I bought this amp,
Luxury AIQIN hifi exquis EL34 tube amp Single ended Class A handmade amplifier finished product advanced Slivier Edition-in Amplifier from Electronics on Aliexpress.com | Alibaba Group
as a cheap alternative for playing guitar through. its designed for stereo and is set up to ultra linear connection (10w x2). it sound really good and i cant fault it the only thing is i hate using solid state overdrive distortion effects with valve amps so im wanting to get the amp to overdrive or run hotter or whatever.
an idea was to maybe have a switch on each bias resistors that i could switch to engage a different ohm value to have overdrive/clean.
I have heard some valve amps use different methods for biasing so i dont know if this would be possible with this amp or what values to use as a starting point or even what resistor or resistors controls the bias on these amps and if i have to make any changes to capacitors to accommodate the changes.
I will attach a schematic and quickly let you know where my knowledge is at as far as all this goes. i used to have a rocket super sustain 120w guitar amp years ago. it had four 6l6 somethings in it i read up how to bias it using maths and a 1ohm resitor. i got tried a few resistors got it sounding real good looked down at it 10 mins later to see it glowing red, went to take a reading and arced a track along the circuit board and destroyed a tube. I fixed it and got it sounding good again. i have re-capped a few valve amps before deciding to see what a new ones like. Ive done a bit of other basic electronic stuff not a lot of technical stuff though. anyhow...
here is the schematic. i bought a valve tester adapter to save doing the 1 ohm resistor calculating hopefully. the left el34b gave a reading of about 81 ma ,the other channel read 79 ma. if you want any other readings just let me know where to take them from.
I havent tried it on the 6n9p 's because i dont know if its made to work on it.
I running about 15watt speakers so a get a bit of drive out of them, any help and advice with making this modifying this amp drive better would be great. cheers
i dont mind if the tubes only last a year or so if it sounds good and keeps my room from icing over
Luxury AIQIN hifi exquis EL34 tube amp Single ended Class A handmade amplifier finished product advanced Slivier Edition-in Amplifier from Electronics on Aliexpress.com | Alibaba Group
as a cheap alternative for playing guitar through. its designed for stereo and is set up to ultra linear connection (10w x2). it sound really good and i cant fault it the only thing is i hate using solid state overdrive distortion effects with valve amps so im wanting to get the amp to overdrive or run hotter or whatever.
an idea was to maybe have a switch on each bias resistors that i could switch to engage a different ohm value to have overdrive/clean.
I have heard some valve amps use different methods for biasing so i dont know if this would be possible with this amp or what values to use as a starting point or even what resistor or resistors controls the bias on these amps and if i have to make any changes to capacitors to accommodate the changes.
I will attach a schematic and quickly let you know where my knowledge is at as far as all this goes. i used to have a rocket super sustain 120w guitar amp years ago. it had four 6l6 somethings in it i read up how to bias it using maths and a 1ohm resitor. i got tried a few resistors got it sounding real good looked down at it 10 mins later to see it glowing red, went to take a reading and arced a track along the circuit board and destroyed a tube. I fixed it and got it sounding good again. i have re-capped a few valve amps before deciding to see what a new ones like. Ive done a bit of other basic electronic stuff not a lot of technical stuff though. anyhow...
here is the schematic. i bought a valve tester adapter to save doing the 1 ohm resistor calculating hopefully. the left el34b gave a reading of about 81 ma ,the other channel read 79 ma. if you want any other readings just let me know where to take them from.
I havent tried it on the 6n9p 's because i dont know if its made to work on it.
I running about 15watt speakers so a get a bit of drive out of them, any help and advice with making this modifying this amp drive better would be great. cheers
i dont mind if the tubes only last a year or so if it sounds good and keeps my room from icing over
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The only way to get it to distortion (in guitar terms) is to simply have more gain.
First things I'd do is get rid of the NFB and go pentode mode instead of UL. Then I'd simply ditch the other channel, and use both sections of the 6N9 on the used channel.
Two gain stages is not a lot for rock lead, but if you have high output pickups, it'll get you in business.
You could also get another 6N9 or 6SL7 tube and rewire the unused EL34 socket for it. Then you could make a serious guitar amp with a tonestack and all (a tonestack sucks up quite a lot of gain, but gives more options for tone).
First things I'd do is get rid of the NFB and go pentode mode instead of UL. Then I'd simply ditch the other channel, and use both sections of the 6N9 on the used channel.
