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Author Topic: Power ratings on 1960s transceivers  (Read 17655 times)
W8JI
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« Reply #15 on: September 02, 2011, 05:59:22 PM »

The 30L1 is also notoriously unstable. It is one of the few 4x 811 style tube amplifiers without neutralization. The only other commercial 4 x 811 amp I'm aware of that did not neutralize was a Dentron.
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AC5UP
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« Reply #16 on: September 02, 2011, 06:34:02 PM »

Since this thread is hopelessly adrift...

The comments regarding WW II intelligence in the UK reminds me of an interesting conversation I had with an uncle many years ago. He was in the Army quartermaster's corps and stationed in England prior to D-Day. Said he had never seen so much stuff in one place and will never see anything like that again. It was that far over the top. Seems that Unca' Sam routinely double and triple shipped orders as Liberty ships didn't always make it to port and the invasion of an occupied continent is a very big deal requiring a buttload of stuff.

We're not talking about jeeps and guns exclusively. We're talking about everything that goes along with everything else from shoelaces to spare cotter pins to bulldozer mufflers.

The interesting part (to me) was that not everything made it to where it was supposed to go. The Brits had been on severe rations for several years and certain items like spark plugs and radio tubes tended to grow feet and walk away in the dark of night with great regularity. And of all the stuff that disappeared the weirdest thing of all, as far as my uncle was concerned, was the British obsession with gasoline powered lawn mowers. Even more peculiar was how the locals pinched them with total disregard for the Catch 22 nature of the crime... Boost a lawnmower and then what? You can't mow with it anywhere off the Army base because it's obvious what it is, where it came from, and the probable sequence of events that put it in your hands.

D'oh!

Didn't matter. The British take great pride in their gardens and nothing spiffs up a lawn like a proper mowing with a sharp blade.
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N2EY
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« Reply #17 on: September 02, 2011, 06:40:34 PM »

The 30L1 is also notoriously unstable. It is one of the few 4x 811 style tube amplifiers without neutralization. The only other commercial 4 x 811 amp I'm aware of that did not neutralize was a Dentron.

I always wondered about that. It's not as if adding neutralization to a 4x 811A amp is all that complex.

There's an article in QST for June, 1961 that shows a 4x811A GG amp with neutralization, so it wasn't a big secret at the time. The author says the amp was stable on all bands except 10 meters before neutralization was added.

73 de Jim, N2EY

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G3RZP
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« Reply #18 on: September 03, 2011, 02:03:32 AM »

I am slowly rebuilding a 'bargain' 30L1. There were 3 Chinese 811s in it and the plates were horizontal for the filaments to sag into the grid, and one Russian 811 with the plate at 45 degrees! Several of the feedthroughs were broken, the power transformer had been rewound since it no longer had dual primary, only a 230 volt one, the 25k equalising resistors just flap about on wires, and the usual problem, at least on 230 volt 50 Hz, is the power switch had destroyed one of its contacts. And several of the electrolytics have seen better days, judging by the encrustation around the leads.

The rebuild has 4 572Bs, with the grids hard wired to ground, and a neutralising winding of Teflon insulated wire over the filament choke. I've planned the neutralising cap which will be coaxial cylinders with Teflon insulation. There's a hefty 22 ohm HV glitch resistor. The original plate choke is 44 microhenries, so that has about an amp of RF in it on 80: I've a 1 mH choke out of a TU5B (Tuning unit for the BC191) in series, and for the rectifier for metering, I've made a fully shielded (piece of 15mm copper tube) arrangement with a 300pf feedthrough cap for the input: there's a 4pf cap made from 5mm copper tube and Teflon insulated wire from the pi tank input. Plus step start on the AC input and a relay to actually switch the power. Bias in the filament centre tap, as is the send - receive arrangement.

I'd never have bought the thing had I been able to see what it was like inside...
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G3RZP
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« Reply #19 on: September 03, 2011, 02:10:57 AM »

Talking of things walking from Army stores in WW2.

