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Just finished modding my TMB to switch between 6V6's. I still have to find some tubes for it. But I can't wait to fire it up. I'll post some pictures (and hopefully sounds) sometime!

Coco: What kind of 6V6's did you have in the green "Rob Baker Special" I tried out. I liked 'em all right.

That's it for now.

I'm reading a thread over on 18watt.com HERE which discusses 6V6's and EL84's in the same amp. A suggestion was made that the PI tail resistor value of 56k is too high when using the 6V6's (hence the volume drop). "Phil" says the V6's aren't getting a hot enough signal. Is it possible to use the other side of the switch to change the value of this resistor when switching tubes? Is this a bad idea? Maybe it's already been thought of.

Just curious. The volume change really doesn't bother me but I thought I'd entertain the idea.

Those were JJ 6V6s.

You can try switching the resistor with the switch (it's DPDT for a reason after all ).

We tried a 50% lower value in the PI and didn't think it made any differenace to the sound. Plus, driving them hard is not what we particularily wanted to do.

But Try It and Let Us Know How it Goes.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I would like to see those pics if you have them.

I'll be glad to post them. I've been working like fool at my day job all week so the amp has been sitting neglected and un-tested all this time. I think tonight I'll have some time to take some pictures and see how this beast sounds. Lets hope it fires up.

I just got the 6V6's in the mail yesterday. Those guys over at TheTubeStore really are fast. Less than 3 days on a 3 - 7 day delivery.

+1 on the Tube store being fast. I ordered from them overnite once. I placed my order at 4PM and had the delivery guy come in at 10AM. He had already been by once before I got there to open shop. Still , sixteen hours from order to delivery , from Canada to Mississippi. .

LeeMo

Fired up just fine... With a few exceptions.

I wired the inputs backwards. The TMB control pots affect the the normal inputs and vice versa. Simple fix.

The squeal is worse now. I've noticed that it goes away abit when I touch the ground on the speaker output wire. Perhaps I need to ground my output jacks? I really took some care this time separating wires and making sure everything was running at 90 degrees to each other.

Anyway. I've got some work to do... Bummer. Sounds great so far though.

Gutshot of the powertubes.

Congrats on getting it to work first time. When not squealing, how good it it? Or can you crank it enough to tell??

We have to work on that squeal. You have reversed the OT, right?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I can get both knobs up to about 1 o'clock and then it starts to squeal. Before the upgrade I could get them up to about 3 o'clock - 3:30. Up to there it's really nice. But I really would like to be able to crank it. The boost switch is also nice, but it directly imacts the squeal threshold.

I reversed the OT before the mods and it helped a bit. I'm almost sure I kept it the same, but it could have got switched back.

That's not the greatest picture up there so get me to take a picture of anything you want to see. For now I need to switch the inputs and do some chopsticking.

Somebody tell me if I'm about to do something excessive.

My amp has squeal and lots of it. And I like gain and lots of it (at times). So I'm thinking of doing the following, in the following order.

1. I accidentally un-reversed the OT leads on the EL84's when I installed the 6V6's. I'm going to switch them because I know this helped before I did the upgrade.

2. I'm thinking about grounding the output jacks straight over to the mains ground pin. I know grabbing the sleeve on the output cable made the squeal drop a bit. Are there any reasons NOT to do this?

3. I'm going to start dropping the grid stopper resistor and see where that gets me.

I would also like to know if there are any critical signal wires that should be sheilded. Stephen mentioned the leads coming from the TMB pots. I've got a ton of coax so I'm not affraid to use it. Unless it can't handle the current. It's the grey stuff that says Belden 8411 on it. I'll start by wrapping it with grounded wire anyway.

Thanks for any ideas.

Peace,

Adam

BTW does it squeal on both tube sets?

Try reversing the leads.

Dont Ground the jacks to the mains ground. [illegal btw] Ground to the chassis ground at the filter caps/transformer ground.

Try wrapping those wires to the controls with another solid core 22 ga wire grounded at one end.

