This is the first that I have heard of it too, but several have pointed out that it didn't jive with Edcors long delivery times. Aug 15 was rather tight for me especially with all the "stuff" going on in my life now.
Have you looked our political "leaders" and corporate or banking CEO's lately?
I also stated that I could build a better "minimalist" guitar amp that could be sold in kit form for $69 too. Maybe I'll look into that too.
Speaking of stuff going on, my mother in law has been fighting cancer for 4 years. This has resulted in my wife being gone more than she was here. The moment that we all knew would come has arrived. While I was typing this post Sherri called to say that her mother has passed away. I'll be leaving town for an uncertain period of time and I'll get back to this when I return.
I think that is what bugged us. The price was no problem if you get something a little more than a toy.
Had to replace rear brakes on the truck today, Yesterday I don't even remember but I know I was not in the garage. Tomorrow I promised to do a cook-out and go to "Jonesboro Days"
I've busted the $100 limit and pushed back below it by looking for cheaper sources.
I pretty much have given up on the 1W SE amp as it just doesn't have enough Umph for the cheap speakers I want to use.
I'm up to amp design #5 or #6 running three tubes with PP output getting around 2W. I need to settle on a design soon if I'm going to actually build a finished amp.
If I only breadboard it and make an MP3, does it count? Still waiting on back-ordered transformers. They shipped Wednesday but didn't make it before the holiday so I don't expect to see them till Tuesday.
Current design is at $99+change. $99.99 is less than $100 so it is in.
I've busted the $100 limit and pushed back below it by looking for cheaper sources.
I pretty much have given up on the 1W SE amp as it just doesn't have enough Umph for the cheap speakers I want to use.
I'm up to amp design #5 or #6 running three tubes with PP output getting around 2W. I need to settle on a design soon if I'm going to actually build a finished amp.
If I only breadboard it and make an MP3, does it count? Still waiting on back-ordered transformers. They shipped Wednesday but didn't make it before the holiday so I don't expect to see them till Tuesday.
Current design is at $99+change. $99.99 is less than $100 so it is in.
Attachments
Note the change in deadline date.
I gave up on my 5 tube design using old radio tubes. I tried it with a 6 inch speaker and it is nowhere near loud enough, and doesn't have enough gain to scream. I think that the power amp might do OK on 150 volts of B+ but the preamp needs more voltage. I decided to connect the whole thing up to a variable power supply and crank it up. It started sounding pretty good at the point it blew up, which was about 300 volts. One of the 6CU5's expired with no warning, no glow, no sparks, no emission either.
The next design will be capable of using several different output tubes and run them at 320 volts. One possibility is a 6BQ6GT sized sweep tube. That should rock!
I got a bunch of real cheap transformers to test as P-P OPT's, but that will have to wait until I return.
The post about the mid august deadline has been there since at least two weeks ago. I think I saw it when I returned from Key West about the 12th.
What it does not say is how we are supposed to post our demo, when it should be posted to be there in time for voting, etc.
I figure the demo should be on line by Aug 5th to have time for people to judge it.
The recommended operating point of the tubes I'm using is 220V, so I started at 250V and cranked it up till it was beyond the maximum rating (300V). At 325 they seem to be holding their own with no indication of red plating. I've tried two manufacturers and a Russian equivalent and all work fine at 325, so I'll probably crank them till something gives.
My biggest problem is my tendency to keep tweaking the operating points to see how it effects the sound and harmonic spectrum.
What it does not say is how we are supposed to post our demo, when it should be posted to be there in time for voting, etc.
I figure the demo should be on line by Aug 5th to have time for people to judge it.
The recommended operating point of the tubes I'm using is 220V, so I started at 250V and cranked it up till it was beyond the maximum rating (300V). At 325 they seem to be holding their own with no indication of red plating. I've tried two manufacturers and a Russian equivalent and all work fine at 325, so I'll probably crank them till something gives.
My biggest problem is my tendency to keep tweaking the operating points to see how it effects the sound and harmonic spectrum.
Glad to see another mess of wires. I am not as embarrassed by my picture now.
350V and 375V were not very interesting after 20 minutes so I cranked it up a bit.
