Music Electronics Forum - Debugging Your Build

Music Electronics Forum - Debugging Your Build http://music-electronics-forum.com/ en Sat, 21 Nov 2009 02:35:25 GMT vBulletin 60 http://music-electronics-forum.com/images/misc/black/rss.jpg Music Electronics Forum - Debugging Your Build http://music-electronics-forum.com/ Freaky Reverb Hum / Deluxe AA763 http://music-electronics-forum.com/t16205/ Thu, 19 Nov 2009 15:12:43 GMT I built this AA 763 Deluxe Reverb amp that has the Vibrato circuit only and it sounds great until I turn the Reverb up. This chassis is a 5C5 chassis... I built this AA 763 Deluxe Reverb amp that has the Vibrato circuit only and it sounds great until I turn the Reverb up. This chassis is a 5C5 chassis tweed so it's all cramed but it has no hum until I turn the reverb pot and the volume drops and the hum gets loud after about 4. The reverb works but when it starts humming it also starts farting and gets a little crackly. All tubes are fine and I've checked wiring till blue in the face and everything is good. The reverb tranny is by itself on the opposite side of the power,choke and OT. What are some things I can check to find what's causing the hum and drop of volume ? Could be cancellation causing the drop or RF but not sure if that's what it is. ]]> Debugging Your Build Amp Kat http://music-electronics-forum.com/t16205/ Trying layout changes in 5f1 home build http://music-electronics-forum.com/t16120/ Sat, 14 Nov 2009 12:31:22 GMT Hi all. I am new to this forum and new to building. I stumbled on it searching for information about building a 5f1 Champ-like amp and... Hi all.
I am new to this forum and new to building. I stumbled on it searching for information about building a 5f1 Champ-like amp and troubleshooting noises. I am trying to make the amp somewhat smaller with the chassis on the bottom of the cabinet and tubes standing up next to the speaker magnet. But with a Jensen re-issue alnico speaker the 12AX7 tube had to share the side next to the power transformer and the 6V6, 5Y3 and output transformer on the other side. My questions are:

1) I have heard that the 12Ax7 should be as far away from the power transformer as possible. If so, is there any way shield it enough so that it could live right next to it?

2) If you wanted only one input jack how would it be wired? Bridge the 68K resistors or just use 1? Would you still use the 1 Meg resistor to ground?

3) Does it make any difference in the filament voltage if you don't use a pilot lamp?

4) Would the fact that the PT and 5Y3 are on opposite sides of the chassis and require fairly long wires cause problems?

5) Am I an idiot for even trying this? :spin:

Thanks for any advice. ]]> Debugging Your Build HansVG88 http://music-electronics-forum.com/t16120/ annoying noises http://music-electronics-forum.com/t16096/ Fri, 13 Nov 2009 02:08:53 GMT :thumbsdown: i'm getting a sizzle/crackle/popping sound when quickly changing chords or strumming fast/hard. it's as if the amp doesn't like a signal with multiple frequencies. it get's worse if i use a fuzz pedal. the noise sounds like the crackling and popping you here on old records.
it could be a bad speaker but i sure hope not. it's a new weber alnico 10". i've ordered new power tubes but i doubt that's it. otherwise, the tubes that are in it died awfully quick.
i see terms like oscillation, blocking distortion, crossover distortion on here alot and being as paranoid as i am i wonder if i have those symptoms. i'll attach my schematic in case i made an obvious mistake. any suggestions?

Attached Files

Design.pdf (104.2 KB)

]]> Debugging Your Build yunger http://music-electronics-forum.com/t16096/ hummm issues http://music-electronics-forum.com/t16070/ Wed, 11 Nov 2009 15:17:22 GMT I figured I'd move to this forum to get some help.

I've built a 5E3, I used Fender's / Webers layout from parts sourced here and there. Cap's from weber, as are the pot's.
Resistors are from my local electronics supplier.
Tubes are NOS, or used from a Filmosound amp I had started to mod into a 5E3, but I decided I wanted two channels.
Chassis and eyelet board are from ebay.

The layout went well, soldering it was a breeze.

I powered it up, and had some hum, actualy lots.
I swapped tubes, to no avail. the hum seems to disappear when I pull the PI, but not the pre amp tube.

I moved the grounds from the brass plate, to a star ground as follows;
Bias, 1st & filter caps have a shared ground
2nd & 3rd filter caps shared ground.
Ground from tone, Volume and jacks
separate ground from the bypass caps for V1 & 2.
Separate ground from output jacks.
PT and mains ground all tied to the chassis.

