Power amp pop and scratch

[porcupunctis]

I'm looking for some troubleshooting advice.

I'm currently using a pair of non-bottlehead semi-monoblock 300B power amps.  This will only last until I get my paramour built (another story). 

After about 5-10 minutes of warm up, the right channel makes some popping and scratching noises that remind me of a turntable needle aggressively attacking an old, dusty, dirty record.  It will either clear up after a few minutes on its own or if I thump the top of the transformer cover (think Fonzy from Happy Days) it will clear up and not come back until the next turn-on cycle.

My research indicates this is a cathode short.  I tried swapping the tubes but the problem stays in the right channel. 

To confess, they are Dared 300Bs.  Even after I replace them with the Paramours, I will want to use them somewhere else, so I'm hoping I can track this down.  Once the noise is cleared, they really don't sound too bad.  The worst thing about these amps is that you have absolutely no space at all to upgrade or modify.

Thanks in advance for any pointers.

[Grainger49]

My favorite suggestion is to reseat the tubes several times.  Just pull them out and reinsert them about 6 times.  The metal on the tube socket and the tube pins can get a little corrosion on it.  This is just a mechanical cleaning.

If that doesn't help, do a tube swap, both the driver and output tube.  If it swaps channels then swap back only one.  You will find which tube is the problem.

Report back when you try this.

[porcupunctis]

Thanks, I should be able to conduct a proper experiment this weekend.  Also, I just realized that thumping one amp probably affects both so the problem may have actually moved with the tube and I hadn't realized it.

Mostly want to make sure there isn't a problem with the amp.

thanks,

P.S. I'll be looking for your advice on my Paramour build.  You seem to know your way around those pretty well.

[Grainger49]

Randall,

I have built one Paramount, the right channel for poster Paully.  I have watched over his shoulder as he has performed a number of modifications.  I am his technical resource when making more complex modifications.

I will be happy to help.

[porcupunctis]

The problem continues and seems to follow one particular tube.  I recently purchased Doc's SEX from RAMF 2004 and I'm using that in my main system right now.  I've moved the crackly 300b's to lighter duty.  I've decided to live with the startup crackle until the Paramours are assembled.

Grainger, I'm getting ready to build some good ol' Paramours, not Paramounts.  I was able to procure an un-assembled set of Paramours with the C4s upgrades for what I think was a great deal.  I'm about to send the plates off for anodizing and have been considering many upgrade options.  I have a ton of questions.

1. I want to build them as a mirrored set.  Is that a crazy idea?
2. Are the Magnequest iron updates really worth it?
3. Wardsweb describes a resistor change to the c4s board that I'm not sure about.  What's up with that?
4. Any other upgrade/advice/suggestions?

BTW:  Doc's SEX amp is just plain stunning both visually and sonically.  Can't wait to get more time in the listening room.

[2wo]

Mirroring a pair is trickery. There are a lot of stupid little things that can catch you up. Unless you are sure of your ability to take what the directions say and convert it to what they mean, well maybe save it for the upgrade cycle.

I say build it stock. OK, if you must, go ahead and get those expensive coupling caps.

       

[Doc B.]

If you are going to build a mirror image set, take Grainger's advice and number everything, and then also make a drawing of the new connections. That way only four or five connections will probably get screwed up ( voice of experience ;^)> ). It's quite a mind bender to flip everything around when the socket pins stay in the original orientation. You will find that some resistors won't span the new distances between terminals and many wires will have to be cut to fit rather than premeasured. Back in the old days I had to tell folks we wouldn't support kits built backwards because they were always such a pain to sort out. Nowadays maybe the community can help walk you through it - but if you ask me for help I will probably just screw it up worse.

[porcupunctis]

Got it.