[HomeBrew] 6AG7/6146 xmtr progress

[kwylow zinjanthropus]

All:

Been putting some time into the project while I read your comments. Good stuff here! So far, I took note on the notes that my xfmr choice may be marginal. I also had a 800 VCT, 465 mA xfmr laying around that was about the same girth as the 600 VCT, 250 mA xfmr. I'm going to use that instead. Additionally, I'm not going to bridge rectify the transformer. Instead, I'll do the traditional method of full wave rectification by taking a diode of each "high" leg of the transformer and series them together at the cathode side of the diodes to the L/C  filter. I may do a variation of the Johnson Courier method of putting he 12 Hy choke on the center tap of the xfmr and ground. In that way, I'll reduce the h.v. tension on the choke. 

I just built the 6AG7 osc. chassis.  I'm using the osc coil from a Viking 1 parts rig combined with  a 100 or 140 pf transmitting cap. Feed through "caps" will be homebrew (I'm using #10 compressed fiber washers, 2 soldering lugs, and a #10 bolt to pipe through the DC, filament, and RF output (this is o.k. to do, right?)

I'm going to have to mount four more things to the chassis to make it complete: a key jack to key the 6AG7, an xtal holder, and a switch to select between the xtal and an outboard VFO. 

Tank circuit...well, someone commented that I was using a broadcast cap. That is true for the loading circuit. Traditionally, they have been the source for loading caps in the past. I don't think I'm using a broadcast cap for the plate circuit (unless the Cardwell cap I'm using was used as such and it doesn't appear to be a multi section receiver cap with all these healthy looking insulation on it and the large thick plates). Additionally, I decided to limit my  operations from 160-20. I'm not going to go 15 or 10 meters (I'll let my Ranger do the talking there). Hopefully, with the reduced amount of voltage I'm going to run on the power supply and with my selection of bands not including 10-15,  the tank circuit problems discussed will be reduced. I took a look at some of the other designs and also took a look at mine (again). I can get the farthest point of the coil to be within 2" of the bandswitch. The coil is 90 degress out of line with the bandswitch. Also, I forgot that a neutralization cap could be two wires twisted together. 

Back to the power supply: I suspect with the reduced voltage (at 400 x 1.414 rms) or now 560 VDC (maybe less with the choke), I'll be running on the order of around 50 watts or less. Additionally, I can now run the 6L6 plate modulation circuit with this supply. I'll have to figure a power supply voltage divider so I can get useful voltage for the 6AG7 driver and 6146 screen circuits. 

Let me know your thoughts. Cal, n6KYR



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