Coolong a Collins 30S-1 Amp - Amplifiers Forum at eHam.net

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eHam.net Forum : Amplifiers : Coolong a Collins 30S-1 Amp

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Coolong a Collins 30S-1 Amp	Reply
by N2ZYZ on October 28, 2009	Mail this to a friend!
The vacuum tube in this Collins 30S-1 was replaced from a stock 4CX-1000b to a 4CX-1500b (thanks Dave!!). The amp now does a full 1.5KW+. As such it can get HOT so I welded up a heat extractor. http://www.youtube.com/watch?v=_YxCIytSFG0

RE: Cooling a Collins 30S-1 Amp	Reply
by N2ZYZ on October 28, 2009	Mail this to a friend!
OOOps one too many Os shpuld read "Cooling a Collins 30S-1" :-)

RE: Cooling a Collins 30S-1 Amp	Reply
by W8JI on October 29, 2009	Mail this to a friend!
Of course it runs hot. The 30S1 was designed as a 1kW dc input linear amp, or 2kW PEP on SSB. The cooling system is for that dc input power, as is the negative feedback system Collins built into the control grid circuitry. If you are really getting 1.5 kW output you are beating the tube up and everything else. It is also probably not very linear. If you really want a 1.5kW amp buy or build one designed to run 2.5 to 3 kW dc input, especially grounded grid. Then it will do what you want. Otherwise you would be better off to preserve that nice old piece of gear and run it the way Collins intended. The signal will be cleaner and it will live much longer when operated accoring to the manual. The fact you switched to a 4CX1500 does not change the grid circuity, power supplies, and cooling capacity. Tom

RE: Cooling a Collins 30S-1 Amp	Reply
by K6AER on October 29, 2009	Mail this to a friend!
In addition to what Tom has mentioned, changing out the 4CX1000A for a 4CX1500B is not a seamless swap. The 4CX1500B has small dimples inside the cooling fins and as a result the tube must be run at much higher air pressure in order to maintain sufficient cooling. It is possible to actually have less cooling by placing the 4CX1500B in the amplifier for the cooling fins are more restrictive. For you to have the additional capability of the 4CX1500B you will need to increase the blower pressure. Your nice quiet amplifier will be roaring in the ham shack.

RE: Coolong a Collins 30S-1 Amp	Reply
by HFRF on October 29, 2009	Mail this to a friend!
<<It is possible to actually have less cooling by placing the 4CX1500B in the amplifier for the cooling fins are more restrictive.>> The above is utter nonsense. 4cx1000A needs 28cfm @.25" for 1000w dissipation 4cx1500A needs 18cfm @.23" for 1000w dissipation Using a 4cx1500b makes a 30S1 a completely superior amplifier if you raise the screen voltage to about 360vdc. An unmodified 30S1 can get you 1000 to 1200 watts out operating it more less within Collins specs. The geniuses on this site don't understand the difference between peak tube plate dissipation and average plate dissipation under SSB and CW operation. Using the 4cx1500B will easily get you 1500watts out with little increase in load to the 30S1 since it is overbuilt. The average Plate dissipation for SSB is so far below the average dissipation capability of the tube, an increase in power out of 1500w out is nothing significant. The same people make the same ridiculous remarks day after day here. They should be banned from this site. http://hfvhf.noip.us/4cx1500b.pdf http://hfvhf.noip.us/4cx1000a.pdf

RE: Coolong a Collins 30S-1 Amp	Reply
by HFRF on October 29, 2009	Mail this to a friend!
Here is another data sheet for the 4cx1000A that has slightly different air flow requirement ratings. http://hfvhf.noip.us/4cx1000.pdf The point is that the 1500b tube and the 1000a tube have virtually the same cooling requirements since the slightly different cooling cfm's and static pressures balance out to about the same airflow. Also, some people (not too smart) scold users that modify their 30S1 amps under the assumption it is pushing the limits of the amp. They should follow their own advice considering what they design. Look at the blower delivery for the blower specified in the Ameritron AL1500. It puts out 20cfm @.1 inches of water but the tube needs 20cfm @.23". This means that the blower in the AL1500 is too wimpy to cool the tube at anywhere near 1000 watts dissipation. It supplies closer to 500 watts worth of cooling just to keep the 3cx1500a7 just below the tube's 250 C limit. http://hfvhf.noip.us/ameritron blower.pdf (see graph numbered 1) http://hfvhf.noip.us/3cx100a7.pdf

RE: Coolong a Collins 30S-1 Amp	Reply
by K6AER on October 29, 2009	Mail this to a friend!
The original post called for his 30S1 with a installed 4CX1500B to be capable of 1500 watts of dissipation. For the 8660/4CX1500B to handle that the CFM on the tube would need to be at 34 CFM at .6 inches of water pressure. That is off the Eimac data sheet. I stand by my statement of what the amplifier will sound like. I have two friends who have gone there on their 30S1and the amplifier sounds like a room air conditioner. Now if you are only using the amplifier in SSB duty cycle that is different. You can reduce the air flow but the amplifier is not a sophisticated amplifier and has no heat sensing of the anode. It would be prudent to cool the tube for worst conditions.

RE: Coolong a Collins 30S-1 Amp	Reply
by HFRF on October 29, 2009	Mail this to a friend!
Key down (continuous) output of 1500 watts requires 2500 watts in. 2500w in - 1500w out = 1000w continuous dissipation not 1500. The blower in the 30S1 will easily supply well over the needed air to cool the 4cx1500b at 1000 w dissipation. I am sitting next to one now. As always, none of your statements are correct.

RE: Coolong a Collins 30S-1 Amp	Reply
by K6AER on October 29, 2009	Mail this to a friend!
HFRF, How are you doing on your ham license?

RE: Coolong a Collins 30S-1 Amp	Reply
by W8JI on October 29, 2009	Mail this to a friend!
The Collins amp is, from the factory, under pressurized. Adding the 4CX1500 really does not cure the problem of not enough blower to run over a kilowatt out if average power is high. As a matter of fact the 1500 and 1000 will both have about the same dissipation capacity unless you up the blower size. The second problem with the S1 is the grid circuit. It is intentionally designed to go very high negative if any grid current appears. This was to protect the 4CX1000 grid, which will cook with any grid current. So while looking at blower specs on the pages Dick quoted, you might also look at grid current and the bias system in the S1. If you run the SLIGHTEST amount of grid current the bias will wobble all over the place. The problems are airflow is too low, so the 1500 watt capable cooler is wasted. You still have the air for 500-600 watts dissipation with the factory blower. the other problem is the Collins is set up to pull grid voltage rapidly more negative when any grid current appears, so you have to keep the control grid at zero current. Tom

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