plotting out deluxe rvb with some dumble bits

[martin manning]

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.
...
Other than additional filtering, is this resistor serving a purpose I’m not seeing?

The 43VAC is on the low side for a bias tap. Take the input resistor down to 100 ohms or 47 ohms. It has more effect than one might think because the current going through it is spiky. The 10k is for filtering and for its role in the divider.

[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.

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.

Not complicated at all. Simply disconnect the PT bias tap lead from the board. Connect either pin 4 or pin 6 of the rectifier socket to the bias board where the PT bias tap used to be. Then replace the 470Ω with a 100K. That's all (other than possibly fine tuning the value of the 100K to obtain the desired bias range).

The tremolo will be unaffected. The only thing the bias voltage does in the tremolo circuit is ensure the trem tube is in hard cutoff whenever the trem is turned off by the footswitch. Stomp the footswitch to turn the tremolo on and that negative bias voltage at the trem tube's grids will quickly rise to zero volts allowing the tube to conduct.. This makes for a fast turn on of the LFO which is normally slow to start up.

Try it. You have nothing to lose and a lot to gain.

[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.
...
Other than additional filtering, is this resistor serving a purpose I’m not seeing?

The 43VAC is on the low side for a bias tap. Take the input resistor down to 100 ohms or 47 ohms. It has more effect than one might think because the current going through it is spiky. The 10k is for filtering and for its role in the divider.

I think the lower bias tap might be a reflection of the lower B+

[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.

Not complicated at all. Simply disconnect the PT bias tap lead from the board. Connect either pin 4 or pin 6 of the rectifier socket to the bias board where the PT bias tap used to be. Then replace the 470Ω with a 100K. That's all (other than possibly fine tuning the value of the 100K to obtain the desired bias range).

The tremolo will be unaffected. The only thing the bias voltage does in the tremolo circuit is ensure the trem tube is in hard cutoff whenever the trem is turned off by the footswitch. Stomp the footswitch to turn the tremolo on and that negative bias voltage at the trem tube's grids will quickly rise to zero volts allowing the tube to conduct.. This makes for a fast turn on of the LFO which is normally slow to start up.

Try it. You have nothing to lose and a lot to gain.

I will definitely try this down the road.. however/—

This project is a mad scramble to have a super road worthy amp, ready to ship in about a week or so. I’ll have to ship the cab ahead, and will fly down with the chassis, assembling it between rehearsals.


There are a number of possible issues to work through, so I need to keep things simple where I can. I have a big show this Saturday, and then I can hopefully finish and work out any bugaboos

[martin manning]

I think the lower bias tap might be a reflection of the lower B+

Could be. For reference the Hammond 290BX PT I used (DR replacement) bias tap is 50VAC. I think you can get what you need with a lower input resistor value.

BTW, if you use the HV supply to feed the bias circuit you will want to reduce the size of the filters. Otherwise, after the main power is switched on the high source impedance will prevent the bias voltage from reaching a safe level for several seconds.

[imo1]

Bias is sorted, at least for building circuit. Put a 100r 3w in and am getting from -33 to -40 unloaded. I think it will be in range and, if not, should be easy to sort.

Power supply is connected and testing around where it should be. Next step is connecting all the bits and seeing how close I am with circuit load. I anticipate tweaking PS dropping resistors a bit.

[imo1]

Got my voltages in order.
I was expecting a little higher output from the PT, but with the Weber “cap” rectifier I’m getting 400 at OT. Used a 1.5k for P3, then 15k and 2.2– getting 385 at P3, 295 at P4, and 285 at P5

Now off to actual circuit examination

[martin manning]

400V with no power tubes installed?

[imo1]

No, this is with full circuit, including load. I already had done the testing without tubes.
I’d roughed in the PS resistors, but obviously couldn’t fine tune until I had circuit load.

[imo1]

I am gonna order a speaker today. Need to get it shipped ahead of me to austin. I’ve got the warehouse ET65s in my other cab(2x12) and like that a lot for my main amp, so, without really knowing what the amp will sound like, but anticipating some similar characteristics, but at a lower power level, this seems like the best bet for now.

I anticipate figuring some stuff out once I have it in the field.

[martin manning]

Great! It will be interesting to see how the channels balance out and what kind of OD character it has.

[imo1]

Man! everything worked right out of the gate! Though I will never have the thoroughness of the great builders, I am definitely becoming better at slowing down to avoid troubles later.

ALl the voltages are where they need to be. Everything sounds good. The power node to the reverb is a little lower than stock(@375) But I didn't want to lessen the drop from the first node too much to lessen any filtering.
Main channel has a great sound and climbs little into distortion if you push it. That is with the 220k to ground. I'm gonna play it and see if I want to clean it up some more.
Set the OD trimmer to 25k and honestly it sounds pretty close. I like having the tone controls on it.
The bass is better than a standard deluxe, though even with the bigger core transformer, stiffer filtering, and smaller cathode caps, still have that deluxe quality. I think ultimately it comes down to power to push the low end. I feel like I'm pushing it about as much as I can with this form. I have it sitting right at about 400v and 21mA on the 6v6's.

The cool thing is that if I had to play the amp without my pedalboard, outside of a couple of delay/time based things I use, I would feel pretty covered.

Now, to put some miles on it, and then need to figure out some type of solution for a front panel eventually

[didit]

Sounds like it sounds perfect.

Congratulations ..

[martin manning]

Nice! Where did you end up putting the level controls in the circuit?

[imo1]

Ok. check this out. Super quick vid just to get a sense of what the baseline is. I have the volume at about 9 on the amp. guitar volume is rolled down to about 6 and you can hear that chime. It is amazing! Almost like a AC15. I hit the PAB and you can hear the jump, and when I hit the OD with it, it is pretty heavy. The iphone doesn't pick up the top end. It isn't scratchy or screechy, but has this glassy top that really speaks to me.

I tried to put video in the link but couldn't get it to work.
Here is a link:
https://vimeo.com/1111119897?share=copy#t=103.272