bobloblaws 7/22/2018 7:45 PM
Fender Twin High Impedance Speakers
I have a 74/75 Fender Twin here that doesn't seem as loud as it should be. I was doing some troubleshooting, then on a whim I checked the impedance of the speaker cabinet. It turns out to be 16 ohm whereas the OT is looking for 4 ohm. I measured each of the two speakers individually and I was shocked to discover they are 32 ohms each and have been wired in parallel for 16 ohms. They at least appear to be original speakers, blue label Fender branded, typical for that era I think. At first I wondered if they might be defective, but both are virtually identical impedance, coincidence? Has anyone ever come across Fender speakers as described?

B.
 
J M Fahey 7/22/2018 7:57 PM
If they are as described, Iīd rather mistrust the meter.

What does it show on lowest ohm scale with probes touching each other?

What does it show when you read a standard resistor in the range 10 to 30 ohm?
 
bobloblaws 7/22/2018 8:07 PM
Quote Originally Posted by J M Fahey View Post
If they are as described, Iīd rather mistrust the meter.

What does it show on lowest ohm scale with probes touching each other?

What does it show when you read a standard resistor in the range 10 to 30 ohm?
No, my meter is fine Jaun. For example I have another Twin here which I measured at the same time, just under 4 ohms as expected. On auto range and the lowest manual range it shows 0.1 ohm with probes touching. A 16 ohm carbon comp measures at 16.3 ohm.
 
Justin Thomas 7/22/2018 8:07 PM
And check your meter battery...

That said: Ampeg used 32R speakers in the SVT and a few others, and still does on occasion. There is at least ONE Fender thst came with 32R speakers; they didn't really care as long as tje total was right. I think ypur speakers were replaced long ago. They may look original, but I doubt tharlt C10N was originalin that 67 Princeton Reverb I got in, either. Date code matched, though...

Someome may hve just "fixed it" toget through the gig & then forgot to fix it right later. Happens all the time.

Justin
 
bobloblaws 7/22/2018 8:17 PM
Quote Originally Posted by Justin Thomas View Post
And check your meter battery...

That said: Ampeg used 32R speakers in the SVT and a few others, and still does on occasion. There is at least ONE Fender thst came with 32R speakers; they didn't really care as long as tje total was right. I think ypur speakers were replaced long ago. They may look original, but I doubt tharlt C10N was originalin that 67 Princeton Reverb I got in, either. Date code matched, though...

Someome may hve just "fixed it" toget through the gig & then forgot to fix it right later. Happens all the time.

Justin
Interesting. Do you have any idea which Fender amp had the 32 ohm speakers?

Edit: I just did a quick search. Looks like they might have come out of a Rhodes.
 
Leo_Gnardo 7/22/2018 8:58 PM
Quote Originally Posted by bobloblaws View Post
I just did a quick search. Looks like they might have come out of a Rhodes.
Right! Rhodes "suitcase" amp has 4 x 32 ohm 12 inch speakers. Tough thing to find when you need 'em.

Fender Bassman Ten combo, a fearsome foursome of 32 ohm 10 inchers. What's good, these days Jensen offers 50 watt MOD speakers with 32 ohm voice coils. They claim these also work in an SVT cab.
 
Enzo 7/22/2018 9:13 PM
I have a 10" 32 ohm new in the box for an AMpeg 8x10. Always wondered what else it could be used for.
 
Justin Thomas 7/22/2018 10:34 PM
Leo,

Since an original SVT cab only handled 280W to begin with, your 50Watters should do better in an 8x10". That's why Ampeg really pushed buying both cabinets. Also remember, there were no "bass speakers" back then... Ah, the good old days before all the modern "bass" speakers...

Justin
 
Enzo 7/22/2018 10:50 PM
Well, there weren't real bass 10's, but surely those 18s and even many 15s weren't made for full range.
 
nevetslab 7/23/2018 11:13 AM
Back in the 'old days', one had to resort to JBL 154C's that were intended for LF horn-loaded enclosures, or 130A or 130B woofers. Then, the LE15A's came into being, and not long after, the D140F bass speaker. Altec had their similar woofers that mounted into the theater A2 front-loaded boxes, and the smaller 825 cabint...Voice of the Theater line. Seemed to take years before real 10" bass speakers appeared (from EV)
 
Justin Thomas 7/23/2018 12:33 PM
But what is "real?" In my opinion, what they call "bass" speakers now sound like crap. I much prefer a Showman or Bassman cab or vintage Ampeg. What mattered was how thrymade the cabinet; and it could sound just as good for guitar.

