[ARC5] BC-459

[brianclarke01 at optusnet.com.au]

Hello Steve,

I wonder if there is a measurement or a memory problem.

The BC-459 was designed for screen modulation. The RF PA circuit is not Class C; it’s somewhere between Classes B and C. The military documentation says the RF output is 12 W with 625 Vdc from the dynamotor. With 800 Vdc , the best you could expect is about 20 W.

If you changed the 1625 grid bias for Class C, and increased the drive from the 1626 to 65 Vrf, the best you could expect from a parallel pair of 1625s, ICAS, is about 108 W. The 1626 would need considerable help.

If you could re-arrange the 1625 circuitry to push-pull, and could get the 1626 to deliver 80 Vrf to the 1625s, grid No.1 to grid No.1, ICAS, you could get 120 W. That would require major redesign of the VFO and RF PA tank, to start with.

But all you mention is modifying the BC-459 for the higher DC plate Voltage, nothing else.

73 de Brian, VK2GCE

From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On Behalf Of sbjohnston--- via ARC5
Sent: Thursday, 27 February 2025 10:42 AM
To: arc5 at mailman.qth.net
Subject: Re: [ARC5] HP 23 for ARC5

Maybe 15 years ago, I repaired and semi-restored a fairly beat-up and already-modified BC-455 receiver and BC-459 transmitter and set them up for operation as a pair on 40 meter CW.   I was making a typical surplus Novice station I suppose.

I wanted to power the transmitter from a Heath HP-23 - so while I was fixing and restoring the transmitter, I also upgraded any components that would not stand the higher PA plate voltage.  Knowing the ruggedness of the 1625 tubes, I did not hesitate to exceed their rating.  With a transmitting capacitor in series with the output (to a existing SO-239 in the upper left corner of the front panel) the transmitter tuned up normally and I got the 100 watts output you would expect.

Very satisfying results. I treated the 1625s like they were 807s or 6146s, and they did not have a problem handling the extra voltage and power.  Of course, bear in mind that tubes of various vintages and manufacturers may vary in how much abuse they can stand, so your results may not be exactly the same as mine.

My approach was to leave the power supply alone and modify the transmitter to accept the voltages if offers.  And it worked out most excellently.


Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
http://af4k-crystals.com/
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