hi everyone looking in,....i'm in search of answers .....I have built a handful of amps,an 18 tmb,a 36tmb, a howler monkey, an angella,dual single ended with 6aq5's (dropped plate and grid volts to suit), and am now working on a howler monkey again,but with 4 6aq5's in the output
The Howler Monkey Push Pull 6AQ5 Guitar Amp - SolOrb.com
all I have done is added a tube parallel each side in an effort to get 18 watts and hopefully 10 watts clean....all in a tidy box for rehearsals
problem is low volume...the first one I made for my son worked well as a practise amp but not loud enough for rehearsals...so I thought add 2 tubes more and I should achieve this ........but no it dose not seem any louder than the original 2 tube version.....so I am wondering is the phase inverter not strong enough to push 4 tubes.....my limited knowledge cant answer these question....I'm just an assembler with a bit of understanding
only thing different is the B+ is 265V and 2 extra tubes in parallel
the sound is clean but I use a 12ax7 so as to roll on distortion from the guitar as needed.....I have wired the output transformer so its reflected resistance is 4000 ohm on 4 x 6aq5....
so any advice would be appreciated...regards rifraf50
The Howler Monkey Push Pull 6AQ5 Guitar Amp - SolOrb.com
all I have done is added a tube parallel each side in an effort to get 18 watts and hopefully 10 watts clean....all in a tidy box for rehearsals
problem is low volume...the first one I made for my son worked well as a practise amp but not loud enough for rehearsals...so I thought add 2 tubes more and I should achieve this ........but no it dose not seem any louder than the original 2 tube version.....so I am wondering is the phase inverter not strong enough to push 4 tubes.....my limited knowledge cant answer these question....I'm just an assembler with a bit of understanding
only thing different is the B+ is 265V and 2 extra tubes in parallel
the sound is clean but I use a 12ax7 so as to roll on distortion from the guitar as needed.....I have wired the output transformer so its reflected resistance is 4000 ohm on 4 x 6aq5....
so any advice would be appreciated...regards rifraf50
Just adding two more output valves won't change the output power much without halving the impedance, which you did.
Can the output transformer handle the extra power?
Make sure the power transformer can deliver all voltages at the higher current requirements.
The grid leak resistors for 6AQ5s are specced at 500k max for cathode bias, so for two in parallel should have no more than 250k grid leaks. Not much different from the 330k you have now, so that shouldn't be a problem for the phase inverter.
Perhaps you have too high expectations of the doubling of power? It's only a few dB difference.
The biggest difference between a 50W and a 100W guitar amp is the feel, not the loudness.
Can the output transformer handle the extra power?
Make sure the power transformer can deliver all voltages at the higher current requirements.
The grid leak resistors for 6AQ5s are specced at 500k max for cathode bias, so for two in parallel should have no more than 250k grid leaks. Not much different from the 330k you have now, so that shouldn't be a problem for the phase inverter.
Perhaps you have too high expectations of the doubling of power? It's only a few dB difference.
The biggest difference between a 50W and a 100W guitar amp is the feel, not the loudness.
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hi....the output tranny is rated for 20 watts with 8k reflected at 8 ohms...I used the 16 ohm tapps with an 8 ohm speaker to give a reflected resistance of 4000 ohms ....with 4 tubes pushing 4.5watts in theory should give me 18watts.....I've made 18watt tmb's (6bq5's)and they leave this for dead.....but I don't know enough in general to understand why the grunt isn't there.....this is not as loud as the angella super single ended amp I made with 2 6aq5's(subbing the 6v6's) putting out around 9-10 watts
I have another OT 2500k at 8 ohms....30 watts....if I connect 8 ohms to 4ohms taps this will give me 5000 ohms......would this be more comfortable for the 6aq5's....I did notice 1 tube was red plating.....not so sure on the matching but they were NOS,....perhaps the cathode resistors need to be a little softer ? say 180 or 200 ohms?
I have another OT 2500k at 8 ohms....30 watts....if I connect 8 ohms to 4ohms taps this will give me 5000 ohms......would this be more comfortable for the 6aq5's....I did notice 1 tube was red plating.....not so sure on the matching but they were NOS,....perhaps the cathode resistors need to be a little softer ? say 180 or 200 ohms?
as a guitarist,i prefer to thrash a small amp and to hell with the consequences!!!!....I used a 71 blackfaced fender twin reverb (100watts rms)for 10 years always having to be carefull not to blow everyone of the stage with it....so now I'm loving these little amps...making and playing them and passing them on,so all the help I get will be graciously received......rifraf50
Even if the conditions are ideal, doubling the output power only provides 3dB worth of extra loudness. It's a "perceivable" difference, but as loudness increase something closer to 1.2x. So for the sake of perceived loudness, merely doubling the output power does pretty much nothing to write home about. Clean headroom will be improved some, though. Effectively both amps will be about as loud (at practical settings) but the higher power stays "cleaner" and "tighter" for a tiny amount more.
