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PostPosted: Mon Apr 14, 2014 9:59 pm 
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Holy Ghost
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Got the Heyboer OTs and worked with Brent Bodrug from SlyFi Chapel Studio to pick the best. We had a Hammond, an MPS and two Heyboers, each with different steel laminations - 1 with M-27 and 1 with M-6. In the end it was a Heyboer M-27 winning the shoot out.

With the M-27, we found the amp had fantastic clean tones (no exaggeration here) at low volume but a bit too fizzy when overdriven. I am suspicious of the self split output design as it is not really a well balanced output design but a quasi push-pull output design.

Also found it didn't need the boost at all nor did it need tone controls.

So now we're thinking about dispensing with the boost circuit and using that second tube for a PI feeding the dual triode ECC99 in true push pull might be the ticket. But then that's pretty much a redesign.

Before that, I will probably probably try the octal 6SN7 tube before I move on to the next phase because maybe it's just the ECC99.

More to come!

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PostPosted: Tue Apr 15, 2014 11:24 pm 
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This is looking like It could be fun expirement.
Was looking at ecc823 as another option.
One question is a are you limited to 3 tubes total due to plate curent draw for the power transformer ?
Whats it like 22ma per plate of a 12au7 or is that both plates?


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PostPosted: Wed Apr 16, 2014 8:16 am 
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Holy Ghost
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The power transformer we are using currently for the prototype is a
Hammond 269EX.
43VA.
380V C.T. @ 71ma
6.3V @ 2.5A.

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PostPosted: Wed Apr 16, 2014 10:22 pm 
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Holy Ghost
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Running about 45 ma total or 22.5 per triode which is borderline max. so it runs pretty hot. Need to see how long the tube lasts. :nono

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PostPosted: Fri Apr 18, 2014 8:19 pm 
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Holy Ghost
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Went back to Brent's studio today with the mods all wrapped up in the chassis again. This time in his familiar studio.

Again we never found the need for the boost so that concept is now dropped. Even though I doubled the coupling cap from the boost, it still sounded thin and bright. Feeling is if you want over the top distortion, use a pedal. But there was not a lot of need for a pedal during our testing tho it sounded totally rockin with one!

The fizz we were hearing on OD seems to be gone or at least inaudible due to the Conjunctive Filter we put in and hotter bias of the ECC99. It has been maxed out! What I saw on the scope was a flattening of the lower half of the sine wave on clipping so it was biased hotter to avoid that. It then became quite symmetrical on clipping.

Now the surprise - I had some really old 12AU7 and 12BH7 I wanted to try them again. When I packaged up the amp for the studio, I had added a bias switch. So in went the BH7 flipped the switch and it totally sounded like a Marshall. BIG surprise. It had better dynamics and feel but a little less headroom in a good way. It was the winner in Brent's mind. The AU7 was also tried and it stood it's ground but lost some more headroom. A dual bias is "probably" going to be part of the design at least as an option.

I will have to get some new BH7s to see if the new production stock sound as good as the old ones I had on hand.

So the plan now is to build a brand new version incorporating all the latest changes and finalize the board layout.

We might still increase a coupling cap or two or maybe play with some bypass caps to thicken it up but it's almost there.

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PostPosted: Mon Apr 21, 2014 8:02 pm 
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Holy Ghost
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I have since rebuilt the TriFly and plan to get some more feedback on it. I dropped the boost control idea but since added a boost switch to gain it up a bit and fatten it as well. Brent and I picked the transformer based on tone and clarity and we also changed the output tube to an older model with a bit less headroom but more tone. It had better definition than the original but there is a switch to enable a quick swap for comparison. I redesigned the board and popped it back into the chassis for the next round.

The board is not final and the prototype looks like a prototype.

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GUTS

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PostPosted: Mon Jul 23, 2018 5:34 am 
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SPAM!!


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