Transmitter Cabinet layout?

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KI4YAN:
I have finally gotten my radio room built, and my rack cabinet rolled into the corner where it will sit. I've had some of these parts for almost 10 years now, and things have been put together, taken apart, put together, taken apart a few dozen times...

I am working on trying to get things organized and actually get the framework of this cabinet going, and am looking for advice on how best to manage airflow in and out of the cabinet, how to deal with RF and AC in and out of the cabinet, and ideas on how to mount some of the heavy iron. I haven't built a door for the back of the cabinet yet.



It's a 1950's DuKane intercom rack, the rails are 19" wide but they were originally not drilled or tapped. Equipment was just stuck in the rack and holes drilled willy-nilly. Some of them line up, some don't. The plan is to lay the rack on it's back and set panels in until the front face is full, preferably the panels in their final resting places, and drill & tap the rails for the correct screws in the correct spacing-if I need to weld up and grind back a hole, I can do that easily.



I have accumulated a small pile of blank steel rack panels-these are the ones that are bolted into assembled racks during shipping to help them keep their shape, so some of them are 20g, some are 18g thick. There's also a 1/8" thick aluminum one in there and another chunk of aluminum that's 1/8" thick and 20" wide-I'd have to shave an inch off to make it into a rack panel.

This is the HV transformer, it's 5" wide and 7" tall, and about 4" thick, as far as the core dimensions go. 1KVA at 2300V.



The modulation iron is roughly the same size-it's a Kenyon T-495.

Over the years, the plan has slowly evolved, and I've finally nailed down some specifics. I have my RCA Ham Tips exciter built, the VFO is temperature stablized (after several years of goofing with it) and the drift isn't too bad. I also have the little SS rig I have been working on, and plan to have an auxiliary jack that will have keying and audio outputs so I can use it as an exciter as well.

The final amplifier will be a 4-125A, modulated by 4-65A's. I considered a pair of 4-125's modulated by a pair, and also a pair of 4-65's modulated by a pair, but this configuration seems to take best advantage of the parts I have already, and I can crib directly from the Eimac data pages, where data for the 125 by 65's is layed out and listed, with grounding recommendations and all. I also have a few ARRL handbooks that have similar final amplifiers.

Tonight, I am thinking about how to route airflow through the cabinet, and how to keep the cabinet stable on the casters. Airflow seems like I might put some vents in the bottom panel, and vents in the top of the cabinet or in the top panel. Stability seems to demand putting the heavy iron as low in the rack as I can get it, but then I wonder about putting the modulation transformer down next to the power transformers-worried about hum pickup.

Opcom:
Quote from: KI4YAN on November 12, 2017, 07:28:28 PM


Opcom comments
BTW sorry for the text size, it was not able to be corrected, no idea why it happened.

I have finally gotten my radio room built, and my rack cabinet rolled into the corner where it will sit. I've had some of these parts for almost 10 years now, and things have been put together, taken apart, put together, taken apart a few dozen times...

I am working on trying to get things organized and actually get the framework of this cabinet going, and am looking for advice on how best to manage airflow in and out of the cabinet, how to deal with RF and AC in and out of the cabinet, and ideas on how to mount some of the heavy iron. I haven't built a door for the back of the cabinet yet.

If you are absolutely sure everything will fit in the cabinet, that is great, and a fine time to work on the cabinet and the mains input cable/fixtures for it, and cooling.
It is unconventional but if you anticipate a dusty floor then it is not a bad idea to intake the air at the top and exhaust at the bottom. It works well as long there's enough airflow to create gentle turbulence. It also gives an opportunity to push air down onto the final RF section if that's to be at the top. It also presumes a closed cabinet except for the inlet and outlet. That's a real nice looking cabinet!



It's a 1950's DuKane intercom rack, the rails are 19" wide but they were originally not drilled or tapped. Equipment was just stuck in the rack and holes drilled willy-nilly. Some of them line up, some don't. The plan is to lay the rack on it's back and set panels in until the front face is full, preferably the panels in their final resting places, and drill & tap the rails for the correct screws in the correct spacing-if I need to weld up and grind back a hole, I can do that easily.

Perfect! Done than several times and on steel Bud racks so full and heavy that a block and tackle from the ceiling beam was required to stand them upright! Watch out for pinching/severing fingers when putting the final panel into place, that is the only dangerous part of the exercise.



I have accumulated a small pile of blank steel rack panels-these are the ones that are bolted into assembled racks during shipping to help them keep their shape, so some of them are 20g, some are 18g thick. There's also a 1/8" thick aluminum one in there and another chunk of aluminum that's 1/8" thick and 20" wide-I'd have to shave an inch off to make it into a rack panel.

