1966 fender blackface bassman ab165 50 watt head

[ledzeppelinwasprettygood]

hi i traded in some gear and picked up this head on ebay. i just had some questions about it.

first i saw that it has a groundswitch. im not sure of what to do with it and i want to be safe.

i have a marshall jcm900 1960A cab that i want to plug it into and i wanted to make sure i had the proper settings. i believe the amp is 50 watts into 4 ohms. but i dont know a whole lot about amps. just what i read on harmony central pretty much.

any advice or comments would be much appreciated

[Richard]

What do you do with a ground switch? Get rid of it. The ground switch connects the amp's chassis (ground) to either of the wires in the cord, preferably neutral. If it's in the wrong position and you touch the guitar strings and something that actually is grounded, you will get shocked, just like touching inside a lamp socket. If you have the amp on and its humming a lot, te ground switch should be flipped. Replacing the power cord is pretty easy. If the cord has already been replaced, the ground switch should have been disconnected.

Your amp should be happy with a 4 ohm load. (Fenders seem to be pretty tolerant in this area)

[RickyD]

Here's what you do with the ground switch.

Plug in a guitar cord and turn up the amp to 3 or 4. Dangle the other end of the cord in front of the amp. Now flip the ground switch. It will either hum a lot louder or a lot softer. The setting with the least hum is the correct setting.

Back in the mid-late 60's, it seems like all but as very few bass players in town used that Bassman with the 2x12 cabinet. The very few exceptions mostly used the Ampeg B15.

[Regis]

Have you done any electronic work, that is, soldered a kit or built a pedal or worked on a guitar amp internally?

If so than you can do a couple of mods to your Bassman head that will help.

Replace the power cord with a grounded one and disconnect the ground switch because you won't need it.

This page will tell you how, or if you don't feel comfortable doing it have a qualified tech do it for you.

What is the impedance of your JCM900 cab? If it's 16 ohms it's not a good idea to run your Bassman through it. I'm not sure if you can rewire a 16 ohm cab to 4 ohms, maybe somebody else can chime in here about it.

The Bassman has a 4 ohm output transformer, and it's usually ok to go up to 8 ohms but 16 ohms isn't good, the amp would probably freak out.

[Enzo]

A 4x12 cab, assuming the four drivers are the same type, can be made up for 16 ohms three ways.

1. four 4 ohm drivers wired in series
2. four 64 ohm drivers all in parallel
3. four 16 ohm drivers wired in series/parallel.

1 is darn unlikely, and 2 is silly, although those are 32 ohm drivers in the Ampeg 8x10. Leaving 3. Four 16 ohm drivers can be rewired in prarllel to create a 4 ohm total.

Problem solved.

[ledzeppelinwasprettygood]

more bassman

according to the auction a new ten foot three prong cable was added, so i assume that means the ground is no longer necessary.

also according to the auction, the tubes and caps have been replaced.

as far as my cab goes, i believe it is 4 or 16 ohm mono, and 8 ohm stereo. it has a little switch on the back that lets you choose "ohmage" so im assuming i flip the switch in the direction saying four ohms and im good to go?

also, i was wondering if anyone could recommend the best kind of speaker cable to use in this situation. i guess they're all the same, im just a layman is all. thanks

[Regis]

Enzo, good on you, that's what he needed to hear.

LZWPG, yes, switch it to 4 ohms and go for it. If you ever consider getting another one you could do what I do and run two Bassmans into a stereo cab with a stereo chorus, it sounds awesome, pretty loud tho. Here is a link to a page I did on my rig.

I had been using my Traynors for a long while but recently switched back to my Bassman tops.

[bob p]

Just in case LZ is considering any other mods to that BF Bassman, I'm going to go into Vintage Anal-Retentive mode for a minute, and recommend thinking twice before performing mods on a BF Bassman. Sure, switch the cord over from 2-prong to 3-prong. You need to do that for safety. Have the electrolytic caps in the amp replaced if necessary that's recommended maintenance. Beyond that, please don't hot-rod or cobble-up a BF amp. That's wat Silver Face Fenders are for, preferably the later ones.

[Regis]

Bob, I mostly agree with you, however I don't see any harm in redoing the bass channel into something more usable. If he kept the old parts and didn't drill any holes it would be easily reversable. Shoot, he could probably sell those tubular blue caps for twenty bucks apiece on ebay. Come to think of it, I have a couple of those in my junk box. Hmmm.....

LZ, regarding the speaker cables just go to your local music store and get a decent 16 guage speaker cable, a three footer should do it. Don't spend more than $15 and don't buy Monster cable, they suck as a company and as a product.

[bob p]

indulge your inner cheapskate: lamp cord makes pretty good speaker wire, especially for short distances. and it costs next to nothing.

for speaker wire i just go to the local home improvement store that sells wire by the foot. i get the largest gauge available.

Bob, I mostly agree with you, however I don't see any harm in redoing the bass channel into something more usable. If he kept the old parts and didn't drill any holes it would be easily reversable.

note to self: don't buy a BF amp from Regis.

in all seriousness, i woudn't by a BF amp from anybody who's been cobbling on it -- regardless of what they've been doing. as it turns out my reasons for not buying the amp are the same as your reasons for modding it -- because people consider the mods reversible. i guess i'm going to drift into a minor rant about this...

personally, i don't want to plug into an amp that some amateur has been modding. i don't want to trust some amateur with my electrical safety, and i don't want to pay a premiuim for an amp that isn't what its advertised to be -- something "original." when somebody has "reversibly modded" a BF amp, the buyer has to go through it with a fine tooth comb, looking for artifacts of mods and restorations, paying attention to the quality of someone else's work. often times someone else's work isn't up to snuff. buying a used amp on ebay can be a dangerous thing.

for anyone who may be considering "reversibly modding" a BF amp, keep this in mind: serious collectors don't want a BF amp that has been modded, regardless of whether you have reversed it or not. if you mod your BF amp and reverse the mods, you will have done irreparable damage to your amp. it will have gone from museum piece / collector status to player status. serious collectors inspect the solder joints, and subtract appropriately from the pruchase price for any evidence of unnecessary modification and/or amateur tinkering.

[ledzeppelinwasprettygood]

http://blueguitar.org/new/schem/fend...4_vs_aa165.pdf

i want to do that

[soundmasterg]

He should keep the blue molded caps in the amp unless they are leaky, which is rare for those. They're great sounding caps, but not worth $20 apiece.

[bob p]

one other thing i would add about "reversible mods" is that i would bet that most amps that get reversibly modded and then restored back to their "original" state typically get sold as an "original" amp when they aren't an "original" amp any more.

because everyone selling a cobbled amp wants the most they can get out of the sale, there's a financial incentive for someone who's reversibly modded an amp to lie about its condition. an astute buyer will offer less for an amp that has been molested, so the less than forthcoming seller will conveniently fail to disclose that the amp has been modded, and its the buyer's job to beware.

if the buyer doesn't recognize that the amp has been modded, and the seller doesn't tell him about it, he's been defrauded. nobody likes to be the guy who bought the amp that he thought was original when it wasn't.

LZ, your link is 404.

[ledzeppelinwasprettygood]

http://blueguitar.org/new/schem/fend...4_vs_aa165.pdf

[TD_Madden]

I've never sold ANY of my amps...much to my wife's dismay.