Seems applying 410V to tubes designed for 300V max, along with 16W plate dissipation on a 4W rated tube may result in faulty operation.
Although, after I killed power and let it set for a while and then powered it back up at 250 It seemed to run fine. They never did red plate, but one tube did start flashing.
Seems applying 410V to tubes designed for 300V max, along with 16W plate dissipation on a 4W rated tube may result in faulty operation.
Although, after I killed power and let it set for a while and then powered it back up at 250 It seemed to run fine. They never did red plate, but one tube did start flashing.
Yes it has, but the one that moves the deadline out to October just appeared today. There was a question about the rules to which I replyed that they had been discussed, but never clearly listed. SO.....see post #419.
The deadline change is good since I bought a plane ticket to Pittsburgh this afternoon for a tomorrow morning flight with no firm return date. That will be determined by how loud the boss yells when he finds out I'm not there Tuesday morning.
Sorry about the confusion concerning the completion date. I put this at the end of my post #332 --
-- and within the hour, I was quoted and had agreement:
If there are any more significant changes, I'll put them in a bulleted separate post, in bold caps, so they don't get lost in the shuffle.
**********************************************
In other news, I have my pentode preamp section up and running. It's working quite well with several tubes, including the 12SJ7 and 6AU6. It looks best on the scope, though, with an old type 77 pre-octal tube. Maybe I'll wind up with an amp that's REALLY retro, and only sounds good with a pre-WWII lap-steel guitar...
-- and within the hour, I was quoted and had agreement:
If there are any more significant changes, I'll put them in a bulleted separate post, in bold caps, so they don't get lost in the shuffle.
**********************************************
In other news, I have my pentode preamp section up and running. It's working quite well with several tubes, including the 12SJ7 and 6AU6. It looks best on the scope, though, with an old type 77 pre-octal tube. Maybe I'll wind up with an amp that's REALLY retro, and only sounds good with a pre-WWII lap-steel guitar...
Last edited:
George, I'm sorry to hear of your sad news. Our family has also lost several of its elders within the past six months. Even when you know the time is approaching, the passing of a loved one is still difficult.
My wife and I send condolences to you and Sherri, and wish you strength and inner peace in the days and weeks to come.
My wife and I send condolences to you and Sherri, and wish you strength and inner peace in the days and weeks to come.
I had to go back and re-read some posts. I miss-read October as August...Duh!
Lots of time to play then.
I'm playing with Pentode/Triode combo tubes. I started collecting some I thought should be good for low power output stages some six months ago. Turns out the Soviet tubes I wanted to play with have a direct western replacement. I thought they should be good for something in the 2-4W range.
The amp challenge proved to be the impetus to actually do something with them.
In addition to them I decided to stay with Pentode/Triode combination tubes for the preamp and driver stages.
It should be easy to figure out what I'm playing with.
Output 6F4P/6DX8/6DQ8?
Input stages 6GH8/6LX8/6BL8/6U8/6KE8...
What is with the EIA base designations 9AE and 9DC?
They are the same pin out!
Lots of time to play then.
I'm playing with Pentode/Triode combo tubes. I started collecting some I thought should be good for low power output stages some six months ago. Turns out the Soviet tubes I wanted to play with have a direct western replacement. I thought they should be good for something in the 2-4W range.
The amp challenge proved to be the impetus to actually do something with them.
In addition to them I decided to stay with Pentode/Triode combination tubes for the preamp and driver stages.
It should be easy to figure out what I'm playing with.
Output 6F4P/6DX8/6DQ8?
Input stages 6GH8/6LX8/6BL8/6U8/6KE8...
What is with the EIA base designations 9AE and 9DC?
They are the same pin out!
Yeah, those 6AU6's seem like they could have a lot of potential, inexpensive and common. Would be nice to see an amp show up those way too expensive EF86's in all those Vox's, Dr. Z's, 18 Watt's. Sort of the little guy kicking the big guy in the shins. I guess you could tell which tube I would like to see in your amp.In other news, I have my pentode preamp section up and running. It's working quite well with several tubes, including the 12SJ7 and 6AU6. It looks best on the scope, though, with an old type 77 pre-octal tube. Maybe I'll wind up with an amp that's REALLY retro, and only sounds good with a pre-WWII lap-steel guitar...
