Vintage valve heads and huge vintage cabs

[Thunderhead]

[quote name='Mr. Foxen' post='310031' date='Oct 19 2008, 08:42 PM']Contact cleaner and some screwdriver wok totally osrted the master volume, some service the guy's amp tech gave, think he just put new valves and new speaker wire in the cab (seems thin and crap, dunno if that needs embiggening), then charged an arm and a leg from the clueless kid. Didn't even take amp out of case as screws were still clogged with crud.[/quote]Maybe... someone did change the two blue filter caps at some time.

However, they should have changed all four! And the bias cap (the single blue one on the top board). The two resistors on the blue caps and the large red one going to the next cap look newer than the rest of the amp too. It's still possible this work is fairly old - what brand are the blue caps?

But if the guy didn't open it up, it means he probably didn't check the bias much less adjust it, so who knows whether the valves are running even remotely right... modern valves often run at quite a different current from the old-production ones it was designed for.

There's no real reason to go for super-heavy speaker cable (it doesn't make that much difference), but really thin crappy wire is not a good idea. Stripped-down mains cable is as good as anything, really. It's at least as important to check that all the connections are good (properly soldered, not push-connects) and the jacks are decent, since a poor speaker connection can fry expensive things like the output transformer if you're unlucky.

Edited October 19, 2008 by Thunderhead

[Mr. Foxen]

[quote name='Thunderhead' post='310077' date='Oct 19 2008, 09:54 PM']Maybe... someone did change the two blue filter caps at some time.

However, they should have changed all four! And the bias cap (the single blue one on the top board). The two resistors on the blue caps and the large red one going to the next cap look newer than the rest of the amp too. It's still possible this work is fairly old - what brand are the blue caps?

But if the guy didn't open it up, it means he probably didn't check the bias much less adjust it, so who knows whether the valves are running even remotely right... modern valves often run at quite a different current from the old-production ones it was designed for.

There's no real reason to go for super-heavy speaker cable (it doesn't make that much difference), but really thin crappy wire is not a good idea. Stripped-down mains cable is as good as anything, really. It's at least as important to check that all the connections are good (properly soldered, not push-connects) and the jacks are decent, since a poor speaker connection can fry expensive things like the output transformer if you're unlucky.[/quote]

How's bias adjusting work? Was curiously looking for something adjustable inside like trim pots or equivalent and saw nothing. What does it do if its wrong? Cook valves or be too quiet? Reckon if my head or guitar cab sells, will be a new fancy speaker and a trip to a reccomended amp tech, amybe a set of JJ Teslas (although totally clueless on valves).

Aso, how the hell do you mic these dudes up? Quiet inside even if you put your head in it

Edit how's this look for a driver? [url="https://www.carvinguitars.com/products/single.php?product=NE18-8"]Carvin neodium[/url]
Weigh saving probably ain't worth it with a single driver, cab is the weight.

Edited October 19, 2008 by Mr. Foxen

[Thunderhead]

[quote name='Mr. Foxen' post='310093' date='Oct 19 2008, 10:21 PM']How's bias adjusting work? Was curiously looking for something adjustable inside like trim pots or equivalent and saw nothing. What does it do if its wrong? Cook valves or be too quiet?[/quote]If there is no trimmer, you need to replace a fixed resistor. You can also replace it with an equivalent value of resistor+trimmer, if you want to make it easier in future. Usually there are two resistors in a bias circuit like this, one in series with the diode and one in parallel with the cap. Normally the one to change is the one in parallel with the cap - larger for more bias voltage (less valve current) and vice versa. If you find the resistor is something like 47Kohm, you can replace it with a 33kohm and a 22k trimmer for example - that will give you range both above and below the original value.

If the bias is too low, the valves will run too hot and this will shorten their lives, though not usually kill them immediately. If it's too high the valves will run too cold and you will get crossover distortion (which doesn't sound nice) and the amp won't sound very punchy. There is no absolutely 'right' value usually, as long as the valves are running between about 50% and 70% of their rated dissipation it will be fine - the higher the power of the amp, the more likely it will need to be low rather than high though (which applies to this one I think).

[quote]Reckon if my head or guitar cab sells, will be a new fancy speaker and a trip to a reccomended amp tech, amybe a set of JJ Teslas (although totally clueless on valves).[/quote]JJs are a good choice, they're among the most reliable modern valves. If you get them from a company that tests them well you're even less likely to have trouble - I've had the best results from Ruby Tubes I think.