If simply -louder- is your goal then there are better chances to meet that objective by upgrading to more sensitive speaker system than by increasing output power. The scale is logarithmic so doubling output power gives you practically nothing and more perceivable upgrades (e.g. 4x - 10x more power) start to require an entirely different design in practically all aspects. Simply much easier to acquire those extra dBs with speaker setup.
Did you check all voltages?
Four 6aq5s at 265V into 5k should give you 20 clean watts. Red plating is most likely caused by a wiring or component fault although a bad valve is a possibility. Swap them around to see if it follows the valve or stays in the same location.
Be careful with overheating these little ones: because the glass is so close to the anode, it will melt easily!
Four 6aq5s at 265V into 5k should give you 20 clean watts. Red plating is most likely caused by a wiring or component fault although a bad valve is a possibility. Swap them around to see if it follows the valve or stays in the same location.
Be careful with overheating these little ones: because the glass is so close to the anode, it will melt easily!
Agreed on pushing the 6AQ5's.
I am known for abusing tubes, and about 10 years ago I got a large box full of 6AQ5's in poor condition. There were over 1000 tubes AFTER I threw out all the broken ones, and ones with less than 7 pins remaining. I cleaned up the remaining tubes and sorted out the tubes that were in good physical shape. I saved those (several hundred) for a future project, but they are still untested used tubes.
Many of the remaining tubes had corroded pins that would break off when inserted into a socket, so I tossed those that had pitted pins, and had about 75 tubes that were good enough to experiment on. I did my usual "how many watts can I get out of a pair of these" tests, and found that there is only a watt or two of dissipation between "red spot on the plate", and "hole in the glass"! The 6AQ5 usually red plates in a small spot, and the glass will soften in that area. Long term use in this region will cause the vacuum to suck the glass inward until there is a hole.
Granted this was about 10 years ago, so I don't remember the exact details, but I made a breadboard with 10 or 12 6AQ5's wired up in push pull. I tinkered with it for a while, and eventually grew frustrated with trying to match up 10 or 12 used tubes well enough to keep one or two from red plating. The thing did scream, and sounded rather unique when it worked, but broken pins and trashed sockets from digging out the broken pins eventually convinced me to throw the entire mess into the trash.
It did put out well over 50 watts, more like 75 at the onset of nuclear meltdown, which proves that 4 tubes should be easy. I don't remember the driver tube I used at the time, but it was almost certainly one of the computer tube variants of the 12AU7 since I have a similar big box full of several different ones. Probably a 5963, but could have been 5965, 6463, 7044, or 7119.
I have several test OPT's that I configure for different loads by using 8 ohm loads on the 16 ohm tap, and all testing is done with a variable power supply. I just turn it up till it glows, then back up a bit. I decided that it would be far easier just to wire up a pair of 6L6GC's so I gave up on the big bunch of tubes in parallel idea.
I would try the second OPT just to see if that is the issue. Some OPT's just don't like being used at half, or double their rated impedance.
I am known for abusing tubes, and about 10 years ago I got a large box full of 6AQ5's in poor condition. There were over 1000 tubes AFTER I threw out all the broken ones, and ones with less than 7 pins remaining. I cleaned up the remaining tubes and sorted out the tubes that were in good physical shape. I saved those (several hundred) for a future project, but they are still untested used tubes.
Many of the remaining tubes had corroded pins that would break off when inserted into a socket, so I tossed those that had pitted pins, and had about 75 tubes that were good enough to experiment on. I did my usual "how many watts can I get out of a pair of these" tests, and found that there is only a watt or two of dissipation between "red spot on the plate", and "hole in the glass"! The 6AQ5 usually red plates in a small spot, and the glass will soften in that area. Long term use in this region will cause the vacuum to suck the glass inward until there is a hole.
Granted this was about 10 years ago, so I don't remember the exact details, but I made a breadboard with 10 or 12 6AQ5's wired up in push pull. I tinkered with it for a while, and eventually grew frustrated with trying to match up 10 or 12 used tubes well enough to keep one or two from red plating. The thing did scream, and sounded rather unique when it worked, but broken pins and trashed sockets from digging out the broken pins eventually convinced me to throw the entire mess into the trash.
