[Boatanchors] HRO-5TA1 Questions

[Al Klase]

On 11/16/2015 8:25 AM, Joe Connor via Boatanchors wrote:
> I need some help with this receiver. I've recapped it, replaced the out-of-spec resistors and aligned it. It's working very well. I'm using a 5886 power supply (170V B+). I am attaching a link to the schematic. http://www.nostalgiaair.org/Resources/397/M0012397.htm
Here are my issues: 1. The S meter does not move at all. How do I 
troubleshoot the meter itself and the S meter circuit? This is my first 
non-working S meter.......Joe,

1) "Ohm" the meter movement with a DMM.  I'm guessing on the order of 
100 ohms.  The digital instruments only source about 0,5 mA, so you 
won't prang the meter.  Avoid old analog ohm meters.
2) "Ohm" the switch.
3)  You should observe a fairly high DC voltage on both sides of the meter.

The meter sits in a bridge circuit.  One side is a reference voltage 
generated in the screen-grid feed, R10, R30, and R32.  The other side of 
the bridge is R11 and the plate resistances of IF amplifiers V5 and V6.  
R30 is used to balance the bridges, zero current in the meter, with zero 
input signal. i.e. full plate current through the tubes.  When the IF 
gain is reduced by the AVC or the RF Gain control applying a more 
negative voltage to the grids of the RF and IF amplifier tubes, the 
current through V5 and V6 is reduced, and the current through the meter 
increases.

Hope that helps,

Al

Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/