Phono on Audio Research SP-14 not working

[davstev]

Hi All,

I've just purchased a near mint A-R SP-14 preamp, with original boxes, and manual. Pristine.

I would be very happy, but, I can't get a sound out of the phono stage. There's one 6922 tube in the stage, which lights up when powered up. The line stage works fine, btw. MM cart into the phono RCA jacks in the back, selector on Phono. Nothing.

When I turn the gain up with phono stage selected, no music, but a fairly evident noise floor. It's possible the tube was damaged in transit, and doesn't work, even though it looks fine and lights up? (note: I don't presently have another tube to sub in to check this).

The seller bought it from an estate sale before reselling, so he didn't test it. He's not an audio guy.

Thanks for your thoughts.

David

 

[arts]

Hi David,I'm just over the bridge in Chateauguay.

It is quite possible that the tube,for a multitude of reasons,can be defective. Although it is rather rare for both sections to fail simultaneously,especially with both heaters lit.
This preamp is a bit of an odd duck,with the SS and the one tube in the phono phono stage.I am an ARC guy myself,and despite using the SS & tube combination in several models,I've never figured out that philosophy,haha!

Start by changing the tube.It is a common type,and is available just about everywhere.I would advise against ''vintage'' tubes,as I believe ARC originally used and recommends modern Russian replacements,such as Sovtek.Unfortunately,unless you are technically savvy,if that doesn't fix it you're gonna need a tech.

Cheers,

Art

 

[davstev]

Hi Art,

We've met, you came over to my house in Villeray and purchased an SME arm from me back in 2016!

Hope all's well. Thanks for the tips. From what I've read, the Sovtek's are reviewed poorly. I know that everyone has an opinion in the world of hifi and should be taken with a grain of salt, but the Sovteks are usually described as comparatively blah. Why wouldn't a well-selected vintage tube like Amperex or Siemens add a bit more flavour? What could be the problem with that?

Cheers
David

 

[Bob]

do some diagnosis with a copy of the schematic. no sound in both channels? and if
the tubes are dedicated per channel then swap. try all the other inputs - could be the
selector switch. try a pair of replacement tubes...

 

[fredtroy]

Regarding well-selected vintage tube like Amperex or Siemens, absolutely, go for it. ARC site contains schematics, wish you luck getting it working.

 

[arts]

Hey David,how are you? Haha,small world eh.That arm is on a TD-160 at the moment

The problem with ''vintage'' tubes is twofold; quality and pricing. There is a LOT of garbage floating around out there,and fakes are legion.Right down to the boxes these days.

Unless you do a lot of research,or buy from someone with a bulletproof reputation,you just might get taken.And there are a lot of sellers out there who tout matched sections,quoting transconductance figures etc.etc. and engaging in all of the usual hyperbole,but have certainly never given the tube a listen in actual operation.May have more crackles and pops than a baby rattle,and hisses like an old steam engine,but damn,look at those numbers! You might recall I'm a little jaded and sarcastic......
And after a lifetime in the industry,I have seen far more defective big-reputation tubes than anything modern,with the exception of Chinese.

I think many of the reputations for certain modern tubes were ''cultured'' by people with agendas,if you know what I mean.Frankly,the Russian 6H23P-EB is an incredibly good version of this type.

If you are interested,Audio Research will happily sell you a brand-new tube that has been tested and meets their criteria.After all,when this unit was made they certainly weren't supplying Amperex or Siemens as OEM.

 

[davstev]

do some diagnosis with a copy of the schematic. no sound in both channels? and if
the tubes are dedicated per channel then swap. try all the other inputs - could be the
selector switch. try a pair of replacement tubes...

No sound in both channels of the phono stage. Line stage working fine. The tube is in the phono stage, not the line stage. Single tube.

I need to get my hands on a tube to sub in to see if that is the issue, if the tube's shot (despite looking totally fine and glowing when plugged in and fired up).

 

[davstev]

Hey David,how are you? Haha,small world eh.That arm is on a TD-160 at the moment

The problem with ''vintage'' tubes is twofold; quality and pricing. There is a LOT of garbage floating around out there,and fakes are legion.Right down to the boxes these days.

Unless you do a lot of research,or buy from someone with a bulletproof reputation,you just might get taken.And there are a lot of sellers out there who tout matched sections,quoting transconductance figures etc.etc. and engaging in all of the usual hyperbole,but have certainly never given the tube a listen in actual operation.May have more crackles and pops than a baby rattle,and hisses like an old steam engine,but damn,look at those numbers! You might recall I'm a little jaded and sarcastic......
And after a lifetime in the industry,I have seen far more defective big-reputation tubes than anything modern,with the exception of Chinese.

I think many of the reputations for certain modern tubes were ''cultured'' by people with agendas,if you know what I mean.Frankly,the Russian 6H23P-EB is an incredibly good version of this type.

If you are interested,Audio Research will happily sell you a brand-new tube that has been tested and meets their criteria.After all,when this unit was made they certainly weren't supplying Amperex or Siemens as OEM.

All good advice, Art. Thanks for the ideas. Mostly, just trying to get a sound passing through the phono stage at this point, will consider the myriad tube options in the near future.