Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Make it loud here.
Post Reply
User avatar
MrShake
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 635
Joined: Tue Oct 24, 2006 5:51 am
Location: Boston, MA
Contact:

Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by MrShake » Sun Jul 11, 2021 9:05 am

1) Restoring My Bassman Ten:

Hey, everyone. I’ll try to keep this kinda brief, but in trying to figure out some internal things about my 1974 Bassman Ten, I realized I had a lot of other confusion about SF Bassman amps and wondered if any experts here might advise on exactly what I've got going on with my workhorse.

So, I’ve never been an amp expert, that’s part of the reason I love my Bassman Ten. I’ve posted positively about it since I got it in 2008, and it’s worked reliably for years. Shortly after I got it, it turned out it needed some work. Two of the original speakers crapped out and I believe the filter caps and maybe some preamp tubes were on the list. I'm almost certain the filter caps were changed, but I'm not going in that doghouse. When I bought it, I had just moved to a new city and didn’t know where to take it, so took it some place at random I saw nearby. My instructions were basically "I don't need anything fancy or hot rodded, just please get it back to 'about stock'." Just a beat-up player/workhorse of an amp. Part of my problem is that I knew even less about amps back then than I do now. I honestly can't remember what was done to it, so I opened it up for a cleaning and to take a careful look inside and was a little surprised.

The underside of the chassis was gross. Had a sticky layer of dust and grime. I was worried it was from a smoking amp in the past, but it may have just been 45 years of smoky clubs. I scrubbed and wiped off as much as I could, carefully, got most of it, but now I'm a little paranoid about the cause. Of course, it could have been there since I bought it.

The power tubes were not 6L6s like I expected, but a mismatched pair of 5881's. One Made In Russia, one from the USSR. I've never changed them. I've never needed to. The amp has just WORKED. It ended up not being a gigging amp, but a living room one. Jams with friends, drug it to a dozen big loud rehearsals, maybe half a dozen gigs. I've never pushed the MV that hard (outside the gigs), and never noticed any tonal problems. I hear these make for lower clean headroom. The power tubes start to get a little growly at about 6.5+. Rarely have I had the need to get it up above that in bars and rehearsal rooms. But I had no idea. I've found myself largely unable to overdrive the front end unless I turn both channels to 10 and hit it with the hottest cheap humbuckers I've got, and that's how I like it. I'd love to maximize clean headroom on this thing for my pedalboard to paint on, so 6L6s and a biasing will be necessary, I just don't have the money at the moment.

The tube brackets don't grip the short ("wafer"?) bases of the tubes as well as I'd like. I occasionally reach back with a paper towel before I turn on the amp and make sure they're secure. Now I realize why. The brackets actually have a tendency to push the tubes out just a little, squeezing a bit against the curved glass bottle. I do not like this. I don't want arcing. I intend to remedy this as soon as I can afford some new tubes and a biasing at the local tech. Eventually.

BUT THE BIGGEST QUESTION: I took some pics. I watched some repair videos online of my model, the 50W, pre-UL version, and they consistently have a cap visible in the chassis -- that is straight up missing inside mine. [HIGHLIGHTED IN PICTURE BELOW]. Where I've seen that cap in other examples online, it's connected from the bias adjustment pot to (I believe) a ground spot on the chassis near the power cord input. I wish I'd noticed this when I had the thing apart to take better pictures, but can anyone let me know if this is something I should be seriously concerned about? Or if they see any other red flags?

I just wanna get this old beast back to tip-top. Pics:

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file

Image
upload image file


External shots are PRE-cleaning, for what it's worth. It's looking better now.