[quote]Aso, how the hell do you mic these dudes up? Quiet inside even if you put your head in it[/quote]You don't. They were never intended for that! Although you should be able to get some usable signal if you put the mic in line with the port and a fair distance away, that isn't going to be ideal on stage. If that's what you need, you'll be better DI'ing it through something like a Hughes & Kettner Red Box speaker simulator. When you're using one of these, connect both the cab and the Red Box separately to the amp - don't go from the amp to the Red Box and then to the cab as the manual recommends; it's less reliable because it introduces another two connections into the speaker circuit. Connect the head to the cab as normal and then use another cable (it doesn't even have to be a speaker cable this way) from the second speaker jack to the Red Box.

[quote]Edit how's this look for a driver? [url="https://www.carvinguitars.com/products/single.php?product=NE18-8"]Carvin neodium[/url]
Weigh saving probably ain't worth it with a single driver, cab is the weight.[/quote]There's no sensitivity or other proper specs listed - it might be great... or not!

[joegarcia]

This thing is amazing and I'm so jealous. The pics don't do it justice, it's beautiful.
As far as biasing goes, if it's running too hot it will sound amazing but die quicker, if it's too cold the valves will last an age but sound weak.

Can't wait to hear this thing with a new speaker. The current driver sounds ok at low volumes but is very farty when slightly pushed. You can tell the amp sounds great though.

What do peeps reckon to this speaker:
[url="http://www.bluearan.co.uk/index.php?id=BAC18PS76&product=B!amp!C_18PS76_18!dquote!_600W_Low_Frequency_Driver_8Ohm&browsemode=manufacturer"]http://www.bluearan.co.uk/index.php?id=BAC...de=manufacturer[/url]

[alexclaber]

[quote name='joegarcia' post='310249' date='Oct 20 2008, 10:09 AM']What do peeps reckon to this speaker:
[url="http://www.bluearan.co.uk/index.php?id=BAC18PS76&product=B!amp!C_18PS76_18!dquote!_600W_Low_Frequency_Driver_8Ohm&browsemode=manufacturer"]http://www.bluearan.co.uk/index.php?id=BAC...de=manufacturer[/url][/quote]

Qts is rather low. I suspect you'd get much better results from a 3015LF and as the mounting holes are unlikely to be compatible you're going to have some woodwork to do with most 18"s so why not fit a better and cheaper 15"?

If I was replacing the woofer in a horn I'd model the cab in horn resp. to see what fits best.

Alex

[Mr. Foxen]

[quote name='alexclaber' post='310276' date='Oct 20 2008, 10:51 AM']Qts is rather low. I suspect you'd get much better results from a 3015LF and as the mounting holes are unlikely to be compatible you're going to have some woodwork to do with most 18"s so why not fit a better and cheaper 15"?

If I was replacing the woofer in a horn I'd model the cab in horn resp. to see what fits best.

Alex[/quote]

The volume already goes to 1 more than 11, I'm not gonna go round scrimping on having 3 more inches than everyone elses bass cabs.

What variables would you have to measure to model the cab? Its all folded horn shaped inside, so don't even know how you'd go about calculating volume.

Oh, and just been offered a folded horn 15 also, which is totally unecessary, but its tempting.

Edited October 20, 2008 by Mr. Foxen

[alexclaber]

[quote name='Mr. Foxen' post='310294' date='Oct 20 2008, 11:23 AM']What variables would you have to measure to model the cab? Its all folded horn shaped inside, so don't even know how you'd go about calculating volume.[/quote]

You need to calculate back enclosure volume, horn length, throat area, mouth area and flare rate. It's nothing like modelling a direct radiator cab where all you need is net volume and tuning frequency (if ported).

The reason I suggested the 3015LF is I know it's proven in other horn cabs and it has just as much Vd as the linked 18" and higher Fs and Qts which should equal louder and bigger bottom where it matters. So ignoring price it's still better. I haven't paid much attention to 18" woofers suitable for old horn cabs because they aren't terribly relevant to 99.99% of bass players - if you're going to use a horn you're better off with a smaller high excursion driver pushing a smaller throat and a longer path, hence the obsolence of the Acoustic 360 et al.

Alex

[Mr. Foxen]

[quote name='alexclaber' post='310318' date='Oct 20 2008, 11:53 AM']You need to calculate back enclosure volume, horn length, throat area, mouth area and flare rate. It's nothing like modelling a direct radiator cab where all you need is net volume and tuning frequency (if ported).

