plotting out deluxe rvb with some dumble bits

[imo1]

I'm also gonna use the heater winding for the relays. This PT has 5A, so way more than enough, and that way I can use the hoffman components and have a regulated supply going to the relays

[martin manning]

When testing the power supplies, I did not put any loads on them. My goal is just to be sure that I have voltages in the right ballpark and no shorts or other errors.

On the relay supply, I might rather go with the 5 VAC supply and run it on regulated. If you use the heater supply, you’ll have to have the relay ground floating, and that means that there is the possibility of shorting with inadvertent contact to ground. The relay coil voltage is not that critical and a voltage doubler rectifier connected to the 5-volt winding will be pretty close to a 12VDC spec voltage, or 5VDC spec using a FWB. You could also use a doubler and a 5V regulator.

[imo1]

Thanks Martin. That makes sense on the relay. I’m using the Hoffman boards and 5v relays, so maybe just use the bridge rect and cap on the end.
Hopefully my voltages are close with resistor drops. I’m coming out similar to the deluxe power supply. I think it’s a couple of 10k.

I’ve got most of the drilling and mounting of switches. Waiting on a couple of pots and various parts. I’m gonna build out the power supply and the relay circuit while I’m waiting.

I’ve got a few shows coming up this week. My goal was to have all mechanical stuff built out before so that I can build circuit starting next week

[imo1]

Had some great shows up here in the PNW, put everyone on planes home and back at it.
I've got almost all the mechanical stuff done. I'm starting to populate boards.
Tomorrow I'm gonna test B+, heaters and bias, and then attach it to my power supply caps and resistors.
I have the relay power off the unused 5V winding. I was gonna attach it to the rectifier socket and then to the board, but realized one of the 5v windings also connects to the DC. IF I were ever gonna go back to a tube rectifier I would have to change the first to PS caps anyway, so I guess I would also need to figure out another solution for the relays as well.

The only thing I'm still mulling over is where exactly to put PS node 5. I have the first 4 in the cap can. I have a 5 pin tagboard by V1. I could pull the P4 there through a dropping resistor and then a 16uF to ground. It would be easiest to use the mounting lug as the ground lug, but that kind of lessens the effect of the preamp grounds all coming to the one point. The amp is getting a bit crowded, but I could also put another tag board in if needed.

I'll try to get some photos. for now, here is the most current layout and the PS schematic with perspective voltages

deluxe_blues_powerv4.png

deluxe_blues_layout_v3.png

[imo1]

I got power supply up and running. B+ seems definitely in the realm. Right now, my relay supply(from the 5v windings) is reading about 7.1. I know it will come down some with the loaded circuit, but probably gonna have to run at least one more diode to get it close(right now I have a bridge rectifier a cap, and another diode before I'm taking it). Neither of the relays is plugged in yet, so there is no load at all.
I'm using Martin's bias circuit that he used for his Deluxe, but even without any load, the most negative voltage I can get is about 26v. I'm gonna try dropping that first resistor back down to a 460r from the 1.2k and see if that helps.

I'm using one of the Weber caps that emulates a GZ34, and I'm getting about 416-17 no load(outside of the dropping resistors) at B+. This seems that it should be pretty close. My initial string is a 10k, 22k, and 2.2k

Hoping to get most of the circuit built this week. I got a gig opening up for Buddy Guy this Saturday, so need to do a little practicing too!

I found a way to get the final node in the circuit. My "trimmer" is attached to a tagboard, and the ground on that is using the ground lug. Just running out of space, and I like the more substantial pot.

IMG_4601.JPG

IMG_4603.JPG

IMG_4604.JPG

[martin manning]

Good progress!

I got power supply up and running. B+ seems definitely in the realm. Right now, my relay supply(from the 5v windings) is reading about 7.1. I know it will come down some with the loaded circuit, but probably gonna have to run at least one more diode to get it close(right now I have a bridge rectifier a cap, and another diode before I'm taking it). Neither of the relays is plugged in yet, so there is no load at all.

Sounds like a good plan. It's nice to know the HV supply is in good shape.

I'm using Martin's bias circuit that he used for his Deluxe, but even without any load, the most negative voltage I can get is about 26v. I'm gonna try dropping that first resistor back down to a 460r from the 1.2k and see if that helps.

It's expected that you might need to adjust that input resistor for the PT's bias tap voltage.

I'm using one of the Weber caps that emulates a GZ34, and I'm getting about 416-17 no load (outside of the dropping resistors) at B+. This seems that it should be pretty close. My initial string is a 10k, 22k, and 2.2k

It might drop more than you want, but you can go with straight SS rectifier and boost it if needed.

