Sad to hear John Birkett passed

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Phoenix
who u callin ne guy bruv
who u callin ne guy bruv
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Sad to hear John Birkett passed

Post by Phoenix » Thu Jun 30, 2022 4:19 pm

Sad to hear of his passing
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reverend
no manz can test innit
no manz can test innit
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Re: Sad to hear John Birkett passed

Post by reverend » Fri Jul 01, 2022 6:20 am

I remember visiting his shop in Lincoln as a teenager. It was like entering Aladdin's cave, if Aladdin had been entranced by RF goodies instead of gems and gold.

Safe onward journey JB.
if it ain't broke, keep tweaking

Shedbuilt
no manz can test innit
no manz can test innit
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Re: Sad to hear John Birkett passed

Post by Shedbuilt » Wed Jul 06, 2022 12:06 pm

Sad news indeed. Had many chats with John, back in the day.

Albert H
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Re: Sad to hear John Birkett passed

Post by Albert H » Thu Jul 07, 2022 3:29 am

I used to buy transistors and trimmers from him. He had boxes and boxes of these little stud-mount transistors marked 587BLY. They looked like 2N3375s. He thought that they went to 30 MHz, but I did a little research and discovered that they were 35V max, 200 MHz Ft aircraft transistors! He wanted £3 each for them, but I went up to Lincoln and offered to buy several boxes for £0.50 per transistor. He got me up to £ 0.65 per device.

I had already experimented with these things and found that with a 2N3375 driving them, and a 30V rail, I could get around 90 Watts for 1 Watt drive, I came up with a nice board layout, and had a few hundred boards etched. The PA ended up with a 2N3966, into a 2N3375, then the 587BLY. At 30V supply, they would do just on the magic 100 Watts after the lowpass filter, if critically tuned.

I found a source of (nominally) 24V AC transformers which, when rectified and smoothed gave a fraction over 30V on load.... These PAs, driven by a little 100 mW driver board kept lots of stations on the air in the UK and in Europe in the early to mid-80s!

I found one of these old rigs last year in a box of miscellaneous junk when I was cleaning out my garage. I took the lid off the exciter box, and found that it was one of my early doubler exciters with a SP8629 prescaler IC driving some CMOS chips for the synthesiser. It was controlled by a 4 MHz reference crystal, and the frequency was set by including or omitting diodes to set a division ratio. I cleaned it up, and gave it a go into a dummy load. About 15 seconds after switch on, (when the PLL had locked and the PA switched on) it was producing 97 Watts on 94.4 MHz! It's now in regular use by a friend of mine down in southern Germany!

Birketts' cheap components made cheap rigs possible!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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