Super Reverb Build Problems

[mjenki14]

Update

OK, still haven't made much progress but here's what I've done. I went through and checked again the wiring of the input jacks. I found that the layout and the schematic read differently so I rewired just the normal channel differently. I tested the resistance from the tips to the pins on the tubes and on both channels I was reading approximately 68k. I was getting near 1 meg for the resistance to the ground on both channels input 1. I assume they are wired correctly now.
Last night I spent around two hours checking the connections from the board to the pots and tube sockets. I made sure everything was corrected correctly and the board was laid out correctly. I couldn't find anything that was supposed to be different. I'm not trying to say I have done everything perfect, I'm just not able to find and variances between the layout and the board connections.
This morning I gave the amp another shot. The tubes heated fine and the same plate voltage. When I flipped the standby switch, a slight crackle began coming through the speakers. It sounded like it was a tube type crackle. The crackling stopped after twenty seconds or so and I tried to plug in a guitar to both inputs and got nothing. I tapped on the tubes and heard nothing through the speakers.
I checked the speaker outputs again and they seemed fine. I figure signal is getting to the speakers because you can hear the crackle and a very faint "woof" when you flip the standby switch.
I'm no guru of electronics and am in way over my head probably but I have a theory which I would like to run by everyone. I think when I first turned on the amp and heard the very loud hum for 3-5 seconds before the fuse blew that I had the tubes running way to hot. I think they were drawing so much current they blew the fuse. That would account for the loud hum. Since the noise was coming through the speakers, I'm assuming the speaker wiring and output jack wiring is sound as well. Here's where I'm confused. Now that I have replaced the fuse and dropped the plate voltage significantly, I get no sound but the voltages seem to be ok. Could the no sound now be because I ruined the tubes during that initial startup? Would that account for the current status? I wish I could swap out all the tubes and give it a shot, but I don't have any extra tubes. I don't mind buying them but I would rather not spend the money if it doesn't look like thats the problem. What does everyone think?
Thanks for reading all these long posts. I really appreciate all the help and feel free to boss me around till we get this fixed!
Thanks again,
Michael

[octal]

I think that isolating the problem to at least the preamp or power amp section would be a good way to divide and conquer.

With the amp on, take your multimeter, set it to either the ohms or diode check function, secure the black probe to the chassis and briefly touch the red probe to pin 2 of the 12AT7 phase inverter tube (the one closest to the 6v6s.) You should hear a distinct pop out of the speaker when you do this. If not, the problem is most likely in the PI or output stage. If you do hear a pop, then your problem is in the preamp. You're just going to have to narrow it down and concentrate on whichever stage you're losing the signal in.

[octal]

Another thing- are pins three and eight of the 12at7 phase inverter connected together at the tube socket? It's kind of hard to see in your picture.

[bnwitt]

I think Doug Hoffman has a great page on wiring the typical Fender hi/lo jack assembly. Take a look:

http://www.el34world.com/charts/CommonHookups.htm

It is really tough to tell what you have done since all of the board wiring is white. Is that how Marsh shipped the kit?

[mjenki14]

Update 3/29

OK got some good news and some more (but smaller i hope) problems. From the advice of bnwitt, I rewired my inputs to the hoffman style, but still no sound. So I took octal's advice and tried to separate the problem between preamp and power stages. I found that tapping the last preamp pins before the 6L6s caused sound through the speakers so I focused on the preamp. I began checking the voltages on the tubes sockets. I saw I wasn't getting any voltage on the first tube so I checked the wire coming from the filter caps it wasn't connected correctly. An under board wire had come undone and the connection had been lost. I fixed this and fired up the amp and could immediately tell a difference. The normal channel worked great! Everything sounded like a classic super reverb! Needless to say, I was pretty excited.
But then.....
I plugged into channel 2 and did not get the same results. The sound was exponentially softer and the only thing you could seem to hear was the lows. The sound seems barely audible compared to the normal channel. Oh and now the fun continues.....
Does anyone have any ideas of where to begin or things I should check for besides the normal stare at the layout and schematic for a few hours? I'm not exactly clear on the signal path of the reverb channel so I don't really know where begin looking. As always, any help is always appreciated and thanks for the help with the problems. I have tomorrow afternoon off so I will be trying to get the amp running before a rehearsal tomorrow night.
Michael

[mjenki14]

I think Doug Hoffman has a great page on wiring the typical Fender hi/lo jack assembly. Take a look:

http://www.el34world.com/charts/CommonHookups.htm

It is really tough to tell what you have done since all of the board wiring is white. Is that how Marsh shipped the kit?

Yeah thats how they send the kit. All the same color wire definitely makes things a little more confusing.

