6v6

[quote name='Musicman20' timestamp='1396444238' post='2413693']
Whatever I do next, and get time for, it will be with like minded similar aged people.
[/quote]

I feel quite sad that you had to bring age into it, I've always felt like music transcends all that

I play with (and as a result socialize with ) people who are a wide range of ages, and always have done, "like minded" is the only requirement IMO, combined with a bit of commitment and musical ability obviously.

Anyway, karlfer I hope you get it worked out.

[quote name='TimR' timestamp='1396425401' post='2413304']
Blimey. You don't own them mate. Show a bit of perspective.

Have they actually cancelled rehearsals for the gigging band yet? Do you actually need rehearsals if you are gigging regularly?

Many of us are in two or three bands and manage it quite well.

Why do you have to be bandless? If the gigging band is going well stick with it. If it starts to look like you're not gigging enough, join an additional band.

I assume that this 'university' band are playing originals and unlikely to be gigging regularly and will very probably be a flash in the pan.
[/quote]

Bit harsh but I tend to agree.

Sounds like the communication could have been handled better, but plenty of people (myself included) play in more than one band without issues.

I don't really get the "loyal to just one band" thing at all, provided you have the time to play with different bands and be sufficiently committed, mix it up and play with them IMO, it's all good experience.

I agree you should take your time and see how things work out rather than just quitting.

[quote name='Happy Jack' timestamp='1394707096' post='2394174']
[color=#282828][font=helvetica, arial, sans-serif]How about something that doesn't need two roadies and a fork-lift truck to move?[/font][/color]
[/quote]

Half the problem with valve amps is everyone (as evidenced by many of the responses here) thinks you need a 200-400w amp to play typical venues, but provided you have the option of PA support for bigger venues you just don't IMO, 100w would probably be fine (I have a 50w Traynor BassMaster that would probably be ample for pub gigs through an efficient cab).

The weight of tube amps is directly related to the power output due to the huge transformers required for big power output, so if weight is a concern you're much better having a cranked 15kg 100W amp than a 35kg 400w amp running on "2".

Cranked tube amps sound better anyway, getting the power stage cooking a bit is the whole point! [size=4] [/size]

[quote name='LawrenceH' timestamp='1394577637' post='2393038']
I've found lightweight poplar fine with both butt and dado joints, glued and screwed, but it was essentially void free. Stuff with large voids in is problematic for finishing and I wouldn't trust it to behave structurally/sonically, I used some horrible far-eastern stuff for a prototype and it was a pain.
[/quote]

Interesting, thanks - the stuff I'm thinking of is the cheap far-eastern stuff which I've used (for non cab-building purposes) in the past. Maybe I'll try some poplar ply next time if I can find some.

[quote name='Bill Fitzmaurice' timestamp='1394571051' post='2392944']
The depth per se doesn't make much of a difference, but the volume of the enclosure determines how the speaker will perform. Too small and the low end will be choked off while the midbass will be boomy.
[/quote]

Interesting! I was under the (evidently misguided?) impression that for bass cabs you had to avoid them being too shallow, so as to avoid reflections from the back of the cab interfering with the response of the driver?

I have an open back 4x10 guitar cab which is only about 9inches deep, could I seal the back of it and put a new baffle in it with, say, a 15" driver? Until now I had assumed this wouldn't work.

Edit: Yes I know I'd need to model the cab wrt volume and the driver specs..

[quote name='richrips' timestamp='1394536973' post='2392310']
Ha Cheers guys, Indeed this thread is rather fruitful to say the least!

6v6, what cab did you build with what outer dimensions? The 12mm I used on the jacks seems very stiff indeed, but I can see benefits to thicker ply if the panels are bigger.

[/quote]

The spreadsheet in post #15 of [url="http://basschat.co.uk/topic/200152-1x12-diy-cab-build/"]my build thread[/url] provides dimensions (I'd have to check if they were the final iteration but they look about right). It's a pretty standard 1x12 cab, probably on the large size of average for a 1x12.

If you used a different jointing method and some bracing I expect 12mm birch would be OK, but I wanted to keep the construction (particularly all the joints) as simple as possible so used 15mm as a compromise, 18mm seemed excessive for this type of box and I didn't want it too heavy.

