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AL-811H tube swap to 572Bs

Discussion in 'Amateur Radio Amplifiers' started by KW4GT, May 12, 2019.

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  1. N8FVJ

    N8FVJ Ham Member QRZ Page

    Oh, I did not read the four tube AL-811H has adjustable neutralization plate. Best to leave it alone unless the amp shows instability. I believe some older amps such as the Collins 30L-1 did not have neutralization- bad news.
     
  2. KW4GT

    KW4GT Ham Member QRZ Page

    Apparently the 572Bs are 'close enough'. I'm good with leaving it alone.
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    Bend to adjust. :rolleyes:
     
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    BTW- HRO (Ham Radio Outlet) shows to have Svetlana 572B tubes still in stock at $89 each. If so I would rather own these vs Chinese. New old stock needs to have filaments lighted for 2 hours before HV applied. Filaments and plate have a getter material applied to maintain vacuum and is activated with heat. After HV is applied, try to heat tube plate with constant carrier to heat up the plate to finish the re-evacuation. 10 minutes should be enough time.
     

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