This is the HV transformer, it's 5" wide and 7" tall, and about 4" thick, as far as the core dimensions go. 1KVA at 2300V.



The modulation iron is roughly the same size-it's a Kenyon T-495.

Over the years, the plan has slowly evolved, and I've finally nailed down some specifics. I have my RCA Ham Tips exciter built, the VFO is temperature stablized (after several years of goofing with it) and the drift isn't too bad. I also have the little SS rig I have been working on, and plan to have an auxiliary jack that will have keying and audio outputs so I can use it as an exciter as well.

The final amplifier will be a 4-125A, modulated by 4-65A's. I considered a pair of 4-125's modulated by a pair, and also a pair of 4-65's modulated by a pair, but this configuration seems to take best advantage of the parts I have already, and I can crib directly from the Eimac data pages, where data for the 125 by 65's is layed out and listed, with grounding recommendations and all. I also have a few ARRL handbooks that have similar final amplifiers.

Tonight, I am thinking about how to route airflow through the cabinet, and how to keep the cabinet stable on the casters. Airflow seems like I might put some vents in the bottom panel, and vents in the top of the cabinet or in the top panel. Stability seems to demand putting the heavy iron as low in the rack as I can get it, but then I wonder about putting the modulation transformer down next to the power transformers-worried about hum pickup.

Cooling is twofold then, cooling for each power tube and then general air clearing of the rack.

If you have the room to allow a 1U space under the lowest panel/chassis, then the bottom floor of the rack could be an air outlet/inlet easily. If I may suggest that one of those 1U fan panels will slide right in. If equipped with the usual 9 screaming TA450 fans, some DC fans would be much quieter. You only need 100-200CFM. A couple rows of holes or a screened slot 1-2" tall in the rear door at the top could be the outlet/inlet for the cooling air. I am guessing you will have a small blower with hoses arrangements or two small chassis-mounted blowers to cool the modulator and RF power tubes.



Why I mention it is from experience with internal blowers but no cabinet blowers in the AM transmitter here. The builder put a blower under the 4-1000 and I added one under the 3-500Z modulators when I installed those and removed the previous tubes. There was no forced air to clear the cabinet and the set got extremely warm, having only heavily screened louvered back doors. The convection was nowhere enough. The subchassis of the bias and screen supplies and everything else inside there was being heated by the big tubes' circulating waste heat to where it was all very hot.

The problem was totally solved after adding a 400CFM low speed centrifugal blower from a VAX6000 on top of the rack where there had been a heavy aluminum panel with many very very small perforations. This kind of fan is not just the most common thing, you will probably want something else, although it is about 4" deep, exhausts sideways 360 degrees for 'zero clearance' between fan and wall, would fit perfectly in/on the backside of the door of a small rack.



That blower is 24VDC but runs silently at 14VDC and does a wonderful job. This set is tall, yours is not and I assume you don't want to put anything on top. The point of that is a large low speed blower run at low voltage, or a bunch of low speed high pitch fans in a 1U tray should be so quiet that you will hear the internal blowers more than the cabinet blower.




[/size]

Opcom:
sorry about the mess.

WBear2GCR:
A few thoughts that are my initial impulses.

4-65s are a bit light.
Use the 4-125s, you can always go up to 4-250s or 4-400s... same sockets.

You said you can weld. It might be easier and simpler to buy pre-drilled strips that are for
racks from one of the rack manufacturers. The biggest ones are Bud and Premier. You may
find others online, since pro audio people use them to go to wood or 'glass road cases.

Have you decided on your B+ voltage? Aka, cap input or choke input PS?

                    _-_-

KI4YAN:
I thought about 125s by 125s, but then I look at the power limits-375 carrier is the legal limit for me, 250W carrier isn't even 2db down there...not even half an S-unit on receive.

I had planned on capacitor input, with a diode bridge. The power transformer isn't centertapped, so it needs a bridge rectifier. That would give 3250V, so I started look for a choke for choke input...would give me 2070V. I am thinking maybe run the transformer on a variac and cap-input for 2500V output, is the correct answer.



I have five of these for filter capacitors, though. They're rated 115uF at 2300V, and were removed from defibrillator units. It's very tempting to run 2kV and give up some power, but I could also put these in series for 4600V rating:



If I put them in series, they'd be ok for 4600VDC at 57.5uF each. And I'd have one left over. What I don't have is a filter choke yet-have been more focused on other things and minding my bank account than seeking out one right now. I figure everything else has come cheap and easy if I waited long enough, the choke will too.

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