[size=4][quote name='richrips' timestamp='1394536973' post='2392310'][/size]
I have a background making surfboards and latest tech on those is to have very low density foam cores, a higher density foam outer, then glass/epoxy skin with carbon where you really want stiffness. This is what's driving my idea of having ply with tough/stiff outer layers and low density inner layers. If thicker ply (say 15mm) with a very light core and tough hardwood outer exists, I'd be interested to see how its weight compares to say 12mm birch.
[/quote]

I'm not an expert, but IMHO you'd want to think carefully about what jointing method you use if you choose a ply with a very low-density core. If you use one of the simpler methods (glue/screw butt joints or biscuits) the joint will surely be much weaker, since the screw/biscuit will be going into really soft wood? Some of the cheap far-eastern ply I've used would probably fall to bits very quickly if you used the method I used on my cab with the void-free birch.

I guess you can reinforce the whole thing with battens on the corners to get around that but I chose to avoid that as it's all extra weight and uses up internal volume.

You've got some great responses here!

FWIW I deliberated over the wood choice for a while and in the end I went with 15mm birch, which is relatively heavy but very strong and stiff.

Seems a reasonable compromise as it meant I needed very little internal bracing, and I did without battens on the corners (biscuit joints + screws, which I recommend as an extremely easy way to make strong joints if, like me, you're not a super-skilled woodworker).

I can probably weigh the cab later if you like, but it's an easy lift despite the relatively heavy ply and the relatively heavy ceramic driver. I've gigged it quite a lot now, and it's solid with no issues at all due to resonance etc.

My advice is just get stuck in - find a way to get winISD working (old laptop kicking around running windows or a windows emulator?) or use an existing design, forget about the tweeter unless you're sure you need it - IMO just keep things simple, and get the box working right, you can always add a tweeter later (I decided I didn't need to).

Personally if you have the 3012HO's already, I don't see the point in investing £££s in more drivers immediately, might as well build one box with what you have and see how it sounds. You can always refit it to the Jack and sell it later if you want something different

I assume you've seen the [url="http://www.eminence.com/pdf/Kappalite_3012HO_cab.pdf"]designs provided by eminence[/url]?

If possible I'd have another crack at getting WinISD working - I ran it under a windows emulator on Linux, so I guess you may be able to do the same on a mac.

[quote name='BettySwallocks' timestamp='1392588560' post='2370480']
Hi Guys,
I am interested in buying a Fender American Standard P Bass near me.
It has a serial number beginning with US12.
Does this mean it will have the custom shop 60's pups installed as long as they have not been swapped out?
Thanks
[/quote]

Should do, I have a (bought new) P-bass with a US12 serial number and it definitely has the CS60's pickups. If you haven't already, you might want to try them first, as they are a little darker than some other P pickups IME.

Nice job!

[quote name='Lozz196' timestamp='1391364185' post='2356252']
There is only one answer to this question, US Fender Precision.
[/quote]

+1

[quote name='blablas' timestamp='1391343557' post='2355937']
making a bass guitar is not really rocket science, basically it's just gluing together some chunks of wood and after that give those chunks the shape you want it to have.
[/quote]

Loving your modesty! If only the reality were the same as that theory - as your build diaries show, there are so many stages to the process, and every one must be completed with absolute accuracy and attention to detail for the desired end result.

I tried once many years ago and the finished guitar was barely playable, so huge respect to you, very impressive skills!

This is great, thanks for sharing!

/me can feel another cab build coming on...

Presence doesn't cut lows, and the control itself is not a high pass filter (I think JapanAxe was referring to how the control works, but that is probably just confusing unless you understand how negative feedback works)

You can think of it as a treble control for the power stage of an amp, whereas the treble control itself works only on the preamp.

The frequency response of the controls are similar in many amps, but the way they interact with the amp and speakers is different, particularly in a tube amp at high volume.

For tube amps the presence control is interesting, because it means you can make the power amp have more gain at high frequencies, which means you can dial in more power-amp distortion for highs by turning the control up (this can be interpreted as "bite" or "chime" depending on the amp and other settings), and this response interacts with any nonlinearity in the power amp and speakers in a different way to the treble control (which mostly just adds highs without affecting the response of the power amp, or the "feel" of the amp for want of a better description).

