply had previously been changed to a traditional Choke
input from the factory doubler supply. The transformer was 120 volt
primary and was limited.

I obtained a Hypersil transformer with 220 volt primary. Its a 1.5 amp
model. I used a replacement Diode board with metering circuit for an
ALpha 77 I found on ebay along with a 40MFD Oil cap. TO finish it off I
used a large contactor.

The amp runs 4000 volts(low tap) on the plate as measured and had 350MA
of idle. I used Tony's Triode bias board and that got me down to 225MA
with the board turned up max. The amp runs HOT and requires a second
fan on top of the cabinet to extract heat.

I planned to alter the Bias board with a 20 to 24 volt 1 watt Zener
diode as described on the website. This should get me 50 something
volts of bias to cut the idle current back more. 100ma?

Has anyone used the EBS-1 bias board? It seems that this approach cuts
the tube off with no drive and has no bias as the drive comes up. I
wonder if this is a worth while system? Any drawbacks?

I do plan to upgrade the blower motor for increased air flow but cannot
find a blower with the motor on the same side as this one. It is no
longer available. I plan to retrofit something in the amp while I am
working on the bias.

C

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Clark Turner
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