reverb trouble shooting on 68 sentura I

[hawaiitone]

here's the skinny - tank makes noise when I give the amp a thump - not the tubes (changed them) - one of the rca cables makes a noise through the speaker when I tap it, the other does not - no reverb - no change when I hooked up a working tank from another amp - any suggestions? Many thanks!

[Isaac]

I don't think I've ever known an amp with a reverb tank that didn't make a noise when thumped. So, to be clear, is this a different noise than the usual "crash" that reverb tanks make when jostled, or not?

[loudthud]

You might try substituting those RCA cables. The drive tube is the 12AU7.

[noel]

If I'm hearing you correctly it sounds like the input side is bad to me.  If you tap it (manually place an input into the system) you get an output.  That seems to tell me the output is working.  So start looking for problems upstream (on the input side).
Hope that helps.
thanks,
Ryan

[jbopper]

As much as I love Sunns, their reverb cables are the bane of my existence.  Virtually all of the reverb problems on my entire fleet of Sunn guitar heads are traceable back to faulty/intermittent reverb cable connector joints.  They were crappy to begin with and after 40 years of wear and tear and oxidation, reverb problems are absolutely guaranteed.  Replace those cables! 

I've also recently discovered that there are lots of intermittent grounds between the RCA chassis jacks and the chassis itself.  Again, years of oxidation and a relatively loose riveted fit holding the jacks against the surface of the chassis.  If any one of these junctions has high resistance, your reverb is dead!  I actually had to run a special grounding bus to every single RCA jack in my '72 Sceptre to get the reverb working and now it's fine.

Good luck!

[HRobert]

Your problem might be with the reverb tank.  I have a 1967 Sentura II and it had the original Gibbs F spring reverb tank.  It worked, but was rather weak.  I contacted Accutronics in Chicago ( many years ago they bought out the company that made the Gibbs F unit ) and they have an identical replacement; the Type 4.  It's great and only cost $43.95 ...including shipping.  Go to the Accutronics web site, Accutronicsreverb.com , and contact Cal in customer support.  He can tell you exactly what you need.  I bought mine with the longer delay time for the reverb,  #AB3A1A.

Rob

[hawaiitone]

Thank you for all the replies! I did try replacing the RCA cables - no luck. Also, the "thump" probably would be better described as the swooshing noise when you shake an amp with a reverb tank in it. I'll keep on this and share my discoveries. This amp came into my life from a guy who was clearing out his garage and no longer wanted it. He gave it to me! The born on date in the chasis 8-20-68. The amp sounds incredible and I can only imagine how much better it will sound with working reverb.

Aloha!

[hawaiitone]

I'll also check the upstream grounds - can I spray deoxit around without risking any damage?

[loudthud]

Does the amp have the little lever to lock the reverb?

[hawaiitone]

Hum... I didn't know of such a thing - where is it on the amp?

[loudthud]

It looks like a little piece of bent steel wire. It hangs down from between the tank and the top wood of the head box midway along the tank.

[HRobert]

Does the amp have the little lever to lock the reverb?

I don't believe that the Gibbs F unit had the locking lver for the reverb.  I think the reason was that the reverb tank was mounted on the top of the amp head, not on the botton as with Fender, or on the side as wit some Hammond organs.

Rob

[EdBass]

This is the reverb lock on my Sceptre. It kinda hides up there, I didn't know it existed until I read the red label on the chassis.

[EdBass]

Oh yeah; this too...

I don't think I've ever known an amp with a reverb tank that didn't make a noise when thumped. So, to be clear, is this a different noise than the usual "crash" that reverb tanks make when jostled, or not?