Hello .. I open this issue not because I have a problem with the amp. I just want to increase the gain. I just changed the v1 tube of normal section from ecc83 to ecc83s and it has a big difference in gain .. I just want to make a mod to get other throttles the gain .. I know that this amplifier is not for much gain I have just seen many that they have this amplifier and I have made many mods on gain just I can not find schematis for these mods .. one of them is called CASCADE… note that I have put a master volume and switch for solid state rectifier…that I only know is put 680nf cap across the v1 cathode . I draw on schematic .. tell me what else can I do ; thanks
There's already a large capacitor (C1) connected across R6, so adding another won't change the gain.
Removing the tone parts C2 and R7 will increase the gain, if you can do without them.
Do you mean the gain of the HI input or the LO input?
The HI input gives twice as much gain as the LO input, +6dB more.
Removing the tone parts C2 and R7 will increase the gain, if you can do without them.
Do you mean the gain of the HI input or the LO input?
The HI input gives twice as much gain as the LO input, +6dB more.
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I don’t mean the hi-lo . I’m fine with that , I use only HI 🙂 .. I found this schematic about a cascade/parallel ..do you know about that ? 
The dual section 12AX7 is currently wired with both sections in parallel.
The other circuit version places one section first, and the other section
after that, hence the name series. It will have more gain, possibly +30dB,
depending on how the circuit is designed.
It will also have more noise and distortion than now. This change will require
rewiring and careful work. If you have no experience, it may be best to
have a friend help.
The other circuit version places one section first, and the other section
after that, hence the name series. It will have more gain, possibly +30dB,
depending on how the circuit is designed.
It will also have more noise and distortion than now. This change will require
rewiring and careful work. If you have no experience, it may be best to
have a friend help.
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I’m ok with experience of tubes amps ( for schematics and layouts yet ) … I just finish my jcm800 project and after I mixed the 1974x … but this schematic ( cascade) is right ?
Appears to be ok, but you don't know how well it will work until you try it.
That circuit seems to be experimental.
That circuit seems to be experimental.
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I am surprised your having gain problems with an amp that was designed for guitar.
Is your guitar low output signal ?
Has your amp lost gain due to old valves ?
You shouldn't have to hack it to get more gain.
Is your guitar low output signal ?
Has your amp lost gain due to old valves ?
You shouldn't have to hack it to get more gain.
Moved to Instruments and Amps.I'm with Nigel on this one. In post #1 TS wrote that using an ECC83S instead of an ECC83 as V1 had a big difference in gain. Since the characteristics (µ, transconductance, plate resistance) of an ECC83 and an ECC83S are identical, the perceived big difference in gain must be the result of the ECC83 not being up to specs (anymore).
Big difference the ecc83s .. but I’m start to make the cascade mod ..I’m talking with guys on 18watt.com forum and it’s pretty cool mod .. with parallel switch make those amp very comfortable …. I’ll post here informations about - what parts add - replace and remove ….😊
Hello guys .. just finish the CASCADE MOD with parallel switch .. and it’s just amazing ��.. the sound is soooo awesome ..I am so happy for my 18 watt ( little monster from now ) … tomorrow I put here information if someone want to make it ….
Right is push-pull el84 … today or tomorrow I draw the layout of cascade mod and infos … I made it quickly because I was curious how it sounds ρα I took around 4 hours to do the mod correctly and carefully. really now when in cascade mode the amp has a lot of flexibility. because it has the cascade gain, it has the v1 gain and the master volume… 2 Gains !! και με το solid staste rectifier switch make the amp little monster… .. \m/
Confirmation bias?
Builder´s pride?
Certainly I would not expect more than 1 or 2dB difference, if that much, purely attributable to tube to tube dispersion, even within "same type".
At most, now we have "normal" gain while old one was worn to death or almost.
Which all by itself might explain perceived "low gain".
Soo I finish quick my work today to coming home and test my 18watt again 🙂 … now with more volume 😛 .. but there is an issue… when it is in cascade mode and the gain is at 8-9. it has an incredible sound. the middle ones are boosted and the gain reaches metal levels… but as soon as I set the gain to 10 (full) the sound gets clogged but not in a bad way .. something like the distortion of orange amps. if I do not understand what I mean .. it is not ugly just as if you are doing something different… however I put the volume of v1 at 10 and the gain of the cascade at 8 …… METAL RULES!
Look into the Stout.
Think they have a version that switches the gain stages also.
18 watt Stout & Plexi amp designs
Think they have a version that switches the gain stages also.
18 watt Stout & Plexi amp designs
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Yes . It’s same with a little other values ….
Update mine because have blockage when the gain pot is on full … I add a trim between pin 2 of pot and the 33k on switch .. I put the gain on 10( full ) and I set the trim as a little when the blockage gone 🙂 . It’s about 40k-50k . But now it’s fantastic 🙂 …. Great mod the cascade .
Update mine because have blockage when the gain pot is on full … I add a trim between pin 2 of pot and the 33k on switch .. I put the gain on 10( full ) and I set the trim as a little when the blockage gone 🙂 . It’s about 40k-50k . But now it’s fantastic 🙂 …. Great mod the cascade .
The wiper of the volume pot is directly connected to the V1-B grid
When the Pot is set to maximum you are probably getting what is called "blocking distortion". It sounds snotty congested and horrible.
Essentially when V1-B grid is overdriven, it becomes forward biased (same thing as a diode) and the grid conducts current via the cathode.
Instead of direct connecting the wiper to the grid, insert a 50K (or higher) resistor between the wiper and grid. This should help if it is blocking distortion.
At the same time, I would also suggest adding a 1M resistor from the grid to ground as this can be a more reliable reference than relying on a path via a mechanical wiper.
When the Pot is set to maximum you are probably getting what is called "blocking distortion". It sounds snotty congested and horrible.
Essentially when V1-B grid is overdriven, it becomes forward biased (same thing as a diode) and the grid conducts current via the cathode.
Instead of direct connecting the wiper to the grid, insert a 50K (or higher) resistor between the wiper and grid. This should help if it is blocking distortion.
At the same time, I would also suggest adding a 1M resistor from the grid to ground as this can be a more reliable reference than relying on a path via a mechanical wiper.