It did put out well over 50 watts, more like 75 at the onset of nuclear meltdown, which proves that 4 tubes should be easy. I don't remember the driver tube I used at the time, but it was almost certainly one of the computer tube variants of the 12AU7 since I have a similar big box full of several different ones. Probably a 5963, but could have been 5965, 6463, 7044, or 7119.
I have several test OPT's that I configure for different loads by using 8 ohm loads on the 16 ohm tap, and all testing is done with a variable power supply. I just turn it up till it glows, then back up a bit. I decided that it would be far easier just to wire up a pair of 6L6GC's so I gave up on the big bunch of tubes in parallel idea.
I would try the second OPT just to see if that is the issue. Some OPT's just don't like being used at half, or double their rated impedance.
the howler
interesting stuff guys.....and many thanx for the replies.....but.....I'm still convinced 18 watts is 18 watts though.....perhaps some of the silver mica caps I used were rated 250v Russian and I didn,t have the right values...eg where there is 470pf's I used 430's so I used it in the 560 spot as well .....I used a 4.7nf in the spot where 3.3nf was supposed to go....it was all I had....I figured it wouldn't make too much of a difference would it?....would it ?
interesting stuff guys.....and many thanx for the replies.....but.....I'm still convinced 18 watts is 18 watts though.....perhaps some of the silver mica caps I used were rated 250v Russian and I didn,t have the right values...eg where there is 470pf's I used 430's so I used it in the 560 spot as well .....I used a 4.7nf in the spot where 3.3nf was supposed to go....it was all I had....I figured it wouldn't make too much of a difference would it?....would it ?
the howler
one of the things about it is that the higher frequencies are more pronounced.....caps?
I suppose what I'm really looking for is anyone knows how to tweak it so it delivers the goods......or maybe a better schematic..
one of the things about it is that the higher frequencies are more pronounced.....caps?
I suppose what I'm really looking for is anyone knows how to tweak it so it delivers the goods......or maybe a better schematic..
What exactly did you do wrt cathode resistors on the output tubes? The schematic shows a shared 150R 2W resistor shared by the two output tubes. If you now have four output tubes sharing the same 150R they will run very cold, which could account for your low volume and too clean sound. The red plating tube could be due to very poor matching and uneven current draw, so you could consider going to individual cathode resistors which would allow you to bias the tubes evenly...
yes I'm thinking its just a bad matchup,...2 x rca,1 x Sylvania,1 x chief brand ....all were sold as NOS......but maybe not,i have no tester.thing is they were only $2.00 ea.....in regards to the cathode resistors,i put a 150/5watt to each pair but to my ears despite 1 red plater it dose sound a little "cold" and "farty"... other than that its fairly quiet,no oscillation or hum.....got me stumped
another thing I did was make an adaptor to go 7pin to 9 and then plug a 12ax7.....I got that hiss you get when you turn up loud (white noise) but volume was still the same so it seemed the 6j6 was effective....still stumped
Start by measuring the voltage drop across your cathode resistors and calculate the dissipation for each pair, that should at least give you an idea how hot or cold your output stage is running...
mmmmmm...plate dissipation for 6aq5 is 12watts max...I am currently running a total of 10 watts per side, plate dissipation of 83.3 % ...cathode dc ma is 80 and plate current is 37.8 dcma....I'm beginning to think the problems further up the line....might have to check those cheap ruski silver mica's.....
the howler
isn't it funny how fixing one issue brings on another.......I found the fault ....it was a bad 1 meg pot,it was new too ,but now I have distortion,....possibly 2nd or3rd order,i don't know if I've got that right?when I hit high notes a second lower harmonic comes into play..almost as loud as the 1st note......
feels like its in the preamp stage, there at low volumes as well......any idea's ?
when turned up the volume is massive .....easy 18watt +
almost there .....just gotta get the cleans coming through now
check out the link on page one ,1st post for schematics....cheers
any help is appreciated....and thanx to those who have made suggestions so far....
isn't it funny how fixing one issue brings on another.......I found the fault ....it was a bad 1 meg pot,it was new too ,but now I have distortion,....possibly 2nd or3rd order,i don't know if I've got that right?when I hit high notes a second lower harmonic comes into play..almost as loud as the 1st note......
feels like its in the preamp stage, there at low volumes as well......any idea's ?
when turned up the volume is massive .....easy 18watt +
almost there .....just gotta get the cleans coming through now
check out the link on page one ,1st post for schematics....cheers
any help is appreciated....and thanx to those who have made suggestions so far....
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