F.O.R.D. SF Bassman

[kriswel]

I was just over at a friends house watching the steelers game and on my way out I see from the corner of my eye a silverface fender put out with someones trash in the alley! walking up to it I thought for sure it was a super but no it's a Bassman Ten. Funny how I had a mild feeling of being let down, hell it's a winter project and it will likely become a Super when I am through with it! Anyway I loaded it in my truck fast half expecting someone to tackle me (after watching the game...)

Got it home and... yeah it's a project alright! I will be able to restore the chassis and cab, it still has the tilt back stands... the speakers are gone but they were kind enough to leave the F cap speaker plug... I don't think I will try to salvage the iron it's in bad shape even if it's in working order. So yeah I think it's going to be a Super. I could be wrong but the Chassis and Cab are the same no? I see extra holes in the face of the chassis and all over but not the tube socket holes. But the mounting holes for the reverb transformer are there just not the holes for the wires. It looks like they both got a certain amount of holes drilled before parting ways in the line.

I will post some better pics... as I start pulling this thing apart.

k

[rafe]

Yeah , like when your get 5 out of 6 numbers on the lottery,  oh crap I only won five grand, It should have been 5 million......Still a real great score and a great project with a good start............

[kriswel]

So I was looking on the field guide for info and found that the cabinet dimensions for a Bassman Ten were taller by 5". Hmm I swore that this amp was the same hight as a Super Reverb I have set a beer down on enough of them to notice a 5" hight difference. So I go do some investigating sure enough it's the same size as a super within 1/2"... what do we have here? the cabinet belongs to a Bantam Bass. Well that's convenient. it has the same dimensions as a BF Super Reverb g/t 1/2". But it is designed for 1x15. I always liked the 115 and it just so happens I have a weber (JBL D-130 clone) 15" kicking around the shop. That will save me some dough. 115 Superverb it is.

[FYL]

Nice find.
 

[kriswel]

Think it might need a cap job? Haha!

Without a hole bunch of experience is it worth trying to salvage transformers this rusty? I know that rusty laminations is not ideal, that being said I have played some amps with pretty rusty laminations. My thought is, not knowing that they work I might as well start with fresh iron if I am going to gut it anyway? Any thoughts?

Wow allot of parasitic suppression going on in this thing... Bass amp, let me guess LFO's? Gotta love CBS designs.

Someone did some mods... and didn't even look at those supply caps... and then tossed it in the garbage when it didn't work anymore??? Without even keeping the tilt back legs corners or casters. At least they could of left me the chassis straps!


FUN FUN

[kriswel]

I guess I could go 4x10 as my 15" speaker does not look like this one http://i101.photobucket.com/albums/m74/mattlindberg/bantam003.jpg anyway and I will need to build a new baffle anyway. I guess I have some options. I was trying to figure out the shape of the baffle.

[Frankenamp]

Time for some Rustoleum I guess.
The Bantam is the BM10's illigit ancestor I have an older BM10 and the circuit tagboard was identical to the bantam. The Bantam's styrofoam speaker wasn't a winner. Sounds like you have some fun ahead of you!


(you could just put in a 15" adapter plate)

[rafe]

Can't you here it ....it wants to be a vibro verb.......

[DummyLoad]

congrats on the nice dumpster dive score...   

the rust is not a problem. get after them with with a wire brush and re-paint the end bells if you wish. personally, i'd leave them alone. check the windings for continuity and if the DCR of the windings are within reason, fire it up on a lamp limiter just long enough to just to see if the trannys are OK - if they are, then gut and rebuild into a 5f6-a bassman.

[Jack1962]

Great find , brother enjoy your new project 

[6G6]

If the transformers are still good, the next step
will be to find out which OT you have.
If it is 8 ohms, you can go 4-10 or 1-15.
If it is 2 ohm, then you'll want 4-10.

Nice score!

[FYL]

Without a hole bunch of experience is it worth trying to salvage transformers this rusty?

This rusty? They're in pretty good shape! Test them and reuse them if they're OK.

[Frankenamp]

If the transformers are still good, the next step
will be to find out which OT you have.
If it is 8 ohms, you can go 4-10 or 1-15.
If it is 2 ohm, then you'll want 4-10.

Nice score!

I'm pretty sure that the OT will be sized for an 8 ohm driver. The PT iron is a little light for a 5F6, as is the OT... but if  (OT) saturation is what your'e after thats the ticket... or you could run the output tubes cathode bias, and all's well.

[bluesbear]

The transformers may be okay. Some rustoleum nand try them out. Whatever you do DON'T wire brush them. That'll just make things worse. Bassman 10's are actually going for fairly good money... to bass players, amazingly! If the condition isn't too bad, it might be worth fixing and selling. Just a thought.
Nice find. I love garbage can equipment. I have a flute, a violin, 2 Gibson SS amps, and a Gibson EB-3, all from garbage cans. I also had a 4 - 12" Vox cabinet I found and sold years ago... and that's just the musical equipment!
Dave

[kriswel]

I thought about fixing and selling, might get a few hundred bucks for it rather than spending a few hundred bucks. Truth is I have never owned a Fender amp, I build them, fix them for friends and turn other amps into them... but I have never had a nice fender combo. People look forward to seeing me with new crazy homebrew, hardly ever finished looking, amps and that has always been my thing. Some people think I have some mojo voodoo skills and if I tell them that they are simple well used circuits they think I am feeding them a line. Not one to argue, i leave it at that.