The late GC3KAV was on Guernsey during the war: his wife and son got away on the last boat, but as the only plumber on the island, he stayed to fix a problem at the hospital. He was jailed for having a radio, but let out to do a plumbing job, and went back to jail with all the bits for a crystal set in his pockets. He and the jailer laid an antenna in the sewer, and thus the BBC news was distributed...Later, he stole a German Staff car by building a haystack over it when one unit moved out and before another moved in, and in the end he had a stock of over 10,000 gallons of stolen petrol in an underground tank intended originally as a septic tank. He also had a good collection of German WW2 radios that he 'liberated'.
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W8JI
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« Reply #20 on: September 03, 2011, 03:23:34 AM »

The 30L1 is also notoriously unstable. It is one of the few 4x 811 style tube amplifiers without neutralization. The only other commercial 4 x 811 amp I'm aware of that did not neutralize was a Dentron.

I always wondered about that. It's not as if adding neutralization to a 4x 811A amp is all that complex.

There's an article in QST for June, 1961 that shows a 4x811A GG amp with neutralization, so it wasn't a big secret at the time. The author says the amp was stable on all bands except 10 meters before neutralization was added.

73 de Jim, N2EY



No matter how well the amp is laid out and built with four tubes, it is impossible to get unconditional 10 meter stability and sometimes 15 meter stability without neutralizing. That's why Collins came up with that silly 20 foot coax and phase of reflections nonsense. The long cable in effects adds an attenuator on the amp input.

All that NFB stuff does is make the problem or repeatability worse. Feedback capacitors across a couple stages that are tuned will not have consistent phase shift.  The stable way to do NFB when user adjustable tuned circuits are present is lifting the cathode through a resistance.

73 Tom
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G3RZP
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« Reply #21 on: September 03, 2011, 05:58:58 AM »

You can do feedback over two or three tuned stages if you are very careful and use phase detectors and servo loops to do the tuning, with some presetting from some form of memory. You also have to do a lot of Bode or Nyquist plots. Even so, there were various transmitters in the late 50's and early 60's of this sort using tetrodes where they had resistors in the filament circuit for feedback as well.

As Tom says, doing it by hand is recipe for disaster.
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N2EY
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« Reply #22 on: September 03, 2011, 08:05:34 AM »

Tom and Peter,

Great stuff on the 30L-1. I've always wondered what really went on with that design.

It's not as if Collins was aiming for the lowest possible price, or had to avoid patent infringement. They even had the Heathkit HA-10 Warrior amp as a guide (it's neutralized, btw). Maybe Collins had a warehouse full of 811As?

Heathkit saw the light in the SB-200, which replaced the Warrior after only a few years.

I can think of only three explanations:

1) By the early 1960s, Collins had spent a lot of time and $$ on ham gear development and took a break from it. Consider how many amateur products Collins introduced between, say, 1952 and 1962.   

2) Tied into 1) above is the relatively short time many Collins products of those days were on the market. For example the KWM-1 came out in 1957, and in just 2 years was replaced by the KWM-2. I bet more than a few KWM-1 buyers weren't all that thrilled, particularly when they saw the resale value of their KWM-1s drop. Same for those who bought a KWS-1. (Note that once Collins had the 75S-3/32S-3/30L-1/KWM-2 line done, there was no new HF ham gear from them until the KWM-380)

3) The T-160L/572B was brand-new in the early 1960s and for several years only made by one manufacturer. 811A was a common, well known bottle made by many companies. Even though the cost of a pair of 572s could be less (when you count the savings in sockets, plate caps, small parts, etc.),  cost was not as much of a major factor to Collins.

Thoughts? Guesses? Stories?

73 de Jim, N2EY

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G3RZP
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« Reply #23 on: September 03, 2011, 09:01:27 AM »

I'm sure that somewhere, I saw a reference to the 572B in the mid 1950s, but of course, I can't find the reference. I find it hard to believe that it was originally designed for HF SSB service though. By 1960, better structures were well known - a pressed glass base like a 7094 would have given a far shorter grid lead. Even if you kept a UX4 type base, you could significantly shorten the grid lead with a pressed glass base. If you went to a 7 pin septar like the 832, you could have multiple grid leads, and reduce the propensity to parasitics. As Class B audio modulator for a 500 watt BC rig, I can see it, but for RF, it is a bit of a compromise.

