Collins 30K-5 - Page 1
Forum section: electronics / rf-microwave

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 06, 2020, 06:55:02 pm
content: Got an old school Collins. Wondering if I can bring it back to life.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 06, 2020, 06:58:04 pm
content: The first thing I need help on is, does anybody have idea/experience of how the damaged porcelain stand-off insulators of the HV transformer can be repaired/restored? Thanks.

author: mag_therm
author_rank: Frequent Contributor
timestamp: November 06, 2020, 09:01:06 pm
content: Firstly, that transformer looks likely to have pcb (polychlorinated biphenyl) oil inside.Check safety and regulatory issues about exposure, using, storing, or disposing of it.If it is mineral oil,Search "high voltage bushings" to find a possible supplier you could inquire with.I had lots of hits showing photos of similar bushings.Alternatively you might be able to get a local machinist to turn them out of a plastic like high density polyethylene (HDPE)

author: radiolistener
author_rank: Super Contributor
timestamp: November 07, 2020, 01:36:11 am
content: What is this? Radio transmitter? Power amplifier?

author: KE5FX
author_rank: Super Contributor
timestamp: November 07, 2020, 04:29:17 am
content: Quote from: radiolistener on November 07, 2020, 01:36:11 am250W AM transmitter, two channels. Designed by Warren Bruene, who was to Collins as Art Fong or Barney Oliver was to HP. Art Deco as f***.Quote from: max.wwwang on November 06, 2020, 06:58:04 pmSee if the Collins Collectors Association still maintains a mailing list or forum. If so, someone there will likely be able to help.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 07, 2020, 08:12:46 pm
content: Quote from: mag_therm on November 06, 2020, 09:01:06 pmThanks! This is very helpful - health and safety first.I'm not sure whether PCB is actually used here. Is there any way to fine it out somehow definitively?Yes, using HDPE as an insulator bushing is a good idea. Seems like you are considering the solution of taking off the broken insulators, rebuilding the wire and the stand-off insulator (with bush) as new. That would be ideal (though a bit challenging). Is there any less ambitious, yet safe and working, options?Will check Collins Collectors Association for idea. Have been in contact with local hams but I think it's very unlikely I can find a spare/replacement transformer for this.And there are many other parts that need to be found or replaced or repaired.

author: mag_therm
author_rank: Frequent Contributor
timestamp: November 07, 2020, 09:01:02 pm
content: Hi Max,Another thought, without knowing your intentions to put it on the air:I think the maximum Amateur power in NZ is 100 or 150 Watt. -??Changing to a lower rated dry type transformer might be possible and cost feasible using a transformer from an old AM amateur rig.That might allow changing the output tube too.Then you could put disposable gloves on and bag that leaking one up into two of those heavy plastic bags and take it for disposal to industrial waste.By the way, I sometimes listen to RZNI Rangitaiki, on 13840 and 5945 as their beam is toward upper USA.Signal is fairly weak , it might pick up as the sun spot activity is increasing now.There is a good description of their transmitter and antenna on the web site.Edit: According to Wiki, polychlorinated biphenyl was commonly used in USA between 1930 and 1977.

author: KE5FX
author_rank: Super Contributor
timestamp: November 07, 2020, 11:47:09 pm
content: PCB-based transformer oil is not a horrifically toxic substance, or it wouldn't have been in common use for 40+ years. The main danger is chronic exposure, which isn't an issue here. We're better off without it in our environment but it's not plutonium.I'd probably try to repair that insulator with epoxy. Wouldn't be optimistic about the odds for success, but it's worth a try. Either that or neutral-cure silicone.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 08, 2020, 02:30:25 am
content: Quote from: mag_therm on November 07, 2020, 09:01:02 pmSince it's too long a way, if ever possible, before it can be back on air, I'm not worrying about that for now. But absolutely no intention to go beyond the legal bounds.I did a bit googling about PCB, it's a viscous liquid. I'm not sure about the typical construction of Collins (and other old era) HV/LV transformers, but I guess the probability of they being filled with PCB should be low?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 08, 2020, 02:32:51 am
content: Quote from: KE5FX on November 07, 2020, 11:47:09 pmAgreed. Thanks for the ideas. I might start with the less ambitious options (to get it working and adequately safe without a perfect restoration).I think making a good and stable electric connection from the broken terminals is more a challenge than for insulation.

