Another Scott 222C

Glassweights · Dec 12, 2008

Decided I need a conventional integrated amp to ease the wife in to my tube mania and so I scored this one. Looks pretty much original to me. The guy that sold it to me at a famous auction site said it was all working and showed it set up on his bench, so I am listening to it . . . but, it clearly should have some cap work done and I am just the guy to do it!

Only one real question, that sorta tall skinny white capacitor looking thing next to the rectifier, it is hot :banana:

is it a cap? I can't really read it, have a couple of schematics. Ok, looked at the schematics and maybe it is a resistor?

So, the big cans are running cool. I am sure I want to replace them . . . maybe if I can find some replacement cans. (I must like this amp because I am too cheap to do that on any other amp.)

I have three types of .1 uf caps on hand. (my other amps will be sad I am using their parts!)

Solen .1uf 630v
Mallory metal poly .1 400v (that is the yellow ones)
Vishay Sprague 715 Orange Drop .1 600v

So opinions on where to put which type would be great!

http://hhscott.com/pdf/fs/222C-C1.JPG <-- schematic is there

I think I listed them in the order an audiophile would, after he puked at having to even consider such lowly caps

My real problem is I don't know which parts of the signal path I should give priority to. There are 10 total .1uf caps in there and normally I would just swap them all out with whatever I had that was acceptable.

Maybe it is really simple, best caps on the circuits I actually use? Hah

I need to test all these tubes, they are all USA, but the power tubes are regular 6BQ5 and I think that is a bad idea? I need the stronger ones instead? EM? The next tubes are 6GH8A, RCA, so that should be good. 12ax7 in all the preamp spots.

And, a nice German square component, I have to look up if that is the dread Germanium unit. . .

It actually sounds pretty nice! I set my Nomad MP3 player to Disco so it would pump up the bass and it started really thumping. Kinda struck me that it thumped a lot harder after it ran 20 minutes.

I am real happy, and my friend who was here is now scheming to drop some $$ into a tube rig also. . . he is kinda rethinking getting a logic3 tube ipod player and maybe getting something like this. hah

NYListens · Dec 12, 2008

The tall skinny thing is a resistor.

Glassweights · Dec 12, 2008

Tall skinny

Thanks for the confirmation on the resister!

Glassweights · Dec 12, 2008

Speakers

Oh I forgot to mention,

I am playing these though some JBL Stadium speakers. They have more bass and are 90db. (Compared to the JBL studio bookshelves I pair them up with in my main system.)

I just have those stadium speakers because my crazy friend had to sell them off right after he got them, and I am always a sucker for a deal.

I guess I could hook up my JBL cabaret cabs, they have some real horns in them, but they are kinda for PA. All my good stuff is for live sound and reinforcement. (dangit!)

Dan

kvflyer · Dec 12, 2008

Well, that is a very nice amplifier. It is similar to the LK-48 kit amplifier.

Here are the items that you may want to address.

1. Replace the square bridge rectifier marked Siemens. It is the bias bridge for the output tubes and it also makes the DC voltage for the preamp tube filaments. No big thing if the filament voltage goes low. However, a major problem if the negative bias for the 7189 output tubes is not enough. Notice the positive side of the bridge rectifier goes to ground. Your output voltage will be negative. You can use a silicon bridge rectifier, available from Radio Shack. 6A 200V, $2.59. http://www.radioshack.com/product/index.jsp?productId=2062583

2. Replace the first resistor after the bias bridge, an 18Ω 1-Watt (brown-gray-black-silver) with a 33Ω 5-Watt resistor. You may have to adjust this value but it is almost always 33Ω. Reason; the silicon bridge is more efficient and the output voltage is higher than the selenium bridge.

3. Replace the .1µfd white American Radionics Ceracaps capacitors. If they are not leaky, they will be eventually. Others will probably disagree but I use Orange Drop capacitors or the yellow Lemon Drops capacitors for coupling capacitors. I would replace all of them. The two that are on the rear of the chassis are in the feedback loop. Not as critical but easy to get to for replacement.