Secretly though, I have always wanted a nice fender combo in my collection. I am totally against cloning and wrongfully badging an amp and would never dream of spending allot of money on something I didn't build myself, but this could be my Frankestein.  It starts life as a Fender... looks like a fender but is still one of my crazy voodoo homebrews at heart, a fender.

I'm going to fix it first and test the Transformers, I have a stack of possible replacements but I think I would like good Hammond replacements. Yeah it's going to be a BF 115 Superverb (Vibroverb in a Super's body) I think it might be my new daily driver.

[kriswel]

Not a huge surprise but the PT has the 5v yellow wires tied to a terminal strip inside the amp already and the PT code is 022798 = Super Reverb. I guess if I can clean it up and it works... there is absolutely no reason to replace it.

[phsyconoodler]

Fix the amp.Use the transformers it has.Play loudly and don't worry about much.You scored big!

[DummyLoad]

Whatever you do DON'T wire brush them. That'll just make things worse. 

we have differing experience/opinion here. care to elaborate?

[kriswel]

OK so, Did the cap job and the voltages are as expected... PT seams alright without having to work too hard.

OT tested primaries blue to red 147 ohms, brown to red 130 ohms. all of them to ground over 400 k but this number keeps climbing?

secondaries to each other or green to ground 0.8ohms should that number not be up in the hundreds of k's?

Well I put some known good tubes in it and fired it up, no smoke but no sound either, not even a hint of a snap, crackle pop of the speaker.

OT shot?

[FYL]

OT tested primaries blue to red 147 ohms, brown to red 130 ohms. all of them to ground over 400 k but this number keeps climbing?

There could be a big cap in the circuit. Unloaded = high current drawn, appears as low resistance. Loaded = no current drawn, appears as a high resistance.

Did you measure in-circuit?

secondaries to each other or green to ground 0.8ohms should that number not be up in the hundreds of k's?

If you measure in-circuit the output jack is shorting signal to ground.

Well I put some known good tubes in it and fired it up, no smoke but no sound either, not even a hint of a snap, crackle pop of the speaker.

Don't go too fast. The amp should be fully checked.

[PRR]

> care to elaborate?

You probably can't do any harm with hand brushing.

Some Ford mechanic with a POWER wire-brush (or coarse-grit sander) "can" schmear the laminations, burr the edges, cause shorts across the thin inter-lam insulation.

I say it isn't rusty enough to affect the sound (bad OR good) and may be ignored. If a customer won't buy the "mojo" theory, scuff it with a Scrubbie and apply a dark wood-finish oil. If a customer HAS to see better-than-new, glop it with Rustoleum.

> all of them to ground over 400 k but this number keeps climbing?

You are reading the filter caps. Ideally they are dead-short in the first micro-instant, rising to infinite resistance after infinite time. 400K with a part-volt test is quite reasonable for electrolytics; proves there isn't some hard-short but does not prove they will hold 400V.

> secondaries to each other or green to ground 0.8ohms should that number not be up in the hundreds of k's?

One side of the speaker secondary is grounded. Maybe the other side if it has a shorting speaker jack and nothing plugged in. The total secondary resistance must be much less than speaker impedance (or it would waste precious power). 0.8 ohms is a fine and expected value. (Check what your meter reads on a dead-short.... I have one which never gets to zero because it reads its own lead-resistance.)

> OT shot?

That's like the last thing I would suspect.

Does B+ drop 11 seconds after power-on? (Showing the tubes actually suck current.)

Tarnish, moth-parts, or wire-scraps in the speaker jack fingers and lugs?

[kriswel]

Thanks,

I lifted the ground switch on the output jack and it is .8 ohms. I also pulled the tubes. I guess I should lift the B+ red wire? the black is tied to ground. But just to be sure I disconnected all the leads and I still get .8 ohms between the secondaries. That isn't right is it? if black is tied to ground and my output signal only sees .8 ohms to ground why would it go to the speaker? I don't fully understand output transformer theory though.

Forgive my ignorance but if nothing looks burnt and I did a cap job on it and the voltages check out what else should I be checking before I see if she smokes. the fuse wasn't even burnt and it was even the right value. I haven't built a current limiter or anything fancy like that, I know it's easy to build... just a light bulb in series right?

Am I missing something else?

[kriswel]

Sorry prr I didn't see you post and you answered some of my new questions.

[kriswel]

Dead short gives me .1 ohm so net .7 ohm

I'll hook it all back up, clean out the tube sockets and tighten them up. and give it another shot. Should I disconnect the feedback loop maybe? I don't see why anything would short there though? I could start changing all the resistors in the output circuit they should all be done anyway but none look burnt. 

[kriswel]

Woohoo she sings! Ok now i'll do a little more maintenance work and try to find her true intended voice before doing any modifications.

