Hitachi SR 603 Transistor Question

[avionic]

The DC offset in the Hitachi was only 4mv in each channel.

Thats excellent.

if you put your ear about 6 inches away you can hear a "hsssss" at about 2 volume

Floor noise -- this may just be the nature of the beast.

 

[Isaac C.]

Ok, thanks for the help! I'll resolder those transistors and check those connections tomorrow.

 

[Isaac C.]

Look your solder connections over for Q801 and Q802 2SD478 and 2SB568 in the power supply.

I put the SC458s back in, one of the 2240s was definitely a dud because now it works as if I hadn't touched the unit in the first place. I checked Q801 and 802 and sure enough the middle joint on 801 was almost as if it was not even soldered in and 802 had a bad joint on one of the outer pins. After adding some solder to these two joints, the noise floor is greatly reduced. At a volume of 2 I have to put my ear against the tweeter to hear it, and at full volume it is only heard a couple feet away.

 

[avionic]

Those regulator pass transistors (801 and 802) have a tendency to unsolder themselves over repeated hot/cold thermal cycles over the years.

 

[ecluser]

This receiver is made with the HA1452W, kind of op-amp. Some become noisy with time. I've seen that they can be very noisy in the first 10 minutes of operation and then the noise floor reduces to acceptable level.

 

[avionic]

This receiver is made with the HA1452W, kind of op-amp

The CR-2040 uses the HA1457 that go noisy as well.