----- Original Message -----

From: g8guh

To: eddystone_radio_users@...

Sent: Saturday, November 25, 2006 4:45 AM

Subject: [eddystone_radio_users] S940 HT Current Draw

I recently repaired an S940 that has an HT current draw that is on
the high side: even increasing the two HT surge limiting resistors
(between the transformer and the 5Z4G rectifier plates) to 220ohm
(from 140ohm) - to try to mitigate for a 117v AC supply on the 110v
primary of the mains transformer (there is no 120v tapping) -
results in 110mA HT current draw when a strong station is tuned in,
with an HT2 of 240v (ie when the RF and IF valves are biased off by
the AGC circuit) and over 125mA when no signal is applied, when the
HT2 line drops to 225v. Most of the current draw variation is in
the cascode RF stage at 12mA (range from 8mA to 20mA) and 3mA from
the pentode RF stage (range from 7mA to 10mA). All the voltages in
these and other stages of the set check out well within tolerance
(most passive components in the first RF stage were replaced during
the repairs). I note that the 6ES8 max anode current spec is cited
at only 15mA, so that tube is working really hard under no signal
conditions (a bit worrying), but my other concern is that the
transformer HT secondary is rated for only 110mA (it is type 3937P)
and the 5Z4G rectifier is rated at only 125mA maximum plate
current. The set appears to be working ok otherwise but I am
concerned over stressing the 6ES8, the mains transformer and the
rectifier.

I cannot find reference to what the normal HT current draw for the
S940 should be in the manual or other literature. Can anyone
comment on this?

Thanks, Gerry, G8GUH, Vancouver, Canada