6g15 build voltage issues

[Dsav94]

Hey everyone,
 
   I've been working on my first tube circuit build and I've run into some issues. I've wired my 6g15 (Hoffman version) and my voltages seem to be off and I'm struggling to find the source of the issue.


V1 (12at7) 
1  255v
2. 0
3. 0
4. 6.2 heater
5. 6.2 heater
6. 262
7. 0
8. 0
9. 6.2 heater

V2 (12ax7)

1. 262
2. 0
3. 0
4 + 5  6.2 heaters
6. 317
7. 46
8. 0
9. 6.2 heater

V3 (6k6)

1  0
2. 6.2 heater
3  326
4. 326
5. 0
7. 6.2 heater
8. 0


These voltages are without tubes.

I've gone over the wiring several times including rewiring all sockets. I suppose it's worth mentioning I am fairly new to all of this but I've done quite a bit of studying.

Hopefully someone knows what the heck is going on here, this is gonna turn me gray :0

Looking forward to the response

Thanks.
Dave

[sluckey]

Those voltages are exactly what you should have with no tubes plugged in. Now plug 'em in and recheck.

[Dsav94]

V1
1. 61
2. 0
3. 1v
6. 65
7. 0
8. 1

V2

1. 138
2. 0
3. 0
6. 228
7. 33
8. 115

V3

1. 22
3. 276
4. 281
5. 0
8  22

All pins not listed are heaters or not used. Heaters are running at 5.8 with tubes in

Also worth noting, signal passes through yet no reverb what so ever. I can hear the tank crash.

[tubeswell]

V2 Pin 3. This is a cathode pin. Have you connected the pin to the corresponding cathode resistor? And Have you connected the other end of this cathode resistor to the ground return path?

[Dsav94]

The 1.5k + 220/35v ? Yes its grounded to the bus.

I promise the soldering was better before I rechecked the points 3 times. Definitely could use to be cleaned up a bit

[sluckey]

Turn the amp off and measure resistance from V2 pin 3 to chassis. Probe directly on the tube socket. What have you?

[Dsav94]

I've got 1469 ohms. I rewired to be nice and clean hoping it would fix what ever issue I was having..

With the tubes its

V1
1. 58
3. 1
6. 64
7. 0
8. 1

V2
1. 139
6  229
7. 34
8. 116

V3
1. 22
3 227
4. 284
8 22


So now for some reason guitar input isnt working. Unit powers, I can hear the tank crash but nothing when I plug into the input 

[shooter]

I hear a high pitched screeching

from the unit or plugged into an amp?

[tubeswell]

I've got 1469 ohms. I rewired to be nice and clean hoping it would fix what ever issue I was having..

So have you got a volt or two on V2 Pin 3 now?

[Dsav94]

I hear a high pitched screeching

from the unit or plugged into an amp?

It ended up being a non shielded wire where it should've been. Fixed it right up. It was from the unit not plugged into an amp

[2deaf]

One of the things you can investigate with no tubes in is why V2 pin 7 isn't one-half the voltage of V2 pin 6.  R15 and R16 should both be 2.2M.

Maybe you have a cheap meter and the voltage on pin 7 isn't really 46V, especially since pin 8 is correct when the tubes are installed.

[Dsav94]

Both resistors are indeed 2.2m. I dont believe my meter is faulty, it seems to be accurate and reads the same at other side of pin 7. What are my options here? Also the issue regarding the input not working ?

[Dsav94]

It dawned on me that a couple of the brown caps were facing the opposite way and they were right around the area giving me problems, so I figured I'd turn em around and give it a shot. Tried voltages again

With the tubes in

V1
1. 60
3. 2
6. 66
8. 2

V2
1. 66
3. 2
6. 228
7. 103
8. 120

V3

1. 22
3. 282
4. 290

These seem to be closer to the voltages I'm looking for. Although, there guitar signal is still unaffected by reverb. Moving forward though, where to next ?

[2deaf]

Now V2 pin 7 is consistent with a meter with a 10M input impedance.  Before, the meter would have to have an input impedance of 464.6K.  Did you change meters?

[tubeswell]

V1 and V2 plate voltages are on the low side. Did you use a 10k dropping resistor in the HT supply? or 100k?

