Hey, I tried something that I thought might be stupid, I put a 8ohm dummy on the other of the two free output jacks while the speaker was in the white jack (8 ohm @ 2.5k primary) and the amp stabilised. I didn't wanna try for too long as I don't necessarily understand if this is good for the ouput tranny.
Does this in anyway help to understand what is causing the oscillation?
old thread
Moderators: pompeiisneaks, Colossal
yippee!
Completely removed the negative feedback wire (orange) from 125ESE to the 22k resistor and the oscillation is gone, yippee!
Is it so that I actually wired a positive feedback loop and need to reverse something to get a negative feedback loop?
Is it so that I actually wired a positive feedback loop and need to reverse something to get a negative feedback loop?
Brightness.
Like some suspected this amp became very dark with Cannabis Rex.
I am about to try some brightness mods for this, these are the ones I have found/thought, what do you recommend?
- Changing the first cathode bypass cap to 0.68uF.
- Adding a 0.01uF cap to volume pot to brighten the low volume clean sound.
- Adding a 0.1uF cap to second cathode.
- Changing 0.022uF PIO coupling caps to Mallory 150's.
- Take off NFB entirely.
- Add small capacitance fast caps parallel to the electrolytic power filter caps.
The amp has a lot of bass response at the moment, I can afford to lose some if it will help to drive enough highs to the Cannabis Rex.
At the moment resistors are as in schematic. First cathode cap is 22uF electrolytic and the power amp cathode cap is 47uF. All filter caps are 22uF.
I am still having the 6N1P as the preamp tube. I was told its close to 12AX7 but it seems that its closer to 6DJ8 instead. Maybe that is cutting highs too?
Boosting input hard with a pedal makes the bass notes sound like there was a problem with the cable, like cutting the signal, is this blocking distortion? No problem at normal signal levels.
I am about to try some brightness mods for this, these are the ones I have found/thought, what do you recommend?
- Changing the first cathode bypass cap to 0.68uF.
- Adding a 0.01uF cap to volume pot to brighten the low volume clean sound.
- Adding a 0.1uF cap to second cathode.
- Changing 0.022uF PIO coupling caps to Mallory 150's.
- Take off NFB entirely.
- Add small capacitance fast caps parallel to the electrolytic power filter caps.
The amp has a lot of bass response at the moment, I can afford to lose some if it will help to drive enough highs to the Cannabis Rex.
At the moment resistors are as in schematic. First cathode cap is 22uF electrolytic and the power amp cathode cap is 47uF. All filter caps are 22uF.
I am still having the 6N1P as the preamp tube. I was told its close to 12AX7 but it seems that its closer to 6DJ8 instead. Maybe that is cutting highs too?
Boosting input hard with a pedal makes the bass notes sound like there was a problem with the cable, like cutting the signal, is this blocking distortion? No problem at normal signal levels.
Re: Brightness.
Use the largest non-electrolytic you have in the range 1u-2.2u.utervo wrote:Like some suspected this amp became very dark with Cannabis Rex.
I am about to try some brightness mods for this, these are the ones I have found/thought, what do you recommend?
- Changing the first cathode bypass cap to 0.68uF..
Probably too high, I'd try no larger than 500pF.- Adding a 0.01uF cap to volume pot to brighten the low volume clean sound.
This will have a "presence" effect if the NFB loop is still in place so some experimentation will be needed to narrow down a value. Make it switchable if possible.- Adding a 0.1uF cap to second cathode.
I don't care for PIOs in guitar amps, YMMV.- Changing 0.022uF PIO coupling caps to Mallory 150's.
This will interact with the value chosen above so again some experimentation or switchability (presence control ?) may help you decide what you like.- Take off NFB entirely.
The difference here will be small.- Add small capacitance fast caps parallel to the electrolytic power filter caps.
Which scheme are you using ?The amp has a lot of bass response at the moment, I can afford to lose some if it will help to drive enough highs to the Cannabis Rex.
