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Author Topic: T-368 modulation question  (Read 1953 times)
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W9BHI
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« on: May 28, 2013, 02:54:31 PM »

The manual says the modulator should be showing 250Ma.
on peaks for about 100% modulation(this is using the carbon mic).
I have the carrier backed down to 350 watts.
I am using an amplified D-104 and the clipper and HP/LP filters have been removed from the speech amp circuit.
I cannot get more than 125 Ma. on the meter.(idle current is 50Ma.)
All the speech amp tubes are good.
Audio reports are good and my scope shows less than 100% modulation.
My Powermaster meter shows 1300 watts on peaks.
One of the 4-125's is a little brown inside with the lettering faded out while the other is clear with bright red lettering.
If one of the 4-125's is bad, would it cause the modulator to not draw enough current?

Thanks,
Don W9BHI
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KA2DZT
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« Reply #1 on: May 28, 2013, 06:41:55 PM »

I'm not an expert on T-368s but, if one the mod tube was weak I think you would see that on your scope,  not being able to make even modulation pos and neg.

The fact that you're not getting 100% modulation seems to indicate you're not driving the mod tubes enough.  You removed the clipper and filters, maybe those changes have somehow reduced the voltage gain in the audio circuits.

Hopefully you'll get help from someone who knows more about 368s.

Fred
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