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[email protected] themend@gmail.com is offline
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Default Restoring a Sherwood S-5000


Ok, pics coming soon...

First step was to take voltage measurements off the bias and HV+ rails. Here's what I got on my S-5000. By the way, there are two variants of the S-5000 that I will discuss later, basically the older, longer version and the newer, shorter version. The one I am working on here is one of the shorter types.

After the 20uf cap coming off the rectifier, there is a 33 ohm 7w resistor connecting to the next cap section, 40uf@500v. According to documentation, this point should measure 415v (plate) but I often find that it reads higher. This particular amp is currently measuring 438v on the plates! This is why you really have to have a 7189 here, or at least a beefy 6BQ5 that is known to handle high plate voltages. I've seen lesser Sovteks arc over in these amps before.

So, according to my Sams photofact, the correct voltages going down the HV+ rail are as follows on the left, and this amp is as follows on the right:

Photofact This S-5000

C1/A - 420v 442v
C1/B - 415v 438v
C1/C - 350v 365v
C2/A - 275v 285v
C2/B - 225v 204v

So right off the bat something looks amiss - All these voltages are a bit higher than listed, but that is ok. What is odd is that they're all higher except for one, which is quite a bit lower. That second section of C2 should be higher than 225v, since everything else is higher than listed. Instead, it's 21 volts lower than listed. I suspect this points to either that dropping resistor or that cap section being leaky. Either that, or current draw after that dropping resistor is higher than it's supposed to be for some reason. We'll have to get to the bottom of that.

Now on to the bias supply. It's interesting to note that the bias supply also supplies DC filament current to the two phono preamp tubes, which makes it even more interesting that I've never gotten a US made 12AX7 to sound good in those positions, getting hum regardless. I suppose it means that it was more induced hum from the surroundings than from the filaments as I had stated earlier, or perhaps there was something amiss in the amp in which I tried it. I will have to re-visit that whole thing once this is finished..

There are no real test points listed in the bias supply other than the final ouptut voltage, which is supposed to be -20v. This amp is currently putting out -21.8, which is probably right on target considering the plate voltage is running a tad high - the extra bias voltage is welcome. In fact, I'd like to see it a little higher, and once the selenium rectifier is swapped out for silicon diodes, I'll expect to see closer to -23v. A real indication of the health of this circuit will be the DC voltages at the phono tubes, since these actually have some current draw to them

Sam's Photofact This S-5000

C3/A - Unlisted -29.3v
C3/B - 24v 22.74v
C3/C - -20v -21.8v
V1 Fil - 24v 22.74
V2 Fil - 12v 11.06


So the bias supply looks good, but the DC voltages to the phono preamp section looks a tad soft. Who knows, filament starving can have nice effects, but It'll be interesting to see what happens when the selenium rectifier and those electrolytics are replaced. I always see the bias voltage increase, so the filament should as well. This SAM's photofact has the polarity of the bias cap backwards, FYI. I will post it all soon when I figure out where to put all the uploads for this project.


It should be noted that this amp currently works and sounds fantastic. No signs of hum, very clean sound, no issues at all except the power transformer gets a little bit hotter than I think it should be. Thermal gun measurements have gotten close to 136F. My experience tells me that the second rev. of the S-5000, which this one is, tend to run a little hotter due to smaller iron. However, I still feel this one is a bit hotter than it should be after two hours of running and I think a power supply rebuild might lower that figure by 10 degrees. Still, for a bone-stock amp built in 1959, this thing is nothing short of amazing.

More to come soon!


-forkinthesocket