2) Silverface Bassman Series Info

I love my amp, I do. It's always sounded good, nice 'n' full, takes pedals like a beast, jumpering the channels and setting everything to "7" is glorious. I'll re-iterate that I'm no amp expert, but it seems like there were a bunch of Bassman variants in the SF era, and I've always wondered how mine differed. I'm aware of:

Bassman Amp (Bassman 50) - 50W head, non-UL
Bassman 70 - 70w head, ultra linear
-----
Super Bassman I & II - piggyback head and cab combo, 100W
-----
Bassman 100 - piggyback or head, 100W, non-UL
Bassman 135 - ultralinear version of 100, now 135W
-----
Bassman Ten - 4x10 combo, 50w (til '77, then 70W)
-----
Bassman 20 - strange early-'80s combo, 18W

I realize that these aren't the same circuit as a tweed or BF. I don't want it to be. As far as my Bassman Ten is concerned, I believe it's got one less preamp tube per channel, so stays clean longer (pretty much to 10, with single coils). But is that the only difference in the circuit? Or were there other changes made in the Bassman Ten that push it further away from the (again, as I understand it), otherwise similar guts of a 50/100? I know there's a lot of specific circuit numbers throughout the years that people compare and discuss, but does the B10 have it's own circuit designation? Or is it simply the same circuit as the 50/100 with a preamp tube removed and a different transformer?

And real-world talk, not specs, how do any of you feel the ultralinear amps from '77 onward compare in feel and sound?

Thanks for the education, everyone. Y'all are real cool, and I love ya. Stay safe.

User avatar
s_mcsleazy
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 16698
Joined: Thu Jul 28, 2011 7:30 am
Location: glasgow

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by s_mcsleazy » Sun Jul 11, 2021 9:15 am

im looking at the board for that and the board for my bassman 50 from the same era and they look very different.
Image

i know fender kept revising the board as the years went on but i've not seen one that looks as stripped back as that one. or maybe the ten circuit is really different. i've never seen a ten in person
offset guitars resident bass player.
'Are you trying to seduce me Mrs Robinson? Or do you just want me to solder a couple of resistors into your Muff?'

User avatar
Sweetfinger
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 191
Joined: Sun Nov 03, 2019 3:23 pm

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by Sweetfinger » Wed Jul 14, 2021 6:43 am

I think the missing cap is the second one in the later Fender bias balance circuit. Your amp has been converted to adjustable bias and that cap, (usually a molded white Mallory) was discarded.
The reason your claws aren't gripping the tubes is because you're using wafer base 5881s instead of the full base 5881WXT. Same tube, different base. The WXT base is a little smaller diameter than a US 6L6, but you can squeeze the claws in. It isn't difficult to install spring tube retainers if you want to continue using wafer base 5881s.
There's not a lot in those amps. I can see some resistors have been changed.
I think every Bassman Ten I've come across but one, had at least one, usually more, blown speakers, and they're 32 ohm if memory serves.
There are several things you can do to tweak and customize one or the other channels, and overall.

User avatar
MrShake
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 635
Joined: Tue Oct 24, 2006 5:51 am
Location: Boston, MA
Contact:

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by MrShake » Fri Jul 16, 2021 4:16 am

Thank you both for taking the time, this is all, believe it or not, very valuable information to me. Literally. I won't have to take it to a potentially unscrupulous tech and say "I dunno, tell me what you think?"

First off, it's nice to be able to side-by-side and definitively say that the Bassman Ten is clearly a different, but similar, animal from the 50/70/100/130 circuit. Hopefully, the pics in this thread will disabuse any future investigators of the notion that a Bassman Ten is simply the combo version of the 50/70w heads. The Bassman Ten is its own beast. My best to Scotland, keep it noisy up there.

And learning that the capacitor issue is a non-issue unless I notice otherwise is a relief. I've ordered some spring tube retainers, should be here this week. The only times I've had any trouble, it sorta pulsed when I turned it on for a moment. Like the power was going through a tremolo effect. Re-seated the tubes and later that day it was fine, so I'm chalking that instance up to those, and haven't noticed any other functional trouble. I like the way it sounds, so there's no rush to change anything, but in the next couple years, I'll be taking it in to get some 6L6s put in and biased to increase clean headroom on the master volume. Thanks so much for your insight, Sweetfinger.

I neglected to mention a couple tangential things in my initial post, for what its worth. First is that part of the draw for this amp was the idea of it doing double duty. I'd just downsized to a small apartment with no room for an amp stable, so the fact that it *could* double as a bass amp was a big appeal. A month or two after I bought the Bassman, my wife got a Jaguar Baritone Custom, in the era before one could by an affordable Bass VI reissue. The pair of them ended up made for each other. Put some drive and flange/chorus on a board in front of it and it's postpunk heaven, fuzz and it's a garage-punk rave-up. It might not be a great bass amp, but it seems excellent for the bass-adjacent as well as a pedal platform for guitar.

