Ok to change these caps? Scott 222D

[aedaza]

Thanks Gordon!

Well, this is the inventory of the caps I think that need to be replaced (Place refers to the area where I think its located i a non-tech way), with the last column indicating what has already been taken care of:

And this is the inventory of caps that I already have:

As you can see, there are some caps that simply dont belong in the amp, but there are some others that I believe can finish replacing the can caps, and the others that are still needed, can you guys suggest me what to get?

Here is also a pic of the amp under the hood before any change (but notice those black caps under the 6U8's. Those where replaced by a local tech. They are supposed to be 4uf@250v according to schematic):

Sorry if the pics are way too big or unnecessary.. If someone is going to help me, Im trying to make it easy!

Thanks!

Alex

 

[aedaza]

Anyone??

 

[GordonW]

The phono stage is the only place where values are entirely CRITICAL. You do not want to vary those values (they HAVE to remain .022uf, though the voltage can be equal OR higher than original voltage rating). Fortunately, it's also a place where the caps fail less often- you may be able to get by with leaving those in there, if the amp seems to work properly. I would measure for leakage across them (check the voltages after the caps, to make sure that DC isn't impressed upon the signal).

The phase splitter cap values are not critical... you can easily use your .047uf K40Y caps to replace the .022uf caps that are there, as long as they physically fit.

Sounds like you have plenty of K40Y 0.1uf caps to finish all the other locations that need 0.1uf caps? That should obviously be fine.

The single 50uf 75v cap in the bias supply can easily be replaced by either the 100uf, 100v Nichicon Muse or one of the 220uf 100v Nichicon Muse caps. Use the 220uf if it will fit easily in the space; otherwise, the 100uf will be fine.

The bias supply, as noted, has a total of FOUR 75uf caps in the can capacitor assembly, wired POSITIVE GROUND. You should be able to, as long as you can make space (I have been able to do this, using a terminal strip and the caps mounted to it, with the terminal strip mounted near the original can cap location), replace these with caps under the chassis (BTW, there is no direct replacement for that positive ground can cap, so the new caps have to be individual caps, mounted either above or below the chassis). These values are not critical (as long as they're at least 75v rated)... the three 120uf 100v Nichicon caps and one of the 220uf 100v Nichicon Muse could easily be wired, positive leads together (grounded to the chassis), to replace the function of the quad capacitor. I'd put the Muse as the last one in line (closest to the bias pot).

BTW: The 4uf black caps are probably the screen caps for the 6U8 pentode section. That value sounds right.

Sounds like other than four .022uf caps for the phono stage, you have enough for everything else...

Regards,
Gordon.

 

[GordonW]

Oops, I misread. The Nichicon 120uf caps you have, are 400v. Those will likely be too big to fit, in the bias supply area.

Sounds like you need two more 100uf 100v caps, or 220uf 100v caps. At least those are really common. For the five total bias supply caps (the four in the can and the single cap), the values really aren't critical at all...

Oh- and that 35uf 500v cap will work to replace the last power supply section I mentioned above (I suggested a 47uf 350v; the 35uf 500v will work there fine).

Regards,
Gordon.

 

[aedaza]

Hi Gordon!

I think we are on track! Ok, I went this morning downtown Medellin to do some shopping. It is very difficult to get some good caps (like the ones you guys talk about all the time), but local techs seem to be ok with the offerings.

This are the caps I got:
You tell me if some or all of them are garbage. Either way, I just want to have for now the Scott running up again and upgrade/change to the proper caps as they arrive someday. I suspect those 0.022 and 0.1 are not going to be of much help...(why are they so smaller and different?)

Also I bought these resistors. They look different than the one in the amp, but everyone said they should work fine. I bought them for the selenium rectifier to diode change, in order to change the first 18ohm R to a 20 or 33 ohm (did my homework!) and the 10W 33ohm resistor if the 20ohm near the rectifier needs to be changed.

With the new caps now in scene, how would you sugest we should change the 100/75x4 can cap and the 50/75 single bias supply cap?

