2nd Gen Build

[martin manning]

Very nice! If you find that you are using one setting for the Ratio control, you could replace it with a fixed divider, but I'm interested to hear how you are using it. IMO the ODS was a continuously evolving concept, with the changes HAD made over the generations being improvements.

For the PI balance, the DC voltage on the cathodes is probably close enough, but as with any adjustment, it's nice to have some margin on either side of the target. Personally I use a scope for this.

[dbharris]

Very nice! If you find that you are using one setting for the Ratio control, you could replace it with a fixed divider, but I'm interested to hear how you are using it. IMO the ODS was a continuously evolving concept, with the changes HAD made over the generations being improvements.

For the PI balance, the DC voltage on the cathodes is probably close enough, but as with any adjustment, it's nice to have some margin on either side of the target. Personally I use a scope for this.

Thank you, Martin!

I'm using the ratio control similar to how I use it in my #102. In either case the volume in the lead channel is a bit louder than clean...maybe 3dB. Depending on my mood or the song I am playing, I set drive around 45% and ratio around 40% for an extension of clean medium gain type tone. Or the drive very high 75-100% and the ratio low 10-20% for a very saturated lead tone.

I need to make my foot pedal and then I am done. I did try out the in between setting for the R/J switch and actually quite like the PAB in this amp. Though I understand many folks don't like that in the 2nd and 3rd Gen designs. My foot switch jack is a 3 pin xlr, so that will not be a foot switchable function for me.

I may give the scope a try again before boxing up the amp. I remember when I built the #102, that I could not get the scope to output meaningful measurements for this purpose. I am using a lower end digital scope. The math functions weren't quite right and visually trying to match the 2 sine waves was not a fine enough measurement. This may very likely be user error on my end and not making the right choices in the settings.

Thanks again to everyone who gave me parts, provided advice, corrected mistakes I made, and shared information on this circuit. As it continues to burn in I am liking it more each day. I plan to record a clip or two at some point in June and will post them here.

-Dan

[dbharris]

Looking good Dan!

Thanks Marc! It's been great following your build threads and helped me quite a bit.

[dbharris]

Hey Dan, the amp is definitely not as gainy as a #102. I found that reducing the 1m2 bypass resistor in the funky entrance to 1m helped in this regard (plus plugging into the FET!). I also found that reducing this value too far makes the OD too dark. Its definately a lively amp. I love mine

This is a great tip. I am going to try that out too before I seal up the chassis. And I totally agree on the FET. I have been spending most of my time on that input.

[martin manning]

Thanks for the run down on using the ratio pot. I recall HAD saying in some article or interview that the Ratio control was a great feature on the ODS. Must have been shortly after its introduction.

I may give the scope a try again before boxing up the amp. I remember when I built the #102, that I could not get the scope to output meaningful measurements for this purpose. I am using a lower end digital scope. The math functions weren't quite right and visually trying to match the 2 sine waves was not a fine enough measurement.

The setup would be one channel on each cathode pair (short the bias test jacks on each side together), same V/div on each, and set sensitivity low enough to fill the screen. Lately I have placed a 1 ohm resistor between all cathodes and ground, and using that as the test point for PI balance. The signal shows the pulses on both sides of the power amp (as alternate pulses) on a single channel, and doubles the amplitude. That requires a couple of extra tie points for the current sense resistors, though.

I also swapped the choke leads today. I could hear a noticeable difference between the two.

I'll have to give this a try.

[Dr d]

Hey Dan, the amp is definitely not as gainy as a #102. I found that reducing the 1m2 bypass resistor in the funky entrance to 1m helped in this regard (plus plugging into the FET!). I also found that reducing this value too far makes the OD too dark. Its definately a lively amp. I love mine

This is a great tip. I am going to try that out too before I seal up the chassis. And I totally agree on the FET. I have been spending most of my time on that input.

