My first Stromberg-Carlson

[Dicky]

Yes Sir that would make it easier for me.  I'll get some pictures up when I get out to the garage.

[Sir Thrift-a-Lot]

Cool.   Start your own thread so people can give you advice on how to proceed.

[Reverend]

Looks like a fun project, congrats on your pickup!

[Sir Thrift-a-Lot]

Thanks Rev!   Wish me luck.

[Sir Thrift-a-Lot]

Well, as you can tell by the dates on these posts, I tend to let projects sit around for a while.   I finally got around to recapping this amp.   I played it for about 15 minutes and it sounded good.   It was actually bass heavy, which I didn't expect.   On my phone EQ I lowered 120Hz and boosted 4k to make it sound good.   

I was cruising along, listening and taking pictures when suddenly, like someone flipped a switch, the music was replaced by a loud buzzing sound.   I took a quick glance at the tubes to make sure none of them looked like they were stressed (and they didn't) then I quickly shut it down.   

You guys have a lot of knowledge, what should I look for as a culprit?   

BTW, don't be too hard on me for how I ciphered those caps in there.   Remember I am remedial and this is the farthest I've gotten with a console pull.   Thanks.

[bmwr75]

How is the input from your phone grounded??  A bad input ground will cause a hell of a buzz.  I don't see any wire going into the input ground lug hole, just your left/right channel wires.

Did you replace the coupling caps (small orange looking ones on the bread board that also has all the small resistors)?

[Sir Thrift-a-Lot]

I did not replace the coupling caps.   I thought they were Micas and didn't need to be replaced.   If it will bring significant improvement I can.

There are wires to the ground, but they may be somewhat precarious.   I'm going to wire up another adapter and see if that helps.

[Sir Thrift-a-Lot]

BTW, what is the function of a coupling cap?   I'm weak on basic theory but should probably know this stuff.

[bmwr75]

I replace coupling caps just for good measure in all tube amp restorations.  My guess is many times they are still good, but do it just as an insurance policy.

Check out this AudioKarma link:  http://www.audiokarma.org/forums/showthread.php?t=443915

What do coupling capacitors do in an a tube receiver or tube integrated amp?
Coupling caps are wired in series between the signal tube anode (plate) and power tube grids and are some of the most important capacitors in an amp because they can affect the sound quality the most of any small value capacitors in a tube amp. Typically, coupling caps are non-polar (doesn't matter which lead is soldered where) and are replaced with high quality paper in oil (PIO) or metalized polypropylene capacitors. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. Coupling caps wired in series block DC voltage and allow AC voltage to pass through to the power tube control grid.

[Sir Thrift-a-Lot]

So, if I'm gathering correctly, you MUST replace power supply caps or risk catastrophic failure.   Coupling caps can have a drastic effect on the sound but aren't likely to take out anything with them in they bite the bullet.   So, the PS caps should be done before powering the amp, but the coupling caps can be done at your convenience.   Would this be a correct statement?   Thanks again for sharing all of your knowledge.

[Resident]

Congrats Stal thats  some clean good looking tubage you have there. 

[bmwr75]

Hey Mark,

I think both power supply and coupling caps are important.  Which is more important?..........don't get me started lying.  I do both on all original tube amps from the 1960s and earlier.

Regards,
Scott

[Sir Thrift-a-Lot]

....don't get me started lying. 

I don't get it.   All I was asking is if a coupling cap failure will damage associated components.   I understand about sound quality and know that can be controversial, but that isn't the question I was asking.

You know so very much more than me and have been exceedingly generous.   I wouldn't deliberately put you in a bad spot.

[Sir Thrift-a-Lot]

Okay, I resoldered the inputs and had two sessions each over an hour tonight with no issues.   Seems it was as simple as dropping a ground at the input.   The first session I had with my phone, then later I put in my Pas3 pre.   It turns out that the bass heavy voicing is my stupid phone, not the amp.   They must do it that way for the earbud crowd.   It also turns out that 80s Sony CD player into Pas3 into SC 6V6 into B&Ws is a very pleasant combination.

I do, however, need some engineering help with one issue.   The SC console was an entirely passive pre, so the inputs are quite hot.   It was literally a 1/4" turn of the volume control to get from silent to a comfortable listening level, then another 1/4" to get to "blow your face off".

What, if anything, should I do to get this amp to a more standard input level?   TIA.

[bmwr75]

The simplest fix is to use some RCA line level attenuators like these:

http://www.amazon.com/gp/product/B0006N41B0?psc=1&redirect=true&ref_=oh_aui_search_detailpage

If that link doesn't work, Google "Harrison Labs 12 dB RCA Line Level Attenuator Pair".

What are the driver tubes in the amp (e.g. the small signal tubes)?  If they are a 12AX7, trying a lower gain substitute might do the trick.  You can read about that here:  http://www.thetubestore.com/Gain-Factor