Scott 299c Troubleshooting

[DoubleJ]

Hi All:

I usually run these questions by Craig but since he is out on his yearly "Fishing Expedition" you guys get the chance to poke fun at the tube newbie.

The Scott 299c runs perfect with my CD player(s) (no hums, no hiss, etc) but the PHONO section does have issues.

I've owned this unit for over a year now but only just recently got into VINYL so I can't really answer if this problem just started or was there all along.

I'll try my best to describe the problem(s):

1. I start to hear static when the volume knob reaches the 9:00 o'clock position (Please note: on this unit the 6:00 position is 0...and also, you have to push/pull the volume knob to turn it on/off) when I have the selector switch on the PHONO section.

Let me expand on what I mean by static. It's not like the static you hear in the old Frankenstein movies when they are bringing the Monster to life, BUT more like the static/white noise you would hear when you are between FM stations. The sound can also be describe as a lower tone of what you would hear when running test tones on a receiver. It is a constant/steady sound with no crackling, pops, or clicks.

This problem exists no matter how long the AMP has been powered up and can be duplicated using different outlets, speakers, and ground loop plugs.

Below is the current configuration of the system:

1. Scott 299c

2. Music Hall 2.1 TT. (Hooked to the Low Mag 2 rca jacks)

3. PR of Belles (I have K-Horns that I frequently swap in with this set-up)

Not a real elaborate or complex set-up that we are dealing with here.

I do understand/accept that there may be some HUMMS and HISSES in a lot of tube amps..and in the most part it is acceptable because you can't hear it when the music is playing. But in my case, you can hear it and it 's very distracting esp when listening to classical music and my favorite, Cello music..

Any ideas what may be causing this?

-Bad tube(s)?

-Pots need a good cleaning?

-Biasing? ( haven't checked the bias in a few months)

Any help/direction will be greatly appreciated!!

JJ

P.S. I'm willing to try any troubleshooting but there is no way am I going to start digging into wires and capacitors and such..I'll leave that to Craig!!!

[mark1101]

I have a Scott 299a rebuilt by Craig and actually it is the quietest amp I own. It does not matter where the volume knob is at the speakers are just about dead silent. It is REALLY quiet. I'm talking with my ear on the Khorn squawker, tweeter, and/or bass horn. No noise.

My Peach Preamp is tons more noisy, with audible tube hiss. But not my old Scotts. I also have an LK-72 not as quiet as the 299, but almost, and again, tons more quiet than my Peach.

Has Craig rebuilt your unit?

It sounds like to me your phono section needs to be looked at. You might want to swap some of the preamp tubes (12ax7's) and see if you can make the problem move or disappear. You can also try swapping phase splitter tubes and see what that does.

Edit: It's a good idea to know that the DC balance and bias are set correctly, and that you have good tubes. The AC balance too, but that takes a more than a multimeter to set the AC balance.

[DoubleJ]

Thanks for the reply, Mark!!

This Scott has been in a few hands of forum members (Spazzz, LWhaples) and Craig did some work to it but not sure at what point.

I also have a Peach that is mated with a Point to Point NosValved ST-70 and I concur, the Peach does have quite a bit of noise associated to it compared to the Scott.

You have pointed me in the direction I hoped for, Mark. I'm still not very clear on what role each tube has in the whole scheme of things so your suggestions have helped a lot.

Thanks again!!

JJ

[mark1101]

The phase splitter tubes should be returned to their original position after experimenting. I'm pretty sure the AC balance is set in conjunction with a particular tube. At least you can find out if you have the simple problem of an adjustment that is off or a bad tube somewhere. Otherwise it may need to go to see Craig.

If the line stage inputs sounded good than most likely it is either a preamp tube or in need of a repair in the phono section.

Have you cleaned the controls?

