Bassman Build-up (a bit long)

[stelligan]

Congrats on no smoke!! I can sympathize with the tight wiring woes. Curved hemostats are your friend....

That presence circuit on the D'Lite has been a topic of discussion before. May be best to remove it from ground and follow something like 102 pictured here: https://tubeamparchive.com/download/file.php?id=20659
The resistor and cap are on the board in 102 but, you can keep the components at the pot.
JazzGuitarGimp is right. If those are 6L6s, bias up to 33-35mv.

Voltages don't seem right at V1 and high at V2. Can't figure why V1 pin 1 is so low and can''t make out the resistor values from your pics. I am sure all here are willing to remotely help. Lord knows they have saved my bacon before(maybe I should avoid frying references). Jelle's offer for help would be a drive well spent if you get stuck IMHO.

It's alive!! You are most of the way there - again congrats.

[ToneMerc]

The BN power schematics are generally based on the 430V B+ 6V6 versions. Since you have 470V B+ you need to increase the first resistor in the power rail from 1K to at least 3.6K. This will decrease the excessive voltage at the PI and align the rest of the rail. Also, try changing your V1 tube, on the A side you have low plate voltage and low cathode voltage.

TM

[ToneMerc]

Just noticed your bias comment, if you are running 6l6's you need to change the bias tail reistor from 10K to 27K. The 10K is for the 22W 6V6 amp as is the layout that you posted.

TM

[JazzGuitarGimp]

One thing you might try; with the power off, measure the resistance from V1, pin 3 to GND. It should be 3.3K, but I am wondering if it's actually closer to zero. Also, make you don't have the 'lytic at this pin in backwards. Also note that the 5uF cap in parallel with the 3.3K resistor will give a false reading until it is fully charged. So keep the ohmeter leads on pin 3 and GND until the reading stablizes.

[stelligan]

The BN power schematics are generally based on the 430V B+ 6V6 versions. Since you have 470V B+ you need to increase the first resistor in the power rail from 1K to at least 3.6K. This will decrease the excessive voltage at the PI and align the rest of the rail.

TM

Good call.

Sorry so late to the thread/build but, I have notes from a Bassman iron D'Lite power supply with dropping string: 3K3, 15K, 10K with 150K FET sim that gave me: V1 190 at pin 1 196 pin 6 and 212, 219 at V2

I may have some I could mail you. Let me know.

First must track down the voltage asymmetry at V1...

[dezmoduo]

Oh boy. Thanks to the responses, I've spent the last two hours looking at what there and whats needed in terms of resistors to get the voltages under control.
I could take a picture, but suffice it to say, the 220K/3W resistors are fine but going up the side from where the 1K/3W should be, all three are 2.2K. (WTH was I thinking?)

I have the proper 3W 1K and 22K items on hand. First there's some salmon that needs broiling.

Unreal.

Gary

[ToneMerc]

Oh boy. Thanks to the responses, I've spent the last two hours looking at what there and whats needed in terms of resistors to get the voltages under control.
I could take a picture, but suffice it to say, the 220K/3W resistors are fine but going up the side from where the 1K/3W should be, all three are 2.2K. (WTH was I thinking?)

I have the proper 3W 1K and 22K items on hand. First there's some salmon that needs broiling.

Unreal.

Gary

Gary, don't even waste your time installing the 1K, at least install a 2.2K there.

TM

[dezmoduo]

Will do. Just getting set up now.

Gary[/quote]

Gary, don't even waste your time installing the 1K, at least install a 2.2K there.

TM[/quote]

[dezmoduo]

The resistors have been changed on the capacitor board. 2.2K,22K, 2.2K (was existing). There is some improvement in the voltages, some are spot on, other still high, but less so, and a couple on V1 are way low to falling off the chart.

I've tapped out a couple of wonky grounds on the common buss.
V3, pin 3 to 8 had a cold/weak joint.
I saw faint blue arcing in one of the pin sockets and I reseated the V5 tube. That solved a little random pop when the master was open.

The amp is dead quiet, the tone is clear and chimey. The OD is not having ANY gain problems what so ever. Notes and harmonics are rising off of chords. (I'll tweak the trimmer down the line)

So as of now, I am looking at lowish output on the clean side. Is that tied into the poor readings on V1? Could be a beat tube, just bought them locally. Inexpensive (not cheap though) matched Yugoslav. I might switch out V1 and V2 or pull a 12AX from my Bassman, but not tonight.

Attached are voltages from the second power up. I haven't changed the bias resistor yet either. I also didn't run the power off trouble shooting on V1, getting distracted by my resistor SNAFU/repair.

Repairs/redo's are tedious & not fun but I will say, when the hunt is on for gremlins, they start making themselves known.

Goodnight from NYC
Gary

[JazzGuitarGimp]

I am still suspecting V1, Pin 3 is shorted to GND, rather than through the 3.3K resistor. In fact, the first place I'd look is at the right terminal of the trimmer pot - the 3.3K resistor lead runs right past it.

[ToneMerc]

Once you get the issue at V1a squared away, the preamp volatages will decreased slightly once both side of tube draws currect. Then go back and tweak the string with power tubes installed. However, be sure to change the bias tail to 27K before you do this.

TM

[JazzGuitarGimp]

V1a is already drawing current. It has 321V - 98V = 223V across its 220K anode resistor. So it's drawing a percent or so over 1mA, which should yield 3.34V across its 3.3K cathode resistor.

[dezmoduo]

However, be sure to change the bias tail to 27K before you do this.

TM

Can I series a 24k & 3.3k until I secure a 27k?

Gary

[ToneMerc]

However, be sure to change the bias tail to 27K before you do this.

TM

Can I series a 24k & 3.3k until I secure a 27k?

Gary

You won't have quite as much adjustment range, but 24K works too so use that. When you rectify the issue at v1a, that will at least get the build normaled up and we can tweak the string.


TM

[dezmoduo]

I swapped the 10K bias tail for the 24K.
In checking the V1 I found that pin 3 lead was going to an electrolytic on the PA board with a 10uf rating. Almost all the layouts show a 5uf. I did find one layout with two 10uf caps there. (The ones paralleled w/the 3k3 and 2k2).
I changed it for a 5uf, thinking that this would put pin 3 near the 1.8 V. No Way. .005 Additionally, I swapped around the tubes V1,2,3 to attempt to eliminate the tube from the equation if indeed one was faulty. Nope.

Voltages all around have come down a bit more.


The resistors @ V1 all test out. I see no apparent globs, cold or missing joints. I cringe typing that because I've found so many glaring mistakes already. It makes me want to look again.

Gary