6v6

[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.

American deluxe precision?

[quote name='LawrenceH' timestamp='1388337161' post='2320921'] Except I did all that and was. These simplexx designs will surely work as well as any other based around these drivers. However, I don't think these drivers are as good as it gets any more [/quote] If you're going to make a statement like that, it would be quite helpful if you qualified it by saying which drivers you do think are as good as it gets (Not being snarky, genuinely interested in good alternatives to the often-recommended Eminence Kappalite, such as the Beyma SM212 which I was recommended, and have used to excellent effect in my recent DIY cab build)

[quote name='0175westwood29' timestamp='1388228829' post='2319633'] not at all, actually at our last gig (and kinda where this idea came from) they mic'd the cab and took a di from my head my sound check took about 2 secs i think he said he kept things pretty flat. he was using a big ish mic tho not a 57 so could it have been a directional mic ? as my amp was between the 2nd guitarist and drums? [/quote] There are *lots* of big ish mics which would be better for a bass cab than a 57. If you've found that some engineers will mic the cab anyway, I'm not really sure why you'd want the effort and expense of doing it all yourself, save yourself hundreds and just buy the guy doing the sound a pint while asking him nicely to mic and DI, problem solved!

[quote name='gjones' timestamp='1388198551' post='2319468'] I sneaked a quick shot of an Alembic owned by Pete Agnew (Nazereth's bass player), that he'd left in the recording studio overnight. Not only was there flatwounds on it but he played it with a pick. I hope he was given it for free by his record company. Here he is with the very bass [url="http://www.drjazz.ch/album/bilder/PeteAgnew-6813.jpg"]http://www.drjazz.ch...eAgnew-6813.jpg[/url] Edit: by the way I do like Nazareth, it's just I think the sound he gets (a good rock tone like Phil Lynott's) with the Alembic, could be obtained just as well with a Fender or Squier P. [/quote] I don't get this at all, seriously, who cares who paid for it, if it has flats, or if he uses a pick?! If someone has a bass which inspires them for whatever reason, whatever it costs (sound/looks/feel/whatever) then fair play to them IMO, and your implication that those using flats (and a *pick*, *gasp*!) should only use a cheap bass is insulting, particularly when directed at an established pro who has more justification for using high end equipment than most of us around here. Back on topic, the main reason to put flats on a nice bass is that nice basses are easier to play, have better resonance and pickups leading to better tone, feel, and inspiration to play better (regardless of string type IMO).

[quote name='0175westwood29' timestamp='1388065838' post='2318222'] Looked at the palmers but there about 300 notes, [/quote] The one I linked is [url="http://www.thomann.de/gb/palmer_pdi09.htm"]£71 from Thomann[/url]

I don't really get why emulsion, seems like an inappropriate choice for wood finishing IMO, but will be interesting to see the results, and hear if the finish lasts or falls off

Have you considered using a DI like the [url="http://www.palmer-germany.com/mi/en/PDI-09-Passive-DI-Box-for-Guitars-PDI09.htm"]Palmer PDI-09[/url] which provides speaker simulation and connects between the amp output and speaker cab? That would probably provide something close to a mic'd up sound without the hassle and disadvantages of micing the cab up.

Gigged the cab again on Saturday in a busy medium sized venue, I had the LM3 running at well over half volume so pretty loud, and the cab stayed really punchy and tight, really impressive considering it's a single 12" cab. Re the treble extension, after some experimentation I've realized that I can reclaim most of the bite and treble I felt was missing by not using my Boss LMB-3. I found the compressor was needed on the Hartke (particularly with the internal speaker) to even out some of the clank and transients, but with this cab and the LM3, it seems to roll off the treble and transients too much, almost like the LM3 has some internal compression built in. So I may just run without any compressor for a while as that seems to work pretty well and probably negates any immediate need for a tweeter or mid driver.

[quote name='brensabre79' timestamp='1387360468' post='2310992'] After about 3 weeks, Peavey Customer support came back with a very short email to say I could change the valves without bias adjustment. I could also substitute KT66 if I wanted to without adjustment - I'm not sure if I'll get any more clean power from these though...? [/quote] This is bad advice IMO, KT66's draw significantly more heater current than 6L6s, and they are extremely unlikely to bias correctly (without some adjustment) in your amp. They will probably work, but unless you're very sure on the power transformer specs, I personally would not risk it - the KT66s will draw 2.4 *amps* more from your heater filament of your power transformer (0.9A vs 1.3A, 6 tubes). It might work for a while, but IME running heater supplies too hot eventually results in power transformer failure.

