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Author Topic: Power ratings on 1960s transceivers  (Read 17587 times)
W9KDX
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« on: September 01, 2011, 06:07:04 AM »

I was looking through some of my old electronics catalogs from the 1960s and I noticed that virtually all of the transceivers, (Drake, Swan, Hallicrafters, Hammarlund) had a minimum of 250 watts PEP on SSB transmitting power.  Most had 400-500 watts.  It seems that today the standard is 100 watts and I was just curious as to whether the rating system changed like it did for stereo equipment, or if there was some other reason that today's equipment was lower powered.

Thanks guys.
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Sam
W9KDX
AC5UP
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« Reply #1 on: September 01, 2011, 07:15:07 AM »

Older tube gear was typically rated by DC WATTS INPUT to the finals since watt meters were relatively rare back in the day but almost every Ham had a VOM. If a pair of 6146's ran 600 volts on the plates and pulled a quarter amp key-down CW that would be 600 x .25 = 150 watts at DC.

Efficiencies varied depending on the tubes used and the band, but the rule of thumb was RF Out = 50% of DC In. In the example above our "150 watt" transmitter would be good for approximately 75 watts into the coax on 40 and 20 Meters. As recently as the mid 70's it was not unusual for a three tube hybrid rig to output 110 watts on 80 Meters and 80 watts on 10 Meters as HF tubes tend to run out of steam toward the upper bands. The advertising was all ballpark numbers, but a good Ham knew the other side of the circuit won't hear the difference between 100 watts and 85 watts.

If you made the Q you were running enough power......  Wink
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G3RZP
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« Reply #2 on: September 01, 2011, 07:50:27 AM »

Not only was it input power (Hallicrafters had a lot of 144 watts plate input SSB rigs), but the higher power ones were using (abusing?) sweep tubes.

Also 100 watts out still allows a reasonable size heatsink.
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N2EY
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« Reply #3 on: September 01, 2011, 08:33:11 AM »

Everything AC5UP wrote is true. Here's a bit more:

RCA released the 6146 in the early 1950s. Its design was partially based on comments from hams and ARRL about what the ideal amateur transmitting tube would be, and the shortcomings of existing transmitting tubes such as the 807.

The 6146 was very popular from the start, for a whole bunch of reasons, and pretty soon most manufactured and ham rigs beyond the economy class ran either one or two 6146s in the final. The EFJ Valiant ran three, modulated by another pair. A pair of 6146s could provide 100 watts of plate-modulated AM RF output without strain, and a bit more on CW. They could do SSB just as well.

In 1959-1960 Collins released the KWM-2. While it was not the first amateur HF SSB transceiver, nor the first to cover all 5 HF bands of the time, it became very popular despite its over-$1000 price. About the same time, Collins released the 32S-1 and 75S-1 matched-pair transmitter-receiver set, which cost even more yet were also very popular.

The KWM-2 and 32S-1 both ran a pair of 6146s in the final, with 800 volts on the plates. 180 watts PEP input, about 100 watts output (depending on band).

The KWM-2 and 32S-1/75S-1 became the gold standard for ham gear well into the 1970s. Competing manufacturers looked to those rigs as the ones to match or beat. They used the basic Collins paradigms, but had to figure out ways to compete.

The most obvious way to compete was to offer lower-priced rigs, which almost all did. The usual method was to offer fewer bands and/or less-costly circuitry and parts. The Collins PTO, mechanical filters, 200-kHz-segment heterodyne scheme and 6146 finals were all subject to cost-cutting scrutiny. Heathkit and a few others went the kit route, too.

In that same era hams began to use grounded-grid linear amplifiers for high power SSB and CW. The venerable 811A,  new tubes specifically designed for "zero-bias Class B" service such as the T-160L/572B and 3-500Z, plus the newly-introduced high voltage silicon rectifiers, made such amplifiers smaller, simpler and less expensive than anything hams had seen before. In particular they made high-power 'phone within the reach of many hams who could only dream of it before.

Such amplifiers had low gain compared to their predecessors; a typical GG amp like the Heath SB-200 required over 50 watts of RF drive. A "100 watt" transceiver or transmitter was a perfect match - buy the rig first, then add the amp when the budget had recovered. Nothing wasted along the way.

(Ironically, Collins never made a matching amplifier using the T-160L/572B or 3-500Z).

All these factors were the prime reasons so many hams went to SSB in the 1960s and left AM behind. They were also part of the reason many hams stopped homebrewing (but google "LWM-3" for an example of what some hams did).

