Re: {Collins} Collins 30L1 resistor/cap board


In general I agree with that assessment.  However, I think the subtlety of the relatively good impulse handling capacity of the carbon resistor, relative to modern film alternatives, is sometimes lost.  We definitely want the resistors to be sacrificial when the circumstances demand it, but we don’t want them to be trigger happy, as film types can be in protection circuits.

I wasn’t able to find much information on the older, higher wattage, carbon composition resistors but looking at the modern device specs, I expect the ceramic composition types to be somewhat more robust – but with a fair overlap of energy ratings between carbon and ceramic types.  Like you, if I could get the original type I’d use it but, failing that, I’d be fairly happy to go with a ceramic replacement. However, I would not put a modern metal film type resistor in e.g. a 30L-1 HV protection line.

Good reminder about checking the fuses, too.  It’s probably the single most important preventative measure to protect the amplifier.  Apart from anything else, modifications such as those to limit the damage from tube flashovers are rendered less effective by delays in blowing the fuses.

73, Peter.

From: Bill Carns [mailto:wcarns@xxxxxxxxxxxxx]
Sent: Friday, 27 October 2017 9:39 PM
To: Peter Hall <P.Hall@xxxxxxxxxxxxx>
Cc: COLLINS@xxxxxxxxxxxxx
Subject: RE: {Collins} Collins 30L1 resistor/cap board

Peter and All,

My perspective would be - I would try very hard to go back with replacement Carbon Comp resistors. They still can be found NOS.

It is that very "Poor" short term overload capability that you do not want to improve upon. That is what Collins was counting on to "protect and serve".

Going with a Ceramic modern replacement will only delay the departure of those resistors when it comes time that you need them. Me, I would use Carbon Comp if at all possible.

Also make sure that your fuses are the proper size. Often they get upsized for various reasons over the years with disastrous results.


-----Original Message-----
From: Collins [] On Behalf Of Peter Hall via Collins
Sent: Friday, October 27, 2017 1:18 AM
To: K2USN <K2USN@xxxxxxx<mailto:K2USN@xxxxxxx>>
Cc: Collins Listserve <collins@xxxxxxxxxxxxx<mailto:collins@xxxxxxxxxxxxx>>
Subject: Re: {Collins} Collins 30L1 resistor/cap board

Ken correctly identified the resistors and their value for you. Carbon composition resistors can be a bit hard to find these days and, in their place, I’ve used ceramic composition types which, while keeping the nominal design power rating, have good short-term overload capacity. Your can buy Ohmite and other types from places like Mouser.

The bigger issue is identifying the cause of the overload, and determining if any other damage was done in what might have been an arc-over in a tube. Does the amplifier still key normally, and is there any bias current showing? Sometimes R17/18 (the 10 ohm resistors) blacken but are still electrically intact. They obviously need replacing but may be functional enough for a very short duration test. It’d be worth testing them with an ohmmeter (after waiting a safe time after switch-off before removing the PSU cover).

I believe there are several PSU replacement options but I used the Harbach one described at:<>

It comes with good instructions but assumes a fair level of familiarity with vintage electronics, and reasonable manual dexterity.

There are a number of good articles on the 30L-1 on the CCA website, including some invaluable guidelines for maintenance in the “rx for your Collins” section. It’s not hard to take apart and re-assemble a 30L-1 but it needs to be done carefully if you’re to preserve the aesthetics and value of a classic amplifier. The 30L-1 manual is on the CCA website and includes instructions for removing the cover. Further useful comments are contained in the other CCA articles; these help in avoiding scratches on the trim ring and other heinous mis-handling.

The 30L-1 is an easy amplifier to maintain but, with the high voltages inside, care has to be taken during servicing. I’d always encourage a hands-on approach but, reading between the lines in your questions, I’d respectfully suggest you might do that in conjunction with an experienced person. The alternative is to get the amplifier serviced professionally and, again, there are some names on the CCA website. No doubt the US forum members can give you current recommendations if you choose that direction.

I’m not sure what you mean by “aligned or calibrated” with respect to the second 30L-1. There are a few basic adjustments (idle current, tune indicator, etc) but they are all described in the service manual.

73, Peter.

From: Collins [] On Behalf Of K2USN via Collins
Sent: Friday, 27 October 2017 12:08 AM
To: collins@xxxxxxxxxxxxx<mailto:collins@xxxxxxxxxxxxx>
Subject: {Collins} Collins 30L1 resistor/cap board

Collins 30L1 Question:

I have a Collins 30L1 Amp. It had been working just fine for quite some time. Then on transmit I heard strong HV arcing noise.
I opened the cabinet, then took off both covers. On the HV side just forward of the transformer I see the original capacitors. They look pretty much OK.
BUT: There is a cover disconnect with a grounder with two large resistors that go from the circuit board up to an insulated pass through to the other side.

Both of these resistors are burned out. I can’t tell the value of either of them. SO: I looked at a schematic, but I am unsure of which two they are, or the values.
Can anyone here advise as to the value of these two resistors so I can change them please.
Also: I understand there’s a modern alternative replacement for the old capacitor board for the 30L1 amplifier. I was told it cost about one hundred American dollars.
Does anyone know where I can buy the replacement board? Perhaps how to proceed with that replacement? I could probably do the job if I could get the gray cover off the rig, but it must have a trick to remove it. I do have photos to show the burned out resistors and condition of the capacitors if anyone could assist me.

ALSO: I also have another 30L1 that needs a set of tubes & maybe to be aligned or calibrated. It has not worked in a while but it is a complete amp except for the tubes. I would like to resurrect that unit also, but I am not sure how to proceed with that one.
If anyone can help, Please let me know what you think… Thanks Ed. K2USN…… K2USN@xxxxxxx<mailto:K2USN@xxxxxxx<mailto:K2USN@xxxxxxx%3cmailto:K2USN@xxxxxxx>> or text 502-741-1811
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