Bassman 10 -- Where's the Love?

[Steve A.]

I've got at least half a dozen customers happy with their old Bassman 10's. Last one just went out the door 3 days ago.

Just wondering how many of those customers have been guitarists...

Thanks for your suggestions on mods! I'm sure that once implemented the guitarists would be very happy with their amps. (I was referring to completely stock Bassman 10's, not ones intelligently tweaked.)

Steve Ahola

[bob p]

Thanks for the great comments, everyone.

Since Leo was so quick to offer discrete recommendations about mods for this circuit (Thanks Leo!) I thought it'd be helpful to post the schematic:



In doing my research on this amp I've read many peoples' accounts that claim that the Fender schematics are inaccurate. I don't think that's fair. I traced the circuit last night and the schematic that I pulled from the FAFG is 100% accurate, without any inaccuracies or omissions. I'm thinking that if people are encountering amps in the field that don't match the schematic, the problem is that those amps have already been modded. The specimen that followed me home is 100% bone-stock and it's in perfect agreement with the schematic.

I'd like to thank Leo for offering precise recommendations re: how to tune the circuit. I spent last night tracing the circuit to determine exactly what's in my amp, and comparing that to the BM/Pro/Super circuits, which are really close, almost identical.

[Leo_Gnardo]

Just wondering how many of those customers have been guitarists.

All but one guitarists. Some "double" on bass. Those that have studios consider Bassman 10 their "secret weapon", works well on any instrument.

Thanks to bob p for the schematic. You can see that .001 uF cap across the first stage plate load, it throws a blanket on the top end. Unless you really love "bayuss wit' no treble", easy to snip this one out.

Note this is one of the rare Fenders that has James EQ stacks. Another one is the PA 100.

[bob p]

Looking at one schematic if you were going to use this for guitar you'd probably want to remove the .0047uf cap between the treble and volume control on the Studio channel for starters. There are also .002uF caps to ground right where the 100k bias resistors connect to the 1.5k grid stoppers. I'd probably look for a custom head cabinet for the chassis since at 75 lbs it is a top-heavy behemoth.

Yes, those are some of the main differences between this amp and it's 40W guitar amp brethren. There's also that 0.047uF cap in the Studio's FMV tonestack that could be cut in half for guitar amp duty. But I'm not quite sure whether I'm going to use this as a guitar amp, as a little bass amp, or as both. So for the time being the plan is to finish doing the functional check out and power tests to make sure it's functioning properly, and then give it some time to be auditioned as a guitar amp and as a little bass amp. I only have 3 days to do the complete checkout before my return privileges expire, and right now that's what I'm focusing on. Based on the price that I paid there's no chance of it going back, but I still want to complete the checkout right away, before I even consider any mods.

P.S. For a vintage amp like this I could see doing some mods and tweaks to bring out the character of a BF/SF amp. As for converting it into a fire-breathing dragoon I think its better to get a less valuable "donor" amp where you can hopefully reuse the iron along with the chassis.

Dare I say it ... even though this thing is 100% bone-stock original, I think this *IS* the less valuable donor amp. I ended up getting this thing cheaper than any of the prices that have been mentioned so far. I was serious when I said that I bought this thing for the price of a SF champ. At my entry point, the prospect of buying just a head cabinet would come close to doubling what I have in the whole amp right now. Yeah, it's a bit top heavy, and easy to tilt. That's because the front/rear casters are really close together. the amp would do a lot better if it were fastened to a dolly that had more front-to-back spacing on the wheels.

[bob p]

Yes they're a bit rare, the prices haven't gone kooky (because no rock star has yet been seen playing thru one, it may happen some day), and built with typical Fender quality. Except for the cab which does tend to fall apart under hard use & damp storage.

I think you're right -- these amps are unloved becuase they don't have star power pumping up their desirability among their fan base. They're sort of like the Silvertone Twin Twelve being cheap, unloved, and a preferred inexpensive modding platform among amp guys... until Jack White started using them and drove the prices skyward. Thankfully there's no big name standing in front of a wall of Bassman 10, so the prices haven't gone crazy.

