Hi John,
Lack of shielding, maybe (RFI from HV circuit)? I think the '575 doesn't have a shield lid in the HV area, but you can try again with the bottom lid in its place.
Regards,
Sebastian.
PS: Pete, please note that John provided pictures in the Photo files area.
Pete Lancashire 10:38am #149306
How about some pictures
. . .
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On Fri, Jun 29, 2018, 10:35 AM John <John@...> wrote:
My 575 mod 122C arrived at the weekend. It did basically work when
brought up gently on a variac. I've been through most of the valves and
replaced a few which were well down on emmision, including the 6AQ5 /V810.
Similarly, most of the paper caps have been replaced with polyester 600V.
I've just been through the cal. procedure and everything seems fine, but
there is now a slight dot-pattern on the trace which I don't recall
noticing when it had the "old" caps and "old" valves in place. As there
doesn't appear to be any Z-mod capability, I'm wondering what might cause
this? Or is it normal? I've checked the -1700V with a P6015 probe, and it
looks clean. There's small amount of ripple on the +2300V anode, but only
c 20V p-p.
Photo album uploaded under "575 dot-pattern trace"
John
