How to change the tubes of a AC4TVH
- Thread starter naviros
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Biasing does not depend if it's Class A (single ended) or class AB (push-pull).
It's whether the amp is cathode biased or fixed bias.
You can make Class A amps fixed bias, or Class AB amps cathode biased, and vise versa.
Oh and the AC4, is cathode biased. You can't just rebias it even though you want to. You'd need to mod it to fixed bias.
It's whether the amp is cathode biased or fixed bias.
You can make Class A amps fixed bias, or Class AB amps cathode biased, and vise versa.
Oh and the AC4, is cathode biased. You can't just rebias it even though you want to. You'd need to mod it to fixed bias.
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dodgethis
New member
Okay okay okay.
If fixed bias amps impliy that their bias can be changed with the use of a potentiometer, what about amps that cannot have their bias changed?
You guys are being confused. Fixed bias amps are amps that have the value of the bias is preset by a non-variable resistor. You can change the bias of amp, yes, but you have to replace that resistor with one of a different value. You cannot change the value of the bias on the fly. Variable bias amps give you this option in the form of a potentiometer. Sorta contradictory to call amps that can change bias fixed bias amps, don't you think?
And yes, there are amps which cannot have thier bias changed. Mesa Boogie is a a very good example of them. Yes, the Mark and Rectifiers have two different bias settings for EL84 and 6L6 tubes but these bias values are set values and cannot be changed. A common mod was to replace the fixed resistor with a pot of sufficient value to make life easier for users.
Let me summarise.
Fixed bias amp = Amp that have preset values of bias due to a non-variable resistor in the circuit.
Variable bias amp = Amp that can have the bias changed with the use of a potentiometer, or variable value resistor.
If fixed bias amps impliy that their bias can be changed with the use of a potentiometer, what about amps that cannot have their bias changed?
You guys are being confused. Fixed bias amps are amps that have the value of the bias is preset by a non-variable resistor. You can change the bias of amp, yes, but you have to replace that resistor with one of a different value. You cannot change the value of the bias on the fly. Variable bias amps give you this option in the form of a potentiometer. Sorta contradictory to call amps that can change bias fixed bias amps, don't you think?
And yes, there are amps which cannot have thier bias changed. Mesa Boogie is a a very good example of them. Yes, the Mark and Rectifiers have two different bias settings for EL84 and 6L6 tubes but these bias values are set values and cannot be changed. A common mod was to replace the fixed resistor with a pot of sufficient value to make life easier for users.
Let me summarise.
Fixed bias amp = Amp that have preset values of bias due to a non-variable resistor in the circuit.
Variable bias amp = Amp that can have the bias changed with the use of a potentiometer, or variable value resistor.
You are confused.
Fixed bias - preset using a variable resistor so biasing can be easier. For what you mentioned regarding a fixed resistor, it's fair to say those amps are fixed bias, but are not intended to be user serviceable. Look at it this way, a potentiometer is a resistor, replacing a fixed value resistor to a potentiometer is just giving the circuit variability. It is still a fixed bias amp however you want to see it.
Cathode bias - no need to bias amp
Have a read, here's a link.
http://acruhl.freeshell.org/mga/main/bias.html
I have both fixed bias amps and cathode biased amps, fixed bias amps that I have use a potentiometer to adjust the bias so the tubes are optimised, these amps also require matched pairs.
Cathode biased amps that I have do not need to be biased, but matched pairs of tubes have to be put in.
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theunknown
New member
Now I'M confused.
Now to confuse you even more.
1. All tube amp can be biased - either easily biased or difficult.
2. Messing with the bias messes the tone as well.
3. A class AB amp can be biased to Class A Spec.
4. By messing with Pinouts and bias...your amp can use different tube.
5. Don't f with the amp if you know nothing abt biasing, you get tasered..
6. Biasing is not just abt adjusting the current, you need to calculate the correct bias. Going by technical spec will usually result in a error of some percentage.
