Twincam

[quote name='HowieBass' timestamp='1463349036' post='3050724'] I'm wondering what valve you have in the preamp stage - I've read that there's a lot of variation across the different makes even when they're supposed to have the same gain factor (eg. 12AX7 or ECC83 valves) - maybe this could be the source of the slight overdriven sound you're hearing? Some useful info here http://www.worldtubecompany.com/mm5/merchant.mvc?Screen=TF-2 and also a guide to the gain factors of various valve types here http://www.thetubestore.com/Resources/Guitar-Amp-Info/Gain-Factor [/quote] I have a jj ecc83s but with the mullard valve in the pre it was about the same. I read it is easy to overload the front end with a modern bass. I do like the sound a lot so no worries just concerned I've missed something.

Caps replaced, heater wires sorted, bias redone and components replaced, new valves. Amp is much better, less noise than some modern ss heads I've had. However the slight overdriven sound is still there much less than before, but it's there from low volume and doesn't change till much higher volumes, so I'm not sure if there's an issue or if it's just the amps natural tone. It's not horrible just a nice little bit of drive going on. I have heard this amps are old school sounding and not clean amps. You can hear the amp in this months noodle comp

[quote name='Beer of the Bass' timestamp='1463328985' post='3050512'] I've now got it reassembled and fully working with the new filter caps and a fresh pair of JJ E34L valves. Here's a gut shot before the valves went in - it's tightly packed in there! After checking the voltages and setting the bias, I had a play with one of my DIY 1x12 cabs. It's a nice sounding little rig, though I haven't had a chance to turn it up yet. I'm pleased at how quiet it is in terms of hiss and hum - I've had modern micro heads with more hiss than this! I definitely need a more bass guitar voiced preamp though, as I like to boost the highs a bit to bring some articulation out of my flatwound strings. The treble controls on this work so high up that I can barely hear a difference when playing with a tweeterless cab. It looks good with these cabs too - I think it will be fun trying it with the pair of them next time I jam... [/quote] Cool looking rig. Be interesting when you do something about the pre. I know what you mean about the treble for articulation, I too use flats and often depending on the amp have to put a little more treble on.

Ok here is mine for the month. I was just testing out my old wem dominator bass and was listening to how it was reacting. I liked this little section so recorded it. The amp is miked with an iPad, and where I positioned it the second time it picked up the rooms sound colouring. Sounds like there is a bit of overdrive been put on, but it's just the amps natural sound it seems? Be interested to hear what people say about the amps sound. https://soundcloud.com/user-531446910/noodle-4

[quote name='Kex' timestamp='1463232774' post='3049784'] Have you told that to Mesa Boogie, Ampeg, Orange et al? Not that anyone buys that old crap now :-) [/quote] Does he not mean that the older stuff was heavier than the newer stuff even of the same technology. As valve and transistor amps these days are lighter and more powerful than days gone by.

[quote name='JapanAxe' timestamp='1463230157' post='3049750'] The rule-of-thumb with impedances on valve amps is you can go safely either way by a factor of 2. So if your Dominator's output socket is rated at 12ohm, you can run it into anything between 6ohm and 24ohm - in practice, you should be fine into 8ohm or 16ohm loads. There should be no problem driving your 250W Celestion - you won't hurt the amp or the speaker. [/quote] Yes that is kinda my understanding. Cool.

I'm now running my 15-17w dominator into a 8 ohm 250w celestion. It seems to work fine and sound a bit better than its original 16 ohm 50w celestion. The dominator is 12 ohm. I've read various other things about valve amps and impedance mismatching. But also is driving a higher wattage speaker with only a small amount of watts ok?

I think I'm just about coming around to the lightweight is better than heavier gear. It's so much more convenient in everyway. And I guess some people do have injuries. I think in the past lighter weight equaled crap. But certainly not anymore. So why not have your cake and eat it.

Hmm I doubt the swr will do a pub gig unless using a pa or are in a quiet band. The Harley Benton no experience but will surely cover more ground. And it's local you can test it out.

[quote name='luckydog' timestamp='1463141112' post='3048942'] Twincam, the caps which couple to the grids (not the cathodes !) can go electrically leaky and increase the bias significantly on just one valve...... Those caps are between the anodes of the preceeding stage and the grids of the output valves, and typically have a couple of hundred volts of dc across them. If they become leaky by only a tiny current, that's enough to increase bias and cause redplating, typically in only one valve. As you say, if that cathode circuit has a fault, it affects the bias of both valves, and they would both tend to redplate. In case of mismatched valves, or even if one is stone dead or missing, one will be biased hotter, but not hot enough in principle to redplate, though you did say it was slight.....?! If the redplate persists with new valves and is always in the same socket, suspect the grid coupling caps ! HTH! LD [/quote] I get you. I've tried swapping the tubes the red plating follows the valve so I don't think there's an issue there. But could be something else to look into. The list is growing! Update soldered in the new power amp bias resistor and cap. No relating at all and the sound is slightly better. There is still the distortion and crackling every now and then, output is still odd. Anyhow that's one more job down. Get the pre valves tomorrow I hope maybe the power tubes too if not Monday I will know if it needs more work.

[quote name='luckydog' timestamp='1463122925' post='3048717'] ^ +1 what Mikey says about replacing those small coupling caps on g1 of both output valves to fix redplate on one valve in that circuit. Shouldn't redplate, that's worth sorting and chances are the rest of the hum might go away too. Be sure to be use correct voltage rating of those replacement caps or err on the generous side - HTH ! LD [/quote] It's a shared cathode bias. So one valve must be duff as the other is fine.

