Revibe Build

[Willabe]

They both show a 1 amp slow blow fuse. That may be a little small, I put in a 2 amp fuse. The filaments will draw around 1.5.

The 1 amp slo-blo fuse is picked for the total mains acv/current draw, the heaters are pulling 1.5A but at 6.3 acv, it's a different thing.

I'd put the 1 amp slo-blo fuse back in.

[sluckey]

Take that 220K bleeder resistor out. What does Node C voltage read now?

Put the 1A fuse back in. It was fine. That 1.5A filament current only causes 79mA of current to flow through the primary fuse. The only reason I used a 1A SloBlo was because I don't have any 1/2A SloBlo.

I don't really suspect that PT. It's been used in quite a few Hoffman style revibes. It's lighter duty than the PT I used, but it should be fine. It does account for the slightly lower B+ than I have.

What I don't get is why is your Node C voltage so low. The currents don't add up correctly. There is twice as much current flowing in your Node C as in my Node C. Why? Either some of your voltage measurments are unreliable or the resistance values are incorrect. That's why I wanted you to verify every component value on that board. Have you done that yet? And the results?

Take a look at the attached chart and you'll see that the currents just don't add up. If I apply the voltage readings from my revibe to that same chart, then Node C current equals total plate current equals total cathode current, just as it should.

I've lost track of what the symptoms are at this point. What works, what doesn't work, hum, etc. Please tell me again.

Does the tremolo LED work yet? There's a good chance that if you connected it backwards at some time it will never work. If that's the case, you need a new one. It's important to use a red or yellow. I used yellow because there are already too many red LEDs in my world.

I was hoping to spot something obvious from your pics, but not so. I've studied your pics and I just don't see anything at this point. I'm at a point to try some signal tracing, either with a sig gen and scope, or listening probe. Do you have any of that stuff?

[EKDENTON]

The plate resistor on pin 6 of V1 was wrong so I changed it. That was the only one I found that did not agree with the layout.Took off the bleeder. Now for voltages I'm getting B+ 269
A. 265
B. 248
C. 215
Right now I am getting some guitar sound but it's with my amp turned so high it should be blasting my face off. It's also burried under the  hum.

No go on the led with the anode (flat side of LED) to the cathode of the tube. On colors I may have to order those colors all I have is ultrabright blue or green.

I don't have any signal generators or even a scope. Wish I did.
Maybe we can go back to the divide and conquer idea and disconnect the vibrato section and see if just the reverb works?

[sluckey]

Check voltages for V1, V2, and V4 again. Also all B+ nodes.

Right now I am getting some guitar sound but it's with my amp turned so high it should be blasting my face off. It's also burried under the  hum.

That hum is a big clue. We gotta find what is causing it. This unit puts out a signal that is only a little hotter than your guitar. It ain't much. And it's easy for hum to become a major factor.

I agree we need to divide and conquer but I think we should disconnect the reverb and fix the vibrato path. The reverb circuit is the tubes across the top of the schematic. The normal dry signal goes through V1B and V4. And V5 simply adds tremolo to the normal signal. If the oscillator is not working you just don't get the effect, but the normal signal should still pass through V4.

The color of the LED determines the voltage dropped across it. Yellow and red work the best in the oscillator circuit. White, blue, and green all have a voltage that doesn't work well. And since your B+ voltages are so low those colors may not work at all.

So, post those voltages once more. Maybe there is a power supply causing the hum. Could be PT, caps, or diodes.

And which make/model voltmeter are you using? Got a fresh battery?

[EKDENTON]

When i started the build i went off  the color bands on the layout and I have no idea how i did this but I had wrote down 3M for the resistor that is parallel with the .047 off V4 pin7. You probably would have spotted that but that resistor is under the cap. When i was writing down the values i must have picked up a color band of a resistor next to that one. So i put the correct 1M in that spot. Rechecked every part again, and now I think i have all the resistors and capacitors correct. I tried it for sound and changing the 3M to the correct value 1M now there is no guitar sound at all now, just back to only hum. 
When I get home tonight I will dig for a red LED, swap that out. and Re-measure all my voltages and post them.


Meter is a new Fluke175. It has a new battery.