I've still got hum. In fact, it seems that the tone seems to really make it worse when turned up.

I tried removing the tone stack, which just made it worse.

I put a piece of co-ax from the Volumes to the PI tube, and that did nothing.

Thoughts?

Attached Images

Leif's 5E3 Chassis 1.jpg (1.65 MB)

]]> Debugging Your Build Leif H http://music-electronics-forum.com/t16070/ Static noise caused by cabinet Vibrations http://music-electronics-forum.com/t16036/ Mon, 09 Nov 2009 22:42:44 GMT Hi all, I have noticed that vibrations from the upper back panel cause static noise on my 5E3, usually it happens after low notes. I have tried... Hi all,

I have noticed that vibrations from the upper back panel cause static noise on my 5E3, usually it happens after low notes.

I have tried to mimic pressing with my finger in the back panel and that creates a static noise.

Any clues?

Thanks ]]> Debugging Your Build tweed http://music-electronics-forum.com/t16036/ Major voltage drop in power amp section http://music-electronics-forum.com/t16018/ Sun, 08 Nov 2009 22:51:54 GMT As soon as I thought everything was good with my 5F2 build, I came across an interesting observation. In my previous thread, I revealed that my... As soon as I thought everything was good with my 5F2 build, I came across an interesting observation. In my previous thread, I revealed that my screen voltage was about 20V higher(around 320) than my plate voltage. Today, before I experimented with a grid resistor, I measured the voltages again and noticed that my screen voltage was around 180, and my plate around 164. I pulled my 6v6 and checked the voltage coming off of the rectifier. I measured 370V. Put the tube back in, and it went back down to 180. I swapped in a 6K6 for the 6V6, both of which were good yesterday, and I got the same results. What happened here? ]]> Debugging Your Build EETStudent http://music-electronics-forum.com/t16018/ Help! Newbuild Bassman with Asymmetrical clipping http://music-electronics-forum.com/t16008/ Sun, 08 Nov 2009 11:51:05 GMT Hello there everyone,

I've scratch built myself a 5F6A Bassman using 6550 output tubes, I'm having real problems with assymetrical clipping at high volume levels. I previously noticed that my supposedly "Matched" pair of output valves were drawing about 20ma difference in idle current, so installed a dual variable bias control circuit to perfectly match the idling current at 50ma per tube. I also increased the amount of negative feedback by replacing the 27K resistor with a 12K.

Putting the amp on the scope, clipping only appears from the output of the phase inverter forward, this remained the same when I changed the PI tube from a 12AX7 to a 12AU7. The clipping manifests itself on the scope as the "bottom" peak of the sine wave clipped with the top intact. Changing to the dual Bias control helped this a small amount, but not as much as I'd hoped. Distortion at full power can only be described as "farty"!

Any thoughts would be much appreciated! ]]> Debugging Your Build priesty http://music-electronics-forum.com/t16008/ 5F1 (sort of) build troubleshooting issues http://music-electronics-forum.com/t15973/ Thu, 05 Nov 2009 21:05:27 GMT I've recently gutted my "Champion 600" reissue amp & built myself a 5F1 reusing the chassis, cabinet, transformers & speaker with plans to replace the speaker in the near future. My build follows the 5F1 circuit closely however I could see no great benefit using a 5Y3 rectifier, using 4 1N4007 diodes instead & the Chinese iron has no center tap. I also have deviated from the original by using the original 18/3 power cord (properly grounded of course), deleting the .047mfd "death cap" & twisted my heater supply lines & added 2 100 ohm resistors running from each leg of my replacement pilot lamp to ground. Upon completion of my project turning the volume control above 3 yielded a "farting" kind of distortion. Researching the problem I found several suggestions so I opened it back up & added a 25mfd/50vdc cathode bypass cap across the 1.5K resistor from pin 3 of the 12AX7 tube & eliminated the 22K negative feedback resistor, both of which seemed to help a great deal however now when I turn the volume above 9-10 I get some sort of oscillation that kind of sounds like a motorboat & hope somebody can assist me in eliminating the problem. So far my thoughts on this have been:

1.) try adding another 25mfd/50vdc cap across the 1.5K resistor from 12AX7 pin 8
2.) reverse the red & blue wires going to the OT (red now runs to A+ supply node - blue to pin 3 of the 6V6)
3.) change the values of the supply resistors from 10K/2W & 22K/2W to 1K/2W & 10K/2W respectively to increase the plate voltages a little

