got the bassman head, but what is this switch for?

[casblah]

Re: got the bassman head, but what is this switch for?

You could do a visual on the filter caps. I'm not sure on the bassman heads, but many old Fenders have an aluminum "pan" which houses the filter caps. You'd prolly notice some oozing, or a chalky-like substance around the ends of the leads on those caps. NOTICE*** The filter caps store a good bit of energy even when the amp is off, and can knock you on your a$$, or KILL YOU if the conditions are right. To "safely" discharge them, turn your amp on, as well as your standby switch (as if you'd be playing it..) then pull the plug from the wall, this should drain the caps to a "safe" voltage, so you can look inside your amp. Maybe do some research on this procedure b-4-u attempt anything... if you should need to.

 

[drew_half_empty]

Re: got the bassman head, but what is this switch for?

i dunno it sounds like...thunder

thats the closest thing i can compare it to

 

[drew_half_empty]

Re: got the bassman head, but what is this switch for?

also, if i plug an 8 ohm cab into one speaker jack, and another 8 ohm in the other one, does that equal a 4 ohm load, or 8

 

[Curly]

Re: got the bassman head, but what is this switch for?

also, if i plug an 8 ohm cab into one speaker jack, and another 8 ohm in the other one, does that equal a 4 ohm load, or 8

the ext. speaker is in parallel, therefore, 2 - 8 ohm loads = 4 ohm

the noise you're describing sounds more like resistor type noises .... poor filter caps often give you ghost notes

you might try a post on the Fender (FDP) forum, in amp mods for some good help

I'd also suggest a book or two - even if you end up taking it to a tech, you'll benefit from the knowledge. Gerald Weber's first book, "A Hip Guide ..." is a good place to start.

 

[Jeff Seal]

Re: got the bassman head, but what is this switch for?

Drew, first off killer score!!....

As has been explained, the three way switch is a ground reversal switch although the chassis always remains grounded, the use of some externally powered effects and such can cause a 60 cycle hum if the polarity from the source is reversed........all of this assumes you're amp DOES have the three prong jack and it is wired correctly (kinda important)...

The "jack" to the far right is not a jack at all but the Hum Balance Control...(take a flashlight and look in it...there should be a slot to insert a screwdriver) if not, it's been modded for something.....

....two 8 ohm spkr's/cabs will result in 4 ohms, but before you get too concerned about it....you should also know there is a switching point in the second jack which ties to the other 4 ohm tap thus bringing it to 2 ohms...

...having said that.....it really doesn't even matter.....you can run any SF or older Fender at anywhere from 32 to 2 ohms and the amp is not going to explode, fry or cause a thermo-nuclear holocaust! Fender made many cabs ranging from 16 to 4 ohms (although most Bassman cabs were indeed rated at 4) and any could be used with any head.......

WHY????.....Fenders run a relatively small amount of plate voltage compared to Marshall's and most EL34 based amps (Music Man's run 700v...), so the impedance difference is not as large between the primary and secondary windings as the higher plate voltage amps where this would create concern..
( back when i was 15.....I ran a BF Showman into a 16 ohm load at practice, and a 1.3 ohm load when we gigged.....never fried!!!!...of course, didn't sound that great either.. :blackeye: again, I was 15 and didn't know...)

The mismatch WILL, however extend or shorten the life of the tubes, in comparison to having it properly matched.....

This is an area of much confusion, but I'll tell you this...You would be hard pressed to find a tech that has replaced a Fender OT of this era because of an impedance mismatch.....more than likely you'll find many that have replaced PT's simply because the Ext. Spkr jack was used instead of the Spkr jack...which MUST be used at all times..... (then the fuse blows, so "naturally" the few uninformed customers I have replace it with a 20 amp and the PT fries.... :smack: )...OT's rarely fail...

...yet again, a mini-novel on the subject, but hope it helped bro!

Jeff Seal

 

[flank]

Re: got the bassman head, but what is this switch for?

thanks for the info Jeff Seal......... your right, i never hear or see a fried fender tranny......but i see marshalls all the time heh

 

[Jeff Seal]

Re: got the bassman head, but what is this switch for?

thanks for the info Jeff Seal......... your right, i never hear or see a fried fender tranny......but i see marshalls all the time heh

Hopefully the newer Dagnall's...jeez... they're just bad!

Jeff Seal

 

[rspst14]

Re: got the bassman head, but what is this switch for?

Do you know how long it's been since the tubes have been replaced? Under normal playing conditions, power tubes last a year or so, while preamp tubes can last 3-5 years. You'd be surprised how many amp owners don't know that, and they don't replace tubes until the amp stops working. Just because the seller claimed that a tech looked at it doesn't mean it really happened. Even if a tech did look at it, he may not have gone through it very thoroughly. If it were my amp, I would replace the tubes and do a complete cap job on it...but I have some experience in working on amps, so I wouldn't have to pay for anything but parts. If you're not experienced with tube amps, make sure you leave it to a pro, or at least read up on the subject very extensively before doing anything. As others have mentioned, you definitely want to convert to a three prong cord as well.

Ryan

 

[Curly]

Re: got the bassman head, but what is this switch for?

