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Author Topic: Collins 30L-1 TUNING?  (Read 7405 times)

Posts: 404


« Reply #30 on: May 19, 2017, 02:05:52 PM »

OK.....not able to get the answers that I am looking for (so far) let's just try to get a consensus of what can be the worst case scenario that can happen to a 30L-1 if any of the 811A tubes suffers a meltdown, short, flashover or any other effect of a tube going bad?

Is there any reason not to continue to use the over-driven "injured" tubes until failure"?

I am willing to "drive them into the dirt" long as there can be no real risk of destroying any of the major parts of the amp.  I am trying to weigh the risk factor against using the over-driven tubes for the remainder of their useful lives vs taking a chance on causing some major and costly problem with the 30L-1.

If I can just get some pertinent answers to this question, it will alleviate my paranoia and let me enjoy the "learning curve" until I can feel safe in installing the new tubes.  

This is my first----and last amp.  Just trying to get to the point of being confident about it's proper use and care.  Trying to use up the tubes that I have already injured before installing a new set.

Sorry to be "beating a dead horse" here, but I am feeling like a fledgling bird getting ready to take my first flight.....and just want a nudge--in the right direction.  Thanx once again and 73

(Can I please get some experienced answers to this one question?Huh)


The best advice and recommendations that you will find is on the site.  The designer of the 30L1 Gene Senti was a well known seasoned RF engineer with Collins.  The genesis of the feedback design was Warren Buene who designed the 30S1.  Gene designed the 30L1 on his own time an brought the design to Ernie Pappenfus who was then the Director of development for commercial and amateur products.  Pappenfus, Bruene and others participated in the design review and signed off on the amplifier.  These were world renowned RF engineers.  There's a lot of negative commentary regarding the design of the 30L1 most of which originates with folks that don't understand the design.  

I'm not the best source for the 30L1 but the following I believe will help to answer your questions.

You are uncertain as to what will happen to a 30L1 with a catastrophic grid or filament short to plate.  First, has someone changed the 100uf power supply caps to something higher than 100uf?  If so, the damage in the event of a tube failure will be proportional to the increase in cap value.  

If the failure is a gas flash, the amplifier should be unharmed but only if the power supply cap values have not been changed higher.  If it is a grid or filament sag to plate expect some of the grid components to be damaged all the way back to the relay and further --- there is help though.

There is a change that will help to protect the radio in case of a short.  Connect a 200V MOV across C2 --- it will save much of the grid circuitry.

That being said, if you find any damage in the grid circuit --- check everything.  The 47 ohm resistors on each grid help to balance the load between the 811A's when driven hard, they should be very close to 47 ohms.

To be done before going to sea trials verify diodes CR17, CR18, and CR19 have been changed to 1N458 and all other components in the grid circuit are good.

Verify that R28 is a 56 ohm 1W resistor.  It was changed from 39 to 56 ohms to reduce the idle current to 110ma.

There's a lot more information and I'll follow as time permits but this is what comes to mind before using the radio.  

Good luck et kindest regards Jim  


Posts: 917

« Reply #31 on: May 19, 2017, 05:15:20 PM »

Regarding the question as to possible damage if something goes south on the tubes:  There are two 10 ohm resistors in parallel in the B+ line, R17 and R18.  If a major short in the tubes or output circuit, both will be obliterated.  Saves stuff!

Posts: 357

« Reply #32 on: May 20, 2017, 06:05:47 PM »

Thanx....nice to know there is some kind of safety feature for the transformer.

Posts: 917

« Reply #33 on: May 21, 2017, 02:56:29 PM »

Removing cover plate causes the B+ line to be shorted.  Turning on amp with it shorted with "test" the two resistors.  One time test!  So if you do plan to do something with cover plate removed, be sure to slip a piece of tubing or similar over the pin so the grounding ring won't short.  Also be aware 2000 volts  will kill you.

Posts: 357

« Reply #34 on: May 22, 2017, 08:52:30 AM »

Very much appreciate all of the responses and tips.  Glad to hear that others are also learning here. 73

Posts: 7

« Reply #35 on: May 24, 2017, 01:03:12 PM »

An excellent tutorial on the 30L-1 (a one hour DVD by Collins repair guru Dennis Brothers),
is available from ER Bookstore, POB 242, Bailey CO 80421-0242.

Price is $39.95 plus $6.75 shipping.

Mr. Brothers goes into the plate alignment with the filament-pins problem,
which can cause a grid to plate short if sagging elements touch.

Even Collins was caught unawares when this issue first appeared.
A friend bought a new 30L-1 in 1976, and it arrived with British made,
United Electron labeled 811As. Those tubes had the plates aligned
at random with respect to the filament pins, and his new amp failed
in the first month of use.  The replacement amp Collins shipped
to him under warantee also had that same tube manufacturer (and same tube fault).

I wound up eventually buying that replacement 30L-1 from him, and replaced the 811A's
with four Cetron 572B's, which are operated at the original power level (about 500W out).
Years later, I gave away those spare UE 811A's to a ham who ran an Ameritron AL-811,
where the tubes are operated with the plates vertical, unlike the Collins design.

I don't know how many 30L-1 transformers were destroyed before
the root cause was discovered.  Collins soon stopped manufacturing
to 30L-1 in the late 70's.  I'm sure it was more than the FCC's new CB linear rules
that decided them to pull the plug on the old 30L-1.

Posts: 1496


« Reply #36 on: May 29, 2017, 09:12:42 PM »

In case you were still wondering, the way you tell whether or not the tubes are still serviceable is as follows:

A) Are the plates warped to the point they are within a few mm of the grid structure (typically at the bottom of the plate)
B) Have they gone soft, producing significantly less than the expected output?

If the answer to either of those questions - especially question (A) - is Yes, then replace the tubes immediately.

Otherwise continue to use them until the output drops below what you desire (B).

J.D. Mitchell BA  - VK3BL / XU7AGA -

Posts: 357

« Reply #37 on: June 01, 2017, 03:44:38 PM »

Thanx, other than a few tiny pinholes and silvered areas on the plates, output is still fine.
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