D'Lite presence wiring question

[drew]

I'm building a D'Lite (layout: http://bad-domain/DumbleLite/D-Lite%20L ... Relays.jpg ; schematic: http://brownnote.net/forum/viewtopic.php?t=274 ), but using a 4K OT with 2-4-8 ohm taps instead of the standard 8K with 4-8-16. I have a few questions about the presence control.

The layout indicates that the jumper from the 6K2 resistor on the mainboard should be connected to the 4 ohm terminal on the impedance selector switch.

Questions:

1. Which terminal (2, 4, or 8 ohm) should I connect the jumper to?

2. Would the different OT require a different value resistor on the mainboard?

3. How is it that the presence control is functional when the impedance is set to one of the two positions that the jumper is not connected to? (Keep it simple; I'm a newb.)

TIA

[Bob-I]

The D'Lite should have the Negative Feedback Resistor (NFB) connected to the 4 ohm tap. The presence works in all impedance positions. As long as you stick with the same number of output tubes you don't need to change the NFB resistor.

[heisthl]

I'm building a D'Lite (layout: http://bad-domain/DumbleLite/D-Lite%20L ... Relays.jpg ; schematic: http://brownnote.net/forum/viewtopic.php?t=274 ), but using a 4K OT with 2-4-8 ohm taps instead of the standard 8K with 4-8-16. I have a few questions about the presence control.

The layout indicates that the jumper from the 6K2 resistor on the mainboard should be connected to the 4 ohm terminal on the impedance selector switch.

Questions:

1. Which terminal (2, 4, or 8 ohm) should I connect the jumper to?

2. Would the different OT require a different value resistor on the mainboard?

3. How is it that the presence control is functional when the impedance is set to one of the two positions that the jumper is not connected to? (Keep it simple; I'm a newb.)

TIA

1. The 4 Ohm seems to be the preferred terminal for the standard(not bluesmaster) PI feedback line.
2. The 6k2 was chosen as a good value for the D'lite supplied transformer. This is an easy value to experiment with - most schematics show 4k7 with 390 to ground (100 watt) or 8k2 with 1k to ground( some 50 watt version) and all three still use the 2k pot with a 1uf cap.

3. The various taps (16,8,4) all have signal on them at all times - the selector just routes it to the speaker. The 4 OHM tap has less voltage (but more current avaiable) than the 8 OHM tap. So which tap you use for FB is important, but any tap can be used if you change the FB resistors accordingly. I think the main reason that the FB values are scaled for the 4 OHM tap is the Bassman transformers that HAD used a lot were 4 OHM only.

[dogears]

Good move on the 4K tranny. Use 6L6 tubes with that.

Also, I would not use the 6.2K This will give a little harshness if used in conjunction with the 390 tail. Keep in mind that you do need to scale the presence cap if you change the tail. The tail is in parallel with the 2K pot. I'd stick with the 4.7K on 4 ohm and 390 ohm tail.

Better yet, experiment with the Bluesmaster values. Many seem to really dig them.

In the end, let your ears choose the way.

[Robert]

heisthl said:

The 4 Ohm seems to be the preferred terminal for the standard(not bluesmaster) PI feedback line.

I've not been aware the preferred terminal was other than the 4ohm one for the BM. It's easy enough to switch, but which one are you suggesting is preferred?

[ayan]

heisthl said:

The 4 Ohm seems to be the preferred terminal for the standard(not bluesmaster) PI feedback line.

I've not been aware the preferred terminal was other than the 4ohm one for the BM. It's easy enough to switch, but which one are you suggesting is preferred?

As far as I know, the BM ALSO uses the 4-ohm tap.

Gil

[dogears]

Correct. BM is on the 4 ohm. I have seen 2 100 watters and 1 50 watter. Even the 50 had it on the 4 ohm.

heisthl said:

The 4 Ohm seems to be the preferred terminal for the standard(not bluesmaster) PI feedback line.

I've not been aware the preferred terminal was other than the 4ohm one for the BM. It's easy enough to switch, but which one are you suggesting is preferred?

As far as I know, the BM ALSO uses the 4-ohm tap.

Gil

[heisthl]

heisthl said:

The 4 Ohm seems to be the preferred terminal for the standard(not bluesmaster) PI feedback line.

I've not been aware the preferred terminal was other than the 4ohm one for the BM. It's easy enough to switch, but which one are you suggesting is preferred?