Read the section in the manual about squeal [and posted here viewtopic.php?t=13&highlight=squeal ] before you start swapping parts.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen. I didn't know I could break the law with this thing (with the exception of noise by-laws). It does squeal on both sets of tubes.

BTW, I read that section, and that's where I got the bright idea to swap that resistor.

Anyway, I'm off to active surplus. I have the day off and I intend to have this problem licked in time to drown out Friday Night house party Hip Hop music from my neighbours.

Worst case. Loose the 470k to pin 2 V2 and put 100K across the pot wiper to ground. Just like the sIII and dump some gain.

Grounding the jacks may work and check the solder conections on the output jacks ground.

Could move the power tube screen resistors directly to the tubes as well.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

UPDATE:

I sheilded the TMB control leads and swapped the OT leads with little success. The normal channel sounds awesome. My test to see if the TMB was okay lasted about 20 minutes and I only played the normal channel! Perhaps I should mention that the normal channel is my favorite (tone and vol @ 3o'clock).

My next step will be EITHER grounding the output jacks or droping the value of the grid stopper resistor. I havn't decided which to do first.

When you say 'shield' did you 'wrap' the leads with that grounded wire?

Do the output jacks first.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

SUCCESS!

I wrapped the leads with the grounded solid core. Made a nice tight bundle. Cleaned up the look of the leads, but I couldn't hear much of a difference.

I grounded the output jacks over to the star ground at the transformers. I also changed the screen resistor to 360k. No more squeal. I can crank it with no problems. I have a feeling I can put the 470k back, but I can't notice much of a tonal difference so I might leave it.

The boost switch doesn't really do much. Maybe I wired it wrong. I can hear a small change in tone but thats it. Does the TMB already have so much gain that the boost would get burried? A word I would use to describe it is subtle. Deffinately not how I would describe the one I tested. But this isnt necessarily a bad thing.

I'm soo happy I got it dialed in. I don't think I'm gonna mess with it much anymore.

Thanks Stephen! (and everyone else)

Great news to hear. What do ou tink made the final difference??

The TMB has a lot of gain, and I've never [had to] put a 'boost' on one. The R-C is switched in across the cathode resistor, R9 on the sIII, but R9 is 2K7. On the TMB, R9 is 820 ohms, so try only switching the 22uF cap in parallel across R9 (820 ohm) and report back.

Again, congratulations on building the first switchable TMB v6.!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I think the output jacks were the culprit. I find it hard to beleive the TMB screen resistor made THAT much difference. I might even change it back to the 470k and see.

I think I like the idea of removing the resistor and just switching in the cap on for the 'boost'. My initial thoughts are that it will inject some really strong/cutting high end into the mix (could be cool). But I'll deffinately try it at some point.

I'm loving this amp. It was really nice before, but driving the 6V6's really hard makes the sweetest creamiest distortion. And switching to the EL84's gives me some abrasiveness which I like. Due to the higher gain, there is slightly less of a tonal difference between the 2 sets of power tubes (not as noticable as the sIII). Still noticeable though. They each retain their core qualities and they compliment each other very nicely. Cleaning up a bit yeilds some really dynamic bluesy sounds and just about anything else. When I plug in I can't stop. Great work on designing such a versitile amp. I'll keep yall posted on any developments.

Good input, we'll have to add that one to the 'Anti-Squeal' notes.



Yeah, I'd try that out. Nice to hear that the TMB version also works so nicely. What you're describing is pretty well what we expected but when you say "Due to the higher gain, there is slightly less of a tonal difference between the 2 sets" do you mean volume difference or really tonal?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I mean tonal. The volume drop is still about the same as the sIII but as with pushing anything really hard, the subtleties get a little burried in distortion. Not a bad thing. It's kind of like the difference between 2 sets of pickups, you hear most of the difference when they're clean(ish), and not so much when you oversaturate the signal. That's all I was getting at.

Sounds great. I got a little excited yesterday and got some noise complaints.