I don't have any experience w. EVs; but if they're efficient I'd probably like them. And don't need a horn to "help" with the treble...

Justin
 
J M Fahey 7/23/2018 7:01 PM
EVs are killer for Bass,very clear and defined sound,which cuts well in the mix.
Similab to 60īs Bass speakers,lots of punchy midrange.

From mid 80īs on Bass speakers were constantly "improved" which means "Thiele-Small parameters were improved so now the 40-80Hz octave is reproduced like never before .... everything else was sacrificed for that "ideal" and now you need 500W into 2 x 10" with half a pound cone each and half a foot long voice coils ... which can not keep up with an unamplified drummer
Not kidding.
Now I regularly see everywhere Bass players with one of those brick sized Class D amps, anywhere from 250W (TC Electronics) to 350/500W (Ampeg/Fender/Aguilar) to 700/1000W (G&K) who are NOT heard, you canīt make out what are they playing, not even what key are they in, just a muddy undefined rumble similar to thunder 10 miles away or the Subway passing underground.
 
Chuck H 7/23/2018 7:24 PM
I'm surprised so many bass players and bass amp manufacturers still lean so hard to the audiophool side of things when SO MANY old recordings sound so good. I really think bass tone peaked with the Ampeg stuff. That was as hi fi as it should have ever gotten. I came up playing in the 80's when bass amps and keyboard amps were synonymous. Many general purpose sound reinforcement type instrument amps are still made that tout things like "Great for bass and keyboards." Now, keyboards have moved into modern pop and rock in the form of synthesizers, so it makes some sense that such an instrument would need a good "sound reinforcement amp". But again, old recordings of Rhodes, Hammond and Leslie stuff sound SOOOO cool, why would people seeking those sounds take such a left turn with the speakers?

And as Juan already noted in his description of the construction, efficiency suffers greatly with specialized speakers. As a guitarist I know there are less efficient speakers that I generally like the tone of, but I can "feel" the lack of efficiency. For real. It's sort of like wearing a condom, for lack of a better explanation. Yes, it's still good. Just not close enough to the bone
 
Justin Thomas 7/23/2018 7:28 PM
^^^^^ THIS ^^^^^
And while I'm at it, they sound like butt-ass-CRAP, too. It seems that "bass amps" aren't even hifi anymore, and more akin to the typical boom-chucka-chucka in every blingster's car.

Juan, it's you & me against the world... But I won't quit playing my 50W Bassman through those crappy 2x15" CTSs....

Justin

Edit: "^^^^^THIS^^^^^" is "what Juan said."
 
Chuck H 7/23/2018 8:17 PM
Ah, screw it. This stuff will all be digitally synthesized so hip hoppers can sample the "tonz" they like. Rock is dead! And so is the tube amp and the "full range speaker". Get over yourself and maybe just spend some time weaving baskets old man. No one wants to "feel" their instrument anymore. The just want to make the sounds everyone else makes. Soon enough it will ALL be played through hi fidelity reproduction gear with the pre EQ set as needed within the sample. I hope your home has a porch. Otherwise you won't have a place to put your rocking chair so you can tell those kids "Git offa my lawn!"

 
The Dude 7/23/2018 8:35 PM
There's a lot of truth in that. I will say this, though. More than once I've seen one of those "modeler kids" plug into their first real tube amp. The smile on their face says it all. They have no idea what they've been missing until they try the real thing.
 
Justin Thomas 7/23/2018 10:01 PM
Not just the kids, either...

