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Collins 30L1 design questions

Discussion in 'Amateur Radio Amplifiers' started by K9AXN, Feb 16, 2018.

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  1. G3YRO

    G3YRO Ham Member QRZ Page

    Yes, as I stated earlier . . . If you look at the circuit diagrams, the FL2000B, the FL2100 and the FL2100B DO NOT take a neutralisation output from the pi-tank. (all 3 use this circuit below):


    Only the FL2100Z (of which very few were sold by comparison) does that - which is stupid, along with all the other stupid mods the Z version has, which makes it unreliable.

    I never mentioned the FL2100Z , for that reason.

    (do you not think that having been working for Yaesu in the UK as an Engineer when these Amps were current models, that I wouldn't know them inside out?!)

    Are you going to apologise now?

    Roger G3YRO
    Last edited: Feb 18, 2018
  2. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page


    One possible reason for the location of the 30S-1 exhaust is the fact that a goodly number of the amplifiers, when used by the military, was that they were installed in communications "shelters" along with a lot more equipment in a very small space. In those shelters, heat exhausts were located along the outer walls and having the 30S-1 exhaust on the back would facilitate getting the heat generated by the amplifier to the outside of the shelter instead of heating the inside.

    I cannot remember the military designation of the shelters being built at the Richardson, Texas, plant during my tenure with Collins Radio. One "popular" shelter model was installed on "duece and a half" trucks and those shelters were packed full of communications equipment. Other shelters could fit a pickup truck!

    When the 30L-1 amplifier was designed, the T-160-L / 572A, which morphed into the 572B, was, basically, new and the military was interested in proven reliability which those tubes did not have. The 811A, having been around for well over 20-years, was a "known" quantity and Art Collins got with RCA (the main manufacturer of the 811A at the time) to make sure that the design of the 30L-1 would not exceed the capabilities of the 811A.

    To be able to meet the military requirements, the 30L-1 is continuous coverage from 3.2 MHz to 30.0 MHz whereas the SB-200 does not have this ability. The 30L-1 has a more complex tuning system which is designed so that the amplifier can be properly tuned by personnel with very little training whereas the SB-200 does require more technical knowledge to keep from damaging the unit.

    Had the 30L-1 been designed 5-years later, there is certainly the possibility that it would have used the 572B tubes instead of the 811A tubes. Since getting decent, new, 811A tubes is now becoming harder and harder to accomplish, a fair number of amateur radio operators are now replacing those tubes with 572B tubes. Because of limitations of the power supply, the amplifier cannot run any more power. However, since the 572B tubes are being run at a considerably lower power level, the tube life is extended several times over that of the 811A tubes.

    I do not own a 30L-1. In fact, I have never owned a 30L-1! But, I have worked on a fair number of those amplifiers as well as quite a few SB-200 amplifiers. I do own an SB-200 right now and owned another one back in the late 1960s and early 1970s. By far, the SB-200 is easier to work on since it does not have as good shielding as the 30L-1. The SB-200 is definitely a "workhorse"!

    Some day, I would like to obtain a 30L-1 amplifier to pair with my 32S-1 / 75S-1 combination just to "complete" the station. Right now, I have those units, plus several other units, paired with my SB-200 (coaxial switch to the input and another switch for control purposes). My 32S-3 / 75S-3A are paired with my Henry / Tempo 2001 amplifier that runs about twice the power of the SB-200.

    Glen, K9STH
  3. G3YRO

    G3YRO Ham Member QRZ Page

    There are very few Heathkit SB200 amps here in Britain . . .

    But a LOT of Yaesu FL2100 amps - probably the most popular Linear Amp ever sold over here.

    And also a fair number of KW KW600 and KW1000 amps too. (the 600 just uses one 572B)

    The whole point of this discussion is that although it seems like "good practice" to directly ground the grids of "grounded grid" Linear Amps these days, it never was on these Amps built back in the 60s and 70s. Yet they still worked fine. (it's easy to criticise designs with hindsight)

    You could say the same about practices in the motor industry - hardly any production cars had fuel injection back in the 60s and 70s, nearly all had carburettors . . . but all modern ones have fuel injection, as it's more efficient.

    Roger G3YRO
    Last edited: Feb 18, 2018
    AC0OB likes this.
  4. W1BR

    W1BR Premium Subscriber QRZ Page

    And yet the Z version was a misguided attempt to fix stability and other issues in the earlier 2100 series...
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I guess you missed post #2 in this thread, when I answered your question: But at the time it was based on 80nH, because that's what your question was.
  6. G3YRO

    G3YRO Ham Member QRZ Page

    Well I was never aware of ANYONE having stability or any other issues with these Amplifiers . . . that was while I worked for Yaesu or ever since. (the only issues were if people tried using the Russian valves, which have very different characteristics to the Cetron 572Bs, and don't even look the same)

    And I certainly never had any issues with mine in the 40 years I used it !