Edit: paragraph

[quote name='Phil Starr' timestamp='1389628783' post='2336280']
We're talking about a number of drivers for all the designs, There's the Fane 8-225 and Precision Devices do a lovely 8 with great extension at the sacrifice of sensitivity. the trick is going to be to home in on th best drivers in their class
[/quote]

I had a look at the [url="http://profesional.beyma.com/pdf/8P300FeE.pdf"]Beyma 8P300[/url], do you have any thoughts on that for a compact bass cab?

[quote name='Thunderpaws' timestamp='1389637164' post='2336408']
I have yet to see a cab with a rotating driver so you can angle it up a bit for home practice/rehearsal then fire it forward again for stage time...sheesht I should apply for a patent on that!
[/quote]

Haven't you just invented a much more complicated way of doing what's already possible with a "kickback" style amp?

Great idea guys, looking forward to seeing (and building!) the results!

+1 on the 1x12 idea as a starting point - I'd like another 1x12 to stack on my existing DIY 1x12 cab so could build your design if the sensitivity and dimensions are compatible with the one I have (loaded with the Beyma SM212 which Phil Starr recommended)

Other ideas are
- Very small cab for home practice, tiny practice rooms or very small venues (really compact 1x10?)
- Something which sounds like an Ampeg 8x10 but much smaller. I've been considering trying a sealed vertical 3x10 build in an attempt to achieve this.

Bear in mind some 250w combos have an 8ohm speaker, so e.g that Mark Bass is only putting out 150w until you add an extension cab.

With PA support it's still probably enough, but something to consider if you ever want to compete with acoustic drums without lots of PA support (e.g subs and on-stage monitoring)

I don't own one (or any barefaced cab before anyone starts with the fanboi stuff...), but the barefaced 69'er may be worth looking in to.

[quote name='brensabre79' timestamp='1388768488' post='2325884']
OK thanks 6v6, I'll check it out tomorrow. It's a bit of a pain to get into as the sockets are on the PCB (I know, not the best) so you have to lift the whole PCB out to get underneath.

Is it OK to switch on the amp with no tubes in then? (Rubber gloves on )
[/quote]

Personally I'd try to avoid powering it up with the PCB lifted, it's very easy to accidentally move something and either hurt yourself or the amp You could do all the continuity tests by sticking the meter probes into the power tube sockets with the tubes unplugged.

The other alternative is measuring components on top of the PCB - e.g all those screen grid resistors are probably sat on top of the PCB where you can probe the leads?

It is generally OK to power up the amp with no tubes, but I'd suggest doing the powered off continuity/ohms tests first as you can derive almost as much info from those measurements and it's much safer.

[quote name='brensabre79' timestamp='1388762702' post='2325761']
Wow, thanks 6v6. I'd better check it out then, as I only got a bias reading on 1 out of 3 tubes!
Would the amp even work if only one or two of the tubes were actually giving any output then?
Maybe this explains why it seemed so underpowered...?
[/quote]

If two of the six are working (one on each side of the output transformer primaries) then the amp would work, but not very well. And yes, if for some reason one or more tubes is not working, the amp would be very underpowered. Not necessarily the case here, but worth checking out

It wouldn't normally be necessary to test the bias on every tube, but if you suspect a fault, it's probably an easy way to gain confidence each tube is working, as it proves the plate, grid and cathode connections are all OK.

I'd also measure the screen-grid current via each of those 100ohm resistors (but don't do this unless you're confident measuring with the amp on and disassembled), as if any of those are burnt out (or otherwise failed open-circuit, e.g dry solder joint) the tube it's connected to won't work but the amp will still make sound, albeit at reduced power.

I agree, with good quality, properly assembled cables this won't make any difference and will make a big mess when you have to do repairs in future.

[quote name='essexbasscat' timestamp='1388749375' post='2325496']
Excellent 6v6 and thank you. Is there any difference in sound quality between the three ? are PEC worth the extra in your opinion ?
[/quote]

I've never tried the PEC's, because I don't believe they are worth the extra - I've used Alpha's exclusively for several years in multiple amp builds, after starting out using CTS.

IMO there will be no difference in sound quality in a passive bass guitar circuit.