Some rigmakers tried to compete by offering rigs with higher power ratings at a competitive price. This would reduce/eliminate the need for a linear amplifier. Such rigs used tubes designed for color TV sets in their finals - up to four of them in parallel. Because the TV "sweep tubes" were produced in much greater quantities, their price was lower, so the overall cost was less than a pair of 6146s. Unfortunately, such tubes became hard to find when tube-type TVs began to disappear.

When the change to solid-state came to amateur radio in the 1970s, the first step was the "hybrid" rigs such as the TS-520, with solid-state low-level and tubes for the final and driver, because the cost of a solid-state final was still too high. When the hybrids achieved acceptance and the cost of a solid-state final became low enough, the natural standard was a power level that matched the classic "pair of 6146s" .

And it still is.

73 de Jim, N2EY

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AD4U
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« Reply #4 on: September 01, 2011, 09:56:09 AM »

Since I love boat anchor radios and have a room full of them, I will chime in.

All boat anchor radios were rated for power input, as already posted.  Power output was usually around 50% of power input.

Many rigs of that era used a pair of 6146 tubes - Collins S line and Heathkit SB and HW rigs to name a few.  These rigs were rated for 180 watts input and around 100 watts output.  Others like Drake and some of the National rigs used sweep tubes (6JB6), but the power rating was generally about 200 watts input and 100 watts output.  100 watts was the power needed to drive the linear amps of the era.

Then there was Swan, Galaxy, Yaesu, and some of the National rigs (and others).  They used (abused) color TV sweep tubes and were rated at 500-700 watts input.  These rigs were aimed at the hams who wanted a strong signal without having to buy an amp.  Two sweep tubes could be had for less than $10 and at that price it did not matter if they had to be replaced every 6 months or so.

I have a Swan 700CX (2-8950 tubes) that will put out 400++ watts PEP on SSB.  My Galaxy GT-550A (2-6LB6 tubes) and my Yaesu FTDX-570 (2-6KD6 tubes) will put out 300+ watts PEP.  

Hallicrafters even sold a transceiver (SR-2000 Hurricane??) that was rated at 2000 watts.

These rigs were not real fussy about having a 1:1 SWR and they did not seem to care if you used a balun or not and you generally did not need a "tuner".  I use these rigs regularly and get good reports.

Dick AD4U
« Last Edit: September 01, 2011, 06:07:06 PM by AD4U » Logged
G3RZP
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« Reply #5 on: September 01, 2011, 11:08:01 AM »

Slight thread drift here...

What was the 572B/T-160L designed for? I cannot believe it was for grounded grid RF, becasue of when it appeared - 1953 or so is it first appearance in a ARRL handbook, and then it's Class B audio ratings. My suspicion is that it was originally intended for modulating a 500 Watt output AM BC station. Back in those days, not many amateurs were using 'slop bucket' as it was termed, so there was no demand for GG amplifiers. Some years later were the days for really extravagant claims for SSB - for example, it gave 20dB advantage over AM, so a 10 watt SSB station was as effective as kilowatt of AM!
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N2EY
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« Reply #6 on: September 01, 2011, 12:38:14 PM »

What was the 572B/T-160L designed for? I cannot believe it was for grounded grid RF, becasue of when it appeared - 1953 or so is it first appearance in a ARRL handbook, and then it's Class B audio ratings. My suspicion is that it was originally intended for modulating a 500 Watt output AM BC station. Back in those days, not many amateurs were using 'slop bucket' as it was termed, so there was no demand for GG amplifiers. Some years later were the days for really extravagant claims for SSB - for example, it gave 20dB advantage over AM, so a 10 watt SSB station was as effective as kilowatt of AM!

I didn't know the 572B/T-160L went back that far! All the references I see are to the very late 1950s and early 1960s, but will check my Handbooks.

It is quite possible that it was designed originally for Class B modulator use. There were a number of triodes designed for "zero bias class B" (actually AB2 because the plate current is not zero at no-signal). The TZ-40 and 811 are two examples. Such tubes greatly simplify the modulator because there is no bias supply and no screen supply. They do require a few watts of audio drive, and in some cases require neutralization (!)

A few hams were using SSB in the 1930s, but the cost and complexity precluded widespread amateur use until after WW2. The development of practical audio phase shift networks and crystal lattice filters made amateur SSB relatively easy by the late 1940s, but relatively few hams went for SSB back then because:

1) It required equipment that was more complex than AM, and required a higher degree of stability.

2) Most existing rigs could not be made to work on SSB without considerable modification.

3) Most existing receivers, when adusted for SSB, lost the AVC and S-meter functions. Few had suitable selectivity settings.

4) "Zero beating" for net or round-table operation required real skill.

