While I've read from some that the Blackheart BH5H has lots of gain, maybe too much, I can not get it to distort on its own. Using any of my guitars (Including my Phiga with 3 humbuckers), so I don't agree that it has too much gain. Turned all the way up I would say I get a little bit of overdrive, but not even as much as the Fender tweed deluxe or Bassman could get turned all the way up. I'm wondering if there is a way to increase the gain from the 12ax7 to get more overdrive sooner.
As it stands I'm using it with my 2x12 cab with Celestion Vintage 30 speakers. I'm also using the amp in triode mode (3w) and not UL (5w). The tubes are inexpensive used ones I had, including a Hodges 12ax7 and Tungsol El84. I'm thinking about doing the turret board PTP wiring modification, which would allow easier modifications, greater space for parts like PIO caps, and easily add the tube rectifier.
Schematic
Any help on what parts need to be changed to increase gain and in what way would be great. I've found some sights on modifying the amp, but none for increasing gain. There is a discussion of the designers own boost mod, but I'm not sure what that is, I think its a treble boost.
As it stands I'm using it with my 2x12 cab with Celestion Vintage 30 speakers. I'm also using the amp in triode mode (3w) and not UL (5w). The tubes are inexpensive used ones I had, including a Hodges 12ax7 and Tungsol El84. I'm thinking about doing the turret board PTP wiring modification, which would allow easier modifications, greater space for parts like PIO caps, and easily add the tube rectifier.
Schematic
Any help on what parts need to be changed to increase gain and in what way would be great. I've found some sights on modifying the amp, but none for increasing gain. There is a discussion of the designers own boost mod, but I'm not sure what that is, I think its a treble boost.
I would get more gain if I replace R6 in the above schematic with something like a 1K instead of the 1.5K right? Also changing R2 for something less than 33k would increase gain. I'm guessing those are the best places to target, but it seems like R6 and R10 are already pretty low. I'm not actually sure if R10 should be touched, but I know some guys are raising R2 and R10 to increase clean headroom for using with their pods, so I figure, the opposite would give me less clean headroom, which is what I'm after.
None of the three resistors you mention would alter the gain at all, they are 'grid stoppers', simply there to help prevent instability.
There really doesn't look to be a lot of gain there at all, an extra stage would be a good idea.
There really doesn't look to be a lot of gain there at all, an extra stage would be a good idea.
Changing R2 to something smaller WILL give you more output out of that 1st stage.
2 AX7 stages should be enough to put you into clipping with an EL84 with hot pickups for sure.
I'd check if either C1 or C5 are open or unconnected in some way.
2 AX7 stages should be enough to put you into clipping with an EL84 with hot pickups for sure.
I'd check if either C1 or C5 are open or unconnected in some way.
Nigel Goodwin said:
Less voltage drop across the resistor. Check commercial amp schematics, invariably the only difference between the "HI" input and "LO" input is the value of the series resistor.
leadbelly said:
I suggest you check the schematics yourself - those are part of an attenuator, well before the valve - NOT the grid stopper which in no way affects the gain.
Nigel Goodwin said:
R2 is NOT just a grid stopper, if it was, it would be 1.5K like the other grid stoppers.
leadbelly said:
Grid stoppers don't need to be any specific value - it won't affect the gain at all, how do you imagine it could?.
Nigel Goodwin said:
By voltage drop through the resistor itself. You are conveniently defining gain at the tube pins for your purposes; step back and include the input circuitry and gain is not the same.
The grid stoppers do not affect gain, except at the very high frequencies where the RC filter begins to have some effects. I don’t know why you even argue about this.
To increase the gain of this amp you could try increasing the value of plate resistors, but to tell the truth, the amp is already pretty much pushing out all the gain you can get. An important point is that the tonestack is attenuating the signal considerably and basically you only have one preamp stage to boost the signal and another one to pretty much recover the signal losses introduced by the tonestack. With this kind of setup its pretty hard to overdrive the output efficiently.
If you want more clipping (which I assume is actually the case) then why not decrease the voltage of the preamp’s plate supply? Won't give you power amp overdrive, though. ...Or you could try a signal booster pedal in front of the amp. Ultimately you could lift the tonestack off the circuit but this will drastically change the amp's tone. If all fails then you might just have to resort to admitting that this amp wasn't for you.
To increase the gain of this amp you could try increasing the value of plate resistors, but to tell the truth, the amp is already pretty much pushing out all the gain you can get. An important point is that the tonestack is attenuating the signal considerably and basically you only have one preamp stage to boost the signal and another one to pretty much recover the signal losses introduced by the tonestack. With this kind of setup its pretty hard to overdrive the output efficiently.
If you want more clipping (which I assume is actually the case) then why not decrease the voltage of the preamp’s plate supply? Won't give you power amp overdrive, though. ...Or you could try a signal booster pedal in front of the amp. Ultimately you could lift the tonestack off the circuit but this will drastically change the amp's tone. If all fails then you might just have to resort to admitting that this amp wasn't for you.