7. You fry certain components when you bias and short circuit some contact point.
8. You send your amp to some half past 6 hack job. You polly fare better doing it yourself.
9. Tube amp biasing is an art form....some amp are biased by looking at Waveform on a scope and not thru any transformer stunt method or Cathode measurement or whatever.
10. In doubt don't do it.
11. You wanna do it..be careful, have someone around you, ICE to call for an ambulance.
1. All tube amp can be biased - either easily biased or difficult.
2. Messing with the bias messes the tone as well.
3. A class AB amp can be biased to Class A Spec.
4. By messing with Pinouts and bias...your amp can use different tube.
5. Don't f with the amp if you know nothing abt biasing, you get tasered..
6. Biasing is not just abt adjusting the current, you need to calculate the correct bias. Going by technical spec will usually result in a error of some percentage.
7. You fry certain components when you bias and short circuit some contact point.
8. You send your amp to some half past 6 hack job. You polly fare better doing it yourself.
9. Tube amp biasing is an art form....some amp are biased by looking at Waveform on a scope and not thru any transformer stunt method or Cathode measurement or whatever.
10. In doubt don't do it.
11. You wanna do it..be careful, have someone around you, ICE to call for an ambulance.
You did not see my point..
1. Dangerous to do this...
I'm a technician..I have a thing for information like this posted on the net. I and many others I believe are willing to teach in a proper environment. Many times, I have seen repair job came in that are totally messed up; usually, due to the owner following instruction off the internet without understanding the procedures or have the proper equipements.
A simply job like removing a resistor for biasing purposes can end up with a broken track and pad...and this, easily avoid if using an electronic vaclovelovelove pump system....
Soldering on components with a large plane require a soldering iron that is able to keep temperature in range. Cheap $15 are not able to do that..
1. Dangerous to do this...
I'm a technician..I have a thing for information like this posted on the net. I and many others I believe are willing to teach in a proper environment. Many times, I have seen repair job came in that are totally messed up; usually, due to the owner following instruction off the internet without understanding the procedures or have the proper equipements.
A simply job like removing a resistor for biasing purposes can end up with a broken track and pad...and this, easily avoid if using an electronic vaclovelovelove pump system....
Soldering on components with a large plane require a soldering iron that is able to keep temperature in range. Cheap $15 are not able to do that..
naviros
New member
Wow, its been a long time since I've been back around this forum. Surprised to see this thread revived... Haha...
In terms of dynamics, hmmm... I would say I'm still working out how my Wampler Pinnacle works with tiny bugger (main reason I'm still on the same brand). The thing is that at different volumes, different positions of the tone switch really really REALLY makes the difference. Then there is also another 4 knobs on my Pinnacle. Its just mindboggling!!!
I sort of figured out how the thing reacts with an overdrive (adds on a very good depth and a full sound to the twanginess), but with a distortion, it just widens up the horizon. I only have the Wampler plugged in right now, I don't even want to think about stacking the two together yet... It'll be too mind-boggling for me... too many knobs... too many possibilities...
Hmmm... Well if you ask me, the two are a good match. Haven't been trying many tubes thus far, so I cannot really comment on those other brands. Maybe when the one I'm using blows, then I'll go out for another pair / combination. I've heard good things about the Mullards.
In terms of dynamics, hmmm... I would say I'm still working out how my Wampler Pinnacle works with tiny bugger (main reason I'm still on the same brand). The thing is that at different volumes, different positions of the tone switch really really REALLY makes the difference. Then there is also another 4 knobs on my Pinnacle. Its just mindboggling!!!
I sort of figured out how the thing reacts with an overdrive (adds on a very good depth and a full sound to the twanginess), but with a distortion, it just widens up the horizon. I only have the Wampler plugged in right now, I don't even want to think about stacking the two together yet... It'll be too mind-boggling for me... too many knobs... too many possibilities...
