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Author Topic: Best way to tune a tube amp?  (Read 819 times)

KG4ABA

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Best way to tune a tube amp?
« on: March 03, 2023, 09:32:14 AM »

Ham friends:

What is the best procedure for tuning a tube amp?  I have a Heathkit SB200 but I suppose the same practice of tuning a tube amp would apply across the board!  Step by step would be helpful...thanks!
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KH6AQ

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Re: Best way to tune a tube amp?
« Reply #1 on: March 03, 2023, 09:50:33 AM »

See page 48 of the SB-200 manual for tuning instructions. After getting it tuned up on each band of interest you can make a log of the settings so that you can skip most of the tuning procedure. After setting things per the knob all it takes is a little touching up of the LOAD and TUNE at your full operating power. Some ops place paper around LOAD and TUNE with marks for each band.

SB200 manual   https://www.qsl.net/wa0kke/manuals/SB-200%20Manual.pdf
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K7LZR

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Re: Best way to tune a tube amp?
« Reply #2 on: March 03, 2023, 03:41:21 PM »

Assuming a good SWR at the output, I've always tuned these amplifiers for maximum output rather than dip/load etc. although I'm from that era and I do understand the hows and whys of the plate dip, load, dip, load procedure.

Never had a problem since beginning in 1977 with tuning for max output into a good load using greatly decreased drive and then slowly increase drive to achieve rated power. 
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K6AER

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Re: Best way to tune a tube amp?
« Reply #3 on: March 03, 2023, 05:41:26 PM »

On a triode amplifier I tune for maximum output while keeping the grid current within specifications.

On a tetrode amplifier I tune for maximum output and keep the screen current within specifications.

All tuning is in CW and is limited to 5 seconds.
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VE7RF

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Re: Best way to tune a tube amp?
« Reply #4 on: March 04, 2023, 12:54:47 AM »

Pulse tune it using 60 wpm dots....and use a PEP wattmeter.  Tune for max output...like say 600 w pep out. 
Make up a cheat sheet for each band.

By pulse tuning the amp, you take a huge load off the xfmr, tank coils, bandswitch, tubes etc.
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WA2CWA

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Re: Best way to tune a tube amp?
« Reply #5 on: March 04, 2023, 05:42:31 PM »

Assuming a good SWR at the output, I've always tuned these amplifiers for maximum output rather than dip/load etc. although I'm from that era and I do understand the hows and whys of the plate dip, load, dip, load procedure.

Never had a problem since beginning in 1977 with tuning for max output into a good load using greatly decreased drive and then slowly increase drive to achieve rated power.

I've been doing this same tune-up procedure on both of my SB-200's for years and years. Never had a problem. Both amplifiers were built in 1969 and both still have all their original parts and tubes. Never diddled with dip and load. Meter switch always stays in the HV position. Both amps have been used on SSB, AM, and CW.

Pete, wa2cwa
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VE7RF

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Re: Best way to tune a tube amp?
« Reply #6 on: March 04, 2023, 10:23:59 PM »

If the plate dip and max PO don't coincide, the amplifier is not neutralized.  In that case, tune it for a dip, instead of max PO. 
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KM4AH

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Re: Best way to tune a tube amp?
« Reply #7 on: March 05, 2023, 04:03:52 AM »

More than one way to skin a cat. I use a pulser or pecker and always have.  But, I will be the first to admit that just because you have been doing something for years doesn't mean you haven't been doing something stupid for years
Anyhow, assuming your grid current meter is reasonably accurate after the pecker I hit it with something high duty cycle like CW or FSK for a couple of seconds and tweak the load if necessary to get the grid current where it should be.
Don't think a typical grid meter will tell you the complete picture with a pecker or high speed CW only.

