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 Post subject: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sat 18, 2012 5:46 pm 
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I recently acquired a circa 1962 Hallicrafters HT-41 linear amplifier.

http://hug-a-bug.com/HT-41.html

According to that site, the amp puts out up to 1200 watts on the SSB.

My question is, if I want to measure or test this output, how would I do that? I am new to the world of ham radio (just beginning to study for the exam) so please forgive any seeming ignorance, I assure you it's not just "seeming"!

Is there something similar to this Bird 694 termaline? This one only tests up to 1000 watts:
http://www.ebay.com/itm/Bird-DA-173-GRM ... 45f69722a7

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sat 18, 2012 5:57 pm 
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Location: Santa Rosa, CA
1. Wait until you get a ham license that would allow you to transmit legally.

2. You will need a ham transmitter capable of 50 to 100 watts to drive this amplifier.

3. Bird makes watt meters that will go above 1 KW, but you will also need a dummy load, like the old Heathkit Cantenna. I think MFJ has a dummy load for amplifier testing.

4. Any ARRL Handbook from the 1960s thru about 1990 should have plenty of info testing a high powered amplifier.

Rich


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sat 18, 2012 6:40 pm 
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No offense intended, but you should probably set this unit aside for the time being. A 1200 watt (input power) linear is not the place to start experimenting: high voltage shocks, RF burns, illegal transmissions, blown tubes, are all possible side effects. Get a tech ticket and comfortable with VHF/UHF ops. Then get a general ticket, a 100 watt HF radio, and comfortable with that. Then you can start looking at a linear.

If, for some immediate reason, you must know the operating condition of your linear, seek the help of someone who already has the license, knowledge, experience, and equipment to do the job. Like any radio from 1961, there's some first steps that need to be taken before powering that thing up.

Have fun yes, but here you need some competent help.

Greg // KE7NJS


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sat 18, 2012 7:15 pm 
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Rich, W3HWJ wrote:
1. Wait until you get a ham license that would allow you to transmit legally.

2. You will need a ham transmitter capable of 50 to 100 watts to drive this amplifier.

3. Bird makes watt meters that will go above 1 KW, but you will also need a dummy load, like the old Heathkit Cantenna. I think MFJ has a dummy load for amplifier testing.

4. Any ARRL Handbook from the 1960s thru about 1990 should have plenty of info testing a high powered amplifier.

Rich


First of all, I'm not planning to transmit illegally. This unit is not connected to any kind of broadcasting antenna, and it will remain so until I have a license in hand. That is why I am interested in a dummy load so the unit can be tested without broadcasting.

I have a transmitter in the range you suggest.

Quote:
No offense intended, but you should probably set this unit aside for the time being. A 1200 watt (input power) linear is not the place to start experimenting: high voltage shocks, RF burns, illegal transmissions, blown tubes, are all possible side effects. Get a tech ticket and comfortable with VHF/UHF ops. Then get a general ticket, a 100 watt HF radio, and comfortable with that. Then you can start looking at a linear.

If, for some immediate reason, you must know the operating condition of your linear, seek the help of someone who already has the license, knowledge, experience, and equipment to do the job. Like any radio from 1961, there's some first steps that need to be taken before powering that thing up.

Have fun yes, but here you need some competent help.

Greg // KE7NJS


Sorry if I gave you the impression I was a cross between Homer Simpson and Al Bundy. I didn't mean to imply that I was an ignoramus, just that I don't have knowledge of how a unit in this watt range would be tested "in shop" as opposed to being connected to a live broadcasting antenna. I have a healthy respect for electricity and have been a home hobbyist doing my own electrical and electronic repairs for decades. My situation is one of lacking information on a specific topic, not a lack of judgment.

I was not planning to acquire the HT-41 at this stage of the game, but the perfect opportunity landed in my lap and I would have been a fool to refuse. I'm simply asking what sort of test gear I should be on the lookout for, so that if an opportunity arises I can act appropriately. I am in this game to learn, and my schedule doesn't lend itself readily to having someone stand over my shoulder and mother-hen me. If I'm going to repair my own transmitting equipment going forward, I need to acquire the tools necessary to do so, and the skill. Hence my post here, where generous help seems to abound. I fully intend to have those "tickets" in hand prior to attempting to use this unit "live". I'm just looking forward and wanting to get an idea of what kind of equipment will be needed, so I can keep an eye out in case a golden opportunity lands in my lap, as this one did.


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sat 18, 2012 8:24 pm 
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Last edited by Mikeinkcmo on Jan Fri 25, 2013 7:49 am, edited 1 time in total.

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sat 18, 2012 9:49 pm 
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It will NOT do 1200 watts output, PEP or otherwise! Those amps were rated for input power
under the old FCC rules. The RCA tubes are extremely hard to find and expensive. Many hams
have converted the HT-41 to 813 tubes for that reason. I'd expect typical power output
to be around 500 watts PEP or CW.

Pete k1zjh

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 2:45 am 
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Location: Albany, NY
The issue with the meters in *most* antenna tuners is that they are usually not very accurate. They're usually only good for checking for and reducing/eliminating your reflected power when tuning your antenna but other than that I wouldn't trust their accuracy for measuring forward or reverse power. It's better to stick with an external meter.

A Bird meter is a good start but even a Bird isn't lab accurate. A Bird is only as good as the slug in it and you need to make sure that you use a slug that is close to the maximum amount of power you're expecting to send through it. The error of measuring a transmitted 50 watts through a 100 watt rated slug is much less than the error incurred by measuring the same 50 watts through a 1000 watt rated slug.


Last edited by 928GTS on Aug Sun 19, 2012 3:15 pm, edited 1 time in total.

