Collins 30L1 design questions

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

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  1. KN1M

    KN1M Ham Member QRZ Page

    No, I ran the orderly room and was also the primary postal clerk for 2 full companies. We had a commo guy who took care of all of that stuff. The paperwork for a 160 man company didn't leave me time to play radio even though I did make time for Heinekin and Seven Sevens. Radio was not on the horizon yet. If I had gone to Signal School I probably would have ended up in the jungle.
    KD2ACO likes this.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    In case anyone cares, I dug out my old original mod sheet I did nearly 30 years ago to change the 30L-1 to direct chassis-grounded grids and replace the DPDT relay with 3PDT to key the bias as well as the antenna I/O; it also changes the amp "keying" circuit to low-voltage, positive keyed (12Vdc/100mA) to make it more compatible with most modern transceivers including most SS ones.

    Attached Files:

    KD2ACO likes this.
  3. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Just read it. Thanks for posting it, Steve.
    1988, eh? I did something like that to my SB-200 5 years ago and thought I was being modern. :p
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The SB-200 definitely works better with directly grounded grids.

    Another "what were they thinking?" moment occurs to me regarding using medium voltage, negative-polarity relay keying; Collins did with the 30L-1 and some copied the same thing.

    I can't imagine I would have ever done that, even in the old "tube" days, as it brings a high enough voltage to get a shock right to a connector on the rear panel -- when there was really no reason to do that.

    But then...some "older" amateur transmitters including Johnson Viking stuff, etc, actually brought a keyed AC line out to the rear panel.:eek: I modified all of those internally to change the 120Vac to 12Vdc, for external T-R relay keying...and did that even as a Novice in 1965. Another "what were they thinking?" moment.:p
  5. K9AXN

    K9AXN Premium Subscriber QRZ Page

    With no equalizing resistors for grid current and no way to read grid current? How did you tune it? No ALC?

    I won't suggest what you should do or not do. What I will do is continue to explain the finer points of the 30L1 so that others can decide for themselves what to change, if anything, knowing how the radio works.

    Have a good day

    Regards Jim
  6. W1QJ

    W1QJ Ham Member QRZ Page

    For many years RF grounding the grids on triode Grounded grid amps through capacitors has been referred to as “ floating the grids”. Prior to Collins adopting this idea all prious amp manufacturers directly grounded the grids in the traditional form with low inductance “ hard grounding”. After Collins started this just about every company followed that protocol. Numerous companies were convinced this was the new standard. Only a slim few companies didn’t buy into it. There seems to be support for both camps these days. Whatever floats your boat I suppose.
    KU3X likes this.
  7. K9STH

    K9STH Ham Member QRZ Page

    The Heath HA-10 "Warrior" has this "floating grid" arrangement and the HA-10 was introduced virtually at the same time as the Collins 30L-1 amplifier.

    Looking at the RCA "Ham Tips" publications, I find that the "floating grid" circuit was suggested for use with the 7094 in the August 1959 issue.

    A discussion of operating in Class "B" of triodes and triode connected tetrodes is in the February 1961 issue.

    As such, I believe that the floating grid arrangement was originally suggested by RCA and then was adopted for both the 30L-1 amplifier and the HA-10 amplifier.

    Glen, K9STH
  8. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Louis, thanks for the introspective reply!

    If a person likes their amplifier, it's the right one for him. There are amplifier designs that I find wanting but I try to refrain from making derogatory comments simply because a person may have an emotional connection with it or it was his first amp, worked his first Asian station, or for a number of reasons not related to technical prowess. That's not for any of us to say.

    NOTE: I am a Hallicrafters nut and always will be simply because my first radio was an S20R to partner with my home brew 6AG7.6L6 transmitter in 1952; tuned it through a small light bulb. So I understand and respect these feelings.

    I knew and at times did the sea trials for Orwin and Stanford at Hallicrafters on the SR-2000 and following SR-400 series radios. They were not perfect; design and improvements were limited by financials and marketability. At the same time I developed a great respect for Warren Bruene, Gene Senti, and DR. Jerry Johnson, Collins engineers.

    Several decades ago, when the allegedly floated grid design surfaced at Collins. Many other developers started to use the design including Heathkit. The Heathkit engineers decided to use the design at the urging of Bill Orr and an internal rift developed which is very visible today. The origin of the rift was misunderstanding of the root design.

    The source of the rift was the voltage divider design used in the 30L1 to develop negative feedback, enable the Automatic Load Control, provide ALC feed to the exciter, and reduce the gain of the amplifier by applying the same feedback to the grid as that applied to the filament. This design originated in the 30S1.

    If the same voltage coupled from the plate to cathode is applied to the grid --- does it not equalize the plate to cathode feedback? The same voltage divider is used in the single ended neutralizing system for grid driven amplifiers. NOTE: The neutralizing design for grid driven amps is not neutralizing at all, it is Equalization and Negative feedback --- and it works in amps that draw grid current or those that do not.

    The divider is the capacity from plate to grid to ground. The person that lobbied against the use of that design at Heathkit misunderstood the circuit. He understood the divider to be from cathode to grid to ground. Had that been true it would have been a faulty design. The attached file represents the Collins 30L1 design --- note(4) is the divider ---- It is not from cathode to grid to ground --- it is the same as the 30S1.

    For the last few years there have been numerous derogatory statements about the Collins 30L1 design and the engineers that designed it --- most based on the lack of understanding of the circuit. I don't have a horse in this race but when folks post disparaging comments about the design or engineers who created them based on their inability to understand a circuit design while being unable to explain their reasons is inappropriate.

    Next topic: The Automatic Load Control, how it works and what it does for you.

    Regards Jim

    Attached Files:

    Last edited: Feb 22, 2018
  9. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Good afternoon Glen,

    Those configurations were used to meter and bias the amp. The use of the float using a 220pf capacitor cathode to grid, plate to grid capacity and choke was a Collins invention. The 220pf cap was selected to provide a 1/44 voltage divider and is series resonant with the grid inductance at approximately 34MHz --- a dead short to ground. It was used to reduce the gain of the amp, to drive the Automatic Load Control, extract ALC for the exciter, and equalize the plate to cathode feedback.

    BTW, I knew DR. Jerry Johnson and was only familiar with Bruene and Senti. Read most of Bruene's manuscripts.

    Have a great day

    Regards Jim
  10. K9STH

    K9STH Ham Member QRZ Page


    I knew Warren Bruene, he had ended up at the "new" corporate headquarters here in Richardson, Texas, and was a member of the Richardson Wireless Klub for many years until he died not that long ago. He was present at the RWK meeting at which I presented the program, not that long before he died. I haven't really been active in the RWK for a few years but, occasionally, I am asked to present a program (on various topics) at one of the meetings. I never met Johnson or Senti even when I worked for Collins Radio.

    Glen, K9STH

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