Another minor mod to wake up the "studio" channel: there's a treble-deadening cap in parallel with the first stage plate resistor, clip it out and hear the high frequencies come thru. Also the stock bass control doesn't seem to do much except at very low frequencies. For a fast fix, I replace the 100K resistor to ground with 22K to 47K, or you can tack on a parallel resistor to get somewhere in that value range.

I know exactly what you're referring to, but in case anyone doesn't follow: that treble-deadening cap is actually on the "Normal" side of the preamp. Thanks for the comments on the James Tonestack mods. I'm not quite ready to start modding the amp yet (still in the proofing stage) but I do appreciate advice from someone with "boots on the ground" experience with this amp.

Great recording amp, and not half bad for gigs where you don't need welding power.

Well, this amp sort of fills a niche for me right now. I've got plenty of coverage in the 100W-300W range for guitar and bass, and I've got the little low-power combos, but nothing in the 40W Fender range, so this amp plugs that hole and rounds things out for me.

and most important:

Bob P - good to see you back!

Thanks, Leo. It's good to be back. There have been some things in my life that have kept me away for a long time (caring for a disabled family member), but I've been away for so long that I decided that I just have to make time for some of those things that I had pushed onto the back burner for so long. The only downside is that I have a captive audience who can't escape the sound of my playing.

[bob p]

WARNING: THIS POST CONTAINS VINTAGE AMPLIFIER HERESY

One of the obvious things that jumps out at you when you check out one of these vintage amps is the "vintage voltage" problem -- voltages everywhere are higher than spec because today's supply voltage is 125VAC not 110 or 117VAC. The result is that on a 6L6 Fender it's pretty easy to pick up 50VDC of B+ that you don't really want, along with an undesirable 8-10% rise everywhere in the amp, and the tonal changes that go with the voltage changes. I've got a little filament transformer that I can install to buck the voltages down, but I'm getting tired of having to do this all the time, so this got me to thinking... (stand back!)

I'm considering doing the unthinkable act of ripping the vintage iron out of this amp replacing it with modern primary-adjusted repro iron, and offering the original iron to someone who needs something that is number-appropriate for a vintage 40W Fender restoration. The value on working vintage iron for amp restorations is ridiculously high, to the point that my PT by itself is probably worth close to my total sunk cost in the amp. And the repro primary-adjusted Chicago iron is dirt cheap, it bolts right into the same mounting holes and it should put my voltages right where they should be...

In the big scheme of things I guess it's not all that uncommon to see "undesirable" vintage amps that share parts with the highly desirable vintage amps to be used as organ donors, and to be honest, I can't see how fixing the vintage voltage problem with a primary-adjusted repro unit wouldn't result in a win-win for everyone involved. To do this, all that's required is to get over the reservations about cannibalizing working iron out of a vintage amp.

I've got my fire-retardant suit on now, so I'm ready to take the flames that I think will be coming from the preservationists.


Feel free to express your opinions. This subject doesn't seem to get talked about very often.

[Leo_Gnardo]

that treble-deadening cap is actually on the "Normal" side of the preamp.

DOH! Woops, right you are, I must clean my spectacles more often.... Same for the 100K "tail" resistor on the bass control I mentioned.

Often I have to mark amp chassis with a sharpie while working on it - whatever amp it is - to keep track of what's what. I see Bassman 10's so rarely, haven't memorized which channel is which viewing from the inside. Now I'll remember!

First one I saw was at a recording session at Marcus studio in London, 1984. Mickey Féat on bass, and a fet-47 on the Bassman 10. Then no more until 20 years later, now I get to work on one every 2 or 3 years. It seems some of the rarely seen amps are coming up for maintenance within the last decade, for instance Ampeg V2 and Sunn tube amps.

[Leo_Gnardo]

Feel free to express your opinions. This subject doesn't seem to get talked about very often.

Good photo! And considering you're about to pick up your Ten at a bargain price, you're not about to "get burned" on the deal. Swapping in a PT to match modern 120+ volt lines, sure beats faffing around with "bucking" transformers. FWIW one of the more important parameters in power supply is the filament voltage. Cathodes running too hot is a problem, and coupled with extra high voltage results in a hyped-up amp & shortened output tube life. So you're wise to be hip to the problem and be ready & willing to do something about it.

