Home › Forums › Design and Building › Effects Design and Construction › Following 2 Power Tube Amp Design
- This topic has 52 replies, 6 voices, and was last updated July 16, 2013 at 5:25 am by Andy.
February 16, 2011 at 12:57 pm #5195
Hello I am glad I found this forum and site! I had just recently read the book and have bought all the parts to build the amp as well, but now I see the design has been changed to have only 1 power tube. Has anyone built the original design with 2 power tubes? Is there any reason that I should not go ahead and build the original version? I liked the idea of have 2 power tubes and being able to remove them and swap them out. Any help or comments would be greatly appreciated!February 17, 2011 at 2:44 am #5336
The design changed because there was not a real tonal advantage to the 2 power tube layout and you could only use 2 6v6s anyway. 2-6v6s get you to about 8 watts of power in the 2Stroke, same as 1-6L6. With the single power tube layout you still can change to all the other workable tubes:6L6, 6V6, EL34, KT-66, etc. On the other hand, there is no real down side (other than more parts) to the 2 tube version.February 17, 2011 at 2:50 am #5337
Thanks for the reply. I was fairly sure this was the case. I am considering still trying the 2 tube design, but I will give it more consideration before starting. Have you had experience with both versions?
A second question, I am thinking of putting an AlNiCo blue in the cabinet. Any other suggestions on good speakers? By the way I love your combo idea using the marshall style cab !!! Great idea.February 17, 2011 at 4:08 am #5338djroge1Participant
I use one 12″ Eminence Wizard speaker and think it sounds great.February 17, 2011 at 6:14 am #5339
I’ve not tried an Alnico Blue in a 2Stroke, but I’ll bet it will sound great. I did test different speakers and speaker configurations with a 2Stroke and found the 8″/10″ combo to be a little more complex sounding than one 12″, but the 1-12 was punchy and seemed to cut through well.March 3, 2011 at 2:43 pm #5343
So I am done with the amp…well sorta…
Its seems to be somewhat working but no guitar sound!
The power is fine, and the tubes seem to work, at least they are lighting up. I have not checked the voltages while its on, yet. I am a bit nervous to try it yet!
Anyway I just get a loud hum from the speaker and the volume knob seems to have no effect. So I have two questions….
1. What is the correct wiring of the input jack> Its seems odd to me like we are wiring all the 3 tabs together? There is a 1M resistor running from 3 to 1 and and wire from 2 to 1? then 1 is grounded and sent to the mini switch as well as to the 1.5K resistor? Is all of that correct? I feel like that is where my problem is but not sure.
2. Well just wondering if I had some wires too long, say like the input wires from the jack to the board, would that make it motorboat? Is that the loud hum I hear? Any help would be awesome!!March 4, 2011 at 12:17 am #5344AndyKeymaster
For #2, that could be a source of noise but likely not what you hear. I would not worry too much about that right now, at least not until you have guitar signal coming out.
For #1, the input wiring is a source of confusion because it doesnt make sense on the surface. It sounds like what you have is right. THe 1M resistor is setting the input Impedance and does go to ground. Your guitar input is going through 3 (in your description, Tip is more accurate) through the 68K to pin 2 on the 1st tube stage.
The way the boost switch works is that it switches between just the 1.5K resistor to ground, or the 25u, or the .47u in parallel with the 1.5K to ground. But the 1.5K goes to ground, this is from the tube cathode and is part of the biasing.
You may need to get in there and get some voltages. Be careful!
Its hard to say where to start, Im sure some of the other members will have some thoughts. Personally, I would make sure the voltages are what you expect first. DC first, then AC. You want to make sure to have the right DC power to the tubes, and AC filament power. Make sure the rectifier is supplying the right voltages. Check the power coming off the Power transformer, all that.
Another thing to check is grounding. Its possible that the guitar signal is getting grounded somewhere and not making it though the amp.March 4, 2011 at 4:51 am #5345
Great thanks for the help! I really appreciate it! I have one more somewhat of beginner I am sure question. Well its two part, first would anyone be willing to send a photo of their input jack wiring so I can be sure I have this correct. I am just confused also as the two diagrams for the input jack are different in the book vs. online. So I was thinking an actual photo clearly showing me the connections vs a diagram might be very helpful.
