Adjustment pots in Gates BC-1H

[W9BHI]

Hello all,
I would like to know how to make adjustments to R3 and R52 in the modulator.
I think that R3 balances the current draw for the two 807 pre-drivers.
I am not sure what R56 in the feedback ladder does or how to adjust it.
Could any of you Gates gurus comment?
Thanks,
Don W9BHI

[W7TFO]

Those would be best set with an audio generator running a 1KHz sine and a distortion analyzer.

The analyzer would need to either sample a broadcast modulation monitor audio output (best), or a properly swamped diode detector hooked to the mod mon sample coil.

You could use a scope, but distortion under 5% is rather hard to see.

In all the years running those type TX in service, never could the specs be bettered by adjusting them from factory (unless diddled by the unknowing).

Just keeping the modulators balanced at idle via the front panel pots is way more important...

73DG

[W9BHI]

I have manuals for the T, G and H but there is no mention of any adjustment on those pots.
Only the H has the R56 in the feedback network.
I put a voltmeter across the two cathodes of the input 807's and adjusted R3 for 0 volts.
I figure that it would at least make the two tubes have the same amount of cathode current.
Thanks,
Don W9BHI

[W9BHI]

Interesting post on Radio discussions .com
07-02-2009, 03:31 PM #5  




BobOnTheJob


 BobOnTheJob is offline Senior Member  
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 Join Date:Jan 2007Posts:3,745




Re: Gates BC1H



Good to hear that it's still in service. I had a BC-500H 30+ years ago (it was all but new then) and with some attention to keeping the 807A's in the audio stage balanced (I learned a neat trick--put a voltmeter between the plate caps of the tubes & adjust the balance pot until the meter read 0 volts--tracked exactly with minimum distortion), the thing was only a db down at 10khz, had -59db noise & the distortion was around 0.5%...and that baby sounded sweet.



When I started in radio in 1967, most broadcast equipment used tube technology, all recorded music was played from records on a turntable by live DJ's, there was no satellite delivery...and radio was fun.

[flintstone mop]

Interesting post on Radio discussions .com
07-02-2009, 03:31 PM #5  




BobOnTheJob


 BobOnTheJob is offline Senior Member  
--------------------------------------------------------------------------------
 Join Date:Jan 2007Posts:3,745




Re: Gates BC1H



Good to hear that it's still in service. I had a BC-500H 30+ years ago (it was all but new then) and with some attention to keeping the 807A's in the audio stage balanced (I learned a neat trick--put a voltmeter between the plate caps of the tubes & adjust the balance pot until the meter read 0 volts--tracked exactly with minimum distortion), the thing was only a db down at 10khz, had -59db noise & the distortion was around 0.5%...and that baby sounded sweet.



When I started in radio in 1967, most broadcast equipment used tube technology, all recorded music was played from records on a turntable by live DJ's, there was no satellite delivery...and radio was fun.

great tip.. and makes perfect sense