At the moment resistors are as in schematic. First cathode cap is 22uF electrolytic and the power amp cathode cap is 47uF. All filter caps are 22uF.
The 5F1 schematic I have shows no cathode caps except for the output tube.
http://www.el34world.com/charts/Schemat ... _schem.pdf
Compare what you have to the later "CBS" Champ with a tone stack.
http://www.el34world.com/charts/Schemat ... mp_cbs.pdf
Mine has decent highs without being overly bright.
Your speaker may be just to dark for your taste ;->
rd
Re: old thread
Although the published 5F1 schematic shows no bypass caps on the preamps, every one I've ever seen has 25uF on the first triode. I think the simplest fix would be to try. 01 coupling caps, instead of .02.
Re: old thread
Removing the low end with a hi-pass filter doesn't sound as bright as a shelving filter. I'd go more on the shelving to achieve more brightness:
680n-1µF on the first cathode and a 100-470p bright cap on the volume.
680n-1µF on the first cathode and a 100-470p bright cap on the volume.
Re: old thread
I found there's little to make a 5F1 both brighter and as good or better circuit-wise. Really, depending on your expectations you might just find yourself chasing your tail, though it's good for learning, especially that hard lesson that there's no free lunch. A bright cap just helps at low volume but most people play their champs turned up. Best place to fight the darkness is at the input or output - single coils, wah as treble boost, boost, GE-7, etc. Best solution and hardest is the speaker. I wasted some money on trying to find a modern 8" that sounded good but nada yet and I'm limited to 3.5" height for my homemade cab. Through an old '60s Jensen 10 in an external cab it sounded absolutely perfect. Sounds good through a G12H30 too. I still need to try the modern Jensen P8R and the cheap Weber everyone likes and the WGS 8 - waiting till I got money to just throw in the trash. My advice to champ builders is don't build for an 8, you are too limited in choices.
Re: old thread
Oh yeh, if you are using a real dinky OT (the real cheap Triode one) you'll get mud and mud is dark. I like the Allen OT a lot in 5F1s - burly but not hifi so still sounds like a tweed champ, and you get 4 & 8 ohm taps.
Re: old thread
Thanks for all the replies.
The output tranny is Hammond 125ESE, guitar is strat with Lollar Special S pickups.
Might be that I back in the day chose the wrong combination of circuit and speaker for highs.
Anyone know a bright circuit that would work with the Cannabis Rex that is close to 5f1? Anyone know any amp that works with CR?
The output tranny is Hammond 125ESE, guitar is strat with Lollar Special S pickups.
Might be that I back in the day chose the wrong combination of circuit and speaker for highs.
Anyone know a bright circuit that would work with the Cannabis Rex that is close to 5f1? Anyone know any amp that works with CR?
Re: old thread
http://www.youtube.com/watch?v=1Rf9SOfAy1E
This seems to have enough of brightness with CR speaker.
The schematic of Blues Jr. is too complicated for me to understand where the brightness comes compared to 5F1.
I wonder if there are some things to do with cabin? I have a solid pine cabin, quite thin walls, solid pine baffle, speaker is mounted through, completely open back.
This seems to have enough of brightness with CR speaker.
The schematic of Blues Jr. is too complicated for me to understand where the brightness comes compared to 5F1.
I wonder if there are some things to do with cabin? I have a solid pine cabin, quite thin walls, solid pine baffle, speaker is mounted through, completely open back.
Re: old thread
Have you tried what we suggested?
Re: old thread
No not yet, will try after holidays.
Will change in the order, first cathode cap, volume bright cap, coupling caps.
Will change in the order, first cathode cap, volume bright cap, coupling caps.
Re: old thread
Didn't see anyone else mention it so sorry if they did. It's the 6N2P that's the same characteristic as a 12AX7.
Re: old thread
No it's 6n1p, which I thought was the same but it isn't!