Yamaha B212 volume problem

[zakman]

Hi everyone  :tu: my first day and first post !   a while back I was given a Yamaha hundred B212 from the early 80's I think, it was working but the volume was very low.I finally got round to taking a look today, first thing I noticed was the speakers, the originals were had been replaced (2x 60watt 8ohm yams) instead it had 2x 400watt 4ohm subwoofers !!!! (the amp is rated at 4ohm) now even my dumb brain knows that aint good lol, no way to match the impedance !  so I hunted round and found 2 tweeters rated 100watt 4 ohms, so hooking them to the subs in series/parallel would give me 4ohms 
Checked polarity etc made sure all 4 were working and gave it a go.
it sounded really good ! just about perfect as I play mostly acoustic,I was sitting playing and feeling smug then tried to crank it up a bit..... same as before  very low volume. Seems about half of what it should be (its a 100watt amp btw)
Only other thing I can find is one channel is off and buzzes like mad. the other channel works great, nice and clear on both high and low inputs but I'm guessing this has nothing to do with the problem (I do a lot of guessing lol)
Any ideas guys ?

[J M Fahey]

1) only as a temporary measure, wire those pieces of C... , sorry, "speakers", in series, so your amp "sees" safe 8 ohms.
Forget about the tweeters; woofer/tweeter impedances don´t mix, they work in different areas, just pull them away.
2) start hunting for a pair real Musical Instrument speakers, even a 12" "guitar" one will be much better than what you have now.
Eminence, Jensen (Mod), etc. or "not famous" Guitar speakers which were pulled from cabinets to put, say, an expensive Celestion V30 instead.
I mention Guitar speakers because you will find tons of them very cheap used in EBay (around $20/25 each), while if you google 12" Bass speaker you´ll find almost nothing.
Given a choice, I much prefer a loud "guitar" speaker, although it will have a little too much midrange and be somewhat bass shy to a dull unefficient Hi Fi woofer (even worse, a sub-woofer).
Your amp is fine, but it has horrible speakers now.
As of the buzzy channel, check visually for cracked solder or tracks around the input jacks , pots and any switches there, it´s very common for somebody to step on the instrument cable and crack things.
Resolder any suspect joint.
Also clean jacks, pots and switches with Deoxit or equivalent cleaning spray.
Good luck.
PS: also google its schematic, maybe you find it, although it´s an *old* amp.

[zakman]

How dare you call my speakers C..... !  hahaha ok yea they probably are,but honestly they sound pretty good, or maybe I'm just such a wonderful guitarist I can make any crap sound good ? ok maybe not !

Thank you for the advice, as you probably guessed I'm no genius with guitar amps  I know basic electronics, enough to keep things alive (usually), anyhow.... now I know where I'm going with it  :dbtu:
I did look on Ebay a few times but nothing turned up, maybe 60watt 8ohm speakers arent that common, also, I'm in the UK which probably makes a difference, no chance of buying one from the USA, the crazy UK import taxes cost more than the items now !
I'll start hunting again but still not quite sure what to look for,if I go with 2 8ohm speakers what sort of wattage would be ok ?

I searched Google for a schematic but cant find this model, I did find one similar that might help though

Thanks again  much appreciated

[J M Fahey]

In the UK look for Celestions , Fane or McKenzie; local is always cheaper.
Search UK Ebay or its equivalent for speakers people pull to install "better" ones.
Get their name and model and google their datasheet.
A manufacturer *may* lie ... but an EBay salesman *will*.
Or, say, a (still working) speaker pulled from a, say, 60 to 80W combo means it stands at least that much.
You don´t even have to buy 2 equal speakers, you can mix, so far as each one stands , say, 20% more than 1/2 your amp output.
So 2 60/80W ones will do.
Do your homework and search around.
Good luck.

[zakman]

Just a quick update..... been looking for a week now and still nothing on Ebay UK....plenty in the states but with postage and taxes your talking over £100 each  :grr (amp is only worth around £100).On the bright side,you can get 4 pair of boots on it  :dbtu: sooooo.......

[probodger]

When you say B100, do you mean a G100 212 ??

like this?


If so search for G100 as from what I've read in the past, these amps were only listed as "B" in Japan, rest of the world knows them as G. You can find service manuals for them online plus the Yamaha site has the owners manual for the Series III version (final version of the model run)
One pictured is a Series II, I bought it a few weeks ago off ebay UK and it came with the mutilated Duo Sonic.

Killer deal as these amps are fantastic and always go under the radar. I need to refurb it a bit, there is a split in the handle and the EQ pots are scratchy, but I'm holdign out on taking it aprt just yet as I've only just got it.

[fred_farkel]

When you say B100, do you mean a G100 212 ??

like this?


If so search for G100 as from what I've read in the past, these amps were only listed as "B" in Japan, rest of the world knows them as G. You can find service manuals for them online plus the Yamaha site has the owners manual for the Series III version (final version of the model run)
One pictured is a Series II, I bought it a few weeks ago off ebay UK and it came with the mutilated Duo Sonic.

Killer deal as these amps are fantastic and always go under the radar. I need to refurb it a bit, there is a split in the handle and the EQ pots are scratchy, but I'm holdign out on taking it aprt just yet as I've only just got it.

I have Yamaha G-100 ll thats in a 2-12 cab that looks like a Fender super reverb. I'm always being asked what kind of tubes I use to get that great great tone. I just reply "Thanks"

[J M Fahey]

*There is* a Yamaha B100 amp, but it´s a 1x15" Bass amp.

[probodger]

Yeah I know, that confuses things more 

[RichardM]

*There is* a Yamaha B100 amp, but it´s a 1x15" Bass amp.

Yep, here's mine.



I also have a G100B-212 that says HUNDREDB212 on the front. Perhaps zakman has one of those?