asr433 simple problem (i hope)

[ericaction]

My wife moved my new console and I know have an issue with my left channel on my asr433 stromberg carlson. It had a tick noise that was barely audible that is still there but now the left channel is quieter than the right. Considerably as the left on about 8 is the same as the left on 5. I swapped the tubes from left to right and it didn't change the issue.

Ground issue? I have yet to open it up as I can see the multicap can has been replaced upon a time. Was hoping go recap it ss soon ss I get the caps itemized and ordered. Besides internal ground anyone have some hints to hunt it down?

Thanks
Eric

 

[Tom Bavis]

The resistors around the 6U8 often change value - I've seen some that were three times the marked value! Check voltages there for a start.

 

[DavesNotHere]

sounds like a plate resistor cold solder joint. or a slightly opened cap lead. check construction for mechanical stress/defects.

 

[ericaction]

Also someone suggested it could be the neon pilot light as it is flickering. Would that effect only one channel - haven't looked at the schematuc . Will open it up tomorrow and see. Does the pilot sound possible as I have read some say snip it out.

Eric

 

[Tom Bavis]

The neon pilot light is also used to generate a low-frequency "balance" signal. Turn it off. Maybe you need to clean the Balance switch. I don't think ANY of the schematics show this correctly, but I may have a few more to check - refer to the 444 schematic, I think that shows it correctly... if you haven't gotten the schematic and instructions from my web page, it's Made In Rochester

 

[ericaction]

I was told to just cut one of the leads. Is that what you mean by cut it off? This site is amazingly helpful for beginners . I appreciate the help, I have built but haven't troubleshoot older tube amps. So I really appreciate not rediscovering the wheel.

 

[Tom Bavis]

Output balance switch, far right on front panel. Switch it to OFF. Pilot light is supposed to flicker when it's ON - it's used as an oscillator.

 

[ericaction]

So when I turn the balance switch ON it ticks really loud, when I turn it off it ticks quietly but enough to drive me crazy and the pilot still flickers. Looks like this was recapped by. A restoration place about 10 years ago and so far the caps are measuring okay.

Any ideas on what is going on with the balance switch as I have never had an amp with this and not really sure what its doing here.

Thanks again.

 

[Tom Bavis]

It's supposed to flicker when in the ON position, be steady when OFF, which is what mine do, as I recall... There are several schematics, all different. I only found one schematic that makes sense and it's one from the bottom of a later 433. In the OFF position, the neon should have a 470K resistor to B+. When OFF, it has a 22 meg, which in combination with the 0.1 uF cap will make it oscillate in the low Hz range. It's possible the switch isn't making contact on one section, or it's miswired (somebody followed one of the OTHER schematics...) See attached...

 

[ericaction]

Thank you so much.
So I opened it up and finally and even though the Can was replaced I shouldn't have assumed that it was completely recapped. I understand now better what that "output balance" is there for - what a strange thing to have as I can't imagine why this was there for the average consumer to turn on and hear that noise and think things were broken.

I suspect that something is going on with that part of my circuit as you can still hear the ticking and its strobes when switch is turnedoff (too a lesser degree). I attached a couple of photos.

The diagram you posted seems to be the same as on my metal. The R74 is the resistor with the output balance and on the schematic says changed from 470K to 220K your thoughts? I don’t see me needing the switch, do you propose a way to bypass it to see if that fixes my issue? or a good way to easily troubleshoot.


Thanks again and any input on anything you see - I haven't worked with something this old, what should I absolutely do before I use this thing, it has been in use by the previous owner and I have played about a dozen records on it but I have too eliminate that ticking as it drives me crazy - but even in this shape sounds really nice for my bedroom second setup.