[imo1]

Thanks. Trying to get all the voltage bits close as it’s a hassle to get the boards in and out.
I did realize I was using some low voltage diodes in the relay power supply. I’m still a little high, but 6.5. I’m gonna get it down to around 6 for now(assuming it will drop a bit under load)

Put a 470r as input for bias. Having the same issue I had with my last deluxe style build. The bias voltage is close on the upstream side of the 10k resistor feeding the bias pot, but still down around 26 on pot side. Doing a simple voltage divider equation, it makes sense. I think I’m gonna drop that down to around 1k, which would give me most of the bias voltage. It seems that -35 is right around sweet spot. I know this lessens the filtering a bit, but is the only way I can get close

[martin manning]

The values below result in 7.5W dissipation (Pa) with the pot at 50%. The bias voltage is -38.6, assuming 400V Va and Vg2. Any adjustment needed should be made using R1.

[imo1]

Are you taking a bias tap off of the B+ voltage? I’m reading your response as yes, tapping off the full 400v. I have a bias tap winding. I assumed, since you first mentioned this in the deluxe reverb thread, that was the case.

I didn’t mark down my AC voltage coming out of the tap, but it seems to be a standard value for this type of circuit

[imo1]

Just for my own sanity--
The typical Fender bias circuit has a divider from 0-10k over 10k depending on pot setting, so if you have -38vDC coming out of the diode, you would have between -19 to -38. I know the 220k grid resistor changes this some, but this would be a ballpark. With your modified circuit, if you have -38v DC, the 10k in series with the pot, going to the 15k to ground would give -22.8 max negative voltage and around -16 minimum.

I am getting around -38 with the 470R in there. In order to get close to the bias voltage I need, I would need to greatly reduce the series resistor. I can go and check the bias tap AC voltage. I could additionally make the "bias set" resistor smaller from 470, but I think I may hit the ceiling of the bias voltage coming out of the tap and still not have enough negative voltage to do what I need.
I'm just checking that I'm not missing something

[martin manning]

The theory of this bias circuit is you use the input resistor to set a level of negative voltage, and then a divider made up of the fixed 10k (upper leg) and the combination of the 10k pot and the 15k to ground make a lower leg which is adjustable from 15k to 25k. With those values a reasonable range is achieved using a standard 10k bias pot. The current draw is not fixed since the resistance to ground varies, and that will cause more or loss voltage drop across the input resistor. That isn’t a big deal if the input resistor is relatively small, as it is when the circuit is fed from a 50-60V bias tap.

[martin manning]

What is the AC voltage on the bias tap?

If you need more negative DC voltage, you can reduce the input resistor further, or you can increase the resistor on the ground side of the pot. The range will be reduced as that gets bigger, though.

[imo1]

I have the bias tap connected to the circuit, but I’m only seeing about 43v AC going in. I tried knocking input resistor down to 230R, but even then, looking at the circuit, I don’t see how to get in the ballpark of what I need.
With the 10k after diode and going to pot and then the 15k, even if the pot is at its lowest setting I’m only gonna get -23 or 24 v. That 10k is creating a voltage divider that would need around -60v at its input to get around -35.
If I stay with the 10k, I would need something like 75-10k to ground and that would give me no sweep.
It seems to me, with this voltage tap, the only move is to greatly lessen the middle resistor. Isn’t it there for additional filtering of bias supply? If I were to take it down to 1k, that gives me around 35-36 v, and would still be an improvement over the original design.
Other than additional filtering, is this resistor serving a purpose I’m not seeing?

[sluckey]

I would just forget about the PT bias tap and connect to one of the HV leads. Then replace the 470Ω with a 100K and see where that lands you. Adjust the 100K up/down until you have the bias voltage range you want, ie, -35V with the bias pot set about mid range.

[imo1]

I would just forget about the PT bias tap and connect to one of the HV leads. Then replace the 470Ω with a 100K and see where that lands you. Adjust the 100K up/down until you have the bias voltage range you want, ie, -35V with the bias pot set about mid range.

I am using the Deluxe reverb boards and chassis. Since the bias voltage is used in the trem circuit, it would be a bit more complicated to create a second bias section. It would also require addition of a couple of tag boards.

I really appreciate the replies and not trying to be difficult!

It seems like adding a lot of extra complexity to something that already works. I like the general amendments to the bias circuit, especially the "fail to max" change. It seems like even if I were to lower the series resistor to 1k, I'm still getting benefits beyond the original circuit in terms of filtering with a 1k 47uF addition. At that point, it seems that I just want to make sure I have enough sweep to account for tube variance in the future.

Is there any other reason for the series 10k beyond additional filtering?