[eleventeen]

Great find! I don't consider those trannies too rusted, by any means.

[DummyLoad]

i'm thinking that the amp lived in high humidy environment it last days... it is probable that some of the carbon comp resistors have drifted - suggest removing all the tubes and measure them - esp. the ones in PS chain, G2, and plate load.

pots probably need a good cleaning as well... like most others here, i think trannies have "character" and not enough rust to worry about.

good to hear she's alive again... 

[kriswel]

Yeah there is mould in the cabinet and chassis. It looks like it lived in a damp basement for several years.

After getting it purring a bit I know for sure that it would be unusable as a guitar amp as is for me. It is defiantly gonna get the AB763 treatment. I know some bass players like them, but I personally don't consider it a good enough bass amp to make me feel bad about drilling new holes in it. Right now it does neither things great and it has the potential to be a great guitar amp. Plus if I put them all in the right places there will be nothing to say it ever was a Ten other than maybe a chassis # or something. Not allot of work needs to be done really. All the eyelets that are in the board are in the right place, I just need to put in a handfull of new eyelets and a few tube sockets... all the mounting holes are there for the choke and reverb transformer as well as the holes for the extra pots that will be needed. The hard work is done already. It's either that or sell it as a working amp, but then what would I do all winter... I will keep all my pictures/info of the transformation and if I ever decide to sell it I will send them with it so it keeps it's history in tact.

Thanks for all the help. I don't work on real vintage amps all that much and your advice is appreciated. 

[eleventeen]

I think you should proceed w/a Super/Super Reverb (or whatever else you want) conversion without the slightest twinge of guilt that you're messing with something of great value. If you can make a nice amp out of a piece of garbage, what the heck could be wrong with that? I'd maybe consider a quick and light wire-brush followed by spritz of black paint on the trannies. Or not. I don't think those are too rusty, but it would be nice if you could STOP further rusting.

[kriswel]

I just BF'd the bias supply and was able to warm things up a bit... she is sounding better by the day. Phsyconoodler was right about "turn it up loud" though and loud it is. I am going to switch the fist channel over to an AB763 normal channel next and then use another gain stage from the studio side to act as the pseudo reverb mixing stage for now but without reverb if that makes sense. I want it to sound like the trem channel on an AB763. I haven't looked at a trainwreck preamp schem in a while but that is sort of the same idea?

I will likely fit the speaker and play it like that for a while. I got some gigs coming up including a Rolling Stones Cover night on Keith's Birthday, I think it would be a good time to unleash my dumpster damsel. Gonna be a noisy night.

[DummyLoad]

dumpster damsel...

 

[kriswel]

When overhauling an old fender amp should you remove the copper plate and replace with buss wire on the pots or keep it and add buss wire or just keep it as is? I know sometimes people remove the pots and wire brush the copper but I think I would just replace it with buss wire if I was going to go this far.

[mresistor]

It's a brass plate, isn't it? Could clean it with brasso.

[PRR]

> 0.8 ohms to ground why would it go to the speaker?

The OT is an inductor.

The ideal inductor has zero impedance at zero frequency (DC), infinite impedance at infinite frequency, and in-between impedance at in-between frequency.

For easy insight, assume the winding is marked "10 ohms" and the DC resistance is 1 ohm.

Get a lot of test gear. Run say 1V audio signal through 100 ohms into the "10 ohm" winding. Measure audio voltage across the "10 ohms". At 1Hz(*) you may see 0.01V. The winding is about 100*0.01 or 1 ohm. Come up to 10Hz and you may get 0.02V, 2 ohms impedance. At these subsonic frequencies, most audio power DOES short-out in the transformer, little gets to the speaker. At 50Hz it may be 10 ohms impedance. About half the power gets diverted to speaker. At 500Hz the naked transformer may be 100 ohm impedance, nearly all audio power goes to speaker.

Those numbers are ballpark for guitar. Cost and weight are vital, we have nothing below 80Hz, distortion is not a sin, and we maybe don't want a full dose of 80Hz (boom and slap). A push-pull Hi-Fi tranny's impedance will be high by 20Hz for good response and THD specs, but that means more cost and weight.

(*) Ordinary test gear does not work well at 1Hz. While some sig-gens go that low, most meters won't. I had a modified VTVM which was verrrry sloooow and flat to 1Hz. You may also use a 'scope set to "DC".

> remove the copper plate and replace with buss wire

Electrically, copper is copper.

Being thrifty, I think the strip is EXCESS money.

But Fender was no fool. He probably did that so the pots could be fully wired (including grounds) and checked BEFORE the guts went in the chassis. In volume production, the cost to re-work mistakes is greater than the cost of the strip.

Leave it alone. A little tarnish AFTER solder does no harm.

[kriswel]

Funny I have always looked at the fender system and thought that a really good point to point system might be faster and less materials but then when you think about it they probably had a post war style assembly line setup and unskilled labour. You can have 2 unskilled labourers assembling more material and it still costs less than a qualified tech, who lags with monotonous tasks anyway.

[bluesbear]

I'd suggest steel wool for the copper plate if you're going to continue using it. I just run a buss wire down the back of the pots and leave the plate alone.
Dave