The development of the SSB transceiver and matched-pair transmitter-receiver changed all that. An SSB transceiver was actually easier to use than AM "separates" - and could cost less. The development of the table-top GG amplifier drove the final nail.

In AM days, running high power meant Big Iron and a serious amount of space, power and money. AFAIK, there were only two transmitters ever made for the amateur market that could run the USA legal limit of 1000 watts DC input, plate modulated. They were the WEFJ Desk Kilowatt ($1700 in the late 1950s, without exciter!) and the Collins KW-1 (if you have to ask the price, you can't afford it). A homebrew AM KW took up at least a 6 foot rack, and twice that space was not unusual. Power requirement was measured in kW, weight in hundreds of pounds, and everything had to be rated for continuous duty. Such stations were common in the late 1950s.

Jump ahead just 5 years, and a ham could have an SSB transceiver and 1200 watt amp on a card table (SB-100/200 combo). And the SSB station often cost less.

btw, the actual advantage of SSB over AM is about 14 dB. This is due partly to the elimination of the carrier, partly to using all the power in one sideband, and partly to the ability to use a narrower receiver.

73 de Jim, N2EY
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G3RZP
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« Reply #7 on: September 01, 2011, 01:23:27 PM »

Jim,

the advantage assumes a receiver improvement that is equally achievable on AM. If you take that away, then 6 dB is the advantage.

The cheapest high power AM must undoubtedly have been a surplus BC610 at about 400/500 watts DC input. Otherwise, as you say, heavy iron. But even 1 kW CW input was not a simple job. I remember in the early '60s, W1JFG was there first thing every morning (EST) on 20m AM. I seem to remember he had a Johnson....

And in those days, hams had at least a knowledge of Ohm's law, which doesn't seem to be the case now...

And I am not getting only at US hams - it seems to be world wide.
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N2EY
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« Reply #8 on: September 01, 2011, 01:30:54 PM »

Peter,

No argument from me on any of that.

Yes the '610 was surely a way to a couple of hundred watts of AM, but you had to do some work to get the rig behaving decently. The Globe King and Viking Five Hundred were other options - not cheap, but they did the job. And of course homebrewing in all its glory.

73 de Jim, N2EY
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G3RZP
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« Reply #9 on: September 01, 2011, 02:35:42 PM »

Jim,

the provenence of the BC610 is the somewhat amusing thing. It was a ham rig - the Hallicrafters HT4.

So was the HRO as a military piece of kit, and several Hammarlund receivers.

One wonders, without the US ham radio industry and American amateur radio operators in the services, how long it would have taken to win WW2.

The strange thing is that although the British at an early stage recruited amateurs to act as a an intercept service, the US never did the same.  Here, we had  people over age for call up, people with disability, still able to do intercept work at home - and very valuable it turned out.

Sorry, thread drift.
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N2EY
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« Reply #10 on: September 01, 2011, 03:13:24 PM »

the provenence of the BC610 is the somewhat amusing thing. It was a ham rig - the Hallicrafters HT4.

So was the HRO as a military piece of kit, and several Hammarlund receivers.

Yes, and several other pieces of ham gear went to war. IIRC, the Hallicrafters S-36 was used for a time in Great Britain to listen for enemy radars - it was the best available receiver for the frequency range.

The HT-4 -> BC-610 story is a bit more than simply rebadging, though. The original HT-4 needed lots of reengineering to meet the vibration, shock and humidity specs of the HT-4. In one early road test, the plates of the final amp variable cap were found on the bottom of the cabinet - it had shaken to bits!

The HT-4 also used some rather odd tubes, and had to be redesigned to use tubes on the JAN VT list of approved types. Interesting how many types on that list were made by General Sarnoff's RCA, and how few by other companies....

One wonders, without the US ham radio industry and American amateur radio operators in the services, how long it would have taken to win WW2.

Yes, they served in many roles. Recently I saw a documentary about the proximity fuze in which one of the administrators said that he would intentionally pair up hams with theoretical physicist types in the research teams. The theory folks knew the formulas and laws while the hams would push for practical solutions.

The strange thing is that although the British at an early stage recruited amateurs to act as a an intercept service, the US never did the same.  Here, we had  people over age for call up, people with disability, still able to do intercept work at home - and very valuable it turned out.

Never realized that, but quite true. I don't know if amateur intercepts fed Bletchley Park, but anything intercepted could have a potential use.

Of course being on this side of the pond, and more than 2 years behind in getting into the fray, some things got missed. the US role was somewhat different. I suspect the US brass considered intercept not so important here, except perhaps for U-boat comms. Or maybe they were afraid of leaks.