Justin
 
Chuck H 7/23/2018 10:24 PM
I remember the first time I played a tube amp. It was a blonde Bassman head. The guy playing through it had an awful guitar he was blanging away on, but I could still hear "something" I always thought was missing from my game. I was probably nineteen years old! Remember that I mentioned that I came up as a musician in the 80's So I played through that amp, and though it wasn't just what I wanted it WAS doing things I always though an amp should do. Like some of that natural compression on the attack and an overall balanced EQ that some how corrected itself relative to playing style. Sort of more expressive and forgiving at the same time. Inside of a month I had a beat to $h!t Marshall head that I traded all my other gear for + some $$$. It was better than anything else I'd ever had before and it actually wasn't very good! And that's when I started modding. Trying to get that turd to sound "right". My next amp was another Marshall, but a better one. I played it for years with very little modification. Then I got the "what if" itch about stacking the channels and I started playing with THAT circuit. And now it's it's been that way ever since.

But it all started sort of late in my gear exposure circumstances with a blonde Bassman head.
 
Justin Thomas 7/23/2018 11:27 PM
My firstamp? Gorilla. 2nd? Crate GX30M. Huge step up. Next, a Marshall ValveState 8200 w. JCM900 2x12. Another huge step up. Then, it died. Then I got my first TUBE amp: a Fender Prosonic.

Game Over. I've never looked back.
Chuck, tubes and rawk will live at least as long as I do. Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers.

Justin
 
Shawnobi 7/24/2018 5:13 AM
I'd suspect that someone (slightly misguided) put in higher impedance speakers to lower the volume on purpose in the hope they could crank it into a 'sweet spot' without it being so loud. I've seen that advice given out to twin owners before on the web.
 
Leo_Gnardo 7/24/2018 5:26 AM
Quote Originally Posted by Shawnobi View Post
I'd suspect that someone (slightly misguided) put in higher impedance speakers to lower the volume on purpose in the hope they could crank it into a 'sweet spot' without it being so loud. I've seen that advice given out to twin owners before on the web.
Good observation. Also, the owner/user of this twin might have wanted to drive a heap of external cabs. Heck all he'd have to do is wire 8 ohm speakers in series instead of deal with oddball 32 ohm speakers. Those wacky musicians - where do they get their ideas???
 
Justin Thomas 7/24/2018 6:30 AM
Quote Originally Posted by Shawnobi View Post
I'd suspect that someone (slightly misguided) put in higher impedance speakers to lower the volume on purpose in the hope they could crank it into a 'sweet spot' without it being so loud. I've seen that advice given out to twin owners before on the web.
Too bad so many people confuse speaker impedance, speaker sensitivity, and power handling...

Justin
 
Justin Thomas 7/24/2018 6:32 AM
Quote Originally Posted by Leo_Gnardo View Post
Good observation.... Those wacky musicians - where do they get their ideas???
...

Justin
 
J M Fahey 7/24/2018 11:53 AM
O=h, I always go for the simplest explanation, unless proven otherwise.

Rather than sophisticated "sweet spot tweaking" (which I donīt call impossible, just less likely) , I merely think somebody pulled a Rhodes cabinet out of a dumpster or similar "recycling operation" (or was about to junk one) , pulled the speakers and posted on EBay/CRaigslist "ORIGINAL, VINTAGE, Period Correct Fender 12" SPEAKERS !!!!!!" and Twin owner bought two, which he then hooked in parallel.
If asked (any/both of them) "do you know those are 32 ohm speakers?" I bet the answer would be "deer in the headlights" look, accompanied by "32 WHAT???"
[IMG]https://raspberriescards.com/wp-content/uploads/2014/07/Deer-Headlights-375x525.jpg[/IMG]
 
bobloblaws 7/24/2018 8:17 PM
Back to the problem at hand, the amp is only putting out 50 watts into 4 ohms. I've verified the power tubes are good, B+ is fine and bias has been set for about 40 mA of idle current per tube. Is it possible that if the amp was used for some length of time with that mismatch that the OT became degraded?
 
Enzo 7/24/2018 8:26 PM
No. The transformer is just wire wrapped around iron.
 
Chuck H 7/24/2018 8:40 PM
This^^^^^^^^^^^^^^^^^^^^^^^^

You would almost certainly hear other symptoms if the OT were compromised. That doesn't mean it isn't, it's just not the first thing to suspect IME. Please give a description of your test method.