I kind of also remember reading somewhere about using shielded wire at 2 key spots in the circuit but I've been unable to find that article again & I didn't take notes when I 1st came across this. Can anybody help shed some light on what I should do or perhaps offer another suggestion & please if possible don't just provide what to do but a bit of an explanation as to why so I can learn & not have to be a bother in the future? ]]> Debugging Your Build http://music-electronics-forum.com/t15973/ Newbie here http://music-electronics-forum.com/t15967/ Thu, 05 Nov 2009 16:06:04 GMT Hi, all. I am new to amp building, having just done two Gretsch 5222 mods successfully. I'm currently in a spot with my 3rd not working properly. I modded it to go back to something I was used to when my first scratch 5E3 Tweed Deluxe build was giving me fits.

So, now I have two different amps that aren't working properly... (I need an emoticon pulling its hair out). After reading through some of the threads here, it looks like I may have found a group who can help me troubleshoot them?

To start, I'd like to get my scratch 5E3 Tweed Deluxe build fixed. If I post all of the voltages I'm getting at various points on the board, can you all help me? Right now, I've checked everything I know to check... resistor values, cap voltages, pins on the 6V6s & preamp tubes. Everything is giving me good readings, but the volume is just pitifully low. I have to volume up to 9 before I get any real sound... a kindergartner could take a nap in front of the cabinet while my husband's playing, no joke. Also, the tone knob does absolutely nothing... either that or its not getting enough volume to hear any difference.

What say you?

Gina Veesaert ]]> Debugging Your Build AmpGal http://music-electronics-forum.com/t15967/ crazy buzzing distortion http://music-electronics-forum.com/t15958/ Wed, 04 Nov 2009 22:45:17 GMT :mad: Hi, i'm at a loss here. this is like the third amp i've built lately and all three of them have this crazy buzzing when the tube starts overdriving. I'm using 6sl7gt preamp and 6l6 power tube from a 5y3 rect.tube. I've tried lowering the cathode resistors. changed the layout thinking maybe that would've helped, everything has been changed out and still won't go away. the only thing that makes it go away is keeping it at low volumes before any overdrive. I ran a distortion peddle into it and it sounded better but only because it covered it up. Here's a schmatic, if someone would like to help
. this is a completly new build.

Attached Images

11-4-2009 6;44;45 PM.JPG (1.02 MB)

]]> Debugging Your Build surefirespider http://music-electronics-forum.com/t15958/ <![CDATA[High B+ Voltage in Build - Can't Find Issue]]> http://music-electronics-forum.com/t15926/ Tue, 03 Nov 2009 03:29:12 GMT I need help troubleshooting a build. It's a 6v6 power section, a When I fire it up I am getting high AC and DC voltages. Also my bias voltage is very low. I have swapped the PT tranny lines, retraced phase inverter wiring and double checked the bias filter to make sure positive was running to ground. I swapped the PT and the problem remained. I can't find an issue other than my voltages are way too high.

I've used a harvested OT and am about to pull it and try an OT I know work.

Before I do this does anyone hav any other suggestions? ]]> Debugging Your Build jlatrace http://music-electronics-forum.com/t15926/ DC voltage on input mystery http://music-electronics-forum.com/t15889/ Sun, 01 Nov 2009 05:30:21 GMT I’m building a circuit that for the most part is a clone of a late 50’s Airline I’ve had for about 35 years. The output and the PI are pretty well in place, and the preamp is built to the point the attached schematic shows. This part of the preamp is schematically exactly the same as the original. The original does not have DC at the input, but for some reason my build does. It’s not the tube—I’ve traded the tubes out between the original and the clone and the original still does not cause scratchy guitar-pot syndrome, while the copy does. With both parallel input stages in place, input section B in the bottom part of the schematic measures +.767vdc on the grid, -.490 at the 100k/.01 junction, and -.494 vdc at the input. This is whether or not input section A, which occupies the other triode of the same tube, is connected to the B+. Now here’s the interesting part: if input section A is disconnected from the input jack, the DC voltage at the input goes to over +6vdc, while dropping to -.88 on the grid.
Many thanks to anyone with suggestions as to where this voltage at the input is coming from.

Attached Images

preamp1.gif (4.9 KB)

]]> Debugging Your Build TigerG http://music-electronics-forum.com/t15889/