"Preservationists" likely won't hassle you, this isn't a tweed Twin.

And making up a detachable wheel dolly, along the lines of the ones Ampeg provided for B-15 etc, an excellent idea. Of course you'll be putting on larger, better wheels I'm sure. You might consider using the sort of knurled thumb-screw attachments like those used to hold Fender heads on their cabs. One in each corner of the bottom plate to spread the stresses around. I could never get over that Ampeg only used one, what were they thinking?

I could see adding some braces to the back panel, to keep it from flapping with low notes. Also some 1x1's to the interior corners, maybe a couple on the baffle too. Those boxes IIRC were butt-joined (rather than Fender's earlier finger-joints) and with aging glue & shrinking wood, they could stand some buttressing especially if you're going to haul 'em around on gigs.

[bob p]

I've already got it, Leo. I picked it up the day that I started this thread. I found it ... dirt cheap ... at my local GC of all places. Normally they're on top of current pricing and they bias their prices at the high end of the range, so I was very surprised to find this one priced as well as it was. The guy who wrote the prices into the GC pricing database must not think these things are worth all that much.

Steve, like you say GC used to offer almost-free shipping on amps, but they don't do that any more. I'm not at all enthusiastic about shipping an amp across the country -- I just had 2 out of 2 purchases arrive damaged last week. I prefer to shop locally, so now I do daily automated scans of the new GC inventory that's within driving distance. In the past month I have had a 6G12, a SF Bandmaster Reverb head, and this Bassman 10 all surface at my local store, at what I thought to be very fair prices. They didn't last long... they all disappeared in a few days. I ended up passing on the Connie and the BM because they were both in poor condition and likely needed major work to put them back in shape. But this Bassman 10 was in great condition at a great price, so...

[bob p]

Swapping in a PT to match modern 120+ volt lines, sure beats faffing around with "bucking" transformers. FWIW one of the more important parameters in power supply is the filament voltage. Cathodes running too hot is a problem, and coupled with extra high voltage results in a hyped-up amp & shortened output tube life. So you're wise to be hip to the problem and be ready & willing to do something about it.

Well, truth be told I've always thought that the Vintage Voltage Adapter was an interesting way to solve the problem for people who have vintage amps that they don't want to mod, but it is sort of a kludge way to solve the problem. The best way to solve the problem is to address it at it's root cause. In other words, if the transformer is the wrong spec for the job, then replace it with something that's right. But try saying that to The Vintage People and see how far that gets you...

I'm also not too hip on using my variac. Too many risks involved with a dial that can move. To me, the obvious solution is to just replace the iron with the right iron for the job, but that involves ravaging a virgin amp, and we all know how unpopular that can be.

"Preservationists" likely won't hassle you, this isn't a tweed Twin.

Oddly enough, those are the amps that need this kind of modernization the most, but they're also the least likely to get them. I guess that was preaching to the choir when I brought up this subject, as this community seems to look at the problems quite differently than the vintage amp collecting crowd. We all realize that there are serious electrical issues that need to be addressed in these old amps, so we're not as averse to making changes that are clearly indicated, even if it involves vintage part replacement. As long as you're not going to worry about vintage authenticity and resale value, it's not a problem. It's the basic choice between whether an amp is going to become a museum specimen that doesn't get played (in which case form trumps function) or whether it's going to become a working amp (in which case form follows function).

And making up a detachable wheel dolly, along the lines of the ones Ampeg provided for B-15 etc, an excellent idea. Of course you'll be putting on larger, better wheels I'm sure. You might consider using the sort of knurled thumb-screw attachments like those used to hold Fender heads on their cabs. One in each corner of the bottom plate to spread the stresses around. I could never get over that Ampeg only used one, what were they thinking?

That thumbscrew idea is excellent. Something along the lines of the fender piggyback head/cabinet fasteners should work out great!

I could see adding some braces to the back panel, to keep it from flapping with low notes. Also some 1x1's to the interior corners, maybe a couple on the baffle too. Those boxes IIRC were butt-joined (rather than Fender's earlier finger-joints) and with aging glue & shrinking wood, they could stand some buttressing especially if you're going to haul 'em around on gigs.