4. Replace the 6BQ5 tubes with either good NOS 7189 or 7189A tubes or you can get the surplus Soviet Military equivalent, 6pi14pi-ev (6П14П -ЕВ). They are available on that auction site. I have purchased many and I am completely satisfied.

5. You could replace the rest of the signal capacitors also. But the ones on the tone controls do not have much voltage on them and still may be good.

Filter capacitors may still be OK but if you feel ambitious, you may at least want to replace the first one after the GZ-34. It takes the most beating and it is near the power transformer and rectifier. Heat is an electrolytic capacitor's enemy.

kvflyer · Dec 12, 2008

BTW, that is one very nice amplifier. I have a few. 222C, 222D, LK-48, LK-48B and of course the 299 series.

kvflyer · Dec 12, 2008

I noticed in the pictures of the underside of the amplifier that most of the Ceracaps have wax dripping. They are paper and the paper will deteriorate. Good thing to replace. I also see that the first filter cap is a Mallory type FP. They seem to be the most reliable. Astron brand are often bad.

Glassweights · Dec 13, 2008

Scott 222c rebuild stage 1

ok,

I used the caps I had on hand to rebuild the scott as far as I could. All the .1uf have been replaced now.

I measured resisters as I went along, they were all within spec but certainly not tight. (5-8%)

The sockets are a bit loose, figured that out when one of the tubes red plated on me, I went all over my work, found nothing. reseated and started measuring voltages, but, it was all good after the reseating.

Anyway, the sound is certainly improved, not by a lot, but it is sounding even better. The bass is much improved, but it is quite loose when a lot of low end is going on at one time. Single bass notes are just awesome.

So, replacing the large cans and adding a bit there, along with replacing the few white caps missed is up next.

But it already blows away my old pioneer amp.

Just in case you don't believe the amazing audiophile system, refer to "his master's voice" below

kvflyer · Dec 13, 2008

If you are having problems with the 7591 tube or tubes having red plates, a very important step still needs to be addressed. That Siemens selenium bridge rectifier should be replaced with a silicon bridge and the first resistor after it, the 18Ω resistor changed to 33Ω, 5-watt. Remember that bridge rectifier provides the negative voltage used to bias the output tubes. Not enough negative bias, and the tubes conduct heavily even with no signal present.

Another thing that will cause red plates on 7591 tubes is an internal heater to cathode short. That can be verified with a tube tester or if you move the offending tube to another socket and the problem follows the tube, you have a bad tube. I have found a few of the old tubes with this problem.

kvflyer · Dec 13, 2008

You may want to get a GZ34 for the rectifier. The 5U4 draws way too much filament current 3A vs. 1.9A with the correct rectifier. It also provides a softer start with B+ because it is a cathode rectifier.

When you get a chance, you may want to change those .25µF bypass capacitor on the phase inverter tube.

Please don't think that I am picking on your work. It looks great! You have a very nice looking amplifier. I really prefer the brown knobs over the optional brass colored aluminum knobs. Metal knobs were a $5.95 accessory!

Check out this site. I think you will like it.

http://www.fmamradios.com/ScottAmps.html

Glassweights · Dec 14, 2008

Thanks for the input!

kvflyer said:
If you are having problems with the 7591 tube or tubes having red plates, a very important step still needs to be addressed. That Siemens selenium bridge rectifier should be replaced with a silicon bridge and the first resistor after it, the 18Ω resistor changed to 33Ω, 5-watt. Remember that bridge rectifier provides the negative voltage used to bias the output tubes. Not enough negative bias, and the tubes conduct heavily even with no signal present.

Hmm, I checked all the voltages on the tubes and wrote them down, the negative bias is at -15.8 -15.48 on the pair with the tube that red plates and -14.93 -15.62 on the pair that is working fine. That one tube's voltage is low. I have not fooled with the bias yet since I am quite sure I need to upgrade these tubes. Do those voltages look low? If it is low I will shut 'er down till it is safe.