We have:
1x 100uf/100v Nichicon
2x 220uf/100v Nichicon
4x 100uf/100v "A" brand
1x 100uf/160v "Sancon brand"

And thinking about the power supply caps to be fitted with the 100uf+100uf JJs can caps, do you think is better to use the Electronics Concept Unylitic 35uf/500 right after the rectifier, to avoid disturbing the rect., and just use the remaining 100uf sections along? (totaling the 6 sections needed also).

It feels like Im learning too... good thing! :thmbsp:

And as usual, thank you very much!

Best,

Alex

 

[aedaza]

And in order to be more clear, I still have 2 0,1 uf caps to be replaced in the preamp section. Just like explained in the spreadsheet (post 25). The rest of the 0,1 caps where already replaced with the initially received caps.

 

[scottfan]

Make sure you replace the selenium rectifier with a 8a 400v unit - $5. Also, replace the 2w 10ohm resistor with a 33ohm.

Just got done replacing mine (222D) tonight and used a 5w 33ohm wire wound. Currently, I'm getting -46.2v at pin 5 of the 1st 12ax7. The target zone is -46 to -48vdc. Before replacing, the old rectifier was putting out -38v! Changing this had a nice effect with the amp's sonics and it hasn't even be recapped yet.

Good luck.

 

[GordonW]

Though the pictures are backwards with the text in your list... those .022 caps should be OK for the phono stage.

I thought you had enough K40Y 0.1uf caps already? If you can use them, they will be very good. There's nothing fundamentally wrong with the 0.1uf caps you just got, but the K40Y caps will probably be better.

I'd just go with the JJ 100uf in that first position. The amp will be quieter. Probably better to just go with the slightly larger resistor (33 ohm 10w) if needed, with the 100uf, than the 35uf (which is smaller than the 20uf + 20uf stock value).

The four 100uf 100v "A" caps should be OK for the bias supply. I'd use one of the 100uf 100v Nichicons as the first cap in that section, then the 220uf 100v Nichicon next (follow the order in the schematic, from the rectifier on), then two of the 100uf "A" caps as the other two in place of the four-section cap. Then, use the other 220uf 100v Nichicon to replace the separate single 50/75. That should result in a very quiet bias supply (good).

Regards,
Gordon.

 

[GordonW]

Make sure you replace the selenium rectifier with a 8a 400v unit - $5.

Well, the bias supply bridge rectifier doesn't have to be 400v. 200v will be fine for that position. It may be easier to get a 200v 10a rectifier... as long as it's at least 8 amps and 200v, it should work just fine.

EDIT: Looking over the specs, even a 5 amp bridge rectifier would be fine. That may be even easier to find...

Regards,
Gordon.

 

[aedaza]

Thank you Gordon and Scottfan!

I do have the bridge for the selenium replacement. It is a 200-400v aprox 8 amp diode bridge. I think I once measured the voltage after the selenium and it was very low too.

Gordon, what type of caps are those 0.1 and 0.022 that I bought? are they generally used in tube amp´s re-cap?

The K40 0.1 where used on the amp already. I received only 8 of them,, and the amp needed 10, so I still have 2 to be replaced under the preamp section.

I will work on the amp today. Hopefuly I will have some good news tonight and will report you guys!

Thanks!

Alex

 

[GordonW]

Those caps (the 0.1 and 0.022) are either mylar or polypropylene film.

I have used a lot of that general type caps (otherwise known as "epoxy dip" caps)... those should be fine.

Regards,
Gordon.

 

[aedaza]

The tech canceled the appointment :sigh:

Postponed for next Saturday... not happy about it,,,

I guess I really need to learn and do this things on my own

 

[aedaza]

Thread needs to be resurrected!

Hi guys. Well I worked sometime on the amp a while ago with a guy who is maybe not a tech yet, but climbing on the learning curve.

We changed the PS filter caps, coupling caps, and some other 0.1 uf 400V caps. We also changed the selenium rec with a diode.

After the initial fire up, the bias was set at 0.42 mvolts per channel, as stated (this was a problem I was having with the amp, but now it seems I can get the bias on spec again! good!)

Now the new problems:...

