The lowest Tune capacitance I can apply with an Air Variable is about 15pF. That minimum Tune C reduces PO by nearly 80%. Yet, with no Tune C connected at all (L network Tank) I see about 1:100 PO w/ reduced plate volts/mA.
The RF Input parallel resonance revisions appear to work fine and I will post Cores, # Turns and awg for each band but for now, 11M working best with 2T, 18awg on a small yellow core. 2nd best for 11M is 2T 24awg same Yellow core. Haven’t tried 20M yet but soon. The 11 position rotary input switch lets me try several combos at a time.
I added RF Input attenuation by shifting 300R of the swamping resistance to a series position in the Grid line (diagram uploaded a few days ago). It’s easier to test when amp not going full-tilt as I cannot drive lower than 5w. That’s with the bottom cover On so I should not make that mistake again. Tidied-up the T-R relay compartment too.
Tune C: I’ve never seen a vacuum variable in real life so I’m uncertain about mounting but I have the room and it looks do-able. I see a Soviet part (eBay: 4-100pF @ 5kv, Approx $150). It’s the cheapest ‘new’ I could find and the specs seem appropriate. No problems with Used but Western V-caps require special brackets, clamps and other hardware. Is there anything I should be aware of when it comes to Soviet V-caps? The vacuum relay I got awhile back works fine despite the 25v coil requirement.
I need to source strap for tank connections too. After the Tune C gets sorted I’ll likely revise the Load C padding. No more vacuum stuff though, wife is starting to notice, lol.
The RF Input parallel resonance revisions appear to work fine and I will post Cores, # Turns and awg for each band but for now, 11M working best with 2T, 18awg on a small yellow core. 2nd best for 11M is 2T 24awg same Yellow core. Haven’t tried 20M yet but soon. The 11 position rotary input switch lets me try several combos at a time.
I added RF Input attenuation by shifting 300R of the swamping resistance to a series position in the Grid line (diagram uploaded a few days ago). It’s easier to test when amp not going full-tilt as I cannot drive lower than 5w. That’s with the bottom cover On so I should not make that mistake again. Tidied-up the T-R relay compartment too.
Tune C: I’ve never seen a vacuum variable in real life so I’m uncertain about mounting but I have the room and it looks do-able. I see a Soviet part (eBay: 4-100pF @ 5kv, Approx $150). It’s the cheapest ‘new’ I could find and the specs seem appropriate. No problems with Used but Western V-caps require special brackets, clamps and other hardware. Is there anything I should be aware of when it comes to Soviet V-caps? The vacuum relay I got awhile back works fine despite the 25v coil requirement.
I need to source strap for tank connections too. After the Tune C gets sorted I’ll likely revise the Load C padding. No more vacuum stuff though, wife is starting to notice, lol.