[txstrat]

Since you have wired the inputs correctly now I would try to find out if the 2nd tube (and the circuit around it) is OK.
Have you changed the tube?
Are all connections and their values alright?
A too high value cathode resistor, for instance, would lower the gain significantly resulting in a lower volume.
Are the bypass capacitors OK?
Is the vibrato thing working (even at low volumes)? If not, the problem might be in the vibrato unit.

[bnwitt]

Does anyone have any ideas of where to begin or things I should check for besides the normal stare at the layout and schematic for a few hours?

Of course staring at the layout will get you no where. You have to use your ohm and volt meter functions to check things out. Your meter is your friend as it gives you the ability to see into the invisible world of electrons and their pathways.

Given what you have found so far, I would unplug the amp, drain the caps and use an ohm meter to check continuity between every eyelet set that has an underboard wire connecting them. This will prove that every underboard wire is still making connection between it's mating eyelets or not. I would also do the same continuity check on wires coming from underboard at eyelets to off board components like socket pins, control pots etc. You should see zero ohms or very close to it if you've zeroed out your meter lead resistance. If you have no zeroing function on your meter, a wire's continuity from end to end should not have much more decimal ohms resistance than the meter leads themselves show when touched together. So if you have 0.2 ohms with leads shorted you should get very close to that checking wires.

Then I would plug the amp back in turn it on and (with your volt meter function) make a voltage chart for every tube. I've attached a Word doc chart for the amp. This is how you troubleshoot an amp. Staring works only at wet tee shirt contests.

[mjenki14]

Then I would plug the amp back in turn it on and with your volt meter function make a voltage chart for every tube. I've attached a Word doc chart for the amp. This is how you troubleshoot an amp. Staring works only at wet tee shirt contests.

Was this file supposed to have the actual values for the voltage on it? If so, I am not seeing the values. Or am I supposed to fill in what I get for each of those values?

[bnwitt]

You are supposed to fill in the values, but here is one with values taken from the original schematic. Bare in mind that the voltages will be proportionaly higher due to higher wall outlet voltages of today (unless of course your PT has been wound to compensate for this). Once you take your readings, you can compare them to the filled out one or to the schematic. The typical voltages are also shown on the layout. Put some electrical tape around the tip of your multimeter leaving only the very tip exposed. This will prevent shorting of adjacent socket pins when taking the readings.

Do all of the ohms tests I suggested before you move on to the voltage tests.

[bnwitt]

Once you fix your problems, you are going to have to bias the amplifier. From your earlier posts, it seems you initially had the bias pot turned to produce the least amount of negative bias voltage, which red plated your power tubes and popped your fuse.

Now you have the pot turned the opposite direction and have -51 VDC at pin 5 of your power tubes which is max bias voltage. That is a good way to start up the amp to make sure you don't red plate the power tubes, but you'll need a bias probe or some 1 ohm resistors between the power tube cathodes and ground to set the idle current of the amp. That will be the last thing you do once the amp is working properly.

[mjenki14]

I haven't been able to check all the voltages today because I've been swamped with work. I'll be able to have them up tomorrow night probably.

Thanks!

[mjenki14]

Ok, I got the chance to go through and fill out all the voltages for the preamp section. I have attached the chart to the post in the word file. I don't know if the voltages are normal or not. Last night I went through and checked all the underboard connections with no luck finding anything abnormal. Today I went through and checked the connections from the board to the tubes and pots again. I didn't find anything. The amp sounds great through the normal channel. Its loud, clean, and articulate. The vibrato channel still barely makes noise compared to the other channel and is completely bass-e. Both the reverb and vibrato don't seem to work even on the muffled quiet signal. I'm completely befuddled.

[bnwitt]

You've got a couple of anomalies on your voltage chart. V5 pin 1 is way too high and so is V4 pin 6 You've either got the tubes wired wrong or the B+ power rail underboard wires aren't right. You keep saying you've checked everything and found nothing wrong. That is not correct. You're missing something or several somethings. Both of these bad voltage readings are in the vibrato channel so it's no surprise that is the channel you're having trouble with.

I gave you a chart with the typical voltages for your amp on it. Did you compare your chart to that one? The reason I ask is you say you don't know if the voltages are normal or not. All you have to do is look at the typical chart I gave you and you'd know they are not. However you are making your wiring checks is not working because you are not finding your problem(s). You need to focus, slow down and study the problem. I can't help you if you don't hunker down and get analytical.

[bnwitt]

At the junction of the 0.02 tremolo capacitor and the wire to V5 pin 1 there is a resistor that should be 220k ohms. That would be red, red yellow bands on the resistor. Is that what you have there?