Install a phase invertor trimmer?

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dragonbat13
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Install a phase invertor trimmer?

Post by dragonbat13 »

I bought some used dlite boards awhile back, after checking all the values, for the most part the boards are pretty much standard D'lite specs. I am building a 2x6l6 using a mojotone tremolux/vibrolux transformer and a multi tap bassman Mercury Magnetics OT I got from Colossus. I am wanting to build a 1x12 combo with an EVM 12L in a brown note Dlite chassis.

I am sure I will be doing alot of tweaking and such, like most have done building a dlite. I plan on building a nice ODS clone later, with one of amplifiednations four preamp tube chassis.

What I want to know is if I should go through the effort modifying the board to install a trimmer in the PI. After some research, I see where this may be something that is helpfull at getting that usable harmonic feedback dumbles are known for. Am I thinking along the right track, or should I let this Dlite be a Dlite and worry more about all the nit pick details when I get to my ODS clone later.

On a side note, was the Dlite closely modeled after any perticular amp, or just a basic design using a dumble influence?

Thanks for any help.
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norburybrook
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Re: Install a phase invertor trimmer?

Post by norburybrook »

for the sake of 3 eyelets I would put one in, it's and easy thing to do at this stage.

Regarding the DLite, I don't know what it's based on but IMHO there are really only a few general ODS types.

Low or HIgh plates, #102 and above are generally all high plates

Classic or Skyline EQ, again #102 and above are generally Skyline

the only odd one out is the bluesmaster as it uses Marshall EQ stack and PI.

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Roe
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Re: Install a phase invertor trimmer?

Post by Roe »

I've experimented a little with this and prefer a trimmer connected to the phase inverter plate resistors. Balancing the phase inverter is very important for getting the right tone and response, particularly at full distortion (when NFB does not help) and if you have problems with ghosting. Another place to install a trimmer is the two 1M resistors connected to the phase inverter tube's grids (like traynor did). I feel the the former helps more than the latter
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martin manning
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Re: Install a phase invertor trimmer?

Post by martin manning »

dragonbat13 wrote: Fri Aug 11, 2017 6:15 amOn a side note, was the Dlite closely modeled after any perticular amp, or just a basic design using a dumble influence?
AKAIK the D'lite concept was a simplified high-plate. No relays, no loop, no PS choke. Here is some description: http://ampgarage.com/forum/viewtopic.php?t=1654#p14312
The links are dead, but the Visio file appears to be there. Can someone open it and convert to .pdf?
Groove1
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Re: Install a phase invertor trimmer?

Post by Groove1 »

I made a .pdf from that visio file – hope it works.
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martin manning
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Re: Install a phase invertor trimmer?

Post by martin manning »

Yes! Looks to be the same as a jpg I saved some time ago. In the linked thread above (2006), Normster refers to it as a simplified Hybrid-A, which predates the more complete understanding of Dumble circuits that exists now.
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M Fowler
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Re: Install a phase invertor trimmer?

Post by M Fowler »

Here is hybrid A
hybrid_a_182.pdf
hybrid rev a parts list.xls
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stelligan
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Re: Install a phase invertor trimmer?

Post by stelligan »

Much discussion back in the day about not connecting the presence pot to the ground bus. I put a few together for myself and friends and went with that. And yes, put in a trimmer at the PI. Good luck with your build.

Tweaked layout with trimmer. Forget where from....
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xtian
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Re: Install a phase invertor trimmer?

Post by xtian »

Roe wrote: Fri Aug 11, 2017 10:08 amBalancing the phase inverter is very important for getting the right tone and response, particularly at full distortion (when NFB does not help) and if you have problems with ghosting.
I would like to learn more about how to adjust the PI trimmer. What do you look/listen for?

My #183 is working very nicely--I hear nothing to complain about. But I never touched the PI trimmer, ever. Just soldered it in, set it mid-way, and left it.
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martin manning
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Re: Install a phase invertor trimmer?

Post by martin manning »

See files section.
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dragonbat13
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Re: Install a phase invertor trimmer?

Post by dragonbat13 »

norburybrook wrote: Fri Aug 11, 2017 9:07 am for the sake of 3 eyelets I would put one in, it's and easy thing to do at this stage.

Regarding the DLite, I don't know what it's based on but IMHO there are really only a few general ODS types.

Low or HIgh plates, #102 and above are generally all high plates

Classic or Skyline EQ, again #102 and above are generally Skyline

the only odd one out is the bluesmaster as it uses Marshall EQ stack and PI.

Marcus
That is the simplest way of describing it that I have found. And I have searched. Somebody should slap that on that sticky in the files section. This site is awesome, but some of the simpler stuff is almost impossible to find sometimes.

I am gonna install the trimmer on the plates.

Appreciate the help.
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dragonbat13
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Re: Install a phase invertor trimmer?

Post by dragonbat13 »

Groove1 wrote: Fri Aug 11, 2017 12:03 pm I made a .pdf from that visio file – hope it works.
Is this the layout to go with the Hybrid A schematic?
Last edited by dragonbat13 on Fri Aug 11, 2017 8:31 pm, edited 1 time in total.
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martin manning
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Re: Install a phase invertor trimmer?

Post by martin manning »

No, but there is a Tweaked D'lite schematic here somewhere.
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Re: Install a phase invertor trimmer?

Post by pompeiisneaks »

My general understanding of a trimmer adjustment would be that you get a known input sine wave, and get a scope on either side of the output of the PI after the coupling caps, before going into the power stage, and measure the peak to peak voltage of the sine wave. One should be larger than the other, dial the pot until it gets to be roughly the same. I would think this may vary depending on the PI tube, as well, so if you replace it, it would be slightly out of balance again. I don't know how critical it would be to get it exact. OTOH, If you don't have a scope, you could likely use a volt meter and set it to AC and measure at the same point and try to dial them to the same voltage and that should also work no? I've never read or seen how to do it, this is just how I imagine you'd be able to do it.

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dragonbat13
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Re: Install a phase invertor trimmer?

Post by dragonbat13 »

martin manning wrote: Fri Aug 11, 2017 8:28 pm No, but there is a Tweaked D'lite schematic here somewhere.
Sorry, I edited the post out from under you.
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