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Author Topic: Heathkit HA-14 drive required.  (Read 432 times)
ZS5WC
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« on: July 17, 2019, 07:47:49 AM »

 ???Why is it so hard to drive these 572B tubes in the HA-14?.
Is it because the grids are not solidly grounded?.
What about filament choke,
80w in and I get 400w Out. this means TX gain is far less than 6dB.

I've reset the input networks, pSU is new, 2.4Kv on the plates.
New Svetlana tubes, they are supposedly high Mu.

Or is this to be expected with the GG configuration or this amp?.

Kind Regards,
William
ZS4L / ZS5WC
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KA4WJA
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Posts: 1098




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« Reply #1 on: July 17, 2019, 08:30:38 AM »

William,
Actually you're seeing 7db of gain...
80w in, 400w out, is 7db....
But, no matter....that still isn't great.

???Why is it so hard to drive these 572B tubes in the HA-14?.
Is it because the grids are not solidly grounded?.
What about filament choke,
80w in and I get 400w Out. this means TX gain is far less than 6dB.

I've reset the input networks, pSU is new, 2.4Kv on the plates.
New Svetlana tubes, they are supposedly high Mu.

Or is this to be expected with the GG configuration or this amp?.

Kind Regards,
William
ZS4L / ZS5WC

The only HA-14 I ever saw in operation (a few decades ago) was driven with a Tempo-One....and with about 100watts (?) drive, outputted about 500 watts....(the same 7db you're seeing).
And, I thought there was a problem....but the guy using it said "it worked well enough"....so, never looked at it...
But, I suspected it was just the power supply wasn't up to the job....as I recall it just couldn't supply the current needed....(I think the HV sagged quite a bit....1800v - 2000v....when trying to make power at voice peaks)
Although, this was a good thing, 'cuz it didn't have a cooling fan (except for a muffin fan the guy sat on top of the cabinet)

I suspect with a good power supply you might get a decent 600 watts out PEP (on SSB) with 100w drive??
But the darn thing will be hot! 


Hope this helps.

73,
John, KA4WJA
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KM1H
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Posts: 5087




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« Reply #2 on: July 17, 2019, 09:22:30 AM »

What band(s)?

What antennas?

That amp had a very limited matching range since there is no Variable Load Capacitor.

An external tuner may help or it can be modified to work with the owners specific antenna.

Carl
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AF6LJ
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Posts: 580




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« Reply #3 on: July 18, 2019, 07:03:48 AM »

And as I remember there is no input circuit in the amp, don't know what the OP is driving the amp with but solid state radios won't like that amp's input circuit. ...
Or the lack thereof.
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Take Care
Sue,
AF6LJ

Don't Kalifornicate My Life
W1BR
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Posts: 4179




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« Reply #4 on: July 18, 2019, 07:42:38 AM »

There is an input matching network on the HA-14, very similar to the SB-200 except for the fixed loading on each band.

I ran one back in the late 1960s.  Even pushed running RTTY with a Collins 32S1 driving it to about 500 watts out!  Didn't know better, but the darn amp never failed!  Had a homebrew supply using a SB-200 power transformer.
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ZS5WC
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« Reply #5 on: July 21, 2019, 12:12:05 PM »

 Grin
Hi John, you are right of course-and interesting story.
Re. no variable load cap-there are padder caps but I doubt if the match is good right accross the HF bands.
All my antennas are balanced 50ohms, so no problem there.

The -170V dc on the keying line caught me by surprise!, as someone in their wisdom had linked the ALC and PTT lines internally.
Wonder why people do these things-..-170v on the ALC rca plug will be detrimental to any modern solid state rig!.
Anyhow, all working just was wondering about the drive levels.

How these "mobile"  amps survived beneath a dash , normally mounted above another rig , and had no cooling fans, really is beyond me.

73 de William. ZS4L / ZS5WC

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KM1H
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« Reply #6 on: July 21, 2019, 03:17:57 PM »

Grin
How these "mobile"  amps survived beneath a dash , normally mounted above another rig , and had no cooling fans, really is beyond me.

73 de William. ZS4L / ZS5WC

Lots of room under the dash in those US land barges of the 60-80's Or remote in the trunk, tune once into the rear mounted antenna and go. Those were not QSY amps. Some serious size wire for the mobile PS primary or run the HV back and live dangerously Roll Eyes

Carl
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