The 2nd is a total beginner question. I am pretty sure I have it right…I have the impedance switch going to positive ( Is this the tip or ground though is my question? ). As of now I have positive as the tip and not the ground.
I just want to say thanks again, this site is awesome and everyone is very helpful! Even for silly question such as mine. I feel like its little things I am not sure of so its nice to be able to find a place to clear them up.March 4, 2011 at 7:59 am #5346AndyKeymaster
I suspect Robin is responding as I type this, but here is my input wiring on my first 2 Stroke (pardon the poor photo and workmanship on this one). You’ll have to trace a bit to see (Robin’s pic is better).
And on second point, you are right. Tip is positive, Sleeve is Ground.March 4, 2011 at 8:37 am #5347
Thanks! This is perfect! I think I might have one wire wrong. Although not sure, I am running from the upper tab to the board, which is the ground I think? I see you have yours running from the middle tab(switch), but again have jumper from the switch to the ground, so that is why I think I have it correct. Well thanks again I cannot thank you all enough for your awesome responses! I hope when I have more experience I can repay some new amp builder!March 4, 2011 at 11:03 pm #5348
Andy’s post has it covered (again). The input jack wiring is the single biggest area of confusion in the 2Stroke layout. Many people have struggled with it. The revised (single power tube) version of the layout is clearer. Check out any Fender Tweed-era chassis layout or schematic for an example of how it’s supposed to be wired up.It sound like you have the input jack tip lug wired to ground so no signal can pass through to pin 2 of V-1. I posted a photo in my 2Stroke photo album of the input jack wiring. Thanks to the creator of this photo, I found it on the web.
Regarding lead length, it’s true that shorter is better, not allowing the signal path to cross back over itself, isolating the heater circuit, etc are all good basic rules. Poor lead dress can lead to hum, hiss, parasitic oscillation and so forth. The 2Stroke can be built to be very quiet (no noise or hum) so if you end up with a noise problem, use the “chop stick” method to push some leads around and see if you can find and resolve the issue. Resolving things like that input jack wiring can result in little ah-ha moments that I think has encouraged a lot of us to continue on with amp building. Good luck with the 2Stroke.March 5, 2011 at 2:40 pm #5349
Thanks again. I have been thinking that I grounded the guitar signal somehow wrong also, but so far I do not see anything wrong. However, I have not had a chance to look at it this week. So hopefully tomorrow will be better! I will keep you both posted. Thanks again for all the help!March 7, 2011 at 5:12 am #5350
Hello everyone. So I am in the middle of checking the voltages. I have a question. So since my amp makes quite a loud hum(buzz) when you turn it on and the volume does nothing to affect this…Is there anyway I can turn on my amp and check voltages without a speaker plugged in the jack?March 7, 2011 at 6:56 am #5351
The short answer is NO, never turn on your amp with no load connected to the OT (unless you want to purchase another OT). You could use a dummmy load instead of a speaker (a coil that dissipates the energy from the OT as heat instead of sound). You can find DIY dummy load coil projects in amp, radio and hifi chat rooms. But, you don’t need to turn the amp on to find the trouble. Using your meter, trace through the circuit, checking for grounds were there should not be one. First check the input jack.March 7, 2011 at 9:02 am #5353
Wait a minute. Do you mean to say that only the shielding is soldered to the 68K resistor from the tip of the input jack? So i use the outer copper braid to run from 68K directly to the #2 pin on V1? I am sure that is my problem if this is so, as of now, I have the 68K wired to the inner conductor and to pin #2 and the outer shield just grounded on the mounting bolt via a grounding star. Wow how did I miss that if I am reading you correctly.
As for continuity if it even matters after my above statement…It was fine up until the V1 side of the 68K resistor, which might now make much more sense!
Again I love this site!
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