[Central-Electronics] 10A

[Jim Candela]

Robert,

   Just a few posts ago, Jon KJ6EK posted on that oscillator, and how he converted to the 6U8 design from the dual triode. I was just playing with mine, and with the 6U8 design (I'm using a 6MU8), I see 10 Hz drift when advancing the carrier level to maximum (70 watts!)

   I think you answered your question, and you might have a 'dud' crystal. Also look at my post about a CB channel 4 crystal (27.005 3rd overtone) to replace the CE 9000Khz xtal.

  FWIW, I just converted my 20A 12BH7 RF driver to a Russian 6H6n. These are similar tubes with much higher Gm. The pinout is the same except the filament uses 4-5 instead of 4,5 together and 9. I get more RF drive with the 6H6n. Might help your oscillator work with a 'dud' crystal.

Jim
WD5JKO


________________________________
From: Robert Nickels <ranickel at comcast.net>
To: central-electronics at mailman.qth.net
Sent: Tuesday, October 18, 2011 12:43 PM
Subject: [Central-Electronics] 10A

Wonder if there are any 10A gurus on the list?

Been trying to track down what seems to be an intermittent problem with 
low power output, down to only about 2 watts, although at times I've 
seen upwards of 5-6 out, which is what I'd expect.   Substituting 
another 9.0 mhz crystal seems to bring the power back up, so I'm looking 
at the 12BH7 master oscillator.   CE changed the design of this 
oscillator in the 20A so I wonder if it may have been problematic.

The schematic says there should be 50V of RF on the plate, yet I can't 
measure any because a scope or VTVM probe kills the oscillator 
(regardless of L2 adjustment).    I get decent sounding SSB even when 
the power is down, so I think the problem is related to insufficient 
drive, and the 9 mhz oscillator could account for that.  I've used a 
dual channel scope to adjust the 90 degree phase difference, and it can 
be brought right on the nose, so I'm thinking the coils L1 and L2 are 
fine, and it's the simple old triode crystal oscillator that was used in 
many similar rigs.   The original crystal oscillates just fine,  but 
maybe just isn't as active?

Such a cool little simple transmitter!  Thanks in advance for any 
suggestions.

73, Bob W9RAN
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