You know the probablility of me making  a wiring mistake is probably much  higher than a bad component, but at this point I am not ruling anything out. I may also swap some tubes out maybe there is a bad one and it is passing the ac from the filament into the signal?

[sluckey]

...the resistor that is parallel with the .047 off V4 pin7... So i put the correct 1M in that spot.

You better take a close look. That resistor/cap does not connect to V4-7. It should connect to V5-2.

While you are at it, verify that all the wires for the tube sockets go to the correct turrets on the board. That's one area that your pics don't cover very well.

[EKDENTON]

Okay, yes your right it is.


 I should have added that (its the one in series) with the 1M's to pins 2 and 7 of V4.


I will  (re)check all the leads again tonight.


Does this Yellow LED look okay?


This 5mm (T1-3/4) clear lens yellow LED is a very bright 5mm LED. Forward voltage is about 2.9V, forward current is 50mA. Very nice, intensely bright LED. Color: Yellow Stock #: G18200

[sluckey]

That LED voltage is too high. You want one with a voltage between 1.7v and 2.0v and about 20mA. Do you still have a Radio Shack? They have a cheap variety pack that contains the LEDs like you need.

[EKDENTON]

No sadly they closed our store years back. Their is nothing here..... it's like living on Mars. I ordered the LED's at electronic goldmine. They have all kinds i just did not know what the forward voltage and amperage should be. They had some red 2V 20mA, they only sell in a 100 package for $5. Got some other colors and sizes also since they are so cheap.

[sluckey]

I bought a bunch from eBay a few years ago. I can send you a care package if needed. LMK. To get the oscillator working you can just put a 4.7K and 22µF parallel on the turrets the LED connects to. Cap negative to ground. Then replace with the LED when it's convenient. Also, if you suck the solder out of those two turrets you can just poke the LED leads into those holes to easily see which ones work best.

Send me a pm if you want to use the exact LED that's in my revibe.

[EKDENTON]

I found a couple 3mm red already have the mounting socket. If i am checking this correct (haven't checked an led with the meter yet) the led lights and the meter reads 1.83v forward voltage. So I will try these. If they don't seem to work i will try the R/C until the order arrives.


I found one that lights red with the red lead of the meter on the anode and lights green when you put the red lead on the cathode.

[EKDENTON]

Okay I found a red led that is works good. It is flashing with the vibrato all the time even with pots full CCW (is this normal?)

The good news is I am getting some guitar signal through now and the reverb is working and the vibrato seems to be working.
The bad news is the signal is still weak and there is still tons of hum and buzz. I pulled the tubes out one at a time hoping a tune replacement might fix it but there was no change in the hum.

After tracing the schematic and the layout several times with a highlighter finding the two incorrect resistors and correcting them I believe everything agrees with the schematic and the layout. I do still have the 6v6 in place of the 6k6. I did  remove the bleeder.

So here are the voltages now.
B+267
A.263
B.245
C.211
V1.
1. 131
2. 0
3. 1.2
4. 3vac
5. 3vac
6. 137
7. 0
8. 1.1
9. 3.0
V2.
1. 109
2. 0
3. 1.42
4. 3vac
5. 3vac
6. 116
7. 0
8. 1.42
9. 3vac
V3.
3. 258
4. 264
5. .002
8. 20.66
V4
1. 227
2. -1.29
3. 1.97
4. 3vac
5. 3vac
6. 218
7. -.42
8. 1.97
9. 3vac
V5.
1. 174
2. -.22
3. 1.27
4. 3vac
5. 3vac
6. varies with vibrato 94-167
7. varies with vibrato .2- to .60
8. 1.58
9. 3vac
Voltages taken with all pots full CCW.

[sluckey]

Finally. A good set of voltage readings that make sense. Everything is in agreement. Your power supply voltages are consistently lower than my voltages by about 50 to 60v but that's just due to the difference in secondary voltages. I'd like for you to temporarily hookup the 100VAC primary tap and recheck only the filter cap voltages. Also measure AC filament voltage because it will increase as well. I don't expect this to help the hum/buzz issues, but you never know. If filament voltage is extremely high don't leave the PT on the 100V tap for too long.

Now let's divide and conquer to determine where the hum/buzz is coming from. Disconnect the wire between the board and the output jack. This will leave only the reverb circuit connected. Reverb will probably sound weak without the normal signal. Does the hum/buzz go away or get better?

