Need Help With a Scott 208!

Seelmerdave your experience with cap charged for 6 months is really interesting. What CD player is it? Maybe I can find a schematic, curious to look at the circuit.

One of my first jobs was TV repair, back when they were almost all tube. We did discharge caps then, but it was a matter of efficiency, find the problem and replace the component as quickly as possible. Since then tube equipment updating/repair has been a hobby, I do check B+, before touching, but haven't come across anything that didn't bleed down. But thinking back, the only tube CD players I have worked on were Cal labs and Carver. What I do recall is that the tube part had their own power supply and the circuits were very simple, which would increase the chance of no bleed down path.
 
The old crt picture tubes were giant caps and held charge nearly forever:D:yikes:
They also recharged themselves. You had to discharge them a few times. They hit pretty good.
 
Seelmerdave your experience with cap charged for 6 months is really interesting. What CD player is it? Maybe I can find a schematic, curious to look at the circuit.

One of my first jobs was TV repair, back when they were almost all tube. We did discharge caps then, but it was a matter of efficiency, find the problem and replace the component as quickly as possible. Since then tube equipment updating/repair has been a hobby, I do check B+, before touching, but haven't come across anything that didn't bleed down. But thinking back, the only tube CD players I have worked on were Cal labs and Carver. What I do recall is that the tube part had their own power supply and the circuits were very simple, which would increase the chance of no bleed down path.
It was a Don Allen Phillips I believe, not aware of any schematics available. I had a similar experience with my SE amp, a Decware SE84, I don't recall how long it was after power down but at least a few hours, and the spark blew a chunk out of my screwdriver.
 
Thanks Selmerdave, you're right, looked at Decware Se48 no voltage divider paths to ground. Looked at Scott 208 paths which has paths to ground for B+ and bias, OP will see the caps drain down.

Nj pheonix, good point, didn't get zapped by any unpowered CRT's, changed high voltage rectifiers all the time, never bothered to discharge the CRT. Always did when changing a CRT. I did get zapped one time by live one, through my finger. Don't recall the voltage, 27K maybe, skin where I got zapped grew funny for a few years and made me more careful.

I have some lineman gloves, but the only time I use them are on some of the higher voltage hybrid vehicles where the energy storage is way up there.
 
the jolt from a cap is relatively short but it hurts. The fact that it doesn't continue for any length of time is the only saving grace. I got hit with about 350 vdc direct off the power supply one time, and it f'n hurt. I kind of sat there and recovered my wits for a little while before doing anything more.
 
I think what we're all trying to get at is that this stuff can be dangerous if you are not careful with it, but if you use proper caution you'll be fine.
 
I think what we're all trying to get at is that this stuff can be dangerous if you are not careful with it, but if you use proper caution you'll be fine.
I know and I appreciate it. But people are just telling me to test this and test that and I tried to stress at the beginning of the thread that I have no electronics experience and don't even know how to use a multimeter. I've been watching youtube videos but I don't always trust what I see (for instance the guy draining filter caps with two clips, a wire, and no resistor). Just a basic primer on where to set the meter, what order to put the clips on (and where), when I should have one hand in my pocket, what I can do with the amp on/off, etc. would boost my confidence greatly. I trust the people here (especially when what they say reinforces each other) more than I trust some random yahoo on youtube.
 
The Capacitors which you need to be concerned about are the big can style electrolytic caps. When you start it up clip the negative lead of your meter to the chassis (you have clip leads right?) and use the probe to check the voltage on the center terminal of the electolytic can cap. When operating it should have over 400 VDC here. Turn the power off and watch how fast the voltage goes to zero. (or less than 5v) . If the voltage drops to zero immediately or within 20 seconds you don't need to drain the caps. They drain themselves for you. Also now you know how to check to see if the can cap is charged before working on an amp. Good Information to know, and good practice. Stay alive by not getting shocked by this 400+VDC supply, Especially while the amp is on!!!
 
Scott -- As a suggestion, you might post your location. Plenty of AKer have been known to help out the new folks such as yourself who are local to their area. That's but one of the things that makes this community so wonderful!

Dave
 
Scott -- As a suggestion, you might post your location. Plenty of AKer have been known to help out the new folks such as yourself who are local to their area. That's but one of the things that makes this community so wonderful!

Dave
Dave, thanks - I'm in Portland OR.
 
In the two can version, both the cans operate at B+ levels, and are each very likely to be dual 30 uF, 500V cans, which was a common staple in Scott units of the day.

Dave
 
Two good Youtube channels you can check out to see videos of techs working on tube amps and explaining what they're doing:

Uncle Doug: https://m.youtube.com/playlist?list=UUuR4hQTXkG_KxozLxwPzEjQ

Guitologist: https://www.youtube.com/user/electrictoothsyndrom

They're both guitar amp oriented, but the principles and techniques you're interested in are the same.

Regarding your 208, have you found a schematic? And do the two can caps have stamped or printed markings? What do they say?
I have not found a schematic, all the ones I see are for the other version. I'll open up the amp in the next couple days and take a look. Sold my 9090db today so my motivation to take this on soon has increased. Then I'll have to tackle the 355... At least it's safer:).
 
The 355 seems to work fine other than the left channel being weaker and the treble is too low. With balance and tone controls I can even it out. Definitely want to get both operating safely and up to spec.
 
Wondering if it's simply the balance and treble controls being off, or would that be too simple and obvious? Both are definitely getting a full recap, and I suppose I should get a variac to bring the 208 up on afterwards. Now that the Sansui is out of the way I'll plug them in and swap tubes to try to track down the red-plate issue.
 
Old pots do tend to drift off value and it can cause mistracking. Other components being off-value can do it too though so you may need to do some signal tracing to find out where in the circuit things start to act different.
 
Wondering if it's simply the balance and treble controls being off, or would that be too simple and obvious? Both are definitely getting a full recap, and I suppose I should get a variac to bring the 208 up on afterwards. Now that the Sansui is out of the way I'll plug them in and swap tubes to try to track down the red-plate issue.
No need for a variac. New caps are ready to use from the factory, and you already know that whatever combination of new and old caps are in the unit now do work.

Make yourself a light bulb limiter, a/k/a dim bulb tester, and use it when you power the unit up the first time after you work on it; this will catch any short circuits you may have inadvertently created through wiring errors or other mishaps.
 
Hello all! Well I think maybe I owe everyone a bit of an apology. I fully intended to take on this project. However about a month ago I sold my 9090db because I needed the money and have regretted it ever since. It's a much better match power-wise for my speakers than the Scott gear. Well a 9090db popped up on CL that had been extensively recapped etc. (see pic) and the seller agreed to a straight trade. I hated parting with the Scotts but as I have no plan to get different speakers it seemed the prudent move. I still plan on getting some inexpensive tube gear in the near future to play with so all the advice hear wasn't just wasted time. Thank you all so much!IMG_0427.PNG
 
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