[Dsav94]

All I did was turn those 2 brown caps the other way. That's another thing I've noticed, these problematic pins (1+6 on v1 & 1 on v2) all have one thing in common. They are the only ones directly connected to 100k resistors. Not sure if that's the problem or not. Even the fender schematic has the 100k

[2deaf]

V1 and V2 plate voltages are on the low side. Did you use a 10k dropping resistor in the HT supply? or 100k?

He's showing 228V on the "C" node, so R18 couldn't be 100K.  Both V1 plates are similar, so R2 couldn't be 100K.  V2 pin 1 is 139V, which isn't alarmingly low.

[tubeswell]

Yep - bit of a stab in the dark. Still, 60V is low on the other plates. So I wonder what else is wrong tho?


Hot tube bias? Assuming 110k for V1a plate load, 282V - 60V = 222v. 222/110,000 = 2mA, whereas normally you'd be looking at 1mA tops

[Dsav94]

Ok, so yall ready for a good laugh?
I feel like such an idiot. I mixed up my 12at7 with an au7. The voltages are now exactly where they should be! Oh geeez. This has been quite the journey. The reverb still isnt working though, so I've got no lead on that

[tubeswell]

That would explain the hot tubes/low plate voltages. Re: the reverb recovery signal, obviously the recovery stage is working because the pan crashes when you bump the unit?


If so, then the problem must be on the reverb driver side.


Check the continuity of the cable going to the pan's output transducer with your R-meter.


Check that you're getting a signal on the RT secondary (and that the RT isn't blown). Hooking a speaker up to the RCA send jack will tell you pretty quick.


If both of those are working, then either your pan input transducer is bad, or your reverb driver stage isn't hooked up properly

[Dsav94]

But what about the lack of incredible reverb? Any ideas?

[tubeswell]

Edited my previous response while you were posting

[Dsav94]

Both of those checked out fine, I even tried a different pan and that didnt change a thing. Noticing my mix knob doesnt seem to affecting the signal at all. 
Should my secondary tap to tank input post have continuity to ground? I understand theres a ground lead wired to the bus, but the output RCA's posts dont have continuity.

[2deaf]

Should my secondary tap to tank input post have continuity to ground? I understand theres a ground lead wired to the bus, but the output RCA's posts dont have continuity.

All of the RCA jacks on your chassis should be grounded to the chassis.  Is your send jack isolated from the chassis?

[Dsav94]

Even the center pin/positive lead should be grounded?

[2deaf]

Even the center pin/positive lead should be grounded?

No.  Just the housing part that connects to the shield on the cables.  One end of the reverb transformer secondary must also be grounded either by connecting it to the RCA jack which is grounded or by connecting it directly to the chassis or by connecting it to a ground bus which is connected to the chassis..

[sluckey]

Even the center pin/positive lead should be grounded?

It's not connected to ground but if you try to read resistance from center pin to chassis it will read very low resistance. If using a cheap meter it will probably think it's zero ohms. That's because the secondary of that RT is very low resistance.

[tubeswell]

But if you are isolating the RCA jacks from the chassis, then you need a ground connection wire from the RCA jack sleeves to whatever other ground return you are using. The pan's transducer coils have to have a ground return path.

[2deaf]

The input transducer doesn't need a grounded conductor, it just needs two conductors from the RT secondary.  The send jack sleeve is only grounded so that the cable shield is grounded.

The return jack is grounded for a ground return path and to ground the cable shield and to connect the reverb tank to ground.

[tubeswell]

The input transducer doesn't need a grounded conductor, it just needs two conductors from the RT secondary.  The send jack sleeve is only grounded so that the cable shield is grounded.

The return jack is grounded for a ground return path and to ground the cable shield and to connect the reverb tank to ground.

The input transducer coil still has to have a ground return - and in a pan with an isolated input jack sleeve, the ground return is through the return jack sleeve, and vice versa for a pan with a ground-isolated output jack sleeve. If a transducer doesn't have a ground return*, you won't get any EM induction between the coil and the magnet - same as for a guitar pup.


*closed circuit

[2deaf]

I think it's the term "ground return" that is throwing me.  The two conductors on the input coil and the two conductors on the RT secondary need to be connected, but chassis ground has nothing to do with it.

[Dsav94]

After trying a whole bunch of things including rewiring the problem area and replacing a cap and resistor, it works! Really appreciate all the help here! Thank you soo much