There is a group of guys modding these things sewatt.com It has a free registration process to go through, but there is also a lot of info about the Epiphone Valve Junior that is very similar to this.
Raise the plate resistors from 100k to 120k will give you a little more gain. Biggest change you can make to increase the gain would be to dump the tone stack completely, bypass it and do what Orange and Vox did with a cut control before the power section. You'll have a lot of mids so if you like a scooped tone you'd need to add an eq pedal before the amp.
Hi there, I will be making a mod for my Bh5h soon which is as easy as replacing a tube and equally easily removed. Its basically a compactron tube (12 pins), which has 3 gain stages as oposed to the 2 gains stages in 12ax7's properly wired/adapted to fit a 9 pin male socket, so you can plug it in the amp as a 12ax7 and you'll be adding an extra gain stage to the amp.
Is the same principle used in the "Soldano Hot Mod". I've seen a little boutique amp head that uses a single compactron tube in the preamp section, I don't remember the name. Also some compactron tubes you can get NOS on ebay for 5 bucks, good deal.
I'll let you know how it works
Fabian
Is the same principle used in the "Soldano Hot Mod". I've seen a little boutique amp head that uses a single compactron tube in the preamp section, I don't remember the name. Also some compactron tubes you can get NOS on ebay for 5 bucks, good deal.
I'll let you know how it works
Fabian
if you want to mess around inside your amp, here are some changes that seem the most obvious to me and simplest to implement.
changing r4 and r8 to 220k will get you more gain. a more r3 and r7 combination with 220k plate resisters would be 1.8k but 1.5k is normal too.
changing c5 to 22mfd-25v or 25mfd-25v will also get you more low end gain. you might then want to string a 220-470k resister paralleled with a .001-.002 cap from the wiper of the treble pot to the top of the volume pot, to bring back some top end bite.
changing r7 to anywhere from 10k-30k will bias the stage extremely cold and get you a certain kind of clipping but not my taste. to offset the effect you could bias the first stage warmer and change r3 to 820ohms.
dumping the tone stack will get you more gain (just disconnect the ground of the midrange to disable tone circuit, could use a switch) or switch to a james or bandaxall stack, it loads the circuit down less.
replace r9 with a 1m pot for a master volume, dime input volume to get all the available drive out of the pre-amp at lower volume. alternatively just replace r9 with a 1m resister to see if the amp has any untapped volume. if this makes it freak out try replacing r10 with 470k.
dropping the pre-amp plate voltages is a good idea too. something like 30k-2w for r16 might get you somewhere. you want the voltage at pin 1 of v1a and at pin 6 of v1b to be reduced, this will lower the headroom of the stages making it easier to clip. you might even try something sneakier by switching around the power supply nodes for pin 1 and 6 and then drop the voltage at pin 6 only by raising r17 instead.
raising the gain of any tube amp will reveal bad grounding issues, insufficient shielding and bad wire dress. so if any mod makes the amp noisy or unstable it might be the layout of amp and not the mod per se. it's best to try mods one at a time to make troubleshooting easier.
if there is space to add another pre-amp tube you could get any distorted sound you wanted up to any high gain marshall.
all my spare time is spent tweaking tube amps and playing guitar.
changing r4 and r8 to 220k will get you more gain. a more r3 and r7 combination with 220k plate resisters would be 1.8k but 1.5k is normal too.
changing c5 to 22mfd-25v or 25mfd-25v will also get you more low end gain. you might then want to string a 220-470k resister paralleled with a .001-.002 cap from the wiper of the treble pot to the top of the volume pot, to bring back some top end bite.
changing r7 to anywhere from 10k-30k will bias the stage extremely cold and get you a certain kind of clipping but not my taste. to offset the effect you could bias the first stage warmer and change r3 to 820ohms.
dumping the tone stack will get you more gain (just disconnect the ground of the midrange to disable tone circuit, could use a switch) or switch to a james or bandaxall stack, it loads the circuit down less.
replace r9 with a 1m pot for a master volume, dime input volume to get all the available drive out of the pre-amp at lower volume. alternatively just replace r9 with a 1m resister to see if the amp has any untapped volume. if this makes it freak out try replacing r10 with 470k.
dropping the pre-amp plate voltages is a good idea too. something like 30k-2w for r16 might get you somewhere. you want the voltage at pin 1 of v1a and at pin 6 of v1b to be reduced, this will lower the headroom of the stages making it easier to clip. you might even try something sneakier by switching around the power supply nodes for pin 1 and 6 and then drop the voltage at pin 6 only by raising r17 instead.
raising the gain of any tube amp will reveal bad grounding issues, insufficient shielding and bad wire dress. so if any mod makes the amp noisy or unstable it might be the layout of amp and not the mod per se. it's best to try mods one at a time to make troubleshooting easier.
if there is space to add another pre-amp tube you could get any distorted sound you wanted up to any high gain marshall.
all my spare time is spent tweaking tube amps and playing guitar.
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