Wooaaahahahaha! that's too funny...
You know how to tell if a stage is levelled ?
When the drummer drool from both side of the mouth.
I had a dilemma. What is it to be, a bedroom amp or a, well louder bedroom amp? The self-split worked well enough and was plenty loud either distorted or through an efficient guitar speaker. But using it with a measly little 8" I wanted a little more clean volume. I wanted to build the low power circuit for this contest but ultimately I want the higher power circuit. I did not want to do two builds so I have been delaying putting solder to part.
Well I think I came up with a way of having my cake and eating it too. Mind you to get the higher power will I have to use a bit of SS boost because I will loose a gain stage for the cathodyne PI. Now just to figure out how to do it with just one switch.
Well I think I came up with a way of having my cake and eating it too. Mind you to get the higher power will I have to use a bit of SS boost because I will loose a gain stage for the cathodyne PI. Now just to figure out how to do it with just one switch.
I'm still plagued by oscillations.
The amp has no GFB.
I suspect either layout (breadboard) or power supply feedback. When it happens I get the signal all the way back to the grid of the first tube.
Breaking the signal path at the output of the tone stack or any point after that stops the oscillation, but disconnecting the output of the first stage to the tone stack does not, but does reduce it.
It's really frustrating
The amp has no GFB.
I suspect either layout (breadboard) or power supply feedback. When it happens I get the signal all the way back to the grid of the first tube.
Breaking the signal path at the output of the tone stack or any point after that stops the oscillation, but disconnecting the output of the first stage to the tone stack does not, but does reduce it.
It's really frustrating
Attachments
Have you tried moving the feed for R3 back to V1?
I take it is high freq oscillation? Do you know the frequency?
You should suspect grounding also, keep the higher current output
grounding independent of the input stage grounding.
Did you consider having your gain control in front of U2? Not that it
would help the oscillation.
I take it those are triode and pentode sections of the 6DX8s, I would
think that it would be better to keep the triode sections closer to the
output stage since there is likely some leakage from the pentode to
the triode so the lower the gain the better. I'm thinking swap U1 and
U2.
If this is the issue, you are getting positive feedback through the leakage,
you could try swapping the drive for R31 and R32 to make it closer to
negative feedback. Still I think the previous solution is better - if it
works but you could try either or both.
I take it is high freq oscillation? Do you know the frequency?
You should suspect grounding also, keep the higher current output
grounding independent of the input stage grounding.
Did you consider having your gain control in front of U2? Not that it
would help the oscillation.
I take it those are triode and pentode sections of the 6DX8s, I would
think that it would be better to keep the triode sections closer to the
output stage since there is likely some leakage from the pentode to
the triode so the lower the gain the better. I'm thinking swap U1 and
U2.
If this is the issue, you are getting positive feedback through the leakage,
you could try swapping the drive for R31 and R32 to make it closer to
negative feedback. Still I think the previous solution is better - if it
works but you could try either or both.
Last edited:
I'm still plagued by oscillations.
The amp has no GFB.
I suspect either layout (breadboard) or power supply feedback. When it happens I get the signal all the way back to the grid of the first tube.
Breaking the signal path at the output of the tone stack or any point after that stops the oscillation, but disconnecting the output of the first stage to the tone stack does not, but does reduce it.
It's really frustrating
Not sure if this would be helpful or not, can't see it hurting though. How about running without the first tube but with the tone stack and then shorting out each capacitor or resistor one at a time. It should not effect the circuit but then again you should not be getting feedback.
Boy I can not wait to hear your amp, looks like it has a lot going for it.
Got the power amp working and am getting 12.5W clean with 6V6s types (7408) and no feedback, 15W with a touch of clipping. Frequency response is 35 - 60KHz -3dB points and I made no effort to use large coupling caps so not sure how much of the low end limit is the transformer. I'm using the output transformer from this gutted integrated amp but also have one chosen for the final design.
Last edited: