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Author Topic: EF Johnson Thunderbolt  (Read 2333 times)
KB4MNG
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Posts: 183




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« on: July 20, 2015, 06:38:20 PM »

What is the proper way to run reduced power on the Tbolt. Tune for max and the reduce exciter power?

Thanks!  Brian nc
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WA2AAR
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Posts: 110




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« Reply #1 on: July 20, 2015, 07:00:00 PM »

Hi Brian
You are right tune the amp for max and then reduce the exciter power. Been doing it here for years.

Bob
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WB2WIK
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Posts: 21623




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« Reply #2 on: July 21, 2015, 08:11:31 AM »

Yes, that's recommended.

Of course the T-bolt has a great deal of gain which is why Johnson always recommended using a 6 dB (or more) attenuator in series with its input when using higher power exciters that run more than 10W output or so.
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KB4MNG
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« Reply #3 on: July 21, 2015, 05:49:27 PM »

If I go by this method, what power can I expect on qrp/5 watts? From what I understand, I should get full power out of the tbolt with 5 watts.

Thanks!
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KM1H
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« Reply #4 on: July 22, 2015, 05:50:11 AM »

On paper maybe but Id settle for a bit less considering circuit losses and tube condition. It also takes more to tickle a lower gain late 40's tube than its more recent ceramic counterpart.

Carl
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WB2WIK
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« Reply #5 on: July 22, 2015, 07:53:18 AM »

If I go by this method, what power can I expect on qrp/5 watts? From what I understand, I should get full power out of the tbolt with 5 watts.

Thanks!

I doubt you'll get "full power" with 5W drive, but should be able to with ~10W drive.  At least, that's my experience with an original unmodified one as I bought back in 1973 (that was a "one owner" unit and the original owner did nothing to it but use it).

"Full power" was 1 kW DC input power, or ~650W output.  The tube are good for much more than that, but not with 2200V on them.
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WA2CWA
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« Reply #6 on: July 22, 2015, 05:11:57 PM »

On my Thunderbolt, if takes about 8 watts drive on the lower bands to get full output. On 10 and 15 meters, roughly 10 to 11 watts.

Pete, wa2cwa
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