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Instruments and Amps Everything that makes music, Especially including instrument amps.

Gibson GA20 - more power
Gibson GA20 - more power
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Old 8th August 2018, 07:44 PM   #21
jimijimi is offline jimijimi
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but there is one thing - when you read the schem, i doesnt say how wanny Watts any given resistor needs to be listed at - how will i know ???
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Old 8th August 2018, 11:18 PM   #22
Printer2 is offline Printer2  Canada
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No, changing the resistance will change the bias on the tubes but does not get you more power. If you want louder get a louder speaker. Otherwise you probably need a bigger output transformer and power transformer. Even then the type of circuit may not give you what you want without pretty much gutting the amp and starting new. And it would be a shame to see a piece of history get trashed for not much gain. Again, the biggest gain you can make as far as making a louder amp is to change the speaker. Doubling the power of the amp only gives you an extra 3 dB, which is like running your stereo and then once channel stops. Not a huge difference.
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Old 9th August 2018, 05:20 AM   #23
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by jimijimi View Post
i dont want distortion, i want loudness
Messing with the GA-20 is not going to get you the outcome you want. Stop even thinking about messing with it.

Go buy a cheap class D 100W amp module and SMPS from some fleabay vendor; hook them up to a pair of 4x12 cabinets full of 100db/w speakers and feed that lot from the signal across the speaker of your GA-20
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Old 9th August 2018, 08:01 AM   #24
jimijimi is offline jimijimi
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seems many here have misunderstood what im trying at

i do not want to be louder because i need to be louder in a room
i want to be louder because i can HEAR that the 6V6 tubes are NOT doing any real work as the amp is set up now - and i just really have a wish to hear how MY BABY sounds when pressed to the max. - i do NOT want to hear the distortion from the preamp and splitter.
i want to hear the overdrive from the power tubes only!!
i want these little 6V6 #uckers to do twice as much work as they are at the moment

you guys are sweet by giving me precautions for not ruining my amp - thanks - but i have already achieved many things with this amp and a pair of crocodile grips:
- octave fuzz
- biased out fuzz
- tremolo
- a tremolo where vib speed was reacting to how hard i played my guitar

ive done similar things with my orig marshall 1959Žers 100w heads - my fender super rev, my teisco, my vox etc

this is how i play guitar

i dont know anything about electronics - all i know is from my experience from playing around with it. the Gibson GA20 is my favorit in this way cuas its so simple , you can with one good eye follow the signal from A to Z

Last edited by jimijimi; 9th August 2018 at 08:21 AM.
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Old 9th August 2018, 08:24 AM   #25
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by jimijimi View Post
seems many here have misunderstood what im trying at

i do not want to be louder because i need to be louder in a room
i want to be louder because i can HEAR that the 6V6 tubes are NOT doing any real work as the amp is set up now - and i just really have a wish to hear how MY BABY sounds when pressed to the max. - i do NOT want to hear the distortion from the preamp and splitter.
i want to hear the overdrive from the power tubes only!!
i want these little 6V6 #uckers to do twice as much work as they are at the moment
Erm, did you read this one?
Quote:
Originally Posted by PRR View Post
In 1953, distortion was RUDE. Amps were low *gain*. They would barely distort even when played HARD, maximum arm effort.

Put a simple booster in front. The "LPB" would be the go-to pedal.

AND--- it may not be working as intended. Stuff goes bad. Usually it goes to crap, but it can just go to low gain (lower than designed).

If you want an amp that "breaks", most/all of the recent low-price tube amps will do that easily. Trade the GA-20 to a fan of old Gibsons.


Best regards!
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Old 9th August 2018, 02:15 PM   #26
voltwide is offline voltwide  Ireland
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Ages ago I tried similar things. And found the driver stage too weak to push the tubes to the limit. I ended up using a 4watt transistor amp feeding the secondary of some mains transformer, the primary driving the grid(s). All in all I could not see the point in this huge effort to squeeze some lame tubes and prefer to build solid state since then.
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Old 9th August 2018, 02:53 PM   #27
Kay Pirinha is offline Kay Pirinha  Germany
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I think the main issue here is the misleading thread title, as he presumably isn't in search of more power at all, but of more gain instead.


Best regards!
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Old 9th August 2018, 06:28 PM   #28
Printer2 is offline Printer2  Canada
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And I will repeat again, how do you know the amp is doing what it should? Ar all the parts in spec? The tubes all good? I gave an example of what it could do in the Youtube vid. Can your amp doing what that amp did? If not you may need more signal into the amp. It should get the output tubes into clipping.



There is no magic swap of a part or two to get more gain out of the amp. The 6SL7 has a 220k resistor on the plate,no increasing that. The 6SJ7 has the gain pushed as much as it can, If you dime the volume you should get enough signal to the output tubes. Whether it is enough for you there does not look to be an easy way to get more given what you have. Without you (and us) knowing what is going on inside your amp health wise I do not think there is much more we can offer. Maybe make a chart of the tube pins and the voltages on them as well as the voltages of the power supply capacitors. Maybe we could see something that is amiss.
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Old 9th August 2018, 06:38 PM   #29
Parafeed813 is offline Parafeed813  Netherlands
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So the objective is less preamp distortion and more power stage saturation.
What about raising the voltage on the 6SL7 by paralleling the 47k in its power supply with another 47k or less, depending on the desired voltage? You may want to put a larger filter cap as well.
The driver will have some more headroom and output swing this way.
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Old 10th August 2018, 04:59 AM   #30
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by jimijimi View Post
i want to hear the overdrive from the power tubes only!!
As others have noted, then you need to drive them harder. Crack that whip and hit the grids with at least 40VPP!

If I remember my gospel-according-to-Tubelab-George correctly, the 6V6 is limited by it's low cathode emission.

So you also probably want to increase the screen current (much easier than trying to increase B+) to get those bottles hitting Ip(max)

I'm presuming you're all across what's going to happen when you do this?

Do note that genuine 6V6s are different to many of today's 6V6-a-likes (which are often other things rebottled).

They're also getting expensive so if you are going to run them close to the edge it might be better for your bank account to substitute in some of the equivalents (e.g. 6AQ5). But they're your tubes.

Last edited by thoglette; 10th August 2018 at 05:10 AM. Reason: Major RobRobinette moment
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