The other (bigger) factor was a speaker replacement with Jensen MOD 10-50s, 8ohms each, rewired for series parallel (or parallel series, I can't remember). It was a decision made with my wallet since the amp was already a bit of a stretch at the time. I know they're not held in the highest regard, but they haven't ever made me feel like I need better, they handle anything I've thrown at them well. Still very Fender-y tube cleans, but I imagine the allegedly increased mids (never been enough of a speaker expert to compare them to others) only bring out the punch. Though I know nothing about the weirdo 32ohm ones it was initially loaded with. These days, putting it at chest level for a gig is like a cannon kick to the chest with the right fuzz.

Image
image uploader

If you haven't tried one, I'd take the opportunity if it arises. I always called it "dark", and I attributed it to the closed back. Maybe it's just the blend with that thick first channel. I've heard it called "dull", but it's more "blunt". Not "fat", but more like a double-weight Fender clean, without the open back ring and twinkle of your Twins or Deluxes or Princetons. The 10"s keep the low end tight with a Russian Muff or a scooped Superfuzz. As the guitarist in a loud, surf/psych garage punk duo, the added weight of those low mids really rumbles. I know virtually nothing about Marshalls (well, even less than I know about Fenders), but some forumites elsewhere suggest it's not a million miles from "if a JTM45 were a Fender model" - my phrasing, meaning just that it still has a distinctively Silverface sound while also seeming a little heftier with more mids. But I'm only parroting, my personal Marshall experience has only been JCM800s. And I know Marshall's history, and I know this isn't a tweed, etc. But I imagine the quad of MOD 10-50s is only going to enhance any similarity others have noticed and only stand to make a big heavy Fender sound more like that.

Either way, I love this damn amp, thanks for helping restore my confidence in it's operation, teaching me more about what I actually have (re: biasing setup and circuit differences), and helping me to get re-inspired by it.

Hope y'all have a good one, everybody remember to turn up.

User avatar
øøøøøøø
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 5056
Joined: Sun Jan 06, 2008 8:26 pm
Location: Los Angeles
Contact:

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by øøøøøøø » Sun Jul 18, 2021 10:57 am

Everything inside that amp looks very original, down to the white Mallory cathode-bypass caps (and bias cap).

If it were mine, I'd go ahead and replace those, and would definitely have a peek in the dog-house as well to check out the power supply filters.

Replacing the bias cap on the small board near the pilot light is non-negotiable, and I'd do that immediately. make sure the new cap is installed in the same orientation as the original, which is reverse of how you'd expect ("+" lead connected to ground), as it's a negative voltage supply.

While I can understand being loath to look inside the high-voltage area, in reality you shouldn't be inside the amp at all if you're not comfortable with such voltages (and educated in how to discharge the caps and render the amp safe for inspection and service).

Any residual charge that's present in the doghouse is also present in the portion photographed (particularly near that 10W power resistor on the transformer-side of the eyelet board, and the output transformer primary leads which attach to the 6L6 tube sockets)

User avatar
johnnysomersett
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 2257
Joined: Mon Jun 01, 2009 1:33 pm
Location: South of London, England

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by johnnysomersett » Sun Jul 18, 2021 1:08 pm

øøøøøøø wrote:
Sun Jul 18, 2021 10:57 am

While I can understand being loath to look inside the high-voltage area, in reality you shouldn't be inside the amp at all if you're not comfortable with such voltages (and educated in how to discharge the caps and render the amp safe for inspection and service).
This is probably the most important part of this entire thread and can never be repeated enough. I had the misfortune to discharge 450v from a filter cap on my old Orange straight into myself many years ago and I can tell you this...it was no fucking joke. I'm lucky to be alive.
Silly Rabbit, don't you know scooped mids are for kids?