Jeff,
good info there ...

just one minor point ... on my BF, the ext. jack is indeed next to the speaker jack. The balance pot is on the underside of the chassis, as in most Fender amps ..
unless they changed for later SF amps?

here's a decent pic of a '66:
Bassman chassis

you can make out the pot on the underside, and the two jacks are to the right of the fuse and two flip switches, in the bottom of the pic

 

[drew_half_empty]

Re: got the bassman head, but what is this switch for?

well, it has been modded for the 3 prong

but I'm still confused about the 3 prong input, was that where the old power cord was plugged into, or? About the screws, theres one on each side of that plug in, and on the acual power cord theres like..a nut holding it in.

But, i am using external effects, and, from what i gather, messing with the toggle switch should fix this, but someone else said if it was 3 prong it was disconnected

I'm really confused, sorry

and, is it cuz of the tubes or not? referring to the thunder-type sound. If not, well, i want it to go away, now, how do i achieve this?

also, as always, thanks for the info jeff, you are the amp guru

 

[Quencho092]

Re: got the bassman head, but what is this switch for?

it is likely the tubes or something else, my peavey classic would do that alot after i played a show with it, replaced the tubes and it was fine...except some thunder remained. Might have something to do with the svetlana's i put in or something else like the transformer?

Those are cheap anywho...

 

[drew_half_empty]

Re: got the bassman head, but what is this switch for?

well, I did some observations

i turned down both volumes all the way, unplugged the guitar, and turned it on, nothing, no pops

turned it up, nothing, no pops

THEN i left the main volume at 7 and master at 3 & turned it off, off standby, off everything, then, turned it back on, as soon as i flipped the standby off, bam, got em, pops & all, no thunder noise, but subtle popping

this help anything?

 

[casblah]

Re: got the bassman head, but what is this switch for?

Perhaps it may be a capacitor issue. They tend to dry out over time. Especially the vintage types found in many older Fender amps. I had a similar problem with "popping" in my S. Reverb, and putting in new filter caps helped it out immensely. If it's a 70's Bassman, it could use a new set of caps ,if it's never been done b-4.

 

[TheArchitect]

Re: got the bassman head, but what is this switch for?

Perhaps the filter caps need changed.

+1

 

[gt5litre]

Re: got the bassman head, but what is this switch for?

The ground switch should not be connected it the amp has a 3 prong plug. It is not needed with the modern 3 prong wiring and if it is take it to a tach and have it disconnected ASAP. The pops could be dirty pots or leaking audio caps on the main circuit board. The audio caps block DC voltages from getting through and if they are going bad they will put hi DC voltages in places where it should not be. Have a tech check it out and have the tubes checked too.

Brent

 

[drew_half_empty]

Re: got the bassman head, but what is this switch for?

could that be one of the reasons that it's overdriving soon?

I realize it's a bassman, but these ones shouldn't break up until about 9, I'm getting some drive at around 5

 

[sanrafael]

Re: got the bassman head, but what is this switch for?

Back to that original question. That switch is kind of a leftover from US power before the 50s. The socket had only two pins. One was ground, and the other hot (and deadly!) And you did not know which was which! The chassis should be connected to ground for safety and for low hum. The three prong plug takes care of this for you; the third pin domes from ground and should go to the chasis. This happens in the ground position on most such switches. The other two positions connect the chasis through a capacitor (to limit the current to a less than deadly value) to one of the two main pins of the plug. If you have no real ground, this gives a bad ground if you select the right one, good enough to keep the hum down (usually), but with the possibility of a nasty, but usually not deadly, shock if you choose the wrong one. Kind of like that old game where behind one door is a beautiful womain and behind the other, a deady tiger, and you have to open one. Hey, people had different values then.

 

[Kent S.]

Re: got the bassman head, but what is this switch for?

Back to that original question. That switch is kind of a leftover from US power before the 50s. The socket had only two pins. One was ground, and the other hot (and deadly!) And you did not know which was which! The chassis should be connected to ground for safety and for low hum. The three prong plug takes care of this for you; the third pin domes from ground and should go to the chasis. This happens in the ground position on most such switches. The other two positions connect the chasis through a capacitor (to limit the current to a less than deadly value) to one of the two main pins of the plug. If you have no real ground, this gives a bad ground if you select the right one, good enough to keep the hum down (usually), but with the possibility of a nasty, but usually not deadly, shock if you choose the wrong one. Kind of like that old game where behind one door is a beautiful womain and behind the other, a deady tiger, and you have to open one. Hey, people had different values then.

Ideally the netural is at ground potential ... notice I said *ideally*. Either way, I've been shocked enough times to know that it hurts! Now, sound wise the netural would have been good enough (soundwise, and most often) ... note that like SR said, this was *before* the advent of the polarized plug.
And, yes, I've meet the tiger somewhat myself when touching another piece of equipment ... not fun!

 

[Bludave]

Re: got the bassman head, but what is this switch for?

but what does a ground switch do?

Back in the day when these Amps were made they did not have grounded plugs (3 prong). When you plug a 2 prong outlet into a polorized outlet sometimes you will get a ground hum. Before polorized plugs you could just turn the plug over. Swithing the ground switch does the same thing as turning the plug over in the wall outlet, it reverses the ground.

As far as cabinets go...... I would say to keep your eye open for the Bassman cabinet that Fender made for that Amp. It will sound really good. If you want ti invest a little Money have it modded to BF specks. It will be pretty hot! :dance: