Tube suggestions for 811H

Discussion in 'Amateur Radio Amplifiers' started by AC2MM, Dec 30, 2018.

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  1. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    Wait, those are Svetlana "572-10" tubes. Are these the same as or interchangeable with 572Bs/811As?
  2. N8CMQ

    N8CMQ XML Subscriber QRZ Page

    I have heard, but it was old info, that the Svetlana tubes were not as good as the China brand.

    As with tube matching, it is something some do while others do not do.
    I have never used matched tubes as I have had tubes drift in value after burn in and have adjusted the circuit for the drift.
    BTW, burn in is important, as you may have a tube drift far enough to be out of spec and come back for repair if not performed.
  3. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    Hum, interesting. Generally I thought Russian Svetlanas were considered better (across all tube types) than Chinese tubes, or at least had better quality control.

    I guess it's just a matter of choosing between $50something dollars each direct from China or 70something from RF Parts.
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    The mu needs to be in the 160 range to replace a proper 811A.

    If it’s not, it’s an audio tube. Also check the voltage ratings compared to the RCA specs.

    Svetlana made what they call their 811 for SET audio amps. Those tubes are problematic in an AL-811 series amp as far as voltage rating, power dissipation, and cutting them off in receive.
  5. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    I figured that out when all the references I found to Svetlana 572s were for audio. Chinese it is. I'm certainly not paying $200 each for NOS Cetrons.

    Another thought occurred tonight. While I was working with the amp into a dummy load Sunday evening I had space heaters on in the basement. I did at one time kick the breaker (I presume it's a 15 amp circuit but I'm not entirely sure) as all the basement outlets are on that circuit. My results were varying a lot and it didn't occur to me that line voltage might depending on which of two space heaters were on versus off according to their thermostats. I'm going to work on that some more, playing with the amp with all other large current draw devices off. Either way, even if I get results more in line with what I'd expect, I'm going for a set of 572Bs. I can always sell them to someone else if I move up to a different amp before I use them (or sell them along with this amp when I move up.)
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    That amp can be your space heater! :p

    Low line voltage will drop the power down considerably.

    811As are fine as long as you stay vigilant.

    572s are much more robust and forgiving. I wouldn't buy NOS Cetrons either. I don't believe they are worth $200 each when the Chinese versions seem to be fine, especially at the lower ratings this amp will run them at.
    Last edited: Jan 29, 2019
    WD4IGX likes this.
  7. N8FVJ

    N8FVJ Ham Member QRZ Page

    Svetlana 572B will arc over at 2500+ volts plate. Below that the tubes hold up well. Most amps use about 2200 volts plate.
  8. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    1700 at idle on the AL-811H. Lower key down of course.
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    There are well documented issues with the Svetlana 572bs not working well in AL-811 series amps due to the voltage required to cut them off being lower (more negative) than what the amps have unkeyed. If one had to use Svetlana 572's in an RF amp, they ought to be the 160u version.

    I wouldn't bother with the Svetlanas and instead, get the Chinese ones that seem to be a decent replacement for the Cetrons, and are known to work well in power amps.
  10. N8FVJ

    N8FVJ Ham Member QRZ Page

    Good to know. Thanks.

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