Ok feeling better. Thanks for the comments. Guess was just feeling the self doubt creep in.

[quote name='mikeydee' timestamp='1463091773' post='3048616'] Yep UK mains hum is 50hz and will occur from pickup on previous amp valve heaters. This minimised through twisted pair wiring. 100hz noise is what is left on the power supply after rectification and smoothing. In a push pull or class ab amp which is most amps with multiple valves this imperfection is cancelled out by the push pull circuit. In a class a it is left there. The cathode bypass caps job is to filter it out and on the first preamp too. Replacing that cap is inexpensive and worth doing [/quote] Never thought about the pre amp bias. Well if the power amp bias and the tube replacement doesn't work then I guess there's another area to look at. It's starting to give me nightmares.

I just hope new tubes sorts it. After the new caps, cleaned the valve sockets, tidying the ac heater wires, checking the grounds, new power amp tubes (still to come) and new cathode bias resistor and cap (hopefully arriving tomorrow). My current knowledge will be exhausted. Should I of replaced the rectifier diodes? I actually paid top whack for the amp as it is in great condition.

More issues Now the sound isn't right at all a bit of distortion to a lot depending on string that been struck. Tried my girlfriends mustang bass athrough it and the sound was terrible. Tested the valves in either socket one looks like it's red plating slightly but also has a scratch or a crack in the glass. So looks like a pair of valves are needed.

Was unsure how to title the thread. I'm embarrassed at how nice my bass is compared to my lack of talent. So everyone who picks up my bass has been a great player and they say how great the bass is then proceed to play something far from my level. I get the bass back and don't have a reply. Now ive started to feel a bit self conscious even though I believe in a more simple bass playing style and even if I could play at a higher level I wouldn't play anywhere near as fancy as some do. I'm thinking my current ability makes me look a bit all the gear no idea or something to that effect. So much so I've thought about getting a cheap bass so I don't look a plum. My catch phrase is fast becoming "I work on them much better than I play them".

[quote name='PaulWarning' timestamp='1463048079' post='3048033'] I use a Fender Rumble 500 with a T E 1x15 ext cab in a Punk Band with a very loud drummer never run out of steam (I have without the ext cab), in fact I get asked to turn down sometimes [/quote] Was just about to mention the rumble 500 combo it's light and loud without the extension cab. I've not gigged one but plenty say it's loud enough on its own.

[quote name='mikeydee' timestamp='1463038001' post='3047930'] If it is the amp I am thinking of it is a class a output stage with two valves. I would expect that if one of the valves is red plating then so would the other as they are connected to the same cathode bias resistor. Reasons why this wouldn't be the case are the valves are not will matched or perhaps if the input coupling caps are leaking. Worth checking for dc on the grids? Lot of strain on the cathode resistor and cap. If that is dried up then the amp will hum. By the way hum and buzz are different sounds and mean different fault conditions. Sound clips can really help. [/quote] Yes I forgot that it shared the bias. Regarding humming and buzzing I don't like either term as one persons buzz is another's hum. But in this case it was definitely a 60hz buzz or is that a hum? I've ordered new components and a few different size resistors and will check the bias accordingly when they arrive.

[quote name='mcnach' timestamp='1462982422' post='3047564'] I used those before, they were my favourite ones, for flats. The Cobalts are a lot brighter, no doubt, and a bit more midrange I'd say too, but still balanced. I think I could probably tame the sound of the cobalts to sound just like the Fender ones, but not viceversa. They also feel a bit more bouncy to the touch. [/quote] Sounds like there the flats for me.

Success I've re did the heater wires. So much quieter now and almost there, actually I've known some modern ss amps that are worse! Still needs the bias sorted hopefully it will quieten it that little further. And then it's serviced and sorted. Learnt a lot more than I knew previously , feel like I've accomplished something

[quote name='3below' timestamp='1462994298' post='3047719'] My next port of call would be adding a centre tap / humdinger to the heater circuit (assuming it does not have one). Straightforward to implement. [url="http://www.valvewizard.co.uk/heater.html"]http://www.valvewizard.co.uk/heater.html[/url] [/quote] Unless I'm mistaken and I could be but it has one already. The heater wiring really needs looking at and tidying the more I look at it. I am sure it's the bias though since one valve is red plating slightly. And its recommend to change the resistor to a higher value one.

Changed the main filter caps in my wem dominator bass 25 as one was burst. Has had hardly any effect on the noise. Has tightened the sound up a bit but think I preferred the knackered caps haha. But the amp does sound great I think. Noticed a slight red plating on a valve so will replace the cathode bias resistor and the cap next. Back to the buzzing Im not sure where next to check I've had a look at the earth points and they seem fine. Maybe tidy the wiring although it's pretty much as it left the factory is a very clean amp never messed with (till now). Valves maybe (all original mullards), I messed about with the three pre amp valves swapping them about and checking the channels I noticed one of the pre valves sounded a bit different when swapped about. No difference to the buzz. So maybe the power valves? Going to check the jacks too. Any other suggestions? I would like to record with the amp and it would just be way to much noise for that at present.

How do these compare to fender flats, which are fairly bright Imo (for flats) and cover a lot of ground.

[quote name='Painy' timestamp='1462921532' post='3047058'] Isn't it the Stirling SUB that's infamous for its excessively hot output? Pretty sure the standard solution is to swap out the pre-amp for a replacement Stinger pre-amp. [/quote] Yeah I was going to mention that too.