Tube parts are expensive here in NZ - especially transformers.
Here is my latest effort to be thrifty.
Tube choice: I have a bunch of each of these. Just had to figure out how to make them work 😕. Free is thrifty!
PSU: Wall wart for 12vac 2A ($20) 🙁
10v EI transformer from another wall wart on sale $1. 🙂
All filter caps from disposable cameras - no cost 🙂
Mosfet in VVR - 20 from ebay 25cents each (and they worked 😀)
Output transformer: 5w 100v line. Available locally but ebay to the rescue 10 pieces for $1.25 😀
Tone stack: Single knob big muff type - useful over full rotation, unlike TMB.
As few knobs and switches as possible - hence ganged volume.
How does it sound? I spend too much time rewiring my guitars and amps and not enough practicing my playing 😱
This amp makes me want to play more
All for fun
JimG
Here is my latest effort to be thrifty.
Tube choice: I have a bunch of each of these. Just had to figure out how to make them work 😕. Free is thrifty!
PSU: Wall wart for 12vac 2A ($20) 🙁
10v EI transformer from another wall wart on sale $1. 🙂
All filter caps from disposable cameras - no cost 🙂
Mosfet in VVR - 20 from ebay 25cents each (and they worked 😀)
Output transformer: 5w 100v line. Available locally but ebay to the rescue 10 pieces for $1.25 😀
Tone stack: Single knob big muff type - useful over full rotation, unlike TMB.
As few knobs and switches as possible - hence ganged volume.
How does it sound? I spend too much time rewiring my guitars and amps and not enough practicing my playing 😱
This amp makes me want to play more
All for fun
JimG
Very cool... See you are at it again! But why use both LEDs on the first stage? Do you have very high output pickups?
Hi again jazbo.
Several reasons for using the two LED's with the 6BL8 triode.
This is a medium mu triode - not a lot of gain and consumes a (relatively) lot of current to get it.
This back-to-back type of PSU can give the B+ needed but it has a very high impedance;
this is good for beginners and the clumsy (like me) - if you touch the wrong wire it will belt you hard but less likely to do serious damage and will teach you to be much more careful around bigger amps.
The down side is that even a few mA more current draw will drag down the B+ significantly.
(When the power amp here goes into clipping the B+ drops by 40v)
So I choose an operating point (bias) from the anode curves and fix it with LED bias. This gives me a known which won't change as I go on developing the rest of the amp. In this case I decided on just under 6v.
Cheers
JimG
Several reasons for using the two LED's with the 6BL8 triode.
This is a medium mu triode - not a lot of gain and consumes a (relatively) lot of current to get it.
This back-to-back type of PSU can give the B+ needed but it has a very high impedance;
this is good for beginners and the clumsy (like me) - if you touch the wrong wire it will belt you hard but less likely to do serious damage and will teach you to be much more careful around bigger amps.
The down side is that even a few mA more current draw will drag down the B+ significantly.
(When the power amp here goes into clipping the B+ drops by 40v)
So I choose an operating point (bias) from the anode curves and fix it with LED bias. This gives me a known which won't change as I go on developing the rest of the amp. In this case I decided on just under 6v.
Cheers
JimG
Sorry, neither my playing nor my technology will allow that.
So a few words: (or cliches)
Chime and top boost - never use a 22n cap when 10n will do.
Tonestack - my guitar (peavey S type) has 8 pick up combinations. I've never heard such clear difference between the different switch positions in twenty years of ownership.
Sustain like I've not achieved before...at bedroom volume if necessary with the VVR.
This will be my keeper (once I've added a few more knobs and switches 😀 )
So a few words: (or cliches)
Chime and top boost - never use a 22n cap when 10n will do.
Tonestack - my guitar (peavey S type) has 8 pick up combinations. I've never heard such clear difference between the different switch positions in twenty years of ownership.
Sustain like I've not achieved before...at bedroom volume if necessary with the VVR.
This will be my keeper (once I've added a few more knobs and switches 😀 )
This has been on the breadboard long enough. Now I'm going to try some 6AQ5 power tubes.
Changes might be:
2 wall warts - one for filaments, one for B+
Change OPT from 5w 100v line trafo (16k anode to anode) to 15w 100v line trafo (8k a-a)
Adjust Rk to taste
Changes might be:
2 wall warts - one for filaments, one for B+
Change OPT from 5w 100v line trafo (16k anode to anode) to 15w 100v line trafo (8k a-a)
Adjust Rk to taste
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