[quote name='Ghost_Bass' timestamp='1387418190' post='2311835'] Sure i can but Alembic doesen't support any specific valves for their f1x, they stick whatever they can source that meets their criteria. As to watford valves i'm sure they know a lot about valves but is the guy who's going to answer me a bass player? And does he have a f1x? I'm looking for opinins from, BCers who in fact own or owned one of these and tried diferent valves on them, I think this firs person experience it will be more helpfull than an e-mail full of (very usefull) tech talk. Cheers [/quote] IMHO you are over thinking this. You need one replacement 12AX7 tube, there are thousands out there new and NOS, any of which will work OK in your preamp, buy a few and see which ones you like. Also FWIW, I've got good real-world advice from Watford Valves in the past, not just "tech talk", and the F1-X contains probably the absolute most commonly used preamp circuit of all time (it's a completely standard Fender preamp stage), so I'd be amazed if they don't have experience of testing with it.

[quote name='brensabre79' timestamp='1387377475' post='2311267'] I found this Bias mod tutorial for the 5150 amp. the circuit looks alarmingly familiar! [url="http://www.gearo.com/Files/5150biasmod.pdf"]http://www.gearo.com...5150biasmod.pdf[/url] Now I understand what you're all talking about i can probably have a pop at this I would also need to get some bias testing equipment, aren't these simply adaptors that you put under one of the tubes to measure voltage/current? [/quote] Yep, that bias circuit looks basically the same. Note if you are going to do this yourself that the components and pot need to be properly secured to the board (not like the photo in the pdf with some sticky pads, it will break off and leave your tubes with no bias, which is like running your car at max revs in neutral for want of a better analogy, you will trash your tubes quickly) And yes, you can get some adaptors to measure the bias current, or a cheaper way is commonly to install some low tolerance (1%) 1ohm or 10ohm resistors inside the amp, from the power tube cathodes to ground. This is a little more involved than the bias mod so maybe adaptors with the resistors built in are the way to go. EDIT: Also read up on how to safely drain the power supply filter caps, they stay charged for hours in some amps and will give you a potentially lethal shock if you touch them.

[quote name='brensabre79' timestamp='1387272360' post='2309987'] Thanks! I was getting a bit lost with the explanation above as I have no bias adjustment... So it's fixed & non- adjustable. [/quote] Yeah, "fixed bias" just means you apply a fixed negative voltage to set the idle current/operating point of the tube, contrary to what was mentioned by a previous poster "fixed bias" means you often (almost always IME) need to make an adjustment when changing tubes, unless you always use the exact same tubes as the manufacturer-designed bias circuit values were chosen for, even then it's not certain to be exactly right. Cathode bias is, to an extent, self adjusting, but is only common in low power guitar amps, and even then you sometimes need to change the cathode resistor to avoid destroying tubes prematurely. [quote name='brensabre79' timestamp='1387272360' post='2309987'] Thanks! So I'll have to mod the amp to get the most out of the valves in it basically. One for an amp tech as it's way beyond me to start messing about inside a valve amp. I imagine that it's pre-set pretty cold to be very easy on the valves then? [/quote] Well not necessarily - at a minimum, you need an amp tech to measure the idle plate dissipation, and figure out if the bias needs adjusting. Without actually measuring it, you have no way of knowing if it's set cold, hot or just right. If you're lucky, all will be fine, otherwise the tech will either adjust the fixed resistors slightly, or install a potentiometer to enable easier biasing in future. To make it safe for DIY biasing, you'd need cathode resistors and test points installed, but this won't be necessary if you always get a tech to bias it, as there is another (less DIY friendly and much more dangerous) way of measuring the idle current via the output transformer. [quote name='brensabre79' timestamp='1387272360' post='2309987'] I posted in the amps section about this amp, I'm not sure how much more clean volume I will get from this by changing the valves and/or modding the bias circuit. Currently it's a little bit underpowered for my needs - I can just about get the volume i want, but its a bit too distorted at the loud end of the set. Which is a shame because I love the clean sound of this amp, I just need a little bit more headroom. [/quote] Unfortunately, there's only one (expensive) way for you to find out how much more headroom you will get

[quote name='3below' timestamp='1387227183' post='2309678'] Start looking for adjustable bias circuits - e.g. [url="http://hiwatt.org/DIY/bias.gif"]http://hiwatt.org/DIY/bias.gif[/url] Thank you MR Huss, or other amp circuits. It will soon be obvious how to design such a circuit. Next implement it (and the dropper resistors and test points) and make diy biasing easy. It is not that difficult. The pcb on the Peavey of that era should have nice big wide copper tracks and large components. These amps are great for repair / mods for those reasons alone. [/quote] It's even simpler than that IMO, looking at the bias supply in the schematic, there's already a potential divider where you could add in a potentiometer very easily (between R14 and R9, possibly tweaking their values a bit to provide a sensible range of adjustment on the pot), or just tweak the values without the pot if you expect the new tubes to last another 25 years This mod should be very easy for any competent tech IMO, you don't even need them to add cathode resistors and test-points unless you want to enable DIY biasing in the future.

