Hot Sherwood S5000

[oldman55]

Been pretty lucky on my "as-is" buys but may have got a bitten off too much on this one.

There are enough indicators on this that I am sure someone could help me with an initial assessment.

The rectifier/power tubes look to have gotten a little hotter than normal.

This may be over my head as some of the components are stacked three high in a tight chassis. But built like a tank and in great cosmetic shape so gotta get it back up. It was going to be hard enough to do a recap but now, IDK about the OTs.

Two of the EL84 sockets are clogged as if it was used with only the other two tubes. Without a rectifier, can I do a quick check of the transformers? Started to do on another unit but stopped to wait for a SSR. Still dont have one. If I knew they were good, I would just start replacing parts as all controls seem good and cleaned up well.

Most of the resistors near the output are out of tolerance to the high side.

Photos probably tell the story better than I.

Photos:
Front


Belly


Lotta wax


Growth/crud on square cap


Clogged hot sockets


charred resistor lead


cut/flagged at selector

 

[cademan]

You can clean the clogged sockets. I don't see any charred resistors. The power transformer looks fine. The wax bubble on that one capacitor has probably been there since day one. The flat looking capacitor with all the bubbles isn't a capacitor at all but something people around here call a PEC or Packaged Electronics Component.

To me everything looks ok and pretty normal. Checking the transformers can be done without any power.

You can ohm out the output transformers. They're probably ok.

Been doing this over 40 years and that thing looks in great shape. Even the wires coming out of the power transformer look to be in great shape. If the power transformer were stressed, the wires coming out of it at the holes usually will look charred or black due to over heating.

 

[gadget73]

One spectacular thing about Sherwood gear is the parts they used don't go bad that often. The can cap and there might be another electrolytic cap or two in there but thats probably it. Those dark brown shiny caps are mylar, usually tougher than a cockroach.

 

[oldman55]

You can clean the clogged sockets. I don't see any charred resistors. The power transformer looks fine. The wax bubble on that one capacitor has probably been there since day one. The flat looking capacitor with all the bubbles isn't a capacitor at all but something people around here call a PEC or Packaged Electronics Component.

To me everything looks ok and pretty normal. Checking the transformers can be done without any power.

You can ohm out the output transformers. They're probably ok.

Been doing this over 40 years and that thing looks in great shape. Even the wires coming out of the power transformer look to be in great shape. If the power transformer were stressed, the wires coming out of it at the holes usually will look charred or black due to over heating.

Thanks for the response and reassurrance. I've only been doing this for a couple months...and blindly. But thanks to all of you, I have put a few of these amps back into service and am enjoying them.
Guess I've been lucky to have gotten really clean amps to start with. I have no remorse with this one and am really looking forward to hearing it.
Looks like I will have to restuff the caps, replace resistors and go on from there. The rest will test out in the end.
Don't know if a PEC should be replaced but will look into it.

Gadget
Let the cockroaches live?

 

[gadget73]

The PEC should probably be left alone unless it gives you issues. Its in the tone network, so if its going to be stupid you'll find its got too much bass or not enough treble or something along those lines. Basically it'll sound like the tone knobs are somewhere other than in the middle if you set them to the middle.

Both of my Sherwoods still sport all original mylar caps inside. All of them test fine, and I wasn't overly motivated to replace good parts. The S-7000 I think got 3 or 4 new resistors, and two of those I damaged removing them from the cans to re-stuff. The other two were actually off value. Everything else was fine. The S-5500II is all original except for the caps in the bias supply. Everything else is how it left Chicago in 1963.

 

[oldman55]

Here is the resistor by what appeared to be a hot socket. Looks like tin coating?is coming off.

Most of them near the power tubes are out at least 10%.

 

[oldman55]

The PEC should probably be left alone unless it gives you issues. Its in the tone network, so if its going to be stupid you'll find its got too much bass or not enough treble or something along those lines. Basically it'll sound like the tone knobs are somewhere other than in the middle if you set them to the middle.

Both of my Sherwoods still sport all original mylar caps inside. All of them test fine, and I wasn't overly motivated to replace good parts. The S-7000 I think got 3 or 4 new resistors, and two of those I damaged removing them from the cans to re-stuff. The other two were actually off value. Everything else was fine. The S-5500II is all original except for the caps in the bias supply. Everything else is how it left Chicago in 1963.

What are the odds of me replacing some resistors, tubing it and it sings? Before something burns up?

 

[juddboz80]

I've got a S-5000 as well that runs 7189 as output tubes that I'm going thru now. Of all the tube amps that I own I would say this one runs hotter than any other tube amp I own. Every cap I've tested has been spot on, and the resistors I've checked so far have been very close. I'm going to replace the power supply caps just on the safe side and go from there. From what I've read seems like the output and rectifier sockets have had problems due to excessive heat. I gave mine a great cleaning and haven't had any problems so far! Good luck, it's a great sounding amp!

