Reverb 6G15 clone doubts

[Lowerleftcoast]

Hey @sudogeek can you provide a layout to go along with that schematic? If not, can you look over the layout in post #20 to see if I missed anything?

 

[maybeoneday]

I am trying others calculators but still same result 180VDC output (input red-red 280VAC)
On the secondary I measure red-red 280VAC and red-red/yellow 140VAC.

About the layout, can I not leave the B3 filter cap there and do the wiring you suggested? It doesn't fit on my board moving it in that position.

I can adjust the DIYLC file and attach it so everybody can make the changes they think is better.

 

[Lowerleftcoast]

About the layout, can I not leave the B3 filter cap there and do the wiring you suggested? It doesn't fit on my board moving it in that position.

No problem. If the board is already made, just ignore the suggestion to move the last filter cap.

I can adjust the DIYLC file and attach it so everybody can make the changes they think is better.

That is fine, I am sure some of the other shock brothers might have different opinions for the ground scheme.

On the secondary I measure red-red 280VAC and red-red/yellow 140VAC.

Doh. My mistake. So sorry for the confusion. The Hammond 261D6 is rated for 250VAC red to red. To get the 300VDC B+ you will have to use the bridge rectifier. The PT CT will not be used. Heat shrink the PT CT and tuck it away. To get ~300 volts B+, it would need to be wired like this.



FYI it is reading 280VAC unloaded. When it is under load in the circuit the voltage will be lower. Hammond shows 250VAC with a 50mA load.

 

[maybeoneday]

Second try

 

[Ronno25]

I think you've got a ground loop that you'll want to eliminate. I put a red X on it below.

Also, I may be dense, but I thought it was established that one of the tank rca jacks should be isolated. On the diagram you guys have been working with aren't they both grounded? Maybe I'm reading it wrong?

 

[maybeoneday]

Corrected!

I think @Lowerleftcoast meant the tank ground to chassis, only one RCA cable will be grounded, not both. I think he was not talking about the RCA sockets.
I have also added a version without HT CT, with Hammond 290WEX

 

[Lowerleftcoast]

On the diagram you guys have been working with aren't they both grounded? Maybe I'm reading it wrong?

The schematic we are working from has a ground scheme that keeps each ground node together and is referenced to ground at only one point. In this case the one point is through a hum blocking network I have been calling a buffer. This ground scheme isolates all of the jacks from the chassis. Even the RCA jacks. We will have to be creative to connect the reverb tank chassis with the 6G15 chassis to have the reverb tank chassis acting as a shield (Faraday Cage).

I am pretty sure the Ronno 6G15 is not using this *theoretically better* ground scheme. The Ronno version likely has the jacks connected to the chassis so, lifting one side of one of the reverb cable shields will eliminate the reverb tank chassis ground loop. To do that one RCA jack can be isolated or it can be done any other way. (IIRC some tanks have an isolated RCA jack from the factory, so check for that.)

Second try

As mentioned this schematic tries to keep each ground node together. Each ground node has a filter cap associated with it. I have highlighted the layout below with lavender for the node powering the 6K6 screens and the reverb transformer. I have highlighted the node for the other tubes in maroon. Ideally the current in a node should stay close to each node filter cap. IOW, there is an order for connecting the grounds to the ground bus. Essentially all of the lavender should stay together and all of the maroon should stay together. Anyway that is why the bus is not just connecting the three filter caps in a neat little row.

 

[maybeoneday]

Another thing I didn't know, I always thought there wasn't an order for the ground on the buss.

Now should be correct.

 

[Lowerleftcoast]

Now should be correct.

Disclaimer: There are many ground schemes that are perfectly quiet that do not follow these *theoretically best* ideas. The schematic we are using follows most of these *theoretically best* grounding practices.

Have a read through the Valve Wizard (AKA Merlin Blencowe) grounding article. IDK how many times I have read this article. I seem to gain a little more understanding with each read.

