204F-1 Amplifier


Asking $11,500USD

Payment via Cashiers Check or Cash will be accepted.

Front of the Collins 204F-1

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I have for sale a Collins 204F-1 HF amplifier complete with all tubes, spare set of used Eimac 4CX1000A final tubes, one new UG-999A/U N-connector adapter and U.S. Air Force Technical Manuals T.O. 31R2-4-173-2 Change 1 - 15 March 1970 (includes complete schematics) and T.O. 31R2-4-173-9 are included in the sale.

This S-Line vintage amplifier debuted in the 1959 Collins HF/VHF Gound Systems Catalog along with its twin, the 204H-1 that offered automatic tunning. Designed for Commercial and Military applications, the 204F-1 is definately part of the Collins S-Line family of equipments.

Front of the Collins 204F-1

The amplifier in my opinion is in very good physical condition, all of the photographs contained on these pages are of the unit that I have for sale. I have not performed any restorations or modifications to the unit and as far as I can tell from a review against the documentation, it is 100% as shipped from the factory.

The unit resides at my residence in Hendersonville, NC where it can be inspected by appointment and where it will need to be picked up by the purchaser. The unit rests on its original dolly and requires a truck with electric lift gate to move the unit, along with at least two men. I have done this twice now, the last time from NJ to NC when I relocated here, it is no big deal, both times I used a Penske rental truck. its pretty much like moving a refrigerator. It rests on a heavy wheeled dolly and for getting it into your location if needed, there are forged I-bolts at the top of the amplifier for using come along with block and tackle.

Interested parties can reach me via e-mail at n2ckh.com@gmail.com or via phone at 1-828-393-7385.

The Collins 204F-1(AM-2374/URT) is a two channel, 3 stage, RF Linear Power Amplfier, covering 2-30Mhz.

The military designation is AM-2374/URT, Amplifier, RF, Transmitter, 2-30 MHz, 2.5 KW (PEP), 50 Ohm output impedance, part of AN/URT-18.

Dimensions of 204F-1

Dimensions: 70in h x 20in w x 22 1/4in d.

Weight: 580 lbs.

Power: 220-440 vac, 60 Hz single phase. At peak power draws 6 Kilovolt amperes to provide over 2.5Kw output continuous keydown. However it can be run with just one final tube.

This amplfier is a real monster, see the separate photos of myself (5' 11") standing in front of the unit.

N2CKH standing in front of the Collins 204F-1

This amplifier follows the designs of many Collins radio equipments begining in the late 1950's. It uses many components that are in other Collins commercial equipments including the popular S-Line. It has the same styling and paint of the S-line as well, this unit is the big brother of the popular 30S-1 amplifier, many of the exact same parts, including part numbers found int he 30S-1 are in the 204F-1. Many amateurs are familiar with the 30S-1, however not many know anything about the 204F-1.

The 204F-1 is a three stage linear power amplifier that is ment to be driven from a low power exciter at less than 1/2 watt peak. The first stage is a 6CL6 pentode operating in Class A, followed by a pair of 6146 tubes operating in Class AB1, the third stage is a pair of Eimac 4CX1000A tetrode tubes as a Class AB1 voltage amplifier covering 2-30 Mhz. Since the grid is tied to the cathode, no grid amplification takes place. Although the power gain is relatively low, linearity is excellent. Yes, this thing is a full conservitively rated 5Kw plus input continuous duty amplfier, (capable of 4.0Kw plus on transmit ICAS) with two completely separate input and output tuning networks for true QSY from channel A to channel B or let's say 20 meters to 10 meters.

To rapidly QSY between bands once two bands are pre-tuned, you simply change the radio frequency and any antenna selection and move the two channel selection switches on the amplifier. If you want to change to a band not already tuned the calibrated dials make it simple.

The amplifier that I have for sale exists in its full factory configuration. However these units can easily be modified to bypass the first two stages and swamp the input with non-inductive loading network to drive one (or both!) of the 4CX1000A tubes directly from a 100w class radio instead of using an exciter or a radio with a transverter output drive port.

My particular unit was made for the U.S. Air Force and sold as surplus to a company that I once worked for that bought the unit for testing military portable antenna systems near 2Mhz for dielectric breakdown.

KC2CNB standing in front of the Collins 204F-1

Click on any picture below for higher resolution version or come back soon and visit the sectional pages for many more photos that are currently being created.

Here is the whole top 2/3rds of the unit. The bottom houses the power supply, it is all in a 6 foot self contained cabint with hinged front door. The upper and mid part of the door has two fold down panels for access to input and output tuning controls. The top panel has three meters to monitor all critical parameters, the wattmeter is basically a built-in Bird.

Collins 204F, click to enlarge

The picture below shows the front door open and the final section, input tuning section and power supply sections.

Collins 204F with doors open

Power supply section:

Collins 204F power supply

Power on accumulated hours meter with the current reading from its last usage.

Collins 204F power on meter

Click here for more power supply photos

Final tank and chimneys:

Close up of 4CX1000A chimneys

2nd driver stage 6146 tubes.

Close up of 2nd Stage 6146 tubes

Click here for more RF section photos

Here is a close up the plate tuning and the Channel A and Channel B selection switches.

204F input tuning

For a feel of the tuning panel size, here is the tuning panel with my Harris RT-1446 in the rack next to 204F-1 for comparison.

RT-1446 next to 204F

Here are close up photos of the input tuning panel and preselected settings guide when the door is opended up for tuning either or both channel A/B.

204F input tuning

204F input tuning

204F input tuning

Click here for more exterior photos

Below is the amplifiers schematic broken down into parts A, B, C and D. I would like to figure out how to make minor modifications to the circuitry to allow operation down to 1.8 Mhz.

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Click here with right mouse to download full size schematic part A as JPEG file

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Click here with right mouse to download full size schematic part B as JPEG file

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Click here with right mouse button to download full size schematic part C as JPEG file

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