Two gain stages is not a lot for rock lead, but if you have high output pickups, it'll get you in business.
You could also get another 6N9 or 6SL7 tube and rewire the unused EL34 socket for it. Then you could make a serious guitar amp with a tonestack and all (a tonestack sucks up quite a lot of gain, but gives more options for tone).
You are not going to be able to make an OD/clean switch by affecting the bias in the way you describe. Extreme bias conditions will give more distortion, but they significantly affect available output volume and also can make the sound really thin and unpleasant.
You simply need more gain, more 6N9 sections on the signal path. Then you can play in many ways with their (the preamp tubes') bias to affect tone.
You simply need more gain, more 6N9 sections on the signal path. Then you can play in many ways with their (the preamp tubes') bias to affect tone.
so do you mean i need to be able to adjust the power levels of the 6n9 and have like volume/ master or and add another pair of 6n9's so there is two pre stages?
if this is what you ment could i do it cheaply using the existing transformers?
I dont really want to lose one channel, i go through a booster then and old stereo graphic equlizer wth a built in spring reverb and have delay on channel and tremolo on the other with two 8" speakers in the same cab. it sounds good cause i mostly play country, country rock. would rather get the overdrive from the valves than the solid state line booster. the rocket i had a solid state pre, i think it was the output stage that gave it its good over drive sound
If you want to keep it 2-channel, the way to go is to replace the preamp tubes with 6SL7's (almost the gain of an 12AX7) and copy one of the P1 schematics found in ax84.com. I m pretty sure they have something with EL34.
I'd like to advice You don't touch amp. You can buy guitar preamp Digitech RP100 for about 80-100 $ with stereo outputs for two speakers with hundreds guitar effects. It output levels are suitable for Your amp. I have the same and I'm very glad using it with my SE 300B JJ with stereo guitar sound.
Guitar amps get their gain mostly from the pre-amp (especially high gain monsters) and from multiple cascaded stages. Without physical changes to your amp that would be hard to accomplish. However you could make and use standalone pre-amp units and feed the output of that into your amp. Here's an example of one: Amps : Mesa Mark IIc+ Pre PtP : DIY Fever – Building my own guitars, amps and pedals. That's based on the Mesa Mark IIC+ pre-amp. Is there a particular sound you'd like to go after?
Oh, the other thing I would do to the amp if it's for guitar use is disconnect the ultra-linear connection and add a screen supply off your power supply. You could even add a switch to go back and forth easily enough.
6N9 actually is 6SL7.
Like I said; at least get rid of NFB, and rewire the output stage pentode mode instead of UL.
If you want to keep it stereo, then can you add new tube sockets to the chassis for more gain?
Like I said; at least get rid of NFB, and rewire the output stage pentode mode instead of UL.
If you want to keep it stereo, then can you add new tube sockets to the chassis for more gain?
are the pre amp stages for class a and a/b amp pretty much the same?
I play mostly country rock occasionally 80/90's metal rock.
I think i might have to build of track down a cheap stereo valve pre amp.
I used a pre amp with my guitar to get sufficient gain to over drive my valve amp.
A cheap alternative to a valve amp is a soft limiter.
I found one in a very old Wireless World magazine.
Its highly adjustable to give clean or over driven sound.
A cheap alternative to a valve amp is a soft limiter.
I found one in a very old Wireless World magazine.
Its highly adjustable to give clean or over driven sound.
im not quite sure what this would ("add a screen supply off your power supply"), how to do it or what other changes i would have to make, my knowledge is a bit limited.
I found this schematic. im not sure is this is pentode mode?. i think the only difference from the first i posted is the wire from pin 4 on the el34 has been cut and run directly to the 10k 2w resistor.
I done some reading up on NFB and read you can add a pot like presence control. I would like to do the two thing you suggested. as far as i work out the NFB circuit runs from pins3/6 on the 6n9p to the 8ohm blue wire on the output transformer though i could be completely wrong.
if you could draw any necessary on the schematic to add in a presence pot and what value it should be and if anything else has to be altered to remove/adjust the Nfb that would be great.
if the new schematic isnt pentode and you you know how to simply change it could you mark it in a different color from the nfb so i can learn the difference. thanks if you have time to help.
also would changing the 100k volume to 150k or 200k help with gain?
i may buy a couple of pre gain kits when i have more funds and add them in, for now any changes would be good
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What is it exactly what you want to achieve?
