HELP Troubleshooting old Japanese Germanium Transistor amp

[utilisateur]

I have this old Midland SS speaker amp

i got it cheap as there was something wrong with it. Now i cant realy find the source of the problem,
but the amp is putting out around 8V DC

The amp is built around Sanyo Germanium transistors
I can try to trace the schematic as it seems fairly simple,

but maybe you have some general pointers before i do so!?


[size=xx-small]Funny sidenote, the amp pictured in the wiki is the exact unit i have, i think the previous owner put in in there[/size]

 

[fortney]

If you don't get an answer here you may want to check the Audiokarma site.

F

 

[BrianDonegan]

You likely have one or more dead output devices. Can you get device numbers?

After getting the transistors straightened out (before installing any new ones), you will want to replace all of the electrolytic capacitors, as the elecrtolyte in the old ones is likely all long dried out.

 

[utilisateur]

Ah thanks for the answers so far

I had it connected to my ET1000 before and it worked,
one side was just a lot lower in volume.
That was before i started to look for the problem.So i guess the transistors on one side are still okay
That doesn't sound too good though, i dont think the original transistors are still available.

They are Sanyo 2SB492 8B , 2per side
Quote:

Originally Posted by BrianDonegan you will want to replace all of the electrolytic capacitors, as the elecrtolyte in the old ones is likely all long dried out.

Okay i'll take care of the caps first than =)

 

[BrianDonegan]

They are available. Here's one place: Semiconductor: 2SB492 (2SB 492) - GERMANIUM PNP NF TR.25V / 2A / 6W

BDENT might have them as well, but their site is down at the moment.

 

[utilisateur]

Wow thank you, that's great =)

Someone over at Audiokarma suggested Quote:

Since I see only one filter capacitor in the picture, I'm thinking it has capacitively coupled outputs, making offset measurements at the speakers irrelevant.

If thats right (my electronics background is bad and i dont realy understand why i shouldn't care about a measurable Offset of 8V) i might hook it back up to check which channel sounded bad and whether there were any artifact on the other channel ![size=xx-small]?[/size]

 

[ericj]

Quote:

Originally Posted by utilisateur /img/forum/go_quote.gif If thats right (my electronics background is bad and i dont realy understand why i shouldn't care about a measurable Offset of 8V) i might hook it back up to check which channel sounded bad and whether there were any artifact on the other channel ![size=xx-small]?[/size]

yeah, that logic is pretty opaque. If it were capacitor-coupled, there'd be no offset, and there'd be more than one big capacitor.

if you put a resistor across the output and measure the offset again, and it's still there, then no, it's certainly not capacitor coupled. and yes, you should worry about an 8v offset.

 

[BrianDonegan]

Well, BDent is back on line and they have them (B&D Enterprises: Part #2SB492). Let us know the results of your re-evaluation of the output, as you may not need to replace the devices. It could actually just be bad caps.