Now, this is all tuning for SSB which I assume was the OP's intended question.
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SWMAN

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Re: Best way to tune a tube amp?
« Reply #8 on: March 05, 2023, 06:20:42 AM »

 Why are we talking about Peckers here ?
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KM4AH

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Re: Best way to tune a tube amp?
« Reply #9 on: March 05, 2023, 08:57:01 AM »

Why are we talking about Peckers here ?

Are you familiar with the sound a wood pecker makes ?
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WA2CWA

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Re: Best way to tune a tube amp?
« Reply #10 on: March 05, 2023, 10:56:19 PM »

Remember, original poster is asking about a Heathkit SB-200 amplifier. The amplifier was designed in stock form for a 75 to 100 watt SSB drive. The meter Grid position only refers to a range on the meter and not actual values. If you're going to dip and load, using a 100 watt or less exciter, all you really need is the plate meter. There is no neutralizing adjustment on this amplifier. Unless the building process was really screwed up, it's a linear amplifier, and with a few watts exciter applied in the AM or CW position, adjustment for maximum forward power output works fine.  No peckers or diddlers or ah'sssss into the mike are needed.

Pete, wa2cwa
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KG4ABA

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Re: Best way to tune a tube amp?
« Reply #11 on: March 15, 2023, 06:42:28 AM »

Thanks, all...very helpful and I appreciate it.
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VE7RF

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Re: Best way to tune a tube amp?
« Reply #12 on: March 15, 2023, 02:19:34 PM »

Remember, original poster is asking about a Heathkit SB-200 amplifier. The amplifier was designed in stock form for a 75 to 100 watt SSB drive. The meter Grid position only refers to a range on the meter and not actual values. If you're going to dip and load, using a 100 watt or less exciter, all you really need is the plate meter. There is no neutralizing adjustment on this amplifier. Unless the building process was really screwed up, it's a linear amplifier, and with a few watts exciter applied in the AM or CW position, adjustment for maximum forward power output works fine.  No peckers or diddlers or ah'sssss into the mike are needed.

Pete, wa2cwa

Sure, apply 5-20 watts of cxr, then tweak tune + load for max PO.   BUT, it's still not tuned up for 500-700 w pep out.  If u just tune up initially with low drive, THEN increase the drive level, u will get a miss tune every time.  The load control will still have to be advanced a lot more.  When u increase the loading control, you are  DE-creasing the load C.   AS the numbers on the load control increase, the actual pf of the load cap decreases.  IF you use a cxr, with low power initially, fine, but u will have to keep tweaking the drive level higher ( with a cxr)..and keep increasing the load C at each step.

So u end up tuning the amp from low to max power...with an ever increasing CXR.  Just easier to use a pecker, with a 20-50% duty cycle..and a pep wattmeter. The low duty cycle pecker takes a huge load off the tubes, bandswitch, tank coils, tuned input networks, both band switches, and the plate xfmr.    Then perhaps hit it with a 80-100w  cxr, then take a quick plate + grid current meter reading.

The grid and plate current meters are only accurate if a cxr is used.  They are both semi average reading devices.
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N4ATS

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Re: Best way to tune a tube amp?
« Reply #13 on: March 15, 2023, 03:03:39 PM »

External Power Meter , set exciter to FM. Peak tune and load for MAX power , should take less than 6 seconds tops.  Been doing it this way for 45 years...
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VE7RF

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Re: Best way to tune a tube amp?
« Reply #14 on: March 17, 2023, 05:23:56 AM »

External Power Meter , set exciter to FM. Peak tune and load for MAX power , should take less than 6 seconds tops.  Been doing it this way for 45 years...

If they had designed these stupid amplifiers correctly the 1st time around, and had used a calibrated 0-100 skirt on both the tune and load caps..and 6:1 verniers  on both caps,  you would only have to tune the amp up in a few places on each band.

Then make up a cheat sheet.  After that, it's just...'dial it up by the numbers'.   IE: 36.5  tune...and  84.5 load.

That's actually a straight forward mod on a SB-220.   Dunno abt a SB-200.
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