- Dead right channel: I only hear a small hum and barely the music if I turn the volume up.
- Voltage after + Bias Can for 12ax7s filaments circuit:
As you know, I should have -48 Volts aprox after the diode and the last 18ohm resistor on the bias can cap (4x100uf/75V), but I am only receiving -39 volts...

Additional info:
- Tubes have been swaped from one side to another, including preamps, phase splitters and power tubes. Dead channel problem not solved this way.
- With the "Selector" switch set to BAL R, I hear the hum on both speakers, and when set on MONO, BAL L or STEREO, I hear the music on the left speaker and hum on the right.
- The tech soldering skills were,, average. Mine are,,, newbie type. A bad soldering cannot be discarded
- Right after the diode, unsoldering the -voltage from the diode to the amp, I get -59 volts (I think the schematic calls for -58volts)
- Already tried Tape input, Tuner, Extra and Phono.

What do you guys think? Any measure to try? :scratch2: Maybe I soldered something badly? and incorrect connection? A bad +Can Cap?

Thanks!

Alex

 

[tube-a-lou]

the Bias at the first 12AX7 should be -45, as told to me by Greg at NOS Valve, did you
try reversing the connections at the volume pot one side might be dead, and if you
remove the rectifier tube are you getting voltage at all the tubes.

Tube

 

[aedaza]

Thanks Tube-a-lou! I will try to reverse the connections at the volume pot.

When you ask for the voltage at the tubes.. what voltage should I be seeking? On preamp tubes or at all tubes?

FYI,The bias voltage measured at -39 was at the fist 12ax7 without the the rectifier tube.

Thanks!

 

[tube-a-lou]

Then you should lower the first resistor after the rectifier to get to -45, do you have
a copy of the schematic for your 222D to check all voltage points listed there.

Tube

 

[aedaza]

Hi Tube,

But the thing is that I still have the original 10ohm first resistor after the rectifier, and not the 33 ohm often called for after replacing the selenium rec for a modern and more efficient diode.. Dont you find this odd? Having the old 10ohm resistor and still having a low voltage....

What is usually the voltage found right after the diode before the first resistor, when the selenium rectifier is replaced? Is my -59v ok?

Also, are there any key voltage I should focus on? If all of them is the answer, I will do that!

I had a rough day at work, so I think I will do the measurements tomorrow, but if you have ideas, please do share!

Thanks,
Alex

 

[NOSValves]

aedaza,

I received your request for help. It looks to me like Gordan has you covered. If I enter this thread its just going to cause confusion. I see nothing wrong in Gordan's guidance so I'd suggest you just run with it. I'm real busy these days but if for some reason you guy's get hung up feel free to shoot me another PM.

Craig


PS if that bias/heater supply is to low replace that 4 section 100uF 100V can cap.. another clue to it's health is if the residue AC ripple at the point where it heads to the first 12AX7 is over 100mV then it's not doing it's job properly. Many of the later model amps that filter can had a tendency to fail. It's kind of strange since the oldest versions of the Scott amps that can always seems to be fine. They did switch suppliers so I bet that is a clue as to why they fail.

 

[tube-a-lou]

Hi Tube,

But the thing is that I still have the original 10ohm first resistor after the rectifier, and not the 33 ohm often called for after replacing the selenium rec for a modern and more efficient diode.. Dont you find this odd? Having the old 10ohm resistor and still having a low voltage....

What is usually the voltage found right after the diode before the first resistor, when the selenium rectifier is replaced? Is my -59v ok?

Also, are there any key voltage I should focus on? If all of them is the answer, I will do that!

I had a rough day at work, so I think I will do the measurements tomorrow, but if you have ideas, please do share!

Thanks,
Alex

I looked at your schematic on the Scott web site, if you don't have it I suggest
you get a copy of it there, it say's it's -58 and at tube V102 it's -50 so if
your close to that you should be good, but do what Greg say's about the
bias caps and changing those if need be. I have a older 299A and that
has different readings and specs, so these guy's hear know there stuff.

Tube

 

[NOSValves]

FOR THE TEN THOUSANDTH TIME. You can not take the voltages or parts values on Scott schematics as written in stone values. Many different versions of each model were produced. Heck this is true when working on any vintage amplifier models for any manufacturer.