YAOB (yet another one-zero-two build)

[Structo]

Sounds good.

You run your knobs about like I do.

It will only get better from here on.

Do you know where your OD trimmer is set with the amp on?

[aflynt]

Sounds good.

You run your knobs about like I do.

It will only get better from here on.

Do you know where your OD trimmer is set with the amp on?

Thanks! I'm pretty sure I set the OD trimmer to 25.3k to ground with the amp on.

Incidentally, I finally implemented the treble reduction network on the send and return jacks today. The amp actually sounds a bit better with the loop unplugged now! I tried some longer cables to and from the loop and that brought the two a bit closer.

-Aaron

[aflynt]

Here's my final layout of the amp with the little tweaks I did. Hopefully it will help somebody else in the future.

https://tubeamparchive.com/download/file.php?id=23252

-Aaron

[Structo]

Cool!

Thanks for your sharing and documentation.

Not sure if you have already done it but you could post this layout in the files section too, along with the other information already there about #102.

[CHIP]

Aaron, I notice on your layout you have a jumper on the mid pot, yet the original 102 layout doesn't.

[Structo]

I believe it is the same since it is just a variable resistor.

[aflynt]

Yeah. It doesn't really make much of a difference but since the presence pot is wired w/o a jumper I just updated the layout without it for the sake of consistency. I also changed the PT grids back to 5k1 on the layout as per #102 and updated some of the instruction text to make more sense. This layout DOES have my values for dropping strings and other voltage tweaks since I figure my values are likely to be closer for others using old Twin iron.

-Aaron

[CHIP]

Nice job on the layout. It seems it may be confusing since the schematics show the jumper and then the original layout doesn't. I don't know why use the jumper if it doesn't matter.

[aflynt]

Nice job on the layout. It seems it may be confusing since the schematics show the jumper and then the original layout doesn't. I don't know why use the jumper if it doesn't matter.

Right. That's why I changed it this morning. Thanks, btw! I'm going to do up a schematic too once I get a chance.

-Aaron

[jlatrace]

Did you finally determine the hum to be the tube in v1?

[aflynt]

Did you finally determine the hum to be the tube in v1?

I'm guessing it's a combination of that and the Power Transformer like talbany said. It's really not loud enough to be a problem even when recording, so I'm just living with it for now. Someday I'll probably try to trace it down, but for now the amp sounds so good that I'm reluctant to mess with it.

I have been running it on a Variac the last week or so and found that it really sounds best with the supply voltage in the 125v range. At some point I might just get a different power transformer with higher B+ ratings to bring all the voltages up a bit more.

-Aaron

[jlatrace]

When you get back to it take a wooden chopstick and go over every ground, cap and heater joint. Give it a whack or push to see if you can get more than a hum.

Almost every time I have had hum gremlins they came down to either
1. Weak ( but not visibly bad) joint in heaters 2. Same thing at a ground point

But I'd guess a bad/ weak heater joint based on what all you have described.

Good luck, I chased one on these for a year in my 66 blackface DR before the joint got bad enough to be detected. It was a bad original solder joint under the board, I guess Leo missed it.

[aflynt]

When you get back to it take a wooden chopstick and go over every ground, cap and heater joint. Give it a whack or push to see if you can get more than a hum.

Almost every time I have had hum gremlins they came down to either
1. Weak ( but not visibly bad) joint in heaters 2. Same thing at a ground point

But I'd guess a bad/ weak heater joint based on what all you have described.

Good luck, I chased one on these for a year in my 66 blackface DR before the joint got bad enough to be detected. It was a bad original solder joint under the board, I guess Leo missed it.

Thanks for the suggestion! I think I might reflow the heater joints next time I open it up. I was going to replace some of the carbon comps with film resistors to try to reduce the hiss anyway. I'm also going to try two 250pF caps on the send / return treble reduction network instead of 500pF that I have in there now. The 500pF seems to reduce the highs and subsequently the overall volume too much. Especially when that amp is at gig volume.

-Aaron

[jlatrace]

Thank you for the layout. In particular the lead dress detail is outstanding. I'm using it as reference in two builds I have going on, a 183 & another 102.

FWIW - I used carbon comps in my first 102 in the B+ dropping string for v1 & v2 (not in the signal path) and in the phase inverter and my noise floor is very low. So low that when I first hooked up my DLator (and before I learned how to use it) that I spent weeks tracking down the noise caused by me having the DLator return set too high. Also, I do not have the treble reduction network and the amp sounds fine, slightly bright without a Dlator and normal with a Dlator. You might want to remove the 500pf caps and play the amp a while before reinstalling the 250pf treble bleed caps.

[aflynt]

Thank you for the layout. In particular the lead dress detail is outstanding. I'm using it as reference in two builds I have going on, a 183 & another 102.

No problem, and thanks. I'm just glad somebody is finding it useful.

FWIW - I used carbon comps in my first 102 in the B+ dropping string for v1 & v2 (not in the signal path) and in the phase inverter and my noise floor is very low. So low that when I first hooked up my DLator (and before I learned how to use it) that I spent weeks tracking down the noise caused by me having the DLator return set too high. Also, I do not have the treble reduction network and the amp sounds fine, slightly bright without a Dlator and normal with a Dlator. You might want to remove the 500pf caps and play the amp a while before reinstalling the 250pf treble bleed caps.

I used a bunch of the CCs in the signal path on the initial build. They are the rectangular looking brown ones on my layout. Last night I replaced a bunch of them with KOA speer carbon films, reduced the treble reduction caps to 250pF, and reflowed the heater joints. The hum and hiss is pretty much unchanged, but the amp does sound slightly different. It's a bit more stout and together sounding. Less wispy and diffused. I think a lot of that may be due to the negative feedback resistor now actually being 390R instead of 430R (which the old CC resistor actually measured). The 250pF caps in the network do sound closer to the D'Lator sound. That 220k resistor seems to knock off a bunch of volume though.

Next, I'm going to relocate the B+4 and B+5 dropping resistors to the eyelets instead of the circuit board pads. In the process of replacing them a bunch of times to get the voltages where I wanted them some of the top pads got destroyed. Even though they are showing continuity I'm not all that confident in the solder joints on those.

I may wind up finally pulling the trigger on a new PT also. Even though I've said that about eleven times I think I'm actually serious now. This one is starting to hum even more than it was before (just by itself when the amps in standby). It's either down to the Heyboer Twin replacement from Mojo or the export version of the Magnetic Components one (40-18042) with the extra higher voltage taps (345-0).

-Aaron