The reason I suggested the 3015LF is I know it's proven in other horn cabs and it has just as much Vd as the linked 18" and higher Fs and Qts which should equal louder and bigger bottom where it matters. So ignoring price it's still better. I haven't paid much attention to 18" woofers suitable for old horn cabs because they aren't terribly relevant to 99.99% of bass players - if you're going to use a horn you're better off with a smaller high excursion driver pushing a smaller throat and a longer path, hence the obsolence of the Acoustic 360 et al.

Alex[/quote]

So you are saying I should take my vintage cab, and then design and build and entirely new, different shaped cab, with a different sized driver?

This is more an excercise in making the most of what I have already, and making sure the alterations I do have to make (new driver, possibly valves) are the most suitable.

[alexclaber]

[quote name='Mr. Foxen' post='310332' date='Oct 20 2008, 12:12 PM']So you are saying I should take my vintage cab, and then design and build and entirely new, different shaped cab, with a different sized driver?[/quote]

No, I am saying you should stick a piece of ply over the existing hole with a new hole cut in it to fit a 3015LF and then leave it be. I am also saying you shouldn't put a modern 18" into the cab unless you have checked it will work well. Alternatively I would try to find out what the rough specs were on the original driver and then find something similar. Putting an expensive pro-audio driver into an esoteric old cab design is like putting a modern racing engine into an old VW bus - not a good match!

Are you sure it's the driver farting out first and not the amp running out of power?

Alex

[Mr. Foxen]

[quote name='alexclaber' post='310402' date='Oct 20 2008, 01:25 PM']No, I am saying you should stick a piece of ply over the existing hole with a new hole cut in it to fit a 3015LF and then leave it be. I am also saying you shouldn't put a modern 18" into the cab unless you have checked it will work well. Alternatively I would try to find out what the rough specs were on the original driver and then find something similar. Putting an expensive pro-audio driver into an esoteric old cab design is like putting a modern racing engine into an old VW bus - not a good match!

Are you sure it's the driver farting out first and not the amp running out of power?

Alex[/quote]

Consulted with rather more experienced ear of a sound engineer for that, he says its the speaker, amp seemed happy enough, will be trying it with my more modern cab once I lug it to the practice space. Putting a modern racing engine in a VW bus is totally my bag:

[Thunderhead]

I would take a small bet that the cabinet was not designed properly around the driver parameters anyway, but was more likely just copied loosely from something similar and fitted with a fairly cheap driver they could easily get - it's not exactly a pro-audio bass bin, it's a "bass guitar cabinet". Consequently there's no particular reason why a different modern driver will necessarily work any less well, regardless that it may not be perfectly matched to the cab either. I would simply fit the most sensitive 18" driver you can find with at least 300W power handling and a frequency range broadly suitable for bass guitar (ie up to at least 2KHz, rather than cut off below 1K) and see what it sounds like.

The goal is thunderous low-end roar, not accurate clean deep bass reproduction... am I right? .

Edited October 20, 2008 by Thunderhead

[Mr. Foxen]

[quote name='Thunderhead' post='310433' date='Oct 20 2008, 02:09 PM']I would take a small bet that the cabinet was not designed properly around the driver parameters anyway, but was more likely just copied loosely from something similar and fitted with a fairly cheap driver they could easily get - it's not exactly a pro-audio bass bin, it's a "bass guitar cabinet". Consequently there's no particular reason why a different modern driver will necessarily work any less well, regardless that it may not be perfectly matched to the cab either. I would simply fit the most sensitive 18" driver you can find with at least 300W power handling and a frequency range broadly suitable for bass guitar (ie up to at least 2KHz, rather than cut off below 1K) and see what it sounds like.

The goal is thunderous low-end roar, not accurate clean deep bass reproduction... am I right? .[/quote]

You are indeed right. The hot-rod volkswagen is an ideal example. More to look at and go 'woohoo, not only is it totally awesome but it works, makes loads of noise and smoke and stuff' except for the smoke part. Its a copy of an acoutic cab, did side by side photo comparison. As it is sounds more punchy and defined than I expected. Will likely be unning a paralell second rig involving smaller speakers for hearing myself and droning feedback close by.

[alexclaber]

Obviously the goal is not accurate deep bass reproduction, which is why a driver designed for a large extended bass shelf ported cab or a full-length bass horn is not a good idea.