User avatar
Sauerkraut
Expat
Expat
Posts: 2423
Joined: Mon Oct 02, 2006 6:23 am
Location: Berlin
Contact:

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by Sauerkraut » Mon Jul 19, 2021 12:46 am

Happened to me; my Tremolux shocked me senseless last year. It still had the death cap in place, and the ground switch was apparently in the wrong position; seems you just had to touch the chassis in any two places and you’d get zapped. Needless to say, I felt very much alive after that. Quite the adrenaline rush. I have no doubt it can easily cause heart failure and kill you. After that, I was determined to learn enough about amp maintenance not to ever have that happen to me again. But now, although I’ve since removed the death cap, even after I’ve discharged the amp and the meter reads something like 0,5V, I still get a little paranoid.

User avatar
Sauerkraut
Expat
Expat
Posts: 2423
Joined: Mon Oct 02, 2006 6:23 am
Location: Berlin
Contact:

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by Sauerkraut » Mon Jul 19, 2021 1:12 am

øøøøøøø wrote:
Sun Jul 18, 2021 10:57 am
Replacing the bias cap on the small board near the pilot light is non-negotiable, and I'd do that immediately. make sure the new cap is installed in the same orientation as the original, which is reverse of how you'd expect ("+" lead connected to ground), as it's a negative voltage supply.
Good call. The original bias filter cap in my Tremolux was 50V, but I measured a constant 60V running through it. I still wonder how it survived that for 50 years. Looks like they were putting 75V caps in there later, or at least in the OP's amp.

I suspect the missing cap is this one, which perhaps wasn't part of the Bassman Ten's original circuit anyway(?):"This cap was added to silverface amps for hum reduction."

User avatar
MrShake
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 635
Joined: Tue Oct 24, 2006 5:51 am
Location: Boston, MA
Contact:

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by MrShake » Fri Jul 30, 2021 5:21 am

First and foremost, I'd like to thank everybody for weighing in and all the help, seriously, I appreciate it.

Because of that, I'd like to publicly advise anyone in the future to FOLLOW THE GOOD ADVICE AND STAY OUT OF DANGEROUS AMPS. I have a little bit experience with higher-voltage electrical work, but even taking the chassis out like this was dangerous, and frankly, I was foolish to be doing so without discharging. I may have been careful, but that's no excuse. Don't go poking around like I did.

I put some spring tube retainers on and other than that have decided (with a heavy heart) to put in on hold and get it fixed before much more playing time on it.

There's a very reputable specialist tech in my area, but they're so old-school they don't even have an email address. The pandemic sorta wrecked my finances. Eventually, I'll have enough dough to call and get an estimate on (assuming there are no other issues to be fixed):

1) a pair of 6L6 tubes (for potentially increased clean headroom over these 5881s) and a biasing.

2) a recap. I'm not an "all original" purist on this one. Like I said, I'm just about sure I had the filter caps changed in '08, because I know I paid a chunk for some component work. I just wanna basically bulletproof this amp for another 10-15 years. We wanna have kids soon and I wanna avoid unexpected expenses while always having a workhorse tube amp!

3) I'd like to add an effects send/receive on the back. I've got some lonely reverb units. This oughta be pretty straightforward, right?

Assuming a decent tech charges, say, $60 an hour, a new cap kit for the B10 seems to be about $50, and a pair of 6L6s are about $60 (all of that totalling $170), my crappy math says I should probably set aside about $300 for that work here in the golden age of mid-2021. Am I off-base, or does that sound like the right ballpark?

[PS - I took a pair of nasty shocks from an old Sano amp back in the 90s. One was even during a local TV performance and caught on camera. It was no joke. The non-televised one knocked me off my feet. And I wasn't even digging around in the guts, it was the power switch. Please be more careful than my stir-crazy self. I've taken to intensely studying and learning proper amp safety and discharging techniques so that in a year or so, I might be educated enough to safely attempt it myself.]

User avatar
Sweetfinger
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 191
Joined: Sun Nov 03, 2019 3:23 pm

Re: Silverface Bassman Versions and Bassman Ten Cap Question (Pic Heavy)

Post by Sweetfinger » Sat Jul 31, 2021 3:16 pm

MrShake wrote:
Fri Jul 30, 2021 5:21 am
1) a pair of 6L6 tubes (for potentially increased clean headroom over these 5881s) and a biasing.
Depending on what 6L6 you use, you won't get much (or any) increase in headroom. Those Sovteks are labeled 5881, but are not really like the old USA 5881, or a 6L6 either. That's just what Sovtek decided to label them.

Post Reply