[thebes]

Mark's giving good advice. There are four small tubes in the front off the receiver covered with metal tube covers. Switch the left side two with the right side. I'm pretty sure the left-side controls the phono. Same with the middle tubes. Also turn the Selector switch back and forth a few times, may just be a bad contact at the RIAA position. Oh yeah make sure you play lps using the RIAA selection. Finally, try plugging the rca connectors from the TT into both the Low Mag and Hi Mag. The low mag gives the best volume but if you have hiss in one and not in the other in could simply mean tightening the female rca plugs inside the case. If you only have hiss in one speaker try switching the rca plugs around and see if the sound follows, could just be a bad interconnect.

[arfz28]

Doublej, Maybe try hooking your turntable to the mag high input instead of the low mag input, I am not sure what cartridge you have on your turntable but maybe the mag high input would suit it better Also if that doesnt cure your noise problems try swaping your 12ax7 tubes from one side too the other I think craig told me that 2 of the 12ax7 tubes is for the phono section and the other two the amplifier section. Have you ever used deoxit to clean the selector switches and pots on your scott 299c yet that needs to be done every once in a while.

[bkrop]

Try deoxit on the phono input plug sockets remember they have had 45 years to get crudded up.( That is if swapping 12ax7 tubes doesn't affect the sound, 2 are pre amp tubes for everything and 2 are dedicated phono pre amp tubes that the phono signal goes through before it goes through the other everything 12ax7s again. With "extra" and tuner the signal only goes through the everything 12ax7s.)

[ben.]

Heh... that old girl is getting around. I was the second owner of that amp. The phono section was always fine and I would be shocked if it was something more than a tube or gain mismatch, though it obviously has some miles on it. Do you still have the ragged old original box I sold it with?

Let me know if you ever want to sell it. I'd probably buy it back.

[DoubleJ]

First off..Thank you all for your suggestions.

After 2 hours of digging in my "not so organized filing cabinet" I finally found the biasing instructions that Craig provided. So, as you can see, my time table is a little behind and I'll hit it hard (not literally) tomorrow.

Marty: Thanks for the lesson in tube location. The 2 manuals I have didn't provide the information needed so I would have been scratching my head on figuring out which is which.

Ben: No ratty box. Larry packaged it to survive a drop from any height and survive a 10 mile drag on a rocky/rough dirt road

Here is going to be my approach based on what has been suggested. Please feel free to inform me if there is a better sequence:

1. Check the DC "bias" and make the necessary adjustments I have no idea on how to check the AC "bias" Mark mentioned. I only have a multimeter

2. If that doesn't improve or fix the problem, Then I'll swap the tubes around.

3. Maybe by this time, the problem will be fixed if not..I'll dunk the whole unit in "DeOxit". J/K

4. Inspect the RCA jacks as mentioned in another post. This suggestion made me stop and think. I never did feel comfortable on how the RCA cables felt when plugging in the TT. It is a lot tighter and doesn't feel like it fits as well as the CD player.

5. not sure. Probably try variations of the things already mentioned.

6. Complain and whine about Craig's work []

I pretty confident that this isn't a serious problem and by your help and suggestions, we will figure it out.

This is going to be a great learning experience for me and I do appreciate your help, dedication, and patience.

JJ

[lwhaples]

Glad to hear your getting into vinyl. I used the Scott when I was first getting back into it. Hopes it works out for ya!

Larry

[NOSValves]

JJ,

I'm back give me a call anytime 8am to 10pm 810-287-6135. I'm sure it's something simple but keep in mind vintage phono sections are never silent in fact no tube phono stage is dead silent like the CD or Aux inputs even the BBX phono stage has some hum/hiss (mostly white noise at higher volumes). That said it does sound like you have it happening earlier on the volume control then normal. Usually on the Scotts hiss does not become audible on the phono section until 12:00 or more which if using the proper output cartridge would be blasting loud playing music. You should be checking the bias but it would have zero effect on this hiss. The first thing you need to do is install some different 12AX7's in the two far left slots when viewing the amp from the front.

Craig

[oscarsear]

Jeeeze I love this forum.  I have a Scott 299 something that I have never hooked up to anything.  But, I know when I do that if I have even the teeensiest question that there's a wealth of "right now" knowledge at the ready.  Thanks in advance.  Carry on.