Black Face Deluxe Reverb Problem-Voltages

[theundeadelvis]

I just finished my Deluxe Reverb build, and pretty much followed the fender layout (attached) exactly. I'm using JJ 6V6s, a Sovtek 5AR4 rectifier, and 12AX7 tubes for everything else.

The problem is two fold.

1 there's no trem. I used the Mojo opto and have the dots closest to the tubes. Are the leads polarized? I'm confident this problem will be the easier to fix.

2 There's no break-up! I can dime the volume on either channel and it remains clean. It sounds pretty good, but not very loud. Not bedroom quite, but not near as loud as my Lightning with 2 JJ 6V6 tubes. When I biased it one tube was at 26mA and the other was 29mA.

Here are some voltages compared to the volts listed on the Fender layout.

V1 pin 1 mine-182v Fenders-180v
pin 6 mine-230v Fenders-180v
V2 pin 1 mine-90v Fenders-170v
pin 6 mine-72v Fenders-170v

V7 pin 3 mine-474v Fenders-415v
V8 pin3 mine-474v Fenders-415v

Any insight is greatly appreciated ! Thanks!

[theundeadelvis]

Forgot to add that low notes fart out real bad. Like a dying motorboat.

[ampgeek]

Need more info to start any kind of reasonable evaluation.
How about posting up voltages for all tubes and all pins. Really need to see what the cathodes are sitting at to get a better picture of what is going on. Also want to confirm that all tubes are getting adequate heater supply voltage.

The normal trouble shooting advice would include (in no particular order):

Double check plate and cathode resistor values
Triple check for correct wiring and cold solder joints
Quadruple check all grounding points for good solid contact

It would also be nice to confirm that the tubes are all good...even if they are brand new. Can they be subbed into a known working amp for a test?

Dave O.

[ampgeek]

Ooops...forgot to mention also double checking power supply "rail" dropping resistor values as well.

The "Readers Digest" version of the quest is to detemine if and how much current each tube section is conducting. Measure the voltage differential across either a plate or cathode resistor (e.g., one lead of your DVM on one side and the other lead on the opposite side with the meter set for mA DC) and divide the reading by the resistor value.

Still collect and record the absolute voltage readings for each pin as they are important too.

Dave O.

[tele_player]

The "Readers Digest" version of the quest is to detemine if and how much current each tube section is conducting. Measure the voltage differential across either a plate or cathode resistor (e.g., one lead of your DVM on one side and the other lead on the opposite side with the meter set for mA DC) and divide the reading by the resistor value.

With all due respect, that's incorrect, you'd need to set the meter to a voltage scale, NOT a current (mA) scale.

[oldhousescott]

What method are you using to measure the idle current in the output tubes? From your description, it sounds like you are biased very cold. Not sure what's going on with V1 and V2.

Like ampgeek said, post all voltages for all pins.

[theundeadelvis]

What method are you using to measure the idle current in the output tubes? From your description, it sounds like you are biased very cold. Not sure what's going on with V1 and V2.

Like ampgeek said, post all voltages for all pins.

I have a speaker load hooked up, I have neg lead of my DMM clipped to a grounding point, and then I probed the tube pins with the positive lead. Is this not the correct way?

Thanks for all the input. I will try to get more readings tomorrow.

[tele_player]

That's the correct way to measure power tube idle current, IF you've got 1 ohm resistors between the power tube cathodes and ground.

Anyway, that's not really important right now. First, I'd figure out why the voltages on V2 are so low.

[theundeadelvis]

I'm puzzled. The voltages across the 100k resistors that go to the plates of V2 drop from 290volts to 90volts? I clipped my DMM across the both resistors and they read 99k? On V1 they drop from 290 to 180 and 230.

[tele_player]

That's not puzzling, really - it just says the tube is idling at a much higher current than expected. I'd look from problems on the grids of the offending triodes, starting with DC voltage.

If you haven't tried it yet, swap V1 and V2, and see if the problem doesn't change. And check that both tubes are of the correct type.

[theundeadelvis]

here's all the pins on V1 and V2 (I'll get the other tubes shortly)
V1
1. -196
2. 0
3. -1.39
4. 2.4 (AC)
5. same
6. -233
7. 0
8. -2.24
9. 4.29(AC)
V2
1. -90
2. 0
3. -3
4. 4.3
5. same
6. -72
7. 0
8. -2.23
9. 2.38

[theundeadelvis]

OK, got the voltage problem fixed. Tele_player made something click, I had a bunch of tubes laying around and stuck a 12AU7 in V1. Thanks!

Now I uncovered a new problem. The trem bleeds into the normal channel. Actually the trem might be louder in the normal channel then the vibrato channel.

[tele_player]

I'm not sure I get what you're saying there. If you assembled that circuit correctly, using 12ax7 in V1 and V2, your voltages should be correct. If it needs a 12AU7 in V1 to get V2 working, something's not right. Maybe I'm just misreading?

[theundeadelvis]

Sorry, I first switched V1 and V2 and noticed the voltages switched. So then I realized one tubes was bunk. So at first the AU7 was in V2 and then I switched it V2 and where ever it was the voltages were wrong.

[theundeadelvis]

Found a ground I missed. Works great now. Now I want to figure out how get the channels where "normal" does have reverb and trem and where I can jumper them. Thanks for all the help!