by Rob-NYC »
Tue Mar 15, 2016 3:37 am
Eitan, that is not how B+ switching works here. The tube heaters are on at all times when the machine is powered. However no dissipation takes place until B+ voltage is applied at the start of each record.
This switching of B+ at each record cycle was peculiar to AMI-Rowe and I regarded it as stupid and damaging to the filter capacitors.
I modded as follows:
1) Add an outlet controlled by a relay connected to the scan control. The amp is plugged into this outlet.
2) Bridge the B+ contacts on the mute relay in the amp. leave the mute and agc/squelch as-is.
In this as the amp is totally off except when a selection is made and remains full powered until the mach scans out after last selection.
In earlier AMI amps with AGC the inrush from the B+ at each record was used to hasten the release of the squelch voltage all allow the AGC to increase gain faster thus fading up the record until the records level takes over.
BTW: i meant to ask about what looks like a tube missing from that amp. That may be the AGC (automatic volume leveler) tube. If so you may be getting a lot of distortion from loud records as these circuits have a large amount of excess gain to allow the agc to bring up quiet records to the same relative level as loud ones.
Rob
"If we believe absurdities, we shall commit atrocities" -- Voltaire