BTW, what kind of amp is your revibe connected to? Can you try a different amp?

[EKDENTON]

On the 100v tap PS voltages are B+ 301
A-296
B-271
C-236

Filaments are too high at 7.01v
Could try and lower it with resistors?

[sluckey]

On the 100v tap PS voltages are B+ 301
A-296
B-271
C-236

Filaments are too high at 7.01v
Could try and lower them .5v  with 2 150 ohm (no center tap) one on each wire. Should only need to be 1 watt but my math is not that great. 

I like those voltages! Those readings are only 25v lower than mine. Probably didn't help the hum/buzz???

I have several amps that run just fine with 7VAC on the filaments. I think I'd leave the 100V tap connected.

Did you disconnect the wire yet?

[EKDENTON]

No it's connected still let me see what it sounds like

[EKDENTON]

Volume seems pretty good now let me disconnect the wire to the output jack and see what happens

[sluckey]

Ed, read this thread. Start with reply #104 and read through to the end. It's not too long.

http://el34world.com/Forum/index.php?topic=17195.msg174718#msg174718

[EKDENTON]

Thanks.  I'll check it out.  It will be after an hour or two.  My grandkids are in town and we are visiting.

[EKDENTON]

Guess I'm done for awhile, I was trying to take a tube shield off V2 and the tip of the tube broke. That was the only ecc81 I have. Guess I can use ecc83 while I'm troubleshooting until I can get an 81.

[Willabe]

Sorry to hear that.

In most cases you don't need to have any tube shields on while trouble shooting.

[EKDENTON]

Thanks.

[EKDENTON]

I read that thread and tried all of the suggestions you and Doug had for that revibe build that I had not already tried. It stays about the same with everything tried so far. With his the hum was better with the ground lift with mine there was no noticeable change. I tried  two different amps.  I listened to his video and unless it is just the video volume his hum was minor and sounds different. Here you can listen to how it sounds. Sounds like a test from the emergency broadcast channel or almost the pitch when you get an Amber alert. Can it be 120 cycle?

[sluckey]

Turning the mix pot max CCW clearly kills the hum. That's not what you have told us. That indicates the problem is in the reverb circuit.

Divide and conquer. Disconnect the wire I asked you to disconnect. Hum should still be there. Is it?

If so, reconnect the wire.

Now pull V1. Is hum still there?

If so, now pull all tubes. Is hum still there?

If so, you have a power supply problem. Leave all tubes out. Get an electrolytic cap to use for testing. 20µF, 40µF, 100µF, just whatever you have. It must have a higher voltage rating than your B+ voltage. Now connect the negative end to chassis and connect the positive end to node C. You can do this on the board or directly on the cap can, whichever is easier. Gator clip test leads makes this very easy. Does the hum decrease?

Repeat this test for the other three filter caps.

If that hum does not decrease with the above filter cap test it's possible that your bridge is bad. Replace it. You can use four 1N4007 diodes if you don't have another bridge. Doug sells two bridge rectifiers that look almost identical. One is rated for 50V, the other is rated for 1000V. If you used the 50V bridge then it is very likely bad now. Can you verify you have the right one?

[EKDENTON]

Yes,  I did say that nothing had any effect on the hum but that was when the wire was connected to the output jack.


Once i disconnected the wire from the output jack,  turning that pot CCW does kill all sound.


I still have the wire disconnected


That was one reason I did the video so you can see what the controls are doing, and what the problem sounds likesound is like.


So I will reconnect the wire and go through the steps listed.


 

[sluckey]

In case you don't have it fixed by now, I want you to check the ripple voltage on all four filter caps. If you are not familiar with the "MIN MAX" recording mode of your Fluke 175, then read the attached file first.

Now let's do it. You are gonna read the ac ripple voltage on the filter caps and record the average reading for 60 seconds. Here's how...

Set your meter to read AC volts. Connect the black probe to chassis. Connect the red probe to the positive lead of the bridge. (Gator clip leads are very handy for this test.) Press the "MIN MAX" button four times to put the meter in record mode and display the average AC voltage reading. (The display should also show "MIN MAX" and AVG. If not push the "MIN MAX" button some more to cycle through the display modes. Stop when you see AVG in the display.) Sit back and let it record for one minute. Then write that number down.