My concern with simply fitting a high sensitivity 18" is that the lower Qts will badly choke off bass response. Combine that with the shortness of the horn and it could sound like it has no bottom whatsoever. A less tightly damped driver of lower sensitivity could actually have more sensitivity where you need it and thus be louder. And the plus of that is the latter type of driver is cheaper to make due to the smaller magnet.

Alex

[Mr. Foxen]

Right, now two experty sorts are having some discussion on the matter, this is ideal for me learning stuff. Can fairly safely suppose this cab is a clone of the Acoustic Corporation 361, so here are its dimensions:



Anyone have any advice on fitting side handles?

[Thunderhead]

I'm not at all an expert when it comes to cab design! Just going by my experience as an amp tech and the knowledge that this enclosure almost certainly wasn't designed correctly for any particular driver (or possibly even correctly for ANY driver), and so you probably shouldn't spend too much time trying to analyse it. Alex does make a good point about sensitivity of the speaker not necessarily translating into sensitivity of the cab if they don't work together well, but probably none of the drivers available today are intended for anything like this cab and it may be a case of pot luck anyhow...

[Bill Fitzmaurice]

[quote name='Thunderhead' post='310536' date='Oct 20 2008, 10:56 AM']so you probably shouldn't spend too much time trying to analyse it.[/quote]Or salvage it, except possibly for sentimental value. The number of things wrong with that horn design far exceed the number of things about it that are correct. Circa 1970 it was a fine cab, as the driver technology of that time was so primitive by today's standards that even a mediocre horn was far better than everything else then available. But modern driver technology and advances in both horn design and direct radiating cabinet design have relegated it to curiousity status.

[Thunderhead]

[quote name='Bill Fitzmaurice' post='310571' date='Oct 20 2008, 04:23 PM']Or salvage it, except possibly for sentimental value. The number of things wrong with that horn design far exceed the number of things about it that are correct. Circa 1970 it was a fine cab, as the driver technology of that time was so primitive by today's standards that even a mediocre horn was far better than everything else then available. But modern driver technology and advances in both horn design and direct radiating cabinet design have relegated it to curiousity status.[/quote]
So what? It also might sound great - obviously not in any purist or hi-fi sense, but then the same applies to the amp to a fair extent. There is no reason you have to approach everything from a theoretically 'correct' audio design point of view - a characterful, interesting sound can be much more useful musically. If it wasn't, there would be no point in fuzz pedals or anything else that sounds "awful" in an audio purist or electronics engineering sense. Transistors relegated valves to 'curiosity status' somewhere around 1970 too...

[umph]

[quote name='Thunderhead' post='310634' date='Oct 20 2008, 05:24 PM']So what? It also might sound great - obviously not in any purist or hi-fi sense, but then the same applies to the amp to a fair extent. There is no reason you have to approach everything from a theoretically 'correct' audio design point of view - a characterful, interesting sound can be much more useful musically. If it wasn't, there would be no point in fuzz pedals or anything else that sounds "awful" in an audio purist or electronics engineering sense. Transistors relegated valves to 'curiosity status' somewhere around 1970 too...[/quote]
you don't hear people talking about getting that sweet transistor tone from valves.

[Mr. Foxen]

[quote name='umph' post='310679' date='Oct 20 2008, 06:28 PM']you don't hear people talking about getting that sweet transistor tone from valves.[/quote]

That's basically cause solid state stuff is relatively clean, so you don't hear transistors, you just hear whats going in, louder.

Point about the 'wow thats cool' vs. 'bin it and buy a modern rig' is that I have it and I am going to do things with it and am looking to guidance as to the best way to go about it. I have bunches of time to think as I need to save some pennies.

Current challenge is how to get at the speaker. There is no hatch anywhere, reckon the whole middle bit comes out. Plan is detach the wire I can see, lay whole thing on its front, undo screws on the sides and lift the shell off. Sound like the way?

[stevie]

[quote name='Mr. Foxen' post='310683' date='Oct 20 2008, 06:35 PM']Current challenge is how to get at the speaker. There is no hatch anywhere, reckon the whole middle bit comes out. Plan is detach the wire I can see, lay whole thing on its front, undo screws on the sides and lift the shell off. Sound like the way?[/quote]

Looks like an old EV Eliminator copy to me. Have a look here:
[url="http://members.aol.com/xxbase80a/eliminator/box.html"]http://members.aol.com/xxbase80a/eliminator/box.html[/url]

Click on Zeichnung for the drawing. Klappe is the hatch. No guarantee, of course.