[quote name='brensabre79' timestamp='1387283419' post='2310154'] Thanks! It's a non-adjustable bias, but as per my thread in the Repairs section, I might have to get this modded. It's reassuring that changing the power tubes (25 years old) will probably get me a bit more clean headroom. I changed all the pre-amp valves already, but point taken about swapping ecc83 for ecc81 - won't this just mean I have to turn the pre-amp gain up louder to get the same amount of gain though? I'm not really driving the gain stage much to start with, but with the post vol on full, I have to turn up the pre to get the level i need... [/quote] I would definitely get it modded so it can be biased correctly - some manufacturers (like Mesa) claim that their fixed bias amps which aren't adjustable never need adjusting, but IMHO this is wrong, all it does is restrict the tubes you can use and/or force you to run with the tubes not biased 100% correctly. Looking at the block diagram in [url="http://assets.peavey.com/literature/manuals/80300980.pdf"]the manual[/url] is interesting - it doesn't look like the "post vol" is really a master volume as such as there are several gain stages after it, it's kinda a weird arrangement. If it were mine, I'd get the power tubes replaced and properly biassed, then experiment with the fx loop and poweramp in jacks, to figure out if more headroom is available by tube swaps anywhere in the preamp and gain recovery stages (basically figure out which stages are overdriving by isolating them with the volume controls and jacks) If the power tubes really are 25 years old, I think you may be surprised how much more headroom changing them will give (assuming they are knackered)

[quote name='artisan' timestamp='1387286446' post='2310213'] the rhythm guy uses an AER which is damn loud for such a small amp. My brother used a Fender blues deluxe which also makes a right row,he plays a Gretsch too so it can be very cutting. [/quote] If they both switched to something like a Fender Princeton reverb (12-15 watts), or Blues Junior, or any of the numerous small (two 6v6 or EL84 power stage) amps out there, not only will they sound much better, the stage volume will be much more sensible. Probably even a 5w amp like a champ or Marshall class 5 would be sufficient in many venues. Those Fender Blues/HotRod Deluxes and Devilles are really loud, and for some reason they fitted a lot of them with the wrong taper on the master volume, making it very difficult to get any control between nothing and really-way-too-loud.

IMO the guitarists need to get smaller amps. I gigged (guitar) for many years, and it took me a while to realize that, in a pub, even a 15-20w valve amp is generally too much. Most guitarists think they need 50-100w amps, which is just totally wrong unless you're playing festivals and big venues (even then you can mic a small amp), naturally big tube amps only sound good when they're driven hard, which results in totally stupid stage volumes. What amps are they using?

[quote name='Phil Starr' timestamp='1387279960' post='2310092'] I'm pleased it has turned out this way for you, The bass sounds pretty much as I predicted so that is reassuring. The speaker has a pretty well controlled top end and most of the commercially available drivers have a characteristic peak in the 2-4 kHz range which gives them their character. The aluminium Hartke will be particularly characterful which is why the shape control works so well on it, basically it allows you to filter out bits of the peak. I have a hartke 3500 top on which I use the graphic to dial in the more typical bass cab sound when i want it. I'm currently using my Beymas in PA tops and can let you have details of the horns I use, which will give you more extended cleaner tops at the cost of doubling the expense of your cab. I'm also working on a 6" driver based cab to punch out a few more mids which I can share as soon as i get round to it. 10" drivers are too big to be good mid range drivers really. [/quote] Interesting, I'd definitely be interested in details, particularly of the 6" driver based cab - I'm kinda resisting the whole tweeter idea, because I don't like any hiss or bright string-click type sounds to get through - using a dedicated mid driver seems to be a good compromise to add mid presence without too much "hi fi" top end, which I really don't need. Since the existing cab is 8ohms, and fairly big, it would be ideal if I could build a smaller cab with more mids (but still *some* bass) which sits on top, and could potentially be used alone occasionally for low volume rehearsals, and/or a personal monitor when I'm DI'd through a PA with subs. I guess my 10" speaker comment was based on previous experience with guitar cabs - I keep forgetting that speakers designed for bass have much less mid and high content (where in guitar amps I've used 10" and 12" drivers which have a *lot* of mid and treble capability) Thanks again for your help in getting to this point, it's been a really enjoyable process, and overall I'm very happy with the result!