I haven't spent much time looking at the inside of the speaker cabinet, as I've been focusing on the electronics for now. I did pull the speakers to read the numbers and determined that they were all CTS 1975. Everything in the amp ranges from 1973 (OT) to 1974 (PT) to 1975 (speakers) and the pots all fall in the middle. So this is clearly a '75 amp that's all original.

Interestingly, the speaker cab has a square center brace running front-back like a 1960-type cabinet. The baffle is composite, but the panels on the amp cabinet are pine. I have no idea about the joinery that was used, but I like your idea of adding cleats to the inside corners. 1x1 strips with glue and screws should be just the ticket.

Thanks for the great recommendations.

[bob p]

Well, after getting sidetracked in a Twin Reverb repair, I've been through the Bassman Ten top-to-bottom and I've confirmed that the amp is a 100% match to the schematic with no parts substitutions (yet). What's interesting about this amp is that it takes some of the Fender novelty wiring techniques to an all new level:

Looking at one schematic if you were going to use this for guitar you'd probably want to remove the .0047uf cap between the treble and volume control on the Studio channel for starters. There are also .002uF caps to ground right where the 100k bias resistors connect to the 1.5k grid stoppers.

One of the odd things about the Fender assembly line is how they used creativity to assure that every unoccupied pin on a 6L6 socket got used for something. Fender always seems to have grid stoppers and plate resistors mounted across the tube sockets, but this amp takes the Fender weirdness one step farther -- those 0.002uF oscillation suppressors are mounted on the socket, with one lead going from the proximal side of the grid stopper and the other to the cathode pin then passing through the cathode pin to the chassis. What is really odd about this setup is that the capacitor lead that goes through the cathode pin ends up being soldered to the chassis to form the tube's chassis ground! I wish I had taken a photo to document this weirdness, but I ran out of battery.

[bob p]

The Bassman 10 could be a tweakers dream, basically rewiring the Studio channel preamp, phase inverter and power amp to the specs of a BF/SF Bandmaster or Super (minus the reverb and trem.) Although it looks top heavy it could be turned into a Super Reverb sans rev and trem with the four 10s (you might have to replace at least 2 of them.)

All the speakers are good. As it comes from the factory this amp is pretty darn close to a super. It's already got the right PSU iron and the electronics are only a few value tweaks away.

I thought I had mentioned this previously, but maybe I didn't: The Bassman 10 is built upon a Bandmaster/Reverb/Super? chassis. It's already got the holes drilled into it for all of the pots that are used in the other circuits, it's just never been fitted with the extra pots, and the holes are covered up by the faceplate. It would be very easy to add-on the Tremolo/Reverb circuits with no chassis drilling required. All that would be necessary would be to populate the circuit and obtain the proper repro faceplate. The chassis is even pre-drilled for the choke, reverb transformer, and larger size OT that are used in other models. The chassis even has "HEAD" stamped on it, in spite of the fact that it got placed into a combo cabinet.

It seems evident that Fender didn't bother to build separate chassis for all of the different models that used the same chassis footprint. Instead, Fender built one chassis with all of the holes that might be necessary to build any of several amp models, and then the amp model was defined by how they populated the chassis. From a modder's standpoint this means that the chassis could easily be converted from one model to another without any drilling or physical modification.

Since I brought mine home, I've seen a couple listed on the GC web site for hundreds more than I paid for this one. The lower pricing on my amp must have been some sort of local oddity.

[The Dude]

You're making me want to get my old Bassman back. I might just have to make a phone call.

[Justin Thomas]

I consider them an almost-secret weapon... Love 'em.

Justin

[Leo_Gnardo]

Since I brought mine home, I've seen a couple listed on the GC web site for hundreds more than I paid for this one. The lower pricing on my amp must have been some sort of local oddity.

You scored big time - I always like it when friends & customers & fellow MEFsters get a great deal. And you didn't have to pay shipping $$$$ (and get it bashed up that way) either. Good all around. You'll have to try that James stack channel for a while, see how you get along having a little Ampeg flavor built into the amp.