2nd Gen Build

[Raoul Duke]

Classic, seasoned iron, brown caps, Pihers - should sound great! Looking forward to hearing your thoughts about the sound. Great build Dan

[Dr d]

Looks fab! Bet you can’t wait to hear how it sounds. Once it’s up and running, the suggestions will come in as to how to fine tune it. Ian has shared a lot of very useful information and tips from his build.

[dbharris]

Thank you and yes I am pretty excited! Always fun to tweak these amps to dial them in.

My long term plan is to build a low plate classic after this then a bluesmaster. Keeping everything close to stock in the beginning. At that point I will have a better feel for each amps character. Then I will look at tweaking each amp to pair with a particular guitar or type of guitar. But who knows, it will be a while before I get there and things change.

-Dan

[dbharris]

All wired up! Just need to add fuses and run the startup procedure tonight.

PXL_20240509_014756399.jpg

PXL_20240509_014806562.jpg

[dbharris]

All good with the smoke test and forming the caps. Put my startup tubes in and biased the amp. All functions are working. Tone stack is not super effective, but I think that is just the design. Reserving tone impressions as I only played briefly and at low volume. But does strike me as more raw sounding.

Tomorrow I'll swap in the proper tubes and work on biasing the FET, then balancing the phase inverter.

[GAStan]

Congrats on keeping the ever elusive magic smoke contained!

Great looking build! I like your color choice for the heater wires, you'll see why soon...

Have you used the Jupiter caps before? If so what do you think of them?

Edit: spelling

[dbharris]

Thank you! I have not used the Jupiter caps before. As the Spragues get harder to find in stock and always more expensive, these seemed like they might be a good alternative.

Orange and blue for my Florida Gators!

-Dan

[Dr d]

All good with the smoke test and forming the caps. Put my startup tubes in and biased the amp. All functions are working. Tone stack is not super effective, but I think that is just the design. Reserving tone impressions as I only played briefly and at low volume. But does strike me as more raw sounding.

Tomorrow I'll swap in the proper tubes and work on biasing the FET, then balancing the phase inverter.

Yes, the 2nd gen tone stack is a bit underwhelming! I suggest removing the 0.02 cap on the bass pot. You will find that the controls work for you then!

[dbharris]

All good with the smoke test and forming the caps. Put my startup tubes in and biased the amp. All functions are working. Tone stack is not super effective, but I think that is just the design. Reserving tone impressions as I only played briefly and at low volume. But does strike me as more raw sounding.

Tomorrow I'll swap in the proper tubes and work on biasing the FET, then balancing the phase inverter.

Yes, the 2nd gen tone stack is a bit underwhelming! I suggest removing the 0.02 cap on the bass pot. You will find that the controls work for you then!

I will likely try that once I get things settled in. Thanks for the tip!

[dbharris]

Preamp glass for now. V1 and V2 are RCA grey plate 12AX7A. V3 is RCA black plate 12AT7.

PXL_20240510_164414227.jpg

Power tubes are fender branded Sylvania short bottle 6L6GC with double top getters.

PXL_20240510_164448700.jpg

When I swapped the tubes I noted 2 things. First, with the bias set most negative one of the tubes is biasing around 63% so I need to lower the bias board resistor.

Second, there is a distinct "electrical" smell coming from the area of the power amp part of the chassis. Everything seems to measure normal and visually appears normal. So not sure about what is going on with that.

Will work on biasing the FET next.

-Dan

[GAStan]

Second, there is a distinct "electrical" smell coming from the area of the power amp part of the chassis. Everything seems to measure normal and visually appears normal. So not sure about what is going on with that.

Will work on biasing the FET next.

-Dan

Try looking for any arcing in a very dark room.

[Dr d]

Preamp glass for now. V1 and V2 are RCA grey plate 12AX7A. V3 is RCA black plate 12AT7.
PXL_20240510_164414227.jpg

Power tubes are fender branded Sylvania short bottle 6L6GC with double top getters.
PXL_20240510_164448700.jpg

When I swapped the tubes I noted 2 things. First, with the bias set most negative one of the tubes is biasing around 63% so I need to lower the bias board resistor.

Second, there is a distinct "electrical" smell coming from the area of the power amp part of the chassis. Everything seems to measure normal and visually appears normal. So not sure about what is going on with that.

Will work on biasing the FET next.

-Dan

That’s a nice set of valves you’ve got there. I wouldn’t bother changing the bias dropping resistor just yet. For most valves it should be spot on. 63% dissipation is near enough to 60% goal. What % dissipation is the other valve? Secondly, you obviously don’t want any electrical smells. If this has happened after a valve change, then you need to double check that the output valves are holding bias and that there are no obvious signs of arcing around the pins of the output valves. Might be worth cleaning between the pins with a cotton bud to make sure there is no debris present. Also double check the grid and screen resistors aren’t getting too hot before failure. Hope that helps. Hopefully nothing too dramatic wrong!

[dbharris]

Thanks guys. I'll leave the bias resistor alone for now. The other tube biased lower maybe around 55-57%.

I pulled the tubes, sprayed compressed air, cleaned the sockets with deoxit and a toothbrush, looked for any leads that may be close and causing arcing, cleaned the female side of the socket, and then the actual tube pins. I also removed the sticker labels on the glass because it looked like it had gotten slightly cooked and cleaned remaining residue.

Plugged the tubes back in and turned on the amp with the lights off. I could not see any arcing. Smell is still there. But I did notice a strange glow coming from the very bottom of the tube base in the middle looking down through the socket in the chassis. Just on one tube. On the other tubes it looks like there is a dimple there in the plastic. On this one it looks like a small hole.

Picture of the glow. It shows up better if you click the picture for full resolution.

PXL_20240511_113458987~2.jpg

Should I use a little rtv there? Any other suggestions?

I may be disillusioned with NOS power tubes. I bought 2 quads and a pair from LA Vintage and they were great to work with on the purchase end. But so far have had issues with each set

JJs are going back in while I get the FET sorted.

-Dan

[martin manning]

If that is just heater glow you are seeing through the hole in the tube base I wouldn't worry about it. Are you seeing that through the gap between the index pin and the socket? Might the odor be transformer varnish?

[dbharris]

Hi Martin, I think you are correct and it is just varnish. This PT is old and looks a little funky. After I swapped in the JJs, there was still an odor. It seemed like a lot less strong, but at this point my mind may be playing tricks on me.

Also, I could not get this J201 to bias in range. It wanted.low resistance and even with a 1r my Vdd/Vd ratio would only go as high as 1.2. Going to swap in an NTE452 like I should have just used to begin with

Appreciate everyone's help.