author: tkamiya
author_rank: Super Contributor
timestamp: November 17, 2020, 12:08:01 am
content: Are you sure it is a power transformer? I've never seen HV transformer with impedance rating on windings. My guess is it is a modulation transformer (which will have HV going through). As to fixing it, my approach would be to create an "Apron" that fits snugly around ceramic insulation. Clean, file, and flatten the existing bolt, tap a hole and attach screws, then cover the whole thing with acrylic apron. I would rather not take that apart. It's going to be very messy.What kind of voltage does plate HV take? Is it 4-1000A tube?

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 17, 2020, 11:03:30 am
content: PCB's can range from "not that bad" to very toxic, it's a pretty big class of compounds. They are all carcinogens and endocrine disruptors.I would attempt a repair without opening and draining the transformer. You would also likely need a good vacuum chamber to degas the oil again after refill.If you need to go that far I'd suggest making a replacement or finding a spare.Drilling and tapping into the damaged terminals sounds like a solid plan to me.It's a beautiful looking transmitter, hope you get it going!

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 27, 2020, 08:31:32 am
content: Quote from: tkamiya on November 17, 2020, 12:08:01 amWell done. You are exactly right. This should be a modulation transformer. I'm attaching the 'cabling' schematics. It should be T103 shown on the right half the second row from the bottom.I agree, I would also rather not take it apart. Your plan sounds good but the problem is bolt at the top of porcelain stand-off insulator does not go through to its bottom but rather stops in the middle only connected to a wire rounded by another different softish material. The conductor is neither thick nor solid so not easy to expose it clean and remake a good electric connection without compromising the HV insulation too much (including surface creep distance). There's not a hidden partial bolt under the collapsed bolts. They are also too thin to drill a hole and tap on.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 27, 2020, 08:39:48 am
content: Quote from: ChristofferB on November 17, 2020, 11:03:30 amNo, I'm not going that far/dirty. Yes, it's really beautiful and sexy. I hope I can bring it back to life (potentially with some modification). Thanks.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 28, 2020, 11:21:32 pm
content: You can make a new insulated terminal with epoxy "Pig Putty" or just plumbers epoxy, I think they are the same thing. You can do this without opening the transformer. Sounds to me the hardest part would be to get a good connection on the existing lugs before epoxy.Looks like you have your work cut out for you.It's just a few hundred volts so the porcelain seems like typical Collins overkill.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: November 29, 2020, 07:20:26 pm
content: Quote from: Wallace Gasiewicz on November 28, 2020, 11:21:32 pmI agree. A good electrical connection may be the hardest part without making this too messy. Using epoxy to rebuild an insulator sounds like a great idea. Thanks.

author: tkamiya
author_rank: Super Contributor
timestamp: November 29, 2020, 08:06:14 pm
content: Something is wrong. I am not sure if that schematic actually belong to this model.The schematic shows a single 4-125 as a final tube. That is a 125 watt plate dissipation tube. In continuous mode like AM, it won't be sufficient to produce 250 watts. Since this is a commercial continuous duty transmitter, designer won't push it like this. Also, maximum plate voltage is 2.5KV or 3KV depending on application. Plate transformer is tapped at 2500V. Which means no load voltage will be 3.5KV. Also, on typical AM transmitter, modulation transformer is at plate voltage.All that is very long way to say, please be careful. The reason I mentioned making a cone with plexiglass is to withstand high voltage.

author: szoftveres
author_rank: Regular Contributor
timestamp: November 30, 2020, 05:33:30 pm
content: Once I've seen a video where a guy had to make air-tight, porcelain insulated high voltage pass-through points for his project. He used spark plugs. What a brilliant idea!