OTOH US hams not in uniform played roles in industry, research, WERS (a form of civil defense), radio instruction, and other ways. One particular unofficial service was figuring out ways to keep BC receivers working with available parts and tubes.

Even the ARRL Handbook went to war, in a special "Defense Edition" used for training.

btw, after WW2 it was discovered that the Germans had made copies of the HRO for their own use. I think the Japanese did too. High praise, in a way, and a foreshadowing of things to come.

To get back to the subject, WW2 military BA designs are sometimes considered rather odd by hams, particularly in power level. For example, the popular AN/ART-13 uses an 813 modulated by a pair of 811s. Most hams would consider that combo good for 450-500 watts input, yet the AN/ART-13 runs them at less than half that power. Of course this was done because the set might have to work under very trying circumstances (cold, heat, humidity, altitude, improper tuning, failed antenna) without failing, and without operator attention.

73 de Jim, N2EY

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G3RZP
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« Reply #11 on: September 02, 2011, 03:17:05 AM »

Jim,

Intercepts were posted to P.O.Box 23, Barnet, from where they went to Wandsworth prison (!) where a special unit sorted them: a lot went on to Bletchley after that. The listeners were issued with receivers and headphones: the HRO my father had was fitted with a vernier scale for more accurate logging. That never went back with the HRO after the war - it's on my HRO today. The headphones didn't go back, either.

The RSGB took delivery of 3000 copies of their 'Amateur Radio Handbook' the day before war was declared. They worried about selling them - but they needn't have done. By the war's end, they had printed and sold 181,500! Because of its use in training the military, the paper controller specially released paper for it.

Strange that after the war, there was a lot of surplus gear around , but at least in the first few years, it wasn't cheap - a BC348 would cost two week's pay for the average ham.

BC610 - Have you seen  http://www.archive.org/details/VoiceofV1944  and 
http://www.archive.org/details/VoiceofV1944_2
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WA0ZZG
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« Reply #12 on: September 02, 2011, 06:07:17 AM »

Those of you that like the old Collins gear will like this.  A couple of year ago, I ended up sitting with an old gentleman that was the designer of the KWM-2 PA cage and had a chance to chat with him.  He was personally hired by Art Collins because he showed up in the factory parking lot with a 5-band home made SSB transciever running in his car. He was using a pair of 6146's for finals. Nobody had done this before.   His first job was to make a pair of 6146's very linear.  These tubes were actually designed for VHF-FM radios and class C service.  They were not the most linear.  He ended up beating his brains out, until he came up with the concept of RF negative feedback.  That cleaned them up.
He is now in his 90's.  This was his first job as a young man. He was self trained and still lives in Cedar Rapids.
By the way......
The Collins 30L-1 was designed by a Collins Ham in his basement.  811A's are actually modulator tubes in 1KW AM broadcast transmitters, but were used because they could be put on their side and the case made the same size as a KWM-2.  They could also meet Art Collins demand for extreme linearity.

Dave  WA0ZZG
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G3RZP
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« Reply #13 on: September 02, 2011, 07:13:39 AM »

Collins were using negative RF feedback in the early 1950's - Bruene wrote it up in both Electronics and the IRE journal some years later.
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N2EY
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« Reply #14 on: September 02, 2011, 04:56:20 PM »

Fascinating stuff! Thanks for the link to the BC-610 video.

Some historic bits:

- The Collins KWM-2 (1959) was preceded by the KWM-1 (1957). The KWM-1 only covered 14 to 30 MHz, and required a heterodyne crystal for each 100 kHz segment (!) Both rigs used a pair of 6146s in the final.

- The Hallicrafters HT-32 SSB transmitter (1957) also used a pair of 6146s in the final.

- The first manufactured all-HF-band SSB transceiver was the Cosmophone 35. It had many advanced features and predated the KWM-2 by some time. However it was only produced in small numbers for a short time. It used a single 6146 in the final.

- The Collins 30L-1 appeared in 1961.

- I am not sure when the T-160L/572B tube appeared. My 1957 ARRL Handbook does not list it but my 1964 edition does. Since it was not an RCA tube my RCA Transmitting Tube manuals are no help.

- The best clue to the origin of the 572 that I could find is an article in QST for May, 1961. It shows an amp using a pair of United Electronics UE572 tubes, and says the tube is a new type. If so, it explains why Collins didn't use them; the 30L-1 design was probably already frozen before the '572 appeared.

- Like the 811-A, the T-160L/572B can be horizontally mounted (the SB-200/201 did so). Why Collins stuck with 811As is a mystery; perhaps they figured it wasn't worth redesign and retooling.

73 de Jim, N2EY
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