 

[juddboz80]

Here is the resistor by what appeared to be a hot socket. Looks like tin coating?is coming off.
View attachment 899152
Most of them near the power tubes are out at least 10%.

Check the value and if it's good go with it, you might want to check all your solder connections in that area as well, I went ahead and reflowed the solder joints in there while I was messing around

 

[gadget73]

What are the odds of me replacing some resistors, tubing it and it sings? Before something burns up?

Not too bad honestly. The electrolytic caps are probably the most likely to be dead. The usual cautions with the dim bulb tester and whatnot apply of course, this thing is old.

Looks like the crust on the resistor lead may just be moisture. Re-solder it, it'll probably be OK. It doesn't appear to have overheated. Its one of the grid stopper resistors, it carries almost no current.

 

[oldman55]

Tested caps.
I'd be the first one to roll the dice and crank it up if they were in the vicinity. New ecaps and resistors to give it a chance before power up.

 

[Dandy]

Never mind the cockroaches, the tube bug has bitten you pretty badly (but in a good way). I agree with the others that this unit looks nice. I would replace the electrolytics before power up.

Is that an S5000, rather than S5000II? If the former, it looks as if the OPTs are ultralinear (nice).

 

[oldman55]

Just s5000. Waiting on caps/resistors to come in before I power it up. Dont know the difference in OPTs, trying to soak in too much, too fast. Regardless, its my favorite so far in regards to appearance and hopefully will be just as fine in its sound.

Yeah, I got bit. May not be in a bad way but now I have a couple more than I need and will have to part with a couple. Will start with the one I bought as I blame it for my affliction. I have had to block out "tube amp" on my browser so I dont see any more that I can't live without.

oldman

 

[juddboz80]

Never mind the cockroaches, the tube bug has bitten you pretty badly (but in a good way). I agree with the others that this unit looks nice. I would replace the electrolytics before power up.

Is that an S5000, rather than S5000II? If the former, it looks as if the OPTs are ultralinear (nice).

Does the S5000 have 7189 output tubes and the S5000II have 7868 tubes??
I have an S5000 that runs 7189 output tubes....and it sounds phenomenal, I might like it more than my Scott 299a, neither have had the can caps upgraded tho

 

[oldman55]

Guess I should I replace the selenuim rectifier with diodes first also?

 

[gadget73]

It may be OK. Check the output voltage. Also depends if its got one. Both of mine have silicon diodes, but yours is slightly older.

 

[juddboz80]

Guess I should I replace the selenuim rectifier with diodes first also?

Probably should look into that!

 

[Dandy]

The Wiki entry explains ultralinear OPT operation pretty well: https://en.wikipedia.org/wiki/Ultra-linear.

The way to identify this on a schematic is to see if the grid of the pentode is connected to a tap (often 20% or 43%) in the primary of the OPT. This offers less distortion with a small loss of power. A compromise between pentode and triode operation.

 

[primosounds]

Replacing the Se rectifier is easy and straightforward. If your unit looks good in an out, like it may have been well cared for and more importantly used regularly it could be in working condition. I would try to slow voltage ramp up to say 75vac without the tubes and monitor or check voltages at critical points, then when you get to 75vac input, if voltages checkout and nothing got warm or smoked or stinked, install the tubes, hook up some test speakers, and plug in a music source. Turn it on again at say at 60 vac and check your DC voltages especially the CT on the OPT and at the plates on the 7189. Also check for leakage on the output side of the coupling caps, anything over "0" is some leakage. UNLESS, there is fixed bias. With fixed bias the voltage should be a negative number. The Se rectifier is part of the negative voltage bias circuit. The voltage reading should be very close for all 4 output tube grids. If you have a + voltage here, that would mean your bias circuit has a fault and you need to repair it before proceeding. There will be some variation of that reading but they should be close. Check the voltage around the driver tubes. A voltage chart of your unit would be most helpful for knowing what the specified voltage should be, accounting for the difference of the input AC voltage that comes from your variac. IF voltages and other checks indicate that there are no problems keep going with the slow addition of more AC from the variac. At around 75vac if you have not turned on your audio source you can try and play something and hopefullly, you should get music. At this point you can start checking out your preamp section, balance, tone controls, etc. Now that voltages are close to normal you need to be more aware of overheating, and tube runaway, etc. So check the tubes for red plating and over heating components. Best of luck.

 

[oldman55]

including the rectifier tubes?

try to slow voltage ramp up to say 75vac without the tubes and monitor or check voltage