Hi Dan, further to my last comment, a little gem that I gained from Ians build is to do with the gain pot and bass content in the OD. I mentioned that I found that as I reduced the 1m2 resistor, the bass content increased. If you found that in reducing this resistor to a desired value gave you too much bass, you can reduce the bass content by reducing the actual value of the gain pot closer to 100K or lower (no more than say 90K). This can be done by part selection or strapping a resistor across the pot (or depending on your pots actual value, a 1m trim.). My gain pot measures exactly 99K so reducing to a 1m resistor wasn't a problem.....still plenty of clarity. Hope this helps.

[dbharris]

Thanks to all who helped me out on this build! I am calling this one completed. Whenever I order more pihers, I will swap in a 560k for the new NTE that is there now. I did have a 1/2 watt 1M piher and used that to replace the 1M2 in the OD entrance. I like that variation better.

PXL_20240615_183220942.jpg

Tried a new PSVANE and TAD 12AT7 in the PI slot. The PSVANE balanced the best of all but still the closest I could get it was a 0.5mv offset. It's my personal opinion, based on nothing factual, that HAD probably did not balance the PI perfectly until the transition gen and later amps. So, I feel I am close enough.

I swapped the V1 and V2 tubes and like this arrangement better. Final voltages:

Line 122.6vac
Heaters 6.8vac
B+1 455v
B+2 453v
B+3 428v
B+4 282.1v
B+5 273.3v

V1 1-183.4, 3-1.34, 6-185.2, 8-1.33
V2 1-191.7, 3-1.36, 6-189.1, 8-1.41
V3 forgot to write these down

Is it even a 2nd Gen if it's not wearing snakeskin?

PXL_20240615_214628177.jpg

PXL_20240615_214714027.jpg

I played the amp for a while and I'm really happy with it. It just rips on lap steel through the FET. I'll record a couple clips when time allows.

PXL_20240615_214639803.jpg

-Dan

[GAStan]

Great looking build Dan! Snakeskin suits the build and looks at home on top of the High Plate.

If you don't mind...where did you find the knobs for the pots?

[dbharris]

Great looking build Dan! Snakeskin suits the build and looks at home on top of the High Plate.

If you don't mind...where did you find the knobs for the pots?

Hi Glenn,

Thank you!

I ordered these from eBay https://www.ebay.com/itm/144158978478. Close enough for me and the price was right. But these are not the exact type HAD used.

-Dan

[martin manning]

Very nice indeed! How are you doing the panel graphics?

[dbharris]

Very nice indeed! How are you doing the panel graphics?

Thanks, Martin! It's a bit of a PITA but I haven't found anything better yet.

Once I identify the font(s), I create the graphic in Inkscape. Once I have the size and everything right, I export it to Cricut design software (noting what the dimensions were in Inkscape because Cricut always resizes it). I then cut a vinyl stencil with the Cricut machine. I weed out the positive space so I am left with a negative of the stencil.

Apply that to the chassis and tape around it. I spray some automotive grade clear coat into a small piece of aluminum foil or a cup. With a small paint brush, liberally apply the clear coat making sure I get good coverage anywhere the vinyl and chassis meet. That is important to prevent bleeding in the next step. Let the clear dry at least 12 hours. I then take a small ink roller, like for print making art, and evenly apply some one shot enamel (like what is used in pinstriping) to the roller, then roll it onto the chassis. 2 coats of enamel is usually good.

Once dry, remove the tape and stencil. Touch up as needed with a toothpick and more enamel or acetone if removing enamel. I don't clear coat over the top.

-Dan

[martin manning]

Appreciate the complete description. Pretty involved, but it sure looks good!

[Raoul Duke]

Looks really good Dan; and I’m sure it sounds fantastic!

[desertmouth90]

Looks amazing! what sheilded cable did you use?

[dbharris]

Looks amazing! what sheilded cable did you use?

Thanks! The black is vintage correct RG59 that was gifted to me for this build. The thinner silvery cable is RG316, which I did not like working with all that much.

-Dan