[quote name='KiOgon' timestamp='1388753463' post='2325568']
I normally use & recommend CTS pots, they have metal shafts not plastic, the plastic shafts were used in some guitars years ago but mostly in amps. They are also the best 'feel' the best reliability & subjectively - the best for 'tone'.
[/quote]

Interesting - I have a bag of them with plastic shafts (bought about 10 years ago admittedly), some had an inconsistent and light feel to them, so I moved to using Alpha, sound the same and to me they feel better/more consistent. Maybe time to try CTS again next time I order tho.

CTS, Alpha, or if you want to spend a lot of money, PEC.

IME Alpha have a slightly smoother feel than CTS, and a metal as opposed to plastic shaft.

[quote name='brensabre79' timestamp='1388674318' post='2324640']
Well I did it! Adding the Bias mod was actually easier than making the bias probe actually. I wasn't expecting it to arrive in kit form.
I first checked the bias with the old valves in before I did the mod. It was running at about 20mA - which according to the Weber Bias calculator was yielding about 8 watts per valve. So I was getting just under 50 watts out of my 160W amp!
[/quote]

Great news, well done!

Note, idle plate dissipation is not the same as power output - so if each tube is dissipating 8 watts, this just means they are running very cool (which would definitely affect the tone and amount of available headroom due to crossover distortion and premature saturation of one half of the waveform), not that you are only "getting" 8w per tube.

You probably were still getting more than 50w output, but as you discovered, the waveform would distort early (the only way to prove the output power is to run it into a dummy load with a sine-wave going in, then measure the output voltage with an oscilloscope)

[quote name='brensabre79' timestamp='1388674318' post='2324640']
I installed the new JJ 6L6s (matched sextet) which were getting about 18mA. once I'd done the bias mod I checked the plate voltage, worked out that 44mA would get me the 70% max recommended power and adjusted the bias up to 40mA to be safe. this got me about 18 - 20 watts from each valve. So 100 - 120w total, more than double what it was running at!
Sounds good too
[/quote]

Great, sounds like you've got it bang on - I bet you'll be amazed how much better it sounds cranked now it's biassed properly with new tubes


[quote name='brensabre79' timestamp='1388674318' post='2324640']
The only odd thing was that I could not get a bias reading off all the valves (old or new), but as they all lit up and its making a noise I figured this may be an issue with the probe rather than the amp. As it's a matched set the global bias adjustment should suffice, and I've left 10% margin.

Thanks everyone for your help with this, I wouldn't have even attempted it without your wise words! Now to gig it
(I'll be taking a backup amp just in case)
[/quote]

The not getting a bias reading sounds suspect. If the bias probe worked on one tube, it should work on all of them, so this IMO could point to some remaining issue inside the amp.

"they all lit up and its making a noise" just means all the tubes have filament current (not necessarily that they are all working and making a noise)

It could be that the tubes you got no reading from have a fault which needs rectifying, if so you are still not getting full output from the amp and some of your shiny new valves are just expensive lightbulbs

I'd check the following:
- Unplug the amp and drain the filter caps
- (Edit) Unplug all the power tubes to ensure they don't interfere with the readings, we're measuring the amp wiring not the tubes
- Locate pin3 on each of the power tube bases (it should be in the same place on all of them)
- Use the continuity/ohms (buzzer) setting on your meter and prove the plate connection (pin3) of each bank of three valves is connected and there's no broken wires (ie between v5, v6, v7, then again between v8, v9 and v10)
- Test the continuity (buzzer again) between the cathode (pin 8) of each bank of three as above
- Use the ohms (low range, say 200ohms-1k) setting to check the resistance between pin4 of each pair of tubes (e.g between v5 and v6, then again between v6 and v7, then repeat for the other half of the poweramp). This should be around 200ohms (because there are two 100ohm screen grid resistors inbetween). If any are open circuit, you could have a burnt out screen grid resistor (can happen when a tube goes bad)

If none of the above show up any problems, I'd inspect all of the tube sockets carefully for damage, and if all is OK fire up the amp and carefully take some measurements on the highest volts range of your meter (primarily check the plate and screen grid voltages all look roughly the same). Be very careful if you do this and make very sure you meter is on volts not current (don't ask me how I know this ) if you've also been measuring bias.