The bridge rectifier is very high on my list. I can run around during the day on mondays so I will get that done then for sure.

kvflyer said:
Another thing that will cause red plates on 7591 tubes is an internal heater to cathode short. That can be verified with a tube tester or if you move the offending tube to another socket and the problem follows the tube, you have a bad tube. I have found a few of the old tubes with this problem.

Whipped out my Hickock 6000 and measured the output tubes. They are tired but still ok. So I have a little breathing room. I tightened the socket a little, my dental tool is pathetic but I was determined! Cleaned the sockets a bit also.

I think it helped a lot, my house does shake when you walk on the floor. a turntable is completely unworkable here :sigh:

I will swap them around if it recurrs, great idea. I was resisting that because I thought it may be all dialed in, but, troubleshooting will have to take priority!

kvflyer said:
You may want to get a GZ34 for the rectifier. The 5U4 draws way too much filament current 3A vs. 1.9A with the correct rectifier. It also provides a softer start with B+ because it is a cathode rectifier.

Oh, good to know, it bugged me that it was too tall, I figured the 50v drop was good though. I will find one for sure.

kvflyer said:
When you get a chance, you may want to change those .25µF bypass capacitor on the phase inverter tube.

One of them is actually pushing out of the tube like 1/4" !! I need to get that ASAP, It shows open circuit on my meter, so maybe it is working for now. (or maybe it is, open!) But, it is on the list for a capacitor purchase. Pity my capacitor testor need new capacitors before it will work properly.

kvflyer said:
Please don't think that I am picking on your work. It looks great! You have a very nice looking amplifier. I really prefer the brown knobs over the optional brass colored aluminum knobs. Metal knobs were a $5.95 accessory!

I am very grateful for your input. I know you have probably told others these same things a lot of time, so I appreciate you taking the time.

kvflyer said:
Check out this site. I think you will like it.

http://www.fmamradios.com/ScottAmps.html

Very nice! looking for the scott forums too, I hear there are some. Want to read all I can about this gem.

Dan

kvflyer · Dec 14, 2008

Dan,

There was a Scott forum that went on for years. Lee K Shuster was the moderator. The original site still works but the forum does not. What a shame. We could really exchange ideas and for the most part, there were not too many squirting contests going on. Very objective, not a lot of subjective. Best of all, we were very hard core Scott vacuum tube. I miss the site. I have tried to contact Lee a few times but to no avail. Don't know if he is still around or whatever.

The basic site is: http://www.hhscott.com

There is very much information there. More than you will ever want! I suspect you already know about the site. But the "Secure Forum" is what I miss. Maybe, some day!

Don

GordonW · Dec 15, 2008

kvflyer said:
You may want to get a GZ34 for the rectifier. The 5U4 draws way too much filament current 3A vs. 1.9A with the correct rectifier. It also provides a softer start with B+ because it is a cathode rectifier.

Agreed. Either a 5AR4 or 5R4 (both about 2 amp heaters) would be appropriate. The 5AR4 will give a little more power; the 5R4 a little less, but probably longer tube and capacitor life (it'll drop B+ just a bit)...

Regards,
Gordon.

GordonW · Dec 15, 2008

kvflyer said:
8Ω 1-Watt (brown-gray-black-silver) with a 33Ω 5-Watt resistor. You may have to adjust this value but it is almost always 33Ω. Reason; the silicon bridge is more efficient and the output voltage is higher than the selenium bridge.

While you're working in that area, you also need to replace the bias filter cap (usually 50uf 75 volt). IME, those things are frequently leaky... and if they're not leaking now, they WILL in the future. I just use a good 100uf 100v cap there (cheap, effective, a bit overkill, but sounds good and works very well).

Regards,
Gordon.

Blast · Dec 15, 2008

kvflyer said:
Dan,

There was a Scott forum that went on for years. Lee K Shuster was the moderator. The original site still works but the forum does not.

