D'Lite 44 Build Progress

[Structo]

Hey guy.
Your preamp voltages don't seem to fall in line with reported voltages.

Especially if trying for the Dumble tone.

V1 should have around 190,.
V2 around 200v.
Phase Inverter around 300v (280p-300v)

[lord preset]

Hey guy.
Your preamp voltages don't seem to fall in line with reported voltages.

Especially if trying for the Dumble tone.

V1 should have around 190,.
V2 around 200v.
Phase Inverter around 300v (280p-300v)

I am after good tone - not necessarily Dumble tone, if only because I don't really know what that would be. I played a real one for a few minutes 35 years ago and don't remember it that well.

As for the voltages they are higher than reported values. I spaced out and neglected to mention the PI which is around 326. So if I were to bring them down I would need to alter the dropping chain resistor values on the power supply. Is there an idiots guide to calculating better values? Or should I try to drop B+ coming off the transformer down to Brown Note PT specs with a zener diode (i.e. 325-0-325 vs 355-0-355)?

Assuming I bring voltages down to spec is that likely to have any impact on the voltage difference I'm seeing between V2a and V2b?

Thanks!

[lord preset]

BTW, here is the amp in all it's gaudy glory. I'm not big on black or tan.

[ToneMerc]

Assuming I bring voltages down to spec is that likely to have any impact on the voltage difference I'm seeing between V2a and V2b?

Rectify the issue in the pre amp tubes first, that's why I asked you to post the plate and cathode voltages of V1-V3.

TM

[lord preset]

Assuming I bring voltages down to spec is that likely to have any impact on the voltage difference I'm seeing between V2a and V2b?

Rectify the issue in the pre amp tubes first, that's why I asked you to post the plate and cathode voltages of V1-V3.

TM

Ok I remeasured the voltages

Plate. Cathode
V1a 213. 2.15
V1b. 221. 2.01
V2a. 194. 1.71
V2b. 256. 2.45
V3a. 325. 67
V3b. 326. 67

Thoughts?

Thx

[lord preset]

Still looking for suggestions on how to bring voltages down to spec on the preamp and PI tubes. Should I be trying different dropping chain resistor values?

Thx

Assuming I bring voltages down to spec is that likely to have any impact on the voltage difference I'm seeing between V2a and V2b?

Rectify the issue in the pre amp tubes first, that's why I asked you to post the plate and cathode voltages of V1-V3.

TM

Ok I remeasured the voltages

Plate. Cathode
V1a 213. 2.15
V1b. 221. 2.01
V2a. 194. 1.71
V2b. 256. 2.45
V3a. 325. 67
V3b. 326. 67

Thoughts?

Thx

[ToneMerc]

You have some type of issue outstanding at V2, there should not be a 60v delta between the two halves and V2b has a higher than normal cathode voltage. Make sure you do not have plate and cathode terminations inverted and verify right resistor values. Have you swapped V2 to verify that the issue stays with the tube socket?

Once you get some symmetry you can work on the string, as it stands now upstream of B3 has no bearing on that issue at V2.

Take more detailed guts shots from above the board, so we can put more eyes on it.


TM

[lord preset]

You have some type of issue outstanding at V2, there should not be a 60v delta between the two halves and V2b has a higher than normal cathode voltage. Make sure you do not have plate and cathode terminations inverted and verify right resistor values. Have you swapped V2 to verify that the issue stays with the tube socket?

Once you get some symmetry you can work on the string, as it stands now upstream of B3 has no bearing on that issue at V2.

Take more detailed guts shots from above the board, so we can put more eyes on it.


TM

I have swapped V2 tubes and the issue is consistent. I'll recheck terminations/values and post pics tonight. Thanks much.

[lord preset]

You have some type of issue outstanding at V2, there should not be a 60v delta between the two halves and V2b has a higher than normal cathode voltage. Make sure you do not have plate and cathode terminations inverted and verify right resistor values. Have you swapped V2 to verify that the issue stays with the tube socket?

Once you get some symmetry you can work on the string, as it stands now upstream of B3 has no bearing on that issue at V2.

Take more detailed guts shots from above the board, so we can put more eyes on it.


TM

I have swapped V2 tubes and the issue is consistent. I'll recheck terminations/values and post pics tonight. Thanks much.

Tonemerc nailed it. I had two resistor values reversed (noted in pic). Fixing that balanced out the plate and cathode voltages on V2. Now I have 223 plate and 2.1 cathode on V2a, and 226 plate and 2.03 on V2b.