Move the red probe to Node A. (I did all my readings right on the board) Press and hold the "MIN MAX" button for one second to exit the record mode. Now press the "MIN MAX" button four times to reset the record mode to AVG. The display should show "MIN MAX" and AVG. Sit back and let it record for one minute. Then write this number down.

Repeat this procedure for node B and node C. Compare (and post) your numbers. Here are my numbers listed below...

B+ = 530mVAC

Node A = 116mVAC
Node B = 40mVAC
Node C = 11mVAC

[EKDENTON]

Working on reply #73.
I reconnected the wire and confirmed that turning the mix pot full CCW does nothing to the hum.

I pulled V1 and no change. So I pulled all tubes and there is no sound but my amp.

The rectifier matches the photo of the 1000v on Doug's page.

Should I move on to the tests in reply #75 on the capcitors?

[sluckey]

So I pulled all tubes and there is no sound but my amp.

I take this to mean the hum/buzz is still there?

Should I move on to the tests in reply #75 on the capcitors?

Yes. Put all the tubes back in while you are checking the ripple. I think you are about to find the source of the hum.

[EKDENTON]

The buzz was gone with all the tubes out.
All the AC ripple voltages are way off compared to yours. They are as follows:
+ on rectifier 63vAC
A. 62vAC
B. 169 mvAC
C. 2.8 mvAC

Since the measurement on the rectifier is that far off would that be the problem? It is the 1000v rectifier.

[sluckey]

It "appears" that the first cap can (the one with the choke connected) is bad. Or the bridge is bad. Maybe both. Reflow all three solder connections on that can. Any better?

Get an electrolytic cap to use for testing. 20µF, 40µF, 100µF, just whatever you have. It must have a higher voltage rating than your B+ voltage. Now connect the negative end to chassis and connect the positive end to B+. Does the hum decrease? Now move the positive end to node A. Does the hum decrease?

Where did you get your cap can?

[sluckey]

Here's a procedure to check the bridge. You must remove the bridge to check it. Set your meter to diode.

1. Connect the probes across the "AC" leads. Meter should read OL. Reverse the probes. Meter should still read OL.

2. Connect the red probe to "+" lead and the blk probe to "-" lead. Meter should read OL.

3. Connect the blk probe to "+" lead and the red probe to "-" lead. Meter should read about 1V.

3. Connect red probe to "+" lead. Connect blk probe to either "AC" lead. Meter will read OL in either case.

4. Connect blk probe to "+" lead. Connect red probe to either "AC" lead. Meter will read about .5V in either case.

5. Connect red probe to "-" lead. Connect blk probe to either "AC" lead. Meter will read about .5V in either case.

6. Connect blk probe to "-" lead. Connect red probe to either "AC" lead. Meter will read OL in either case.

If any of the above steps does not give these results, the bridge is bad. If you replace the bridge, replace that first cap can also because it has been severely stressed.

[sluckey]

Oh, BTW... You can connect your meter across the speaker terminals and measure the frequency of that loud hum. Just set your meter to measure AC volts and press the Hz button. Should read 120Hz.

[EKDENTON]

I connected a 47uf cap to B+ and the hum is almost gone just a faint hum changing with the vibrato.

The caps I got fir antique electronics. They are our neighbors in AZ.

[sluckey]

You need to replace that cap can.

That video you posted was invaluable. That kind of hum is most often associated with power supply problems. On a new build it's easy to steer toward chasing wiring errors. And it's easy to overlook the possibility of having a brand new bad component.

Looks like AES sells a  JJ 2x100 can. I've had good luck with JJ electrolytics. And I've had good service from AES also. I'm sure if you point them to the last few replies in this thread they will send you a free replacement can.

[EKDENTON]

Okay thanks.

I will still check for the 120Hz.

It's a bit frustrating but I learned some good troubleshooting from this build.

I thought the hum was different, and once you posted the video of the other guys revibe even my bad ears could hear a big difference

This evening when I get home I will measure at the output jack and post the results for future reference. Hopefully this thread will help someone with the same problem sometime.

[EKDENTON]

Question. Would the bad filter cap effect the voltages? Just wondering if there is any concern about going back to the original primary 120v tap, or if this transformer just has low voltages? 

