We discussed many options, but the more scientific and objective we tried to be, the more complicated the task became.
Eventually, we came back to the simplest criterion of all -- which one would you actually build?
So, anyone who wants may enter a design. A schematic is required, photos would be nice, and sound clips would be even nicer, but are not required.
We'll post all the entrants in a poll, and simply ask people to vote for which design they themselves would actually build.
Ha..ha..ah.... good one Printer2.
I finally found the article. It is Amplifier Response Stability & all That by John Moyle.
His treatment was for a transformer peak that caused a potential oscillation due to the level of feedback he was using. I'm not using feedback, but the technique is still applicable.
I finally found the article. It is Amplifier Response Stability & all That by John Moyle.
His treatment was for a transformer peak that caused a potential oscillation due to the level of feedback he was using. I'm not using feedback, but the technique is still applicable.
So by this I understand people presenting designs must vote theirs because it's obvious which one they DID build first.
I've spotted a flaw here. No need to thank me. This voting system must be improved, we have plenty of time to do that. Also, just one vote per person? No podium? No 2nd or 3rd?
Our amp is working it is a bit like a like a single channel Bassman without the cathode follower in front of the tone stack, and lower power like a Princeton. No power amp feedback, gain is very high, seems to work fine but needs some fine tuning. Running a 7025 in the first stage and 5751 in the diff amp driver. 5751 has excellent pair matching.
I doubt that mine still meets the $100 limit. "Feature-Creep" has increased the complexity considerably. (5 gain stages and a full tone stack) That said, I can swap tubes (6HG8, 6KE8, 6EA8, etc) then tweak some knobs, and it still sounds very much the same. Both the Soviet and US tubes work fine.
The worst thing is that the gain varies by over 20% with tubes selected due to the low bias of the pentode G2 in the first stage.
I'll have to go back and do a cost analysis again, them trim some functionality to cut cost.
The worst thing is that the gain varies by over 20% with tubes selected due to the low bias of the pentode G2 in the first stage.
I'll have to go back and do a cost analysis again, them trim some functionality to cut cost.
Thanks bst,
I'm in & have mine designed & priced already, total cost around $80.00 not including speaker or box, I may add a couple more things yet?
I designed for a lot of adjustable harmonic content, from clean to mean.
I'm calling it "THUNDER FROM DOWN UNDER".
I will supply a sound clip as well as pictures etc.
Time to build the little sucker & create some smoke ha!
Cheers
I'm in & have mine designed & priced already, total cost around $80.00 not including speaker or box, I may add a couple more things yet?
I designed for a lot of adjustable harmonic content, from clean to mean.
I'm calling it "THUNDER FROM DOWN UNDER".
I will supply a sound clip as well as pictures etc.
Time to build the little sucker & create some smoke ha!
Cheers
It will be interesting to see how people approach the distortion aspect.
I've got mine to the point where one can dial the power from below 0.1W up to 3W with the distortion staying at about the same level, although the noise floor comes up with power.
First is distortion mode at 0.1W, second is same at 3W before clipping and the third is in clean mode at 1W.
I've got mine to the point where one can dial the power from below 0.1W up to 3W with the distortion staying at about the same level, although the noise floor comes up with power.
First is distortion mode at 0.1W, second is same at 3W before clipping and the third is in clean mode at 1W.
Attachments
Hmmm, blowing things up fast here. Thought we lost a 5881 but it was actually a cap to the grid that turned into an 8K resistor. It sounded a bit odd on the first try, lots of gain and distortion difficult to get a clean sound. I suspected oscillation which I confirmed on the bench with a guitar as input and dummy/speaker load - about 100KHz. Then one 5881 red plated and I shut it down. Suspected the tube for a while then measured with the tubes out and found about 200V on the grid due to the bad cap. Measured 200 mA in the tube that red plated.
Changed the cap, pulled the driver tube so there'd be no chance of oscillation, so I thought, and was too lazy to hook up a the dummy load just to check the bias - big mistake. I believe that one output tube went into oscillation and arced pin 3 to 2 then held an 1/8" wide arc until I hit the power switch. Nearly desoldered pin 3 and fried one of the 100 ohm heater to ground resistors. Fixed it all tested again with a dummy load and it biased up fine - one step forward 2 steps back! The transformer is rated for 200mA on the HV so it states.
I have a good supply of NOS Allen Bradley carbon comp resistors that I'm using, not that I like them. I've been checking values before using them and many 5% are 10% off. These were given to me when a friend emptied out his dad's electronics lab that had not been used in at least 15 years maybe 20-25. I used a string of 2W resistors for the cathode bias and one marked 100 ohms measured 180 after the overload.
I worked a good amount with tubes as a very young kid, shifted to SS by fourth grade, but continued with tube repairs for a while longer. Never saw an arc like that or an interstage cap fail like that.
Changed the cap, pulled the driver tube so there'd be no chance of oscillation, so I thought, and was too lazy to hook up a the dummy load just to check the bias - big mistake. I believe that one output tube went into oscillation and arced pin 3 to 2 then held an 1/8" wide arc until I hit the power switch. Nearly desoldered pin 3 and fried one of the 100 ohm heater to ground resistors. Fixed it all tested again with a dummy load and it biased up fine - one step forward 2 steps back! The transformer is rated for 200mA on the HV so it states.
I have a good supply of NOS Allen Bradley carbon comp resistors that I'm using, not that I like them. I've been checking values before using them and many 5% are 10% off. These were given to me when a friend emptied out his dad's electronics lab that had not been used in at least 15 years maybe 20-25. I used a string of 2W resistors for the cathode bias and one marked 100 ohms measured 180 after the overload.
I worked a good amount with tubes as a very young kid, shifted to SS by fourth grade, but continued with tube repairs for a while longer. Never saw an arc like that or an interstage cap fail like that.
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Wow, guess Tubelab was wrong, this thread is a success. So many people building amps. Feeling a bit guilty because of my latest trolling.
Gonna shut my mouth. If only the rules would let me in. Damn.
Come on in, nothing saying we can't throw you out later.Wow, guess Tubelab was wrong, this thread is a success. So many people building amps. Feeling a bit guilty because of my latest trolling.
Gonna shut my mouth. If only the rules would let me in. Damn.
Pulled the output tubes and still had the oscillation. Turning the mid control on the tone stack killed the oscillation. Moved a ground off the mid pot to a better position and it is gone. Added a gain switch to simulate the 1 vs. 2 input on a Fender and now have excellent clean or distorted tones. The tubes all survived the upsets.
I noticed your fundamental frequency is 1kHz, you may find it useful for a guitar amp to set your fundamental test frequency at around 400Hz.
Many will not agree but 1kHz is the upper limit for guitar note frequencies. Above this all the frequencies are Harmonics--Overtones & not fundamental frequencies of the notes played.
I find it useful to test at around 400Hz.
I have attached a fret note frequency chart to have a look at & you'll see what I mean.
For Audio 1kHz is the test std but for guitar amps I don't agree with that, just my thought's & it may help out.
Cheers
