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Author Topic: Looking forward to building a couple of these  (Read 15921 times)
Crusty_old_rocker
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« on: November 12, 2009, 03:18:27 AM »
A friend and I have ordered a couple of the DC30 kits.

I'm the electronics geek and he's a master luthier.  We are going to make ourselves an SC30 each.

So, I'm doing the soldering and he's going to build a couple of really sweet 1 x 12 combo cabs.  We have come up with a few ideas on reducing cabinet vibration and speaker back wave effects on the chassis which should result in longer valve life and less microphonics.  The cabs will be made of maple with some nice figuring in the wood.  The cabs will be loaded with a Celestion V30, so we should end up with a couple of sweet sounding amps.

We're just waiting on the delivery of the amp kits.  We have our speakers and the wood is being sliced and dressed ready for the cabinets.

Can't wait to get started.

Cheers,

Crusty
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Nickp
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« Reply #1 on: November 13, 2009, 06:13:26 AM »
I'd love to see pics when you're done,
I really like my dc but I have yet to decide to put it in a head or combo

I love the natural wood look, I had a head cab made for me but the dimensions ended up wrong so I scrapped the idea...

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hywelg
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« Reply #2 on: November 13, 2009, 11:35:39 AM »
Be prepared to find a NOS Mullard EF86 to cure microphonics. Even running mine through a separate cab a few feet away didn't prevent the stock valve been horribly microphonic.
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Crusty_old_rocker
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« Reply #3 on: November 14, 2009, 09:22:53 PM »
I am probably going to get the valves from Bob at Eurotubes. What are the JJ EF86 valves like?

Cheers,

Crusty
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hywelg
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« Reply #4 on: November 15, 2009, 11:15:10 PM »
Microphonic...... Can't get past 3-4 on the dial.
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Crusty_old_rocker
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« Reply #5 on: November 16, 2009, 05:38:17 AM »
I wonder how people with a Vox AC30 or Matchless xC30 get by.  There are a lot of combos in the world running EF86 valves that must be all be experiencing the same problem.

Cheers,

Crusty
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Crusty_old_rocker
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« Reply #6 on: November 16, 2009, 05:42:11 AM »
I am going to be using these too:

http://www.tuberings.com/

Cheers,

Crusty
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Crusty_old_rocker
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« Reply #7 on: November 21, 2009, 06:44:41 AM »
The kits have arrived but I'm swamped with work for the next couple of weeks.  How irritating is that?

I have 2 research projects to finish for clients and 120 exam papers to mark from my uni students, damn!

So, it will be about 2 weeks before I can start the builds.  The maple for the cabinets is away getting sliced and dressed.  These 1x12 cabinets should look very nice.

I am looking at adding an extra baffle that will sit between the top of the back of the speaker and the chassis to reduce the back wave hitting the valves.  I am also designing a cushion mount for the EF86 (or EF806) valve.  If my design works, I won't have to contend with microphonic worries.

The cabs will be loaded with Celestion V30s (16 Ohm).  Because the speaker outputs are parallel, the 16 Ohm impedance will lend itself to adding external speaker cabinets without having the impedance drop too low in a parallel configuration.

Cheers,

Crusty
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alwalt
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« Reply #8 on: November 23, 2009, 05:28:38 PM »
well that uses to happen.. some guy Murphy wrote a word or two on the subject...
As for the EF86, I've been an strang animal, lucky as few because I am still running my stock EH EF86,  without a single sign of microphony. I mounted my amp on a head, and it travles a lot to band practice weekly. Lucky me. (Nik sends rings with this tubes).
As far as it starts to wear, I'll go for that mullard. I still have another EH ef86 sitting there as backup.
Good thinking on the 16ohms... I did my 2x12 with 8ohm speaker (4ohm cab) and it's a pain to add other cabs...

I've seen in eurotubes site they have a substitute for the EF86, can't remember the model (EF806 or alike). They say it is better sounding and less micrphonic...
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Crusty_old_rocker
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« Reply #9 on: November 25, 2009, 07:11:14 AM »
Hi Alwalt,

Hopefully the JJ EF806 tubes with the rings will do the trick.  I will be designing a soft rubber mount for the tube socket and the idea of a deflector baffle to steer the speaker backwave away from the chassis should help too.

Have you considered wiring the 2 speakers in your cab in series rather than parallel?  Two 8 Ohm speakers in series will turn your cab into a 16 Ohm cab.  Then if you add another 16 Ohm cab on the other speaker output that will give a total nominal impedance of 8 Ohms.  The trick is ensuring that the additional cab is 16 Ohms.  Wiring a 16 Ohm in parallel with something other than 16 Ohms will give some unusual nominal impedance values.

Cheers,

Crusty
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alwalt
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« Reply #10 on: November 25, 2009, 05:06:55 PM »
Quote from: Crusty_old_rocker on November 25, 2009, 07:11:14 AM
Hi Alwalt,

Hopefully the JJ EF806 tubes with the rings will do the trick.  I will be designing a soft rubber mount for the tube socket and the idea of a deflector baffle to steer the speaker backwave