[sluckey]

When you replace the can your B+ should increase. Once you have everything up and running measure the B+ and A,B,C nodes and compare to your last reading. Recheck ripple too.

If everything works good go back to the 120V primary tap. If works good on the 120V tap, I'd call it done. Your PT spec says 250V on the secondary. Mine says 260V on the secondary. Your dc voltages should all be a little lower than mine.

When you are satisfied that everything is working well, take a full set of voltage readings and write them on your schematic. Might come in handy sometime later.

[EKDENTON]

Okay I have the cap replaced and that was the cause of the loud buzz hum. The reverb section works very good and the vibrato is working but may need some adjustments.A

The voltages were too high on the filaments after changing the cap so I switched it back to the 120v primary tap.  Voltages all look good now.

B+ is 322v, A=317v B=313.7 C=312 not much lower than yours.

It may need a few adjustments though.

 The revibe is pushing either amp I plug into to distortion even on the cleanest settings. I did replace that V2 tube I broke with another 12AT7.

Another thing I noticed is that the vibrato speed pot does not do anything. The speed switch works good but not the pot.

[EKDENTON]

Also I forgot to mention that the JJ brand 12AX7 does not work well in V5 the 60Hz hum is too loud. I changed that one to a JAN brand tube and its much quieter. There is still some hum, but I will keep fiddling with it to get it as low as possible.

[sluckey]

The revibe is pushing either amp I plug into to distortion even on the cleanest settings.

On the schematic look just to the right of V4. You will see a 330K and a 10K voltage divider. Be sure those values are correct.

EDIT... To quickly locate these two resistors follow the wire from the output jack back to the board where it connects to a 220K resistor. The resistor on the left side of that 220K is the 330K and the resistor on the right side of that 220K is the 10K. (orientation is front panel up.)

The speed switch works good but not the pot.

You forgot to connect the wiper to the left lug.

[EKDENTON]

Those two resistors are correct.




 I did not see that jumper on the wiper on my printed layout....should have checked schematic LOL.

[EKDENTON]

I'm thinking it may be the LED bias. If I went with the original  R/C bias would it be 4.7K and a 25uf? From the old fender schematic it looks like that are the values.

[sluckey]

4.7K and 22µF or 25µF are correct.  But just pull V5 first. That will totally eliminate the oscillator circuit. Still distorting? If so, then the LED ain't your problem. AFAIK you are the first to have this distorting issue.

Turn the mix control to zero. Still distorting?

"The revibe is pushing either amp I plug into to distortion". I interpret this statement to mean the signal out of the revibe is too hot and overdriving your amps. Plug your guitar straight into your amp and set the controls as you normally would. Then connect your guitar to the revibe and the revibe to the amp without touching any controls on your amp. Does the amp get much louder, or does it stay about the same volume you had with the guitar connected straight to the amp?

Post a hi rez pic of those resistors I asked about. I'd like to compare to this pic...

 

[EKDENTON]

Pulling V5 and turning the mix full off CCW has no effect. The volume is approx the same direct into amp or through the revibe.
I just assumed the revibe is pushing the amp harder, it could be possible that it is distorted before getting to the amp. It's not a desirable sounding distortion. If you want I can try to record it and post a link this evening.

[sluckey]

If you want I can try to record it and post a link this evening.

Yes, do that. We had pretty good results from the last one you did.

[EKDENTON]

Okay here I made a short video and strummed a few chords so you can hear what I hear. 


https://www.youtube.com/watch?v=TdDjUUFulEY

[sluckey]

Not supposed to do that. That distortion is coming from V1 and/or V4. Try a bunch of tubes in those sockets. I used 5751s (gain of 70) for both of those. Maybe try some 5751s, 12AT7s or 12AY7s.

[EKDENTON]

Okay. I don't have a lot of tubes so I borrowed the 5751 from my plexi PI and put that in V1. I have the ecc81 in V2. That did not have any effect. Still the same.

[sluckey]

Try it in V4 also. And you can pull that 12AT7 from V2 to try swapping into V1 and V4.

[EKDENTON]

I spent the evening swapping tubes. I found about 10 12A_7 tubes of various brands. I tried rotating those around with the 5751. It didn't change the distortion. It must be something else causing it.