Now that's taken care of, I'm back to what to do about voltages being too high across the board. I have to assume this is simply because my PT has a higher B+ than the Brown Note spec (325-0-325 vs my PT 355-0-355).

[ToneMerc]

Ok, good job.
Verify that you indeed have the 150k from the B5 node bleeding to ground. If that is good, go the first resistor in the preamp rail,which according to the layout is 1K, change that to at least 3.3K, maybe as high 4.7K

Then recheck V1 thru V3 voltages


Tm

[lord preset]

Ok, good job.
Verify that you indeed have the 150k from the B5 node bleeding to ground. If that is good, go the first resistor in the preamp rail,which according to the layout is 1K, change that to at least 3.3K, maybe as high 4.7K

Then recheck V1 thru V3 voltages


Tm

150K is bleeding to ground. Check

I swapped out the 1K resistor for 3.3k. Not a lot change. I now have a 4.7K resistor in there and I get:

V1a: 208V Plate 1.8V Cathode
V1b: 213V, 1.8V
V2a: 209V, 1.9V
V2b: 212V, 1.9V
V3a: 306V, 62.5V
V3b: 305V, 62.5V

I can't say I'm hearing any difference. Should I be going higher than 4.7K and/or changing other resistor values in the preamp power rail?

Thx

[ToneMerc]

Ok, good job.
Verify that you indeed have the 150k from the B5 node bleeding to ground. If that is good, go the first resistor in the preamp rail,which according to the layout is 1K, change that to at least 3.3K, maybe as high 4.7K

Then recheck V1 thru V3 voltages


Tm

150K is bleeding to ground. Check

I swapped out the 1K resistor for 3.3k. Not a lot change. I now have a 4.7K resistor in there and I get:

V1a: 208V Plate 1.8V Cathode
V1b: 213V, 1.8V
V2a: 209V, 1.9V
V2b: 212V, 1.9V
V3a: 306V, 62.5V
V3b: 305V, 62.5V

I can't say I'm hearing any difference. Should I be going higher than 4.7K and/or changing other resistor values in the preamp power rail?

Thx

In reality, real Dumbles have preamp voltages all over a range. Initially I started to mention to just change that 1K to a 6.8K, but I wanted to get a feel for a mid point change. If you like it, leave where it is.

You will find that preamp voltages will change and vary among different preamp tubes, even among the same brands. I would roll a few different tubes through it, documenting any changes you do or don't notice, get used to to the amp. In a few weeks if you wish, change the 4.7K to a 6.8K.

What tubes were installed when you recorded these voltages? Are they JJ's?

TM

[lord preset]

Ok, good job.
Verify that you indeed have the 150k from the B5 node bleeding to ground. If that is good, go the first resistor in the preamp rail,which according to the layout is 1K, change that to at least 3.3K, maybe as high 4.7K

Then recheck V1 thru V3 voltages


Tm

150K is bleeding to ground. Check

I swapped out the 1K resistor for 3.3k. Not a lot change. I now have a 4.7K resistor in there and I get:

V1a: 208V Plate 1.8V Cathode
V1b: 213V, 1.8V
V2a: 209V, 1.9V
V2b: 212V, 1.9V
V3a: 306V, 62.5V
V3b: 305V, 62.5V

I can't say I'm hearing any difference. Should I be going higher than 4.7K and/or changing other resistor values in the preamp power rail?

Thx

In reality, real Dumbles have preamp voltages all over a range. Initially I started to mention to just change that 1K to a 6.8K, but I wanted to get a feel for a mid point change. If you like it, leave where it is.

You will find that preamp voltages will change and vary among different preamp tubes, even among the same brands. I would roll a few different tubes through it, documenting any changes you do or don't notice, get used to to the amp. In a few weeks if you wish, change the 4.7K to a 6.8K.

What tubes were installed when you recorded these voltages? Are they JJ's?

TM

I've got a Mullard RI in V1, a Tung-sol RI in V2, and a JJ in V3. I had a pair of Sylvania STR 387s available for this amp, but no decent old glass for the preamp tubes. I am going to sit tight for now and try it out on my Friday gig before changing anything else. I can only tell so much hearing the amp by itself. Thanks again for all the help.

[ToneMerc]

I've got a Mullard RI in V1, a Tung-sol RI in V2, and a JJ in V3. I had a pair of Sylvania STR 387s available for this amp, but no decent old glass for the preamp tubes. I am going to sit tight for now and try it out on my Friday gig before changing anything else. I can only tell so much hearing the amp by itself. Thanks again for all the help.

Sounds like a plan.....enjoy it and you are welcome.

TM