Questions asked here about 1000 times - Bassman 135

[flaj]

Hi, I'm new here, so please be patient and tolerant

I just bought Bassman 135 from the late 70's, and I couldn't find one clear answer for the questions:

1. Is it ok (and safe) to plug one 8 ohm cabinet into speaker out only?
2. Is it ok (and safe) to plug one 8 ohm cabinet into ext. spkr. out only?
3. Is it ok (and safe) to plug one 4 ohm into cabinet out and another one 4 ohm cabinet into ext. spkr. out?

I've read about ultralinear transformer, but I am still not sure 'bout the ext. spkr. being good for the 8 ohm spkr.

Thanks!

[MIJ-VI]

Welcome to TalkBass flaj!

If you search this forum you'll likely turn up a number of threads on the Fender Bassman 135. Here's some info to get you started:

Fender Bassman (Super Bassman, 100, 135) Schematic/Layout:
http://www.ampwares.com/amp.asp?id=29

[flaj]

Originally Posted by MIJ-VI

Welcome to TalkBass flaj!

If you search this forum you'll likely turn up a number of threads on the Fender Bassman 135. Here's some info to get you started:

Fender Bassman (Super Bassman, 100, 135) Schematic/Layout:
http://www.ampwares.com/amp.asp?id=29

Thanks MIJ-VI,

I'm a little confused by the schematic pictured on the website. As far as I know Bassman 100 and 135 had different transformers.
Here is Bassman 100 schematics http://www.drtube.com/schematics/fender/bassman100.gif
And here is Bassman 135 http://www.drtube.com/schematics/fender/bassman135.gif
Now, you can plug TOTAL load of 4 ohm into Bassman 100.
Into Bassman 135 you can plug two 4 ohm cabs.

In the other thread someone wrote, that if you plug one 8 ohm cab into ext. spkr. only (not the main spkr. out) it's ok.

My problem is, that I could never find one clear answer for my questions from the first post. I spent like 2 hours yesterday on looking, but couldn't solve the riddle. Too dump for the search engine probably

[chicago_mike]

I say yes to all 3. I've owned both the 100 and 135 when I was still in my teens. And learned a lot about valves/tubes since then.

Now, the only thing that MIGHT happen, is the main outjack might be a switching jack, killing the ext. speaker jack until a plug is inserted. Thats normal.

The 100 is a 4ohm OT. THe 135 is a UL 2 ohm Tranny. It should be, if not swapped out.

Both heads I bought for 100 bucks and one time a music store in Kenosha had like 10 or more bassman heads, from some touring band, all kinda beat but all super cheap. I wasn't impressed, I was impressed with the brand new Eden heads.

[flaj]

Originally Posted by chicago_mike

I say yes to all 3. I've owned both the 100 and 135 when I was still in my teens. And learned a lot about valves/tubes since then.

Now, the only thing that MIGHT happen, is the main outjack might be a switching jack, killing the ext. speaker jack until a plug is inserted. Thats normal.

The 100 is a 4ohm OT. THe 135 is a UL 2 ohm Tranny. It should be, if not swapped out.

Thanks Mike

Originally Posted by chicago_mike

Both heads I bought for 100 bucks and one time a music store in Kenosha had like 10 or more bassman heads, from some touring band, all kinda beat but all super cheap. I wasn't impressed, I was impressed with the brand new Eden heads.

I'll have to move to US! those amps are kind of expensive here in Europe if in good condition. Taxes, custom duties - you name it. But to hell with it - that heavy brick sounds like it should. Thanks again

[chicago_mike]

I bought those in the early 90's. Sold them a few years later, but I learned how to do mods and rebuild, repair and such with those and then other amps.

I had gotten the Boss parametric eq pedal, couldnt find the bass one, and it helped with being able to get some other tones out of those amps. But hey, my combo at the time was a peavey tnt100! Yes and my car, was a 1981 pontiac pheonix. Oh, I was pimpin back then!

[flaj]

Originally Posted by chicago_mike

Yes and my car, was a 1981 pontiac pheonix. Oh, I was pimpin back then!

