Thank you Mike.
> Try the plate blocking cap ... might not be carrying the current well on
> 160 , input SWR still ok when it drops to 400w?
The input SWR, Ip and Ig seemed OK on all the time.
Also thank you Gerald K5GW
> Hi Han, it seems something in the output circuit is changing value.
Until last evening I tried:
1. exchange two 170 pF and one 500 pF adding caps
with another set of similar caps: no improvement
2. exchange the plate blocking caps (two 0.001 uF 6 kV)
with a 60 mm diameter 1000 pF AC 7 kV disk ceramic
cap: no improvement
3. solder original plate blocking caps in parallel with a
0.001 uF 6 kV bypass-capacitor at the cold end of
the plate RFC: no power down occurred at 160 m.
Seemingly the reactance of the 1000 pF bypass cap
became insufficient specifically on 160 m, and its
capability has rapidly down with the RF current.
I also checked the power from 160 m-10 m.
The average power was approx 850 W with 60 W drive,
Ep= 3200 V, Ip = 400 mA, Ig = 130 mA, efficiency > 65 %.
But I found the power of 20 m band is continuously low
around 500 W - it is the next problem.
As the owner is not active on 20 m band he says OK
with this, but it is not acceptable.
The Chinese made 3-500Z with five plate disks stacked
(non-branded, very similar shape to a tube from Amperex)
must be working well on all the band.
Thanks again,
de Han JE1BMJ QM05BR
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|