My bad - I was mistaken, when the recent BM craze started on this board the info was sketchy and seemed to gravitate towards the 8 OHM tap instead of the 4 OHM.

[DaveBo32]

I just order an 8k OT with only a 8ohm tap at 15 watts. I may need to alter the 6.2k and 390 tail resistors. Since I will be attaching the NFB to the 8ohm tap will my values need to change? Is there a formula used to calculate the prefered values or is it just adjusted by ear? I currently have a hammond OT in my Dlite. My dlite sounds ok, but it's lacking warmth. Sounds a little steril. I think it could be my speaker or OT. I am also using silver mica caps for the treble and brite switch. I heard they can be tone suckers, is this true?

[heisthl]

The 8 Ohm tap has roughly twice the voltage swing (and half the current) so you can double the resistor values and get close. I would try the 8k2/1k with the new O.T. Silver Mica caps are too clean for clones if you follow the recommended component types (VD plates resistors, PS series Orange drops etc.) and you need the ceramic disc caps to give the sound character with their inherent grainyness. Make sure your V1 plate voltages are less than 205 as that can lead to the sterile sound.

[dogears]

Henry, the 8 ohm tap has 40% more voltage, not double. You multiply the resistor by 1.4 to get the scaled size.

Having said that, if you use the 8k/1K pair, you have a hell of a lot more NFB with an 8 ohm tap. That is only 8 to 1 ratio. A Dumble I saw with only an 8 ohm tap actually had an 8.2K over a 390ohm tail! About 21 to 1 ratio.

Keep in mind that changing the tail has a big effect on the knee of the presence circuit. If you want traditional Dumble presence, then you have to stick to the 390ohm tail. Or scale the cap...

The 8 Ohm tap has roughly twice the voltage swing (and half the current) so you can double the resistor values and get close. I would try the 8k2/1k with the new O.T. Silver Mica caps are too clean for clones if you follow the recommended component types (VD plates resistors, PS series Orange drops etc.) and you need the ceramic disc caps to give the sound character with their inherent grainyness. Make sure your V1 plate voltages are less than 205 as that can lead to the sterile sound.

[heisthl]

Henry, the 8 ohm tap has 40% more voltage, not double. You multiply the resistor by 1.4 to get the scaled size.

Having said that, if you use the 8k/1K pair, you have a hell of a lot more NFB with an 8 ohm tap. That is only 8 to 1 ratio. A Dumble I saw with only an 8 ohm tap actually had an 8.2K over a 390ohm tail! About 21 to 1 ratio.

Keep in mind that changing the tail has a big effect on the knee of the presence circuit. If you want traditional Dumble presence, then you have to stick to the 390ohm tail. Or scale the cap...

Thanks for catching that - the 8k2/1k recommendation is correct as it is almost exactly 1.4 times larger than what he has now. The amount of actual feedback voltage available to the presence control does work out to be a little higher. When I've played with this in the past I really couldn't hear much of a difference in actual response although I've never used 6k2. My experimentation was trading 4k7/390 on the 4ohm tap to 8k2/1k on the 8 ohm tap. My current favorite is 9k1/1k on the 8 ohm tap.

[DaveBo32]

Thanks Guys for your help. I should be getting the OT in soon, In the meantime, I'll change out those silver mica's..

Thanks again,
Dave

[DaveBo32]

The 8 Ohm tap has roughly twice the voltage swing (and half the current) so you can double the resistor values and get close. I would try the 8k2/1k with the new O.T. Silver Mica caps are too clean for clones if you follow the recommended component types (VD plates resistors, PS series Orange drops etc.) and you need the ceramic disc caps to give the sound character with their inherent grainyness. Make sure your V1 plate voltages are less than 205 as that can lead to the sterile sound.

Heisthl,
How would I knock down that plate voltage? Mind is reading 207.

[dogears]

Raise the dropping resistor that comes immediateky after the choke. Try a size 1K or 2K larger.

The 8 Ohm tap has roughly twice the voltage swing (and half the current) so you can double the resistor values and get close. I would try the 8k2/1k with the new O.T. Silver Mica caps are too clean for clones if you follow the recommended component types (VD plates resistors, PS series Orange drops etc.) and you need the ceramic disc caps to give the sound character with their inherent grainyness. Make sure your V1 plate voltages are less than 205 as that can lead to the sterile sound.

Heisthl,
How would I knock down that plate voltage? Mind is reading 207.