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Technical Topics => Equipment => Topic started by: Radio Krasnoprudskoe on February 17, 2022, 0521 UTC

Title: Mixing tubes in Ameritron
Post by: Radio Krasnoprudskoe on February 17, 2022, 0521 UTC

Is it ok to mix a 572b tube and a G811 tube in the same amplifier? or bad idea, and I need to save up for 572b?
Thank you!

Title: Re: Mixing tubes in Ameritron
Post by: RobRich on February 17, 2022, 1524 UTC

There are slight capacitance differences and distinct gain differences between an 811a and a 572b. I would suggest not mixing them, as there could be a resulting distributed loading imbalance between the mixed tubes.

Title: Re: Mixing tubes in Ameritron
Post by: Radio Krasnoprudskoe on February 19, 2022, 0248 UTC

Yeah, thank you!
That's what I have noticed too when I switch a single 572b and a single 811A. I want to make sure.
Also, I have this issue, I have the load all the way down to 0 and anything slightly above that the output drops significantly. I have a 1.1 swr on my vertical antenna. Also, at this low load setting the tubes glow, they glow harder when I set it higher. Do you know how I can get it to where the tubes are not glowing and the power is not lost due to a tuning mismatch? I am operating at 6920 khz and the band setting is set to 40 meters.

Title: Re: Mixing tubes in Ameritron
Post by: Polar Bear on February 22, 2022, 2050 UTC

Always use matched tubes..

There are many fine articles online - I would suggest that you read them..

Title: Re: Mixing tubes in Ameritron
Post by: radiogaga on February 23, 2022, 0154 UTC

Quote from: RadioPushka on February 19, 2022, 0248 UTC

Also, I have this issue, I have the load all the way down to 0 and anything slightly above that the output drops significantly. I have a 1.1 swr on my vertical antenna. Also, at this low load setting the tubes glow, they glow harder when I set it higher. Do you know how I can get it to where the tubes are not glowing and the power is not lost due to a tuning mismatch? I am operating at 6920 khz and the band setting is set to 40 meters.

Do you know how to properly tune a tube amp to resonance?
Does your plate current dip at all?
Tubes in amps are supposed to have glowing plates...just not too much for too long.... ;)

Title: Re: Mixing tubes in Ameritron
Post by: Radio Krasnoprudskoe on February 23, 2022, 0321 UTC

Quote from: radiogaga on February 23, 2022, 0154 UTC

Do you know how to properly tune a tube amp to resonance?
Does your plate current dip at all?
Tubes in amps are supposed to have glowing plates...just not too much for too long.... ;)

Yes, I get a resonance point out of the tunning range. I have the load at 0 and that's not enough, it needs to go under 0 for resonance. and the dip in plate current Is very small when i adjust the plate knob. yeah they glow when mistuned. I have tuned it before and it worked. It just won't tune into a perfect match on 6920. It can tune when the swr is over 1.5