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Class C bias means zero Ip in standby, my comment was right out of the Eimac tube manual for Class B modulators and 100 ma PER tube idle current.
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Class B is class B no matter what your using it for.and the tube curves will show you a wide range of bias within that Class. I do that with AM linears such as a Clipperton L and run it deeper into B than for SSB. Actual measured IMD barely changes but the wasted dissipation drops way down to the point I can run 1000W PEP out with just 572B color on voice peaks. Carl ----- Original Message -----
From: Clark Turner clark@... [ham_amplifiers] To: ham_amplifiers@... Sent: Sunday, April 07, 2019 4:56 PM Subject: Re: [ham_amplifiers] Bias Boards 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 On 4/7/2019 11:48 AM, 'Carl' km1h@... [ham_amplifiers] wrote: 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 --- This email has been checked for viruses by AVG. -- Please let me quote you for your parts needs! I offer a discount on Protunes with parts order! Clark Turner 480-695-2898 |