My previous experience with them gave me troubles in stopping parasitics: we will see if this time, it's any better. No Tom, no nichrome!! Or any other snake oil charm....

I was told on a visit to Collins some years back on business that 30LI was originally an amp built by a Collins ham at home, and Art was so impressed he had it put into production. That jibes with what Dave, WA0ZZG heard. Haven't been to Cedar Rapids for years but I can still remember the smell from the corn processing plant!
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W8JI
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« Reply #24 on: September 03, 2011, 09:26:41 AM »

I always wondered about that. It's not as if adding neutralization to a 4x 811A amp is all that complex.

There's an article in QST for June, 1961 that shows a 4x811A GG amp with neutralization, so it wasn't a big secret at the time. The author says the amp was stable on all bands except 10 meters before neutralization was added.

Collins had stabilitly isses in the 30L1 and several of the later transmitters because they hung their hats on that silly negative feedback system. That issue was the root source of the Collins part of a big white paper on how 6146B's were poorly engineered by RCA. KWM2's for example would break into oscillation and blow up the little RF feedback trimmer in that silly circuit.

RCA never planned of people misusing feedback and having stages running right on the edge of stability.

I suspect Collins thought floating the 811A grid on the small mica caps was a reliable cure for not neutralizing the 811's. On a bench, I am sure there are cases where it could work.

73 Tom
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G3RZP
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« Reply #25 on: September 03, 2011, 12:28:31 PM »

Tom,

Wasn't that a W6SAI (or similar call) idea to get 'pseudo super cathode driven' operation?

I can see it being useful for a fixed frequency amp at a frequency where the caps series resonate the grid inductance. Not otherwise - or am I missing something?
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W8JI
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« Reply #26 on: September 03, 2011, 03:00:22 PM »

Tom,

Wasn't that a W6SAI (or similar call) idea to get 'pseudo super cathode driven' operation?

I can see it being useful for a fixed frequency amp at a frequency where the caps series resonate the grid inductance. Not otherwise - or am I missing something?

I think Orr lifted the idea from Collins. Unfortunately it was a bad idea no matter where it started.
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G3RZP
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« Reply #27 on: September 03, 2011, 11:01:20 PM »

The RCA Transmitting Tubes handbook has four 811 amp in it with 220pF capacitors from grid to ground BUT it does have neutralisation. But I do think they are too small.
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W8JI
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« Reply #28 on: September 04, 2011, 02:58:54 PM »

The RCA Transmitting Tubes handbook has four 811 amp in it with 220pF capacitors from grid to ground BUT it does have neutralisation. But I do think they are too small.

They are too small for 160 and 80 meters, that's for sure!
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N2EY
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« Reply #29 on: September 04, 2011, 03:20:06 PM »

The RCA Transmitting Tubes handbook has four 811 amp in it with 220pF capacitors from grid to ground BUT it does have neutralisation. But I do think they are too small.

I found that scnematic in TT-5, dated 1962. It is schematic 5-13. It does not appear in TT-4. The amp is for 80-10, so the caps may be adequate.

As far as I can tell, it is simply a copy of the K6SNO amp from QST for June, 1961. (Also appears in "Single Sideband for the Radio Amateur", 4th edition, 1965. And possibly elsewhere.)

But in both the ARRL publications and the Transmitting Tube book, the grid bypasses are 0.01 uf disks., and there is one for each grid. It looks to me as if the reason the grids aren't directly grounded to chassis is for grid metering and the application of cutoff bias through an external connection. Of course it is possible to perform both of those functions with directly-grounded grids (by not grounding the negative HV*) but K6SNO didn't do it that way for some reason. (Perhaps it didn't occur to him, and with .01 uF from each grid to ground they were pretty close to RF ground anyway.

* Methods of measuring grid and plate current in amplifiers with directly-grounded grids appeared in amateur designs of 1962 and probably earlier.

btw, the 4th edition of "Single Sideband for the Radio Amateur" makes no mention of the T-160L/572B, either in projects nor tube data. But the 1964 and later editions of the ARRL Handbook show data on the tube.

73 de Jim, N2EY
« Last Edit: September 04, 2011, 03:22:01 PM by N2EY » Logged
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