Help with ARC Preamp

[jprossi]

Hi all, I've enjoyed reading posts on AK for a while now, but this is my first post. I've recently acquired some new gear: an Adcom GFA-555 and an Audio Research SP-6c. When I got everything hooked up and switched on the SP-6, nothing happened. The green LEDs for "pre-amp on" and "switched-on" do not illuminate and I am not getting sound. The odd thing is that I have a light plugged into the un-switched outlet on the back of the preamp and it gets power. Also, I can hear a slight pop from the speakers when I flip the mute switch. This is my first tube amp and while I'm hesitant to poke around in a unit carrying over 500 volts DC in places, I was wondering if there's anything I might be able to check in order to get this thing back online. Anyone know of common problems that could lead to this? To my knowledge, it worked before I got a hold of it though it did sit for a couple of years. Worse case, I believe this unit is good enough to be worth having serviced. In the meantime, any help is greatly appreciated!

 

[Blue Shadow]

First thing I would do is pull and reseat all the tubes. Dirty tube sockets could cause issues but complete lack of signal, IDK.

Are all the switches in the right position?

Yes, worth the repair if needed.

 

[diamondsouled]

The SP-6 is an excellent preamp and well worth getting up and running. Like Blue mentions check the tubes and tube sockets. If you have contact spray clean the tube sockets as well as the RCAs. If you get no joy from that and you haven't the qualifications for further trouble shooting give a notice here and someone will point you in the right direction.

 

[primosounds]

There might be a relay the switches the B+ from the mute. If the relay is not working you will not get any joy from your unit. You can check to see if you get high voltage B+ at the main filter cap and then measure if you are getting about the same B+ at tube plate resistors. That would at least let you know if the hi voltage is working.

 

[kirk57]

My $.02 is that if new tubes don't fix it, take it to someone who knows what they are doing (preferably ARC, but it'll cost you).

An ARC SP-6C is not something you want to use to learn how to work on tube stuff.

 

[whoaru99]

Presumably you've checked the fuse(s)?

I understand there is power at the aux receptacle(s), but aux receptacles aren't necessarily fused.

 

[heyraz]

I'd like to add that while checking the fuse, make sure the value is correct.
I've received previously owned equipment with an overrated fuse, which makes me wonder why the original was replaced in the first place.

Also...do the tubes light up? You didn't mention.

 

[jprossi]

It appears the fuse is at least part of the problem. Made the assumption that accessory outlets were all on the same fuse - dumb mistake. The back of the unit seems to indicate a .6 amp slow-blow fuse. I replaced the fuse with one that was in it when I got it: a .5 amp standard fuse. I did get a momentary glow from the LED before it blew. I've had a lot of trouble finding any kind of .6 amp fuse, no less a slow blow. The tech at the local vintage audio place said I would be okay with a .75 amp slow blow and he gave me one to try. He recommended unplugging the unit from the wall, installing the fuse, plugging it back in, and allowing it to remain on stand-by for a few minutes before switching it on. The light came on for a little longer, then went out. I'm figuring the fuse blew, though on this one it's a little harder to see a break in the filament. I've attached a picture of the back panel. I'm not misreading this, am I? As for the tubes, I do not see any light.

 

[Blue Shadow]

Check the fuse with a meter. If a .75 slo-blo is blown, the unit must be serviced.

 

[whoaru99]

Yeah, even if the fuse wasn't larger, repeated blowing of the rated fuse indicates some type of problem.