My first thought was to switch to triode mode and/or drop the HT a bit so the amp would saturate at lower volumes. You'd still need a preamp with enough (clean) output to overdrive the power amp.
But then again, maybe you are looking for preamp (master volume) type distortion in which case you need to add gain stages.
Perhaps a mod can move this thread to the musical instruments forum. There will be more responses there I think.
My first thought was to switch to triode mode and/or drop the HT a bit so the amp would saturate at lower volumes. You'd still need a preamp with enough (clean) output to overdrive the power amp.
But then again, maybe you are looking for preamp (master volume) type distortion in which case you need to add gain stages.
Perhaps a mod can move this thread to the musical instruments forum. There will be more responses there I think.
I drew up some schematics.
So the main points are:
1. change the EL34 to pentode operation, and tap the screen supply from where you previously tapped the plate supply. Use a 220 ohm stopper; value not critical. Plate supply moved 'upstream', to the other end of the choke.
2. remove NFB. This will make the amp distort a lot more, and clip more gradually, giving more control of the level of distortion.
3. change some component values from HIFI values to instrument amp values. The coupling cap should be 22nF, or maybe 33nF. If it is left too large, the amp will "fart out" when it distorts. Also there is no need to have low bass in a guitar amp, it will muddy everything up.
Preamp tubes' cathode capacitor is changed also to a smaller value; could be even smaller like 47µF. Plate resistor is made bigger, to give more gain.
(The 20k in the PSU is just for the sim, because of the other channels current draw.)
I made a few simulation runs, and it seems the amp with these small changes begins to distort more. The distortion is very much 2nd order dominated all the way to hard clipping. Also the distortion increases very smoothly with increasing input. Hard clipping is around 2VPP input, so you'll need some kind of preamp for that.
The 100 ohm resistor at the first PSU cap brings in some sag. If you like this effect (I do), you could increase it. Experiment.
The center picture is unmodded schematic, and right one is modded.
So the main points are:
1. change the EL34 to pentode operation, and tap the screen supply from where you previously tapped the plate supply. Use a 220 ohm stopper; value not critical. Plate supply moved 'upstream', to the other end of the choke.
2. remove NFB. This will make the amp distort a lot more, and clip more gradually, giving more control of the level of distortion.
3. change some component values from HIFI values to instrument amp values. The coupling cap should be 22nF, or maybe 33nF. If it is left too large, the amp will "fart out" when it distorts. Also there is no need to have low bass in a guitar amp, it will muddy everything up.
Preamp tubes' cathode capacitor is changed also to a smaller value; could be even smaller like 47µF. Plate resistor is made bigger, to give more gain.
(The 20k in the PSU is just for the sim, because of the other channels current draw.)
I made a few simulation runs, and it seems the amp with these small changes begins to distort more. The distortion is very much 2nd order dominated all the way to hard clipping. Also the distortion increases very smoothly with increasing input. Hard clipping is around 2VPP input, so you'll need some kind of preamp for that.
The 100 ohm resistor at the first PSU cap brings in some sag. If you like this effect (I do), you could increase it. Experiment.
The center picture is unmodded schematic, and right one is modded.
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thats a good idea. i spent the day study up as much as i can on amps. I still have to research up about pentode, triode and linear modes and what is considered a standard conection.
what i think i will try do is copy/ add on basic pre on to each channel in front of the existing and hopefully be able to power it from the same mains transformer. its says the transformer is 160w and the amp uses 115w. i dont know if that would leave enough to safely power two 12ax7's.
i guess i would just tap into the 225v just before the 82k resistors then try work out what value and watt resistor i would need to bring 225v down to 181v for the 12ax7's and just copy the rest if its that simple?
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hey thanks so much for drawing that up and running it through your computer. i will get some parts sort it
You can use the R2 (in my modded schem) to lower the HT. Increase it to say 330 ohms (10W rating) and you'll have more sag, and lower HT.
Also the 120k plate resistor will lower the preamp tubes' plate voltage as well. This could be 150k, or even 220k. I've done 6SL7 guitar amp stages with 220k plate resistor - it does tend to have less headroom, so more easily distorts.
I would suggest getting extra resistors for experimenting.
Also the 120k plate resistor will lower the preamp tubes' plate voltage as well. This could be 150k, or even 220k. I've done 6SL7 guitar amp stages with 220k plate resistor - it does tend to have less headroom, so more easily distorts.
I would suggest getting extra resistors for experimenting.
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