And have you scoped the signal through the amp to be sure there is no preamp clipping prior to the onset of power tube clipping? This would definitely be something to look for since the amp has already been well dicked with.
 
bobloblaws 7/24/2018 8:49 PM
Quote Originally Posted by Chuck H View Post
This^^^^^^^^^^^^^^^^^^^^^^^^

You would almost certainly hear other symptoms if the OT were compromised. That doesn't mean it isn't, it's just not the first thing to suspect IME. Please give a description of your test method.

And have you scoped the signal through the amp to be sure there is no preamp clipping prior to the onset of power tube clipping? This would definitely be something to look for since the amp has already been well dicked with.
Good point. There is at least one existing pre-amp issue. Specifically, somebody who may or may not be the same somebody who swapped the speakers changed the 1 Meg channel volume pots for 100K. I'll measure the output power again after replacing those pots and checking for other possible problems in the pre-amp.

For the record, I'm connecting the speaker output to a 4 ohm dummy load and attaching my scope probe to the positive terminal on the speaker output jack. Then I take the peak voltage divided by 1.414, square the result and divide by the load impedance.
 
Chuck H 7/24/2018 8:52 PM
Quote Originally Posted by bobloblaws View Post
Good point. There is at least one existing pre-amp issue. Specifically, somebody who may or may not be the same somebody who swapped the speakers changed the 1 Meg channel volume pots for 100K. I'll measure the output power again after replacing those pots and checking for other possible problems in the pre-amp.

For the record, I'm connecting the speaker output to a 4 ohm dummy load and attaching my scope probe to the positive terminal on the speaker output jack. Then I take the peak voltage divided by 1.414, square the result and divide by the load impedance.
What is your input signal voltage/Hz? And what are the panel knob settings?
 
bobloblaws 7/24/2018 9:02 PM
Quote Originally Posted by Chuck H View Post
What is your input signal voltage/Hz? And what are the panel knob settings?
All tone controls at 5 and verb and trem knobs at 1.

130mV sine wave. In this case I used a higher input signal than I normally would since the preamp gain was lower than normal and at a lower input signal I couldn't even get the output to clip.
 
J M Fahey 7/25/2018 7:53 AM
1) use as much signal as needed to make amp clip, both peaks, then remeasure.

2) a scope is great to show things, but not as accurate measuring them, please drive amp to just visible clipping on both peaks, and remeasure VAC with a multimeter, if possible a true RMS one but even a cheap $10 one is acceptable.

Most probably it will not exactly match what scope says.

3)
I've verified the power tubes are good
"Good" as "hey!! ... they work! ... sort of" or "good" as "fresh just out of the box" ?... not the same thing.

Transistors work as good as new for ages or die a violent death; tubes lose emission every hour they are on, from just made to unusable, and degrading is linear ... meaning tubes with quite a few miles on the odometer may very well have lost 50% emission and still "work" .

Please try a fresh quad of tubes, even if momentarily borrowed from another amp.
 
bobloblaws 7/25/2018 8:45 AM
Quote Originally Posted by J M Fahey View Post
Please try a fresh quad of tubes, even if momentarily borrowed from another amp.
That is what I did, I grabbed four tubes from another Twin (which is putting out 80 watts). Same result.

I also tested the tubes in question with my trusty Eico tester.
 
g1 7/25/2018 2:15 PM
If you have access to that other Twin, I would compare the drive signal you have going to the power tube grids.
 
bobloblaws 7/25/2018 4:54 PM
Quote Originally Posted by g1 View Post
If you have access to that other Twin, I would compare the drive signal you have going to the power tube grids.
Yep, as soon as the 1 Meg channel volume pots are in.
 
J M Fahey 7/25/2018 8:47 PM
*Maybe/hopefully* thatīs all there is
 
Rhodesplyr 7/27/2018 12:11 PM
Quote Originally Posted by Leo_Gnardo View Post
Right! Rhodes "suitcase" amp has 4 x 32 ohm 12 inch speakers.
This was the first thing I thought, based on my screenname, when I read about 32Ω 12' speakers. They are, in fact, only used in the earlier 80W Peterson Rhodes Suitcase Pianos, not the later 100W models.

Edit: And they would have Fender labels on them.