Well, back in the 90's my dream car would be http://en.wikipedia.org/wiki/Fiat_126

BTW, that's how my Bassman looks like - not mint, but I call it decent

[billfitzmaurice]

Originally Posted by flaj

Hi, I'm new here, so please be patient and tolerant

I just bought Bassman 135 from the late 70's, and I couldn't find one clear answer for the questions:

1. Is it ok (and safe) to plug one 8 ohm cabinet into speaker out only?
2. Is it ok (and safe) to plug one 8 ohm cabinet into ext. spkr. out only?
3. Is it ok (and safe) to plug one 4 ohm into cabinet out and another one 4 ohm cabinet into ext. spkr. out?

I've read about ultralinear transformer, but I am still not sure 'bout the ext. spkr. being good for the 8 ohm spkr.

Thanks!

The amp doesn't want an 8 ohm load, though it probably wouldn't damage it. For best results run one or two 4 ohm cabs, or two 8 ohm. You can't run off the extension jack only, but there's no point in it anyway as the jacks are parallel wired.

[flaj]

Originally Posted by billfitzmaurice

The amp doesn't want an 8 ohm load, though it probably wouldn't damage it. For best results run one or two 4 ohm cabs, or two 8 ohm. You can't run off the extension jack only, but there's no point in it anyway as the jacks are parallel wired.

Thanks!

What I found on the internet is that Bassman 135 gives you:
on speaker out - 4 ohms if you plug exclusively into it
on ext. spkr. out - 8 ohms if you plug exclusively into it
chicago_mike seems to agree with.

So theoretically I should plug my 8 ohm cab into ext. spkr. out for the best results, or rewire it into 4 ohms and plug it into spkr. out.

Once again, that's what puzzles me - there are always different opinions about whether it is or it is not possible/optimal/safe to run a 8 ohm cab from ext. spkr. out.

Sorry for boring you, just wanted to be 100% sure.

[billfitzmaurice]

Originally Posted by flaj

Thanks!

What I found on the internet is that Bassman 135 gives you:
on speaker out - 4 ohms if you plug exclusively into it
on ext. spkr. out - 8 ohms if you plug exclusively into it

The schematic does show a dual tap, so that's probably right. It is different from the standard Fender arrangement that I noted in my previous post. There's a switch on the extension jack, but exactly what it does isn't obvious. It appears that it shorts the output when neither jack is being used, removing the short when either is plugged in. It might also switch the extension jack to the 4 ohm tap when both jacks are used; that would be the better method, so that both cabs get the same input. But the schematic is vague, so I can't say for sure.

[flaj]

chicago_mike and billfitzmaurice, thank you guys!

Even if the ext. spkr. out isn't 8 ohm (and it 99% is, as you said) hopefully I won't blow anything.

I think your help will be usefull for others who may have the same question in the future!

Cheers!

[BassmanPaul]

My quick glance at the schematic tells me that the speaker jack is 4Ω. if you add a 4Ω cabinet into the external jack the cabinets are in series and the amp switches to the 8Ω tap.

[flaj]

Originally Posted by BassmanPaul

My quick glance at the schematic tells me that the speaker jack is 4Ω. if you add a 4Ω cabinet into the external jack the cabinets are in series and the amp switches to the 8Ω tap.

Thanks Paul.

Seems like the 135 is quite unusual construction, or at least it was unusual back in the 70/80's.

It looks like I'll have to rewire my cab to 4 ohm (or buy a new one).

One more lame question: what wattage should the cab (4 ohm) be to best fit the Bassman 135?

[BassmanPaul]

You cannot rewire an 8Ω cabinet to be 4Ω. If you connect an 8Ω cabinet to the external jack and nothing into the speaker jack the amp will correctly match to your cabinet.

[flaj]

Originally Posted by BassmanPaul

You cannot rewire an 8Ω cabinet to be 4Ω. If you connect an 8Ω cabinet to the external jack and nothing into the speaker jack the amp will correctly match to your cabinet.

Yeap, you're right, bad thinking

[chicago_mike]

THose UL transformers were odd beasts. The SUNN 2000S uses one. I dont think it uses the UL taps though, canno remember. Its the same output transoformer in some Heathkit / Dynaco amps from yesteryear. The 120 and something else to be exact. When you could actually buy a tube power amp kit , build it yourself and have a great sounding amp, even for studio work.

[BassmanPaul]

Originally Posted by flaj

Seems like the 135 is quite unusual construction, or at least it was unusual back in the 70/80's.

No not really. For example the Ampeg Fliptops used exactly the same idea. There are many more examples too many to post.