6g15 'Seaverb' build

[bullkelp]

So some time agao I thought id rebuild by home build 6g15.
When i made my first one 10 yrs ago I used spare parts, made a cab from butt glued pine and old vinyl and lucked out by getting the circuit right the first time. Turned out to be a great tank and i used it live many times.

Infact it sounded so good that I had friends ask for one. So I got a buddy to make up 4 cabs and I set about ordering parts for four builds.

Here is the first of those.

Layout and circuit I followed the same recipe. Concepts from the weber ad-a-verb and TAD were combined with the grounding system from merlin and a ground lift network. All the jack sockets are insulated.

[bullkelp]

Here im populating the turret boards. LAst time I used eyelet board but Ive come to prefer garolite boards and turrets.

[bullkelp]

The chassis and face plates are from Banzai music. Shipping to NZ is very reasonable
The transformers are all hammond

[bullkelp]

Here is the assembled board with ground bus
Ive bought the filter caps inside the chassis this time

[bullkelp]

Mounting in the cabinet

[bullkelp]

Reverb tank mounted to the grill
Everything tested and functioning (tubes and reverb RCA wires obviously not present for photo )

[bullkelp]

I designed the logo and had them made up by a local emblems manufacturer out of brushed stainless
Just adding the mounting holes

[bullkelp]

And the finished article

[bullkelp]

Here is a very quick test recorded thru my phone.
The unit runs quietly, plays well with the large watt bassman.
Does all the drippy splashy things you could hope for.

[tubeswell]

Sounds magic

[ac427v]

Magnificent in every way! Planning,building, cabinet (what a buddy!), and sound.
What tank?

[bullkelp]

Magnificent in every way! Planning,building, cabinet (what a buddy!), and sound.
What tank?

Thanks!
The tank is an older acutronics/belton 4abc13b

[bullkelp]

I see a mod mentioned around the traps :
placing a 220k resistor across the foot switch /reverb recovery circuit

What is the function of this? And is it worth considering for the 6g15? I see it is present in a lot of the onboard reverb amps.

I see it is included in the hoffman 6g16
My unit is not wired with a foot switch and the RCA is insulated and grounded to the common bus bar. Would I just add a 220k resistor in that grounding wire then?

[SEL49]

I see a mod mentioned around the traps :
placing a 220k resistor across the foot switch /reverb recovery circuit

What is the function of this?

This 220K is a dedicated grid leak for the recovery triode. If you unplug the return cable from your tank, your recovery triode no longer has a grid leak to ground and your unit will probably hum or make other undesired noises. The resistor is a good thing. I have one on my unit.

[bullkelp]

Is it something you'd add even in the absence of a foot switch?

[SEL49]

Absolutely! The footswitch has nothing to do with the function of that resistor. But as you have seen, the resistor is unneeded as long as the reverb return cable is securely attached to the tank and the unit.

[bullkelp]

Absolutely! The footswitch has nothing to do with the function of that resistor. But as you have seen, the resistor is unneeded as long as the reverb return cable is securely attached to the tank and the unit.

So what’s this stuff about making the reverb sound sweeter ?
Also the TAD kit has it wired across the reverb return hot and ground

[HotBluePlates]

This 220K is a dedicated grid leak for the recovery triode. If you unplug the return cable from your tank, your recovery triode no longer has a grid leak to ground and your unit will probably hum or make other undesired noises. The resistor is a good thing. I have one on my unit.

... as you have seen, the resistor is unneeded as long as the reverb return cable is securely attached to the tank and the unit.

So what’s this stuff about making the reverb sound sweeter ?
Also the TAD kit has it wired across the reverb return hot and ground

The Reverb Tank's Output runs to the jack TAD calls "Reverb Output" which runs to V1A Pin 2.
It's electrically the same if your 220kΩ resistor runs from Pin 2 directly to Ground, or if it is from the jack's Hot to Ground.

As for "sounding sweeter" folks probably imagine the resistor will interact with cable capacitance to roll off some treble, because "220kΩ" < "∞Ω".  I'm skeptical, as the cable isn't that long from tank to chassis.  And the output transducer of the reverb tank is an impedance-to-ground that is very much smaller than 220kΩ.


I might add this resistor to my 1965 6G15 Reverb (just because).  However, I also don't plan on using my 6G15 Reverb without the tank plugged in...

[bullkelp]

Ok im on to building the second unit.
I have completed it but its not working as it should and I cant quite figure out why.
Its wired exactly (as far as I can see) as the first unit (which works great)

I get reverb but it doesnt sound nice. And if I increase it it starts to make the tank resonate and feedback/ring autonomously.

All the voltages related to v1 (the 12ax7) seem lower than in the working unit. I.e at the node before the voltage dividing resistors im getting 225v on the failing unit and 255 on the working unit and checking voltages at pins around the valve they area all lower.

All the filaments work and give correct ac voltage 3.2-3.4v.

Ive tried different tanks. Ive tried switching tubes between units. No help. Ive tried witching th tank in / out  .

Appreciate any guidance!

[HotBluePlates]

I have completed it but its not working as it should and I cant quite figure out why.
Its wired exactly (as far as I can see) as the first unit (which works great)
...
All the voltages related to v1 (the 12ax7) seem lower than in the working unit. ...

Now is probably the time to post DC voltages from each tube pin.  Consider posting the same voltages from your working unit as well.

Also provide some photos of the malfunctioning unit, and we'll see whether there's a wiring error present that you're unable to see because of your closeness to the project.

[bullkelp]

Here are the exact voltages.

Non functioning unit:
V1 12ax7
Pins.
1. 134v
2.
3. 1.3v
6. 225v
7. 102v
8. 113v

v2. 12at7
Pins.
1. 118v
3. 1.6v
6. 123v
7.
8. 1.9v

V3. 6v6
3. 294v
4. 301v
5. 3.3mV
8. 22v

Functioning unit:
V1 12ax7
Pins.
1. 154v
2.
3. 1.5v
6. 250v
7. 114v
8. 122v

v2. 12at7
Pins.
1. 124v
3. 1.7v
6. 121v
7.
8. 1.95v

V3. 6v6. (note different power tube)
3. 293v
4. 300v
5. 6.2mV
8. 23.1v

[bullkelp]

Righto
I went thru and checked continuity and found it was lacking between the two B power nodes on the board
I pulled the board and found I’d missed the under board jumper (which is above board in the fender design)
I had it the the junction between the 10k and 100k resistors instead of between the two 100k.
Explains the voltages
Case closed ! 
I think I’ll wire these above board from now on

[HotBluePlates]

I pulled the board and found I’d missed the under board jumper (which is above board in the fender design)

Congrats on finding & fixing the flaw!

You obviously expend great care & effort on your builds, so I didn't want to say it had to be a wiring mistake.  But all new builds generally have a wiring, parts-value, or soldering issue if they don't work 100% when first powered up.

Kudos on the quick recovery!