    Roger G3YRO
    K9AXN likes this.
  7. K9AXN

    K9AXN Premium Subscriber QRZ Page

    If we concur that the Collins grid design will result in the grids being a direct short, (No reactance) to ground at approximately 34MH, and will be capacitive throughout the HF bands, and, that the directly grounded grids will be inductive and have close to the same reactance as the Collins design on the 10 and 15 Metre bands, we can go the next issue. The notion that the grids are floated with the Collins design and not floated with the directly grounded grids is an incorrect assumption. This is important because many believe the Collins design is responsible for some form of instability on the 10 and 15 Metre bands.


    Regards Jim
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I came to believe that, myself (the instability) since with every 30L-1 I've serviced, as soon as I used multiple very short and broad copper straps to ground the grid pins and biased the tubes via their cathodes rather than applying negative voltage to their grids, every trace of instability I ever encountered disappeared.

    However, none of this service was on "new" amplifiers; they were always 10-15-20 or more years old. Components, including mica capacitors, age and drift. I've also seen old 30L-1s with 47 Ohm resistors that drifted very high in value or in a few cases opened entirely; another potential issue completely eliminated by directly grounding the grids.

    How many 30L-1s have you serviced?
    W1BR likes this.
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That could be. I owned a 30S-1 for years and of course it was in the house; we also had two of them at the Army MARS station at Ft. Monmouth (ham call sign was K2USA) and they were in normal housing as well (beautiful paneled offices, actually), and of course pushed up against a wall. The discoloration of the paneling directly behind the air outlets was my first tipoff of a possible "problem," there -- that was many years before I ever owned one.

    I think this was a bit of a mistake, too. The 30L-1 doesn't meter grid current at all: Just Ip, Ep and the phase detector that drives the "zeroing" tune metering system. That does add complexity, and it does drift. Have you seen a 50 year-old 30L-1 where that still actually works?:) I'd much prefer a grid current meter, since precise tuning is easily accomplished just watching that: When the tank is tuned to resonance, there's a very pronounced grid current peak that's more obvious than a plate current dip, especially when the amp is fully loaded.

    I don't know about the spectrum coverage of the SB-200; however many modern amps (using tubes) today are very much "continuous coverage," if you simply re-peak the input tuning to accommodate the frequency of operation (that's required with the 30L-1, also). Some are specifically rated that way, like my old Henry 4K Ultra, which was "continuous tuning" from 3 through 30 MHz, no modifications required. That was built back in the early 1970s. It runs 1500W+ output with about 65W drive on any frequency in that spectrum.

  10. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page

    The fact that there are still so many 30L-1 amplifiers in use today, almost 60-years after they were introduced, does say something about the design. There are still quite a number in which the original tuning does work. All of those that I have worked on still have this feature working.

    As to why such a tuning feature was required by the military, you have to consider the average educational level of the "common soldier" during the early 1960s. Not that many even had a high school diploma. The concept was to make things understandable for those with no more than an 8th grade education. Therefore, the idea was that things, like tuning communications equipment, had to be like no more than setting a meter to a specific mark on the scale, turning a knob to a specific mark, and so forth.

    In the fall of 1967, someone in the Collins Radio management became familiar with a technique that told the educational level needed to "understand" written communications. This included the number of words in a sentence, the number of syllables in words, the placement of punctuation, and such. For example, most newspapers were written for a 6th grade education, most entertainment type magazines were written for an 8th grade education, technical magazines were written for a high school education, text books were written for whatever grade level that they were intended for use.

    This technique was applied to the Collins manuals written, primarily, for use by military technicians. It was "discovered" that, for the average Collins manual, several years post PhD education was required to really understand the material! This resulted in a wholesale effort to rewrite the manuals used for current production, and recent production, equipment. To achieve this, it was necessary to hire new personnel, who were used to writing manuals at the necessary education level. Finding such persons was not that difficult. Collins recruited persons who worked for the Heath Company and for Motorola (Motorola two-way radio manuals were considered to be among the best where understanding by 8th graders was concerned).

    To insure that the educational level needed to understand Collins written materials did not "creep up" in the future, every salaried employee was required to take a week-long course in "effective writing". Somewhere, in my files, I think I still have the paper-backed manual that was used for this course. Although I did not really agree with everything taught in the course, there were a fair number of techniques that were definitely useful.

    Glen, K9STH
    KD2ACO and K9AXN like this.

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