MrBukka
New member
Ok peeps i have just joined the AC4TV club, i am really digging this amp. Swapped out the stock tubes for a broken in JJ el84 i had lying around and tungsol 12ax7......god damn tonal bliss (great chimy cleans with alot of fullness, dynamics and clarity, crank it and it sounds fat and buttery)! Of course there is a slight boxiness to the sound but not in a bad way, i felt that it gave the amp some natural compression that sounds nice when cranked and the close back gave some needed bottom end for the 10" speaker.
Funny that i actually didn't like the JJ (it sounded alittle too dark) when i had it in my modded blackheart which currently has a sovtek el84m (great cleans and headroom) and tungsol 12ax7 in it. Besides sounding gd alone, the ac4tv sounded sicker and awfully loud running into my 2X12 ceriatone oversize cab loaded with V30s!
I must say it's a fantastic buy and i cant wait for my ABY switch to be done so that i can run both amps in stereo wahahahaha! Btw faizal i am just curious abt how the ei el84 is treating u?
Funny that i actually didn't like the JJ (it sounded alittle too dark) when i had it in my modded blackheart which currently has a sovtek el84m (great cleans and headroom) and tungsol 12ax7 in it. Besides sounding gd alone, the ac4tv sounded sicker and awfully loud running into my 2X12 ceriatone oversize cab loaded with V30s!
I must say it's a fantastic buy and i cant wait for my ABY switch to be done so that i can run both amps in stereo wahahahaha! Btw faizal i am just curious abt how the ei el84 is treating u?
iwantdigimon
New member
hey bro, u mean u could line out the ac4 to a cab???
iwantdigimon
New member
sweet! and i thought my ac4 did not have a tight bottom end
naviros
New member
The boxiness, to my knowledge / feeling, is from the cabinets. If only I had a spare cabinet lying around to test...
MrBukka
New member
It is true that the construction of the cab is the main attribute to the boxiness and since it is a small amp armed with a 10" speaker it's not bad at all; in fact it sounds better than many other amps out of similar size. To be fair for a cab made of chip board it sounds pretty tight with pretty good resonance and bottom. Of course when I plug it into my ceriatone speaker cab it's definitely an improvement but imo it's not a fair comparison.
naviros
New member
Hahaha... I would just get someone to build me a whole new cabinet, and plug my current 12" drivers in. I'm sure a denser wood will give me the oooohmf I need. Curiously, since the drivers were in a sense made to fit this head, I was wondering if anyone found a better combination in terms of the head to cabinet... (oops, out of thread, maybe I should create a new thread based on cabinet drivers) Not much having a problem with the boxiness, but rather my cabinet making shaking / rattling sounds when I play hard...
Alright, back to the tubes. Nobody tried the new Mullards?! Hahaha... I'm actually quite tempted to switch to mullards, reading about reviews saying its the blues player's dream come true (that it breaks into overdrive really early). I'm currently using an overdrive pedal, so breaking up isn't really the problem, but I'm tempted. Then there is the problem of NOS vs NEW Mullards. From what I've heard, its the NOS thats getting the rave, and the NEW Mullards sound like Sovtek stock...
Either way, might be changing tubes if I fancy soon (after I get my pay...). Stay tuned!
P.S. Most likely its the El84s that will be going... Enjoying the 12AX7 too much... =P Hmmm... Gold Lion or Telam/Polam... Hope they're available here...
Alright, back to the tubes. Nobody tried the new Mullards?! Hahaha... I'm actually quite tempted to switch to mullards, reading about reviews saying its the blues player's dream come true (that it breaks into overdrive really early). I'm currently using an overdrive pedal, so breaking up isn't really the problem, but I'm tempted. Then there is the problem of NOS vs NEW Mullards. From what I've heard, its the NOS thats getting the rave, and the NEW Mullards sound like Sovtek stock...
Either way, might be changing tubes if I fancy soon (after I get my pay...). Stay tuned!