[alexclaber]

If the speaker is knackered and you definitely want an 18" then I'd get the cheapest possible 18" you can find. You don't need the Xmax or thermal power handling of a more expensive speaker, nor do you want the lower Qts of a speaker with larger magnet.

This one looks ok - higher Qts, low-ish Xmax, as full-range as 18"s get:

[url="http://www.bluearan.co.uk/index.php?id=BMASM118N&product=Beyma_SM118N&browsemode=category"]http://www.bluearan.co.uk/index.php?id=BMA...semode=category[/url]

Not cheap but that's 18"s for you.

Alternatively get the original speaker reconed if you can, that'll give you the true warts and all sound.

Alex

[Mr. Foxen]

[quote name='stevie' post='310695' date='Oct 20 2008, 07:05 PM']Looks like an old EV Eliminator copy to me. Have a look here:
[url="http://members.aol.com/xxbase80a/eliminator/box.html"]http://members.aol.com/xxbase80a/eliminator/box.html[/url]

Click on Zeichnung for the drawing. Klappe is the hatch. No guarantee, of course.[/quote]

Not quite same proportions, and there ain't no hatch there. I know the AC ones had a hatch in the back so you could at least see front of speaker. Housemate has paved living room with pedals so can't really enact plan right now.

[Thunderhead]

[quote name='umph' post='310679' date='Oct 20 2008, 06:28 PM']you don't hear people talking about getting that sweet transistor tone from valves.[/quote]Exactly, I was making the point that just because something is old-fashioned or lo-fi doesn't make it no good.

[quote name='alexclaber' post='310704' date='Oct 20 2008, 07:13 PM']If the speaker is knackered and you definitely want an 18" then I'd get the cheapest possible 18" you can find. You don't need the Xmax or thermal power handling of a more expensive speaker, nor do you want the lower Qts of a speaker with larger magnet.

This one looks ok - higher Qts, low-ish Xmax, as full-range as 18"s get:

[url="http://www.bluearan.co.uk/index.php?id=BMASM118N&product=Beyma_SM118N&browsemode=category"]http://www.bluearan.co.uk/index.php?id=BMA...semode=category[/url][/quote]I agree, that looks like a good one. 400W handling so a 150W amp shouldn't trouble it, and reasonable sensitivity at 97dB... not super high, but enough. The frequency range is the widest of the ones mentioned so far too.

[quote name='Mr. Foxen' post='310683' date='Oct 20 2008, 06:35 PM']Current challenge is how to get at the speaker. There is no hatch anywhere, reckon the whole middle bit comes out. Plan is detach the wire I can see, lay whole thing on its front, undo screws on the sides and lift the shell off. Sound like the way?[/quote]It must come apart somehow, at least I hope so! Some horrible old 'hi-fi' cabs are glued together once the speaker is fitted, but I can't see that being done with a cab like this. If there are screws in the sides but not the back, that must be the way.

You may be able to just undo the jack and drop it inside rather than detaching the wires, too.

[Mr. Foxen]

Eyin this: [url="http://cgi.ebay.co.uk/Eminence-Sigma-Pro-18-650W-18-Subwoofer-Driver_W0QQitemZ140271437016QQcmdZViewItem?hash=item140271437016&_trkparms=72%3A1301|39%3A1|66%3A2|65%3A12|240%3A1318&_trksid=p3286.c0.m14"]Eminence[/url]

Bit less high response and bit more sensitve, not much more expensive and in stock copared to Beyma. Plan is to be running two rigs, one with smaller speakers (in theory my 4x10 or my guitar 4x12, in practice other bands borrowed bass rig), so highs ain't such an issue.

Gonna go make a mess trying to take this apart now...

Edit: Bunch of unscrewing later and the center section is still riginly in there. given it a tug, doesn't seemlike paint adhesion.

Edited October 20, 2008 by Mr. Foxen

[Mr. Foxen]

Right, got it apart. Speaker is a Cetec Gauss 8142. Its very vaned.




Occurred to me that the speaker is effectively in a very small enclosure of its own, does that limit excusrsion due to air pressue difference? Making it less likely to break but limiting it? If I put a tougher modern speaker in would there be an advantage to porting it somehow?