I mentioned before about looking at the PT/rectifier/reservoir cap as the source of the (+ and -) DC. This is explained in Chapter 15.3. The idea is to keep the noisy ripple current from interacting with the more sensitive parts of the circuit. Fig 15.5.b shows the PT/rectifier/reservoir cap with what appears to be the most compact configuration possible. You don't have to go that far but it would be *better* to make the wire runs short between these three. The largest current pulses are happening in this circuit and in these wires. On your latest version the reservoir cap negative is not directly connected with the negative end of the bridge rectifier. This version of the layout has the ripple current closest to the second filter cap.

Try to wrap your head around Chapter 15.4

Chapter 15.7 addresses the Ground bus. Fig 15.10.b is what we are trying to approximate with our layout design.

 

[maybeoneday]

Now I get why you moved the 3rd filter cap in that position.

I will definitely read the article!!!

About the bridge rectifier I thought the buss was our negative of the load, should I go to the bridge directly from the reservoir of the 2nd filter cap (6K6 circuit)?

 

[Lowerleftcoast]

I thought the buss was our negative of the load, should I go to the bridge directly from the reservoir of the 2nd filter cap (6K6 circuit)?

I am not sure I know what you are asking.

The 1st cap is the reservoir cap. The artificial CT from the bridge rectifier should connect directly to the negative side of the reservoir cap.

This should be done on every amp. Some amps make this difficult (think every fender amp with a cap pan.) The heavy ripple current flows around the transformer-rectifier-reservoir circuit. Short distances between these parts can help keep hum and buzz at bay.

 

[maybeoneday]

The 1st cap is the reservoir cap. The artificial CT from the bridge rectifier should connect directly to the negative side of the reservoir cap.

This is the answer to my question

Do you think the small ground buffer circuit is something could be added in all amps?

 

[Ronno25]

Ideally the current in a node should stay close to each node filter cap. IOW, there is an order for connecting the grounds to the ground bus. Essentially all of the lavender should stay together and all of the maroon should stay together.

I built my 6g15 like this and also used hum blocker buffer, grouping all my power amp and preamp leads separately on the buss bar. The issue I ran into given the layout I also chose (the original Fender Reverb Unit layout) is it resulted in many and very long ground leads running through the amp. I'm considering rewiring my amp with a bus bar in parallel with the circuit board to allow for short ground leads. This would also be a compromise as it would be difficult to perfectly separate preamp and power leads this way. And especially difficult to connect my buffer to the preamp end of the ground bus (specified by the schematic you guys were using).

Any idea as to what is more important: short ground leads OR grouping the nodes on the bus bar completely separately?

 

[Lowerleftcoast]

Any idea as to what is more important: short ground leads OR grouping the nodes on the bus bar

I would think the long distances pose more of a threat.

Are all of the jacks isolated from the chassis?

Where is the reservoir cap... and the filter caps?

 

[Ronno25]

@Lowerleftcoast The reservoir cap and the other filter caps are in the doghouse on the back of the chassis. The preamp filter cap is grounded with the preamp. The reservoir and 2nd filter cap are with the power amp. All jacks including rca jacks are isolated.

 

[maybeoneday]

Putting the thicker wire should not compensate the long distance?

 

[Lowerleftcoast]

Putting the thicker wire should not compensate the long distance?

No, these are all relatively short distances as far as loss due to length (resistance) of wire.

Even though the ground wires will meter as *0* volts, there is current running through them. If the return current is noisy, it is possible for coupling with the signal which in turn will amplify the noise through the gain stages. Keeping wires short will give less opportunity for wires to act as antenna. Placement and routing of the signal wires is important to keep noise from being amplified.

This is why a ground scheme that doesn't follow a *theoretically best* grounding scheme can be quiet. The noisy bits are not amplified by the gain stages.

I'm trying to fix an annoying hum I have in my 6g15 that increases as the mixer knob increases.

I notice the B+2 is very close to the coupling caps. Try to make some space there. (Green arrows on the picture below.)

Does your 6G15 use a half wave rectifier like the original?

 

[Ronno25]

@Lowerleftcoast It uses a full wave. The same as in post #23 above. I'll give a shot wiggling those B+2 wires. They may be really tight so I might have to replace the wires altogether.