[quote name='brensabre79' timestamp='1387271866' post='2309978'] I suppose I'm trying to find out if old, worn out valves will lose a bit of power and/or distort a bit more compared to new ones, or is it the case that they either work or they don't...? [/quote] They definitely do lose power over time, when the power tubes are realy worn you can lose a *lot* of headroom and definition. If you replace them, make sure you take it to someone who can bias it correctly, as running tubes too hot will reduce lifespan and headroom. A decent tech will also be able to identify if there are other headroom-limiting issues, ie if it's actually the power section saturating as opposed to one of the preamp stages or phase splitter, which could be remedied by swapping for lower gain tubes, or tweaking the circuit/components.

[quote name='gusbass' timestamp='1385797364' post='2292231'] More!! [/quote] Ok then... Here's a picture of the completed cab, along with some impressions having used it for several gigs and rehearsals: Overall, I'm really happy with the way the cab has turned out - I may re-do the grille in the new year as I'm not completely happy with the appearance of the mesh/screws, but overall I'm fairly satisfied with the way the construction and finish has turned out, considering this was my first bass cab build. The sound I'm very happy with - so far I've gigged it with both my Hartke kickback (just the amp, bypassing the internal speaker), and more recently with a Mark Bass Little Mark 3. I'm also working on a DIY hybrid amp, but that won't be ready for a while due to work commitments. To describe the sound, it's deep, punchy and "woody", for want of a better term - you can really hear the natural character of the P-bass come through, whereas with the Hartke internal speaker, it's kinda lost a bit in boom and clank. The bass extension on the new cab is *way* more than the Hartke, despite them both being 12" drivers, I guess a factor of the better Beyma driver combined with a much bigger box. Also the bass is not at all boomy, it's tight, controlled and articulate - whereas the Hartke combo can very easily be provoked into boomy resonance at gig volumes, the new cab is much tighter and deeper sounding. The front ports are also useful as it's not super sensitive in terms of positioning near walls in small pubs. The treble extension is somewhat less than I expected - probably due to the very bright nature of the internal Hartke 12" speaker - by comparison the high end on the Beyma is somewhat muted, but it is there, and can be eq'd to a reasonable extent via the amp & bass tone controls, I just run everything (quite a lot) brighter with the Beyma than with the Hartke speaker. I'm undecided, but I may consider adding a tweeter or midrange driver with a crossover, despite the fact that I normally like a fairly dark sound - the top end performance is OK, but feel like I'm missing a little midrange punch, grind and presence, some gig audience comments seem to confirm this (although comments have been positive overall). Alternatively I may need to just get better at eq-ing the flat response of the cab, compared to the very coloured response of the Hartke combo! An alternative to the tweeter is to build another cab which sits on top - I was considering a smaller cab with a brighter 10" driver, similar to the Barefaced compact/midget stack, but I'm unsure how I'd go about ensuring correct phase response between the two, more investigation/research required!

Many Fender P's already have a switchcraft jack AFAIK, certainly my 2012 US standard has what appears to be one. They are good quality and should last, but provided what you currently have is not faulty it will make no difference whatsoever IMO.

Interesting project! Have you posted your code anywhere ([url="http://github.com"]github[/url]?) - I imagine there are a few of us around who are into programming and open source who may be able to contribute help to getting this working, or at least would be interested in taking a look at the code.

This is kinda what worries me about the whole class-D thing - the power amps are lighter, but they are way more complex, so there's way more to go wrong. Do any of the micro-heads have a reputation for extremely good reliability, or do you run similar risks of failure with all of them?

If it's only the bridge pickup, and you don't want to rout for a full sized humbucker (which is probably the "best" solution IMO as it opens up the options of what you can fit so much), the Seymour Duncan Lil-59 is a decent sounding single-coil sized humbucker. I had one fitted to my Strat for years, to cover heavier songs in our set. There are lots of other single-coil sized humbuckers out there which would also do the job in a reversible way. The other option to consider is wiring the tone controls so the bottom one works only on the bridge pickup - this is what I now do (with a set of Lindy Frailin vintage hots), and you roll off the bridge pickup tone, and boost the mids with an Ibanez tube-screamer overdrive pedal (or similar). This gets close enough to the humbucker tone for me, and retains the single-coil bridge sound when you need it. Yet another option is an active mid boost (Eric Clapton has been using this for years in his Strats), like [url="http://www.dc-developments.com/cornell_active_circuit_ST.htm"]this one from Cornell.[/url] If you go for fitting a full sized humbucker, check out the Wikinson pickups if you want something inexpensive but good, I don't think they do single-coil sized humbuckers tho.