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 4:50 am 
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I'm looking for an HT-41 myself right now to complete my sx-111 & ht37 setup.

Like others have said you will need a tranmitter (not transceiver) dummy load and a meter of sorts.


Todd


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 3:00 pm 
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I other thing I forgot to mention. That amp does not have a tuned input. It dates from the tube era, where the exciter's tank circuit provided a flywheel effect for the full 360 degrees of the drive signal waveform. A solid state exciter will not like working into an untuned amplifier input--the input impedance is all over the map over the waveform cycle. If you are using a solid state rig with a built in antenna tuner, it may help provide a good match between the exciter and amp.

Also, that amp will require a transfer (DPDT) antenna relay when used with a transceiver.

I own a HT-41 that was gutted, and I am converting it a pair of 813 tubes in what is going to be a total redesign of the old HT-41 carcass. It is going to be mated with my Ht-32 and SX-101A.

Pete

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 3:12 pm 
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Pete,

Please keep us posted on how the 813 conversion goes. I recall reading of a couple of people who ran into instability issues with the 813 tubes in the HT-41. I don't think I still have an email about this sent to me several years ago but I will forward it to you if I still have it since it gave some details of the problem and cure.

I have a pair of HT-41 amps here, one has a repainted case and it supposedly works but I haven't tried it yet. I have a nice working HT-41 paired with my HT-37/SX-111 station. Besides the 7094 tube availability issue the HT-41 is a nice moderate power vintage amp but best used with tube type rigs. It is much lighter than the HT-33 (original with 4CX300A tubes) that I have paired with a HT-32B/SX-115 and it is also considerably lighter than the HT-31 I restored for a friend that is going into his SR-500 console.

Too bad the 7094 didn't catch on as it seems like a nice tube but the price/availability is an issue now if you aren't willing to substitute. There used to be a good relationship between RCA and the ARRL handbook editor and there was a transmitter using the 7094 in the Handbook shortly after the tube was introduced.

Rodger WQ9E


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 3:31 pm 
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Thewasp wrote:
Like others have said you will need a tranmitter (not transceiver) dummy load and a meter of sorts.

Why not a transceiver?

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 5:14 pm 
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Rodger

It is going to be a full conversion. I am not using any of the original parts except the power transformer and chassis. I even have a pair of vacuum relays for QSK CW. The plans are to include full WARC and 160 Meter coverage, and tuned input.


Here's my SB-220 after being reworking for full QSK and 160 meter coverage:

http://i117.photobucket.com/albums/o46/ ... CF1451.jpg

http://i117.photobucket.com/albums/o46/ ... CF1448.jpg

The SB-220 was a basket case. I rebuild it from the ground up, and included active bias control, 160 meter coverage, vacuum relay for QSK CW, and some of less than worthwhile Harbach upgrades. It is now working FB with the Omni VI in full QSK CW.--still on the original 3-500Z Eimacs. Added a new black front panel and also vernier tuning for the plate capacitor. It now covers all the WARC bands as well. As you can see, a lot of changes were made :)

Pete

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 5:24 pm 
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Very nice work Peter. I worked on quite a few SB220s and always believed that they were just a starting block for better things

Yes, I know you'd need a TR relay with that final but FOR TESTING, any 100W power source would work...

Best,

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Sun 19, 2012 10:23 pm 
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Since this amp does not have a tuned input, if you want to use it with a modern solid state transceiver you might get by with using an antenna tuner between the transceiver and the amp. A 100 watt unit should do. As far as a dummy load, look for the Heathkit Cantenna, they can sometimes be found for reasonable prices at swap meets or eBay. It does require a gallon of mineral or transformer oil for cooling.


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Mon 20, 2012 7:26 am 
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Unusualdesigner wrote:
Thewasp wrote:
Like others have said you will need a tranmitter (not transceiver) dummy load and a meter of sorts.

Why not a transceiver?



See Peters reply about the tuned input. Also I dont think a transceiver would hear anything as the HT-41 is one way. Maybe someone can verify this.


Todd


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Mon 20, 2012 2:42 pm 
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Thewasp wrote:
Unusualdesigner wrote:
Thewasp wrote:
Like others have said you will need a tranmitter (not transceiver) dummy load and a meter of sorts.

Why not a transceiver?



See Peters reply about the tuned input. Also I dont think a transceiver would hear anything as the HT-41 is one way. Maybe someone can verify this.


Todd


You can put it after a transmitter, but then it would always have to be run to get on the air. It couldn't be put in standby without a RF bypass relay on the RF input and output.

I've used DPDT coaxial relays to put similar amps in or out of line. They are expensive these days. There is no reason why the relay couldn't be keyed by the transciever to drop it out of line during receive.

All modern amps have built in antenna relays. Many use open frame relays with dielectric insulation that can handle the RF voltages.

I replaced the clunky mechanical relay in the SB-220 with vacuum relays for almost instaneous break in CW operation. One other issue is that modern transceivers aren't able to handle the voltage and current requirements required by some antenna relay coils.

Pete

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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Aug Mon 20, 2012 5:04 pm 
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Ive converted those to 4-125A's and 572B's which work better on 10-15M than 813's. It would also look nice converted to 6M next to the HA6 transverter. Modernize the PS and get some decent power.

The 7094 was RCA's attempt at modernizing the 813 but it failed miserably since they couldnt take any abuse.

Carl


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 Post subject: Re: Test Output of Hallicrafters HT-41 Linear Amp
PostPosted: Apr Mon 30, 2018 2:00 am 
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Location: hillsborough, nc
Anyone interested in one with new caps and 4-125As??
Wilson


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