I get emails from the forum all the time. I don't know why it doesn't work for you.
Brian

kvflyer · Dec 15, 2008

Hi Brian,

Are you telling me that you can access the HH Scott forum? Try clicking the link at the bottom of the page that says, "Join Scott Forum". That is where I am talking about. I have gotten emails from members too. But the forum doesn't seem to work. If you get it to work, please let me know.

Here is a link to the "Secure Forum" http://secureforum.com/~vhhscott

Emails to Lee Shuster have gone unanswered.

Thanks,

Glassweights · Dec 15, 2008

Further progress

I went to my bud's guitar store and bought a 5AR4 today.

He sent me home with yet another amp to look at. (20 minutes later I am like, yup, needs buncha caps and he won't want to pay for that!)

But back to this amp. I found a total hoss of a rectifier and installed that and the 33 ohm resister.

Also replaced the funky .25uf/200v caps.

And for fun I replaced the first 20uf/450v cap after the power transformer. Then I stuck 100uf in the next slot.

I picked that value after careful consideration. That and the fact that it was the only big 450v cap my parts house had. :banana:

Everyone overcharged me everyplace I went, but I was glad to get some parts locally for a change.

BTW, check out this one cap I pulled out in the pic below.

Dan

FalconEddy · Dec 16, 2008

knifefighter said:
BTW, check out this one cap. . .

Yeah, that's one of those American Radionics that puked!

Good to see you replaced it.

I still see four 330K grid leak resistors in there. You'll probably want to change them out to 200K or 220K if you plan to run new production tubes. But, you may want to check on that with Jim McShane first. (300K is the max grid resistance for those power tubes in the RCA Tube Manual, and the new production tubes just aren't as robust as the vintage type).

. . Falcon

kvflyer · Dec 16, 2008

FalconEddy said:
.....
I still see four 330K grid leak resistors in there. You'll probably want to change them out to 200K or 220K if you plan to run new production tubes. ....
. . Falcon

Don't remember exactly but doesn't the 222C have bias pots? Or are they AC balance? If it has bias pots, I think you can get by with adjusting for the correct idling current. (Trivia question: In transistors, didn't they call that the quiescent current?)

Glassweights · Dec 16, 2008

New measurements with the 5AR4

Ok, so I finished and took the photos above, but I was not going to fire it up until I was ready to take the time and measure all the new voltages.

The good news is, with all the improvements the voltages are really starting to be consistent from tube to tube and the bass response is very acceptable for bass that is periodic. (I have not tested a constant bass heavy piece yet) I can make it slam enough to scare my old Australian shepherd. (He hates thunder!)

The bad news is the 5AR4 allows way too much plate voltage for even old school 6BQ5 tubes. So I reinstalled the 5U4GB until my 6p14p-EB tubes arrive from deep inside a bunker in the old soviet block.

Here are the voltages I saw on the tubes in this order: Original, 5AR4, then back to the 5U4GB

Pin#

2) -15.6 --> -18 --> -18.44
3) 1.6 mv --> 1.5mv --> .6mv
7) 385 --> 424 --> 401
9) 327 --> 360 --> 343

So, this proves my power rail capacitors leak even though they are not hot. Unless the 100uf is doing nice things to keep the voltage up? If I am correct that the first two caps I replaced were leaky, then clearly I should change out the next two. It also occurs to me they could have reformed a bit while I have been testing and working on it?

So, what ya think, am I right to assume the best thing to do is use the 5U4GB until I get some tubes that can handle those plate voltages in? Or am I trading tubes strain for Power transformer strain:scratch2:

About the resistor 330 resistors, my friend said it was a hum balance circuit. I have to admit, I am not as hip to the circuit theory as I should be. More reading is in the works! I assume the -18.44 is my new bias and if I lowered those resistors I could expect the value to go up.

Is that what I want? I found a Oscillator on epay and it should arrive some day and I can try my hand at checking the waveforms with my oscilliscope and report back.

By the way, the amp is just sounding better and better!:thmbsp:

Totally worth the investment! My death metal biker babe wife likes it so once I get a cabinet built for it, it can live in the front room even!

Dan

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