P.S. Most likely its the El84s that will be going... Enjoying the 12AX7 too much... =P Hmmm... Gold Lion or Telam/Polam... Hope they're available here...
MrBukka
New member
Yoz naviros, to answer ur question on cab material and driver: it's definitely true that a cab that's made of denser material such as birch ply, walnut and etc is gonna make the sound much better. As for drivers since the AC4 only accepts 16 ohm load it's kinda tough looking for a replacement from main manufacturers such as eminence and celestion since they don't carry 10" speakers with 16 ohm load (mostly 8 ohm), but u can try Weber that carries a variety of really nice alnico and ceremic magnet drivers that has 16 ohm load (check out their vintage alnico blue clone!). Alternatively u can mod ur AC4 with a 8 ohm speaker output to give u more speaker choices.
As for tubes, i too read that the current mullards r kinda stale in terms of tone (too neutral sounding), i personally used mullard tubes and i really enjoyed it cause it brought out the natural tone of my setup so i guess it's back to the what suits u the best theory. If u wanna compare a stock sovtek tube to a ri mullard tube, there is no comparison. The ri mullards beat sovtek hands down, cause of it's superior tone, built and quality. Surprisingly the ri mullards r abit of different frm the nos mullards, besides the improved durability, they tend to stay clean longer, when overdriven they still sound smooth albeit not as smooth as nos mullards but still classic mullard tone.
So if u r wondering which one to get just think what tone and characteristics u r after, either new or old u can't really go wrong cause they r both from the same veins. By all means try out the nos tubes if u can get ur hands on them at reasonable price and experiment! Haha btw just a small tip for u, guru goose has adviced me that the best el84 is the EI el84, which imo is a very good option as well besides the JJs inthe AC4TV (why u wanna change them?). The only problem for me is that EI tubes r rather inconsistent in terms of their QC (it may die out for no reason at times) so u gotta make sure that u get a good one and pray. If u get the gd ones, u will be on ur way to tone heaven haha!!!
As for tubes, i too read that the current mullards r kinda stale in terms of tone (too neutral sounding), i personally used mullard tubes and i really enjoyed it cause it brought out the natural tone of my setup so i guess it's back to the what suits u the best theory. If u wanna compare a stock sovtek tube to a ri mullard tube, there is no comparison. The ri mullards beat sovtek hands down, cause of it's superior tone, built and quality. Surprisingly the ri mullards r abit of different frm the nos mullards, besides the improved durability, they tend to stay clean longer, when overdriven they still sound smooth albeit not as smooth as nos mullards but still classic mullard tone.
So if u r wondering which one to get just think what tone and characteristics u r after, either new or old u can't really go wrong cause they r both from the same veins. By all means try out the nos tubes if u can get ur hands on them at reasonable price and experiment! Haha btw just a small tip for u, guru goose has adviced me that the best el84 is the EI el84, which imo is a very good option as well besides the JJs inthe AC4TV (why u wanna change them?). The only problem for me is that EI tubes r rather inconsistent in terms of their QC (it may die out for no reason at times) so u gotta make sure that u get a good one and pray. If u get the gd ones, u will be on ur way to tone heaven haha!!!
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naviros
New member
Hahaha... its always nice to try around. The JJs are indeed golden in their tone, was considering the Mullards because of their earlier break up. Maybe I can coax some good overdrive tones without pedals (then can sell pedals off! Hahaha...).
Wah... EI abit hard to find leiz... Discontinued already right? In tone heaven with the JJs already, but what characteristics does the EI yield? Quite curious ^.^ Google only produced sketchy details. Maybe goose will like to comment? (btw, tempted by the seventheaven... waiting list long?)
Wah... EI abit hard to find leiz... Discontinued already right? In tone heaven with the JJs already, but what characteristics does the EI yield? Quite curious ^.^ Google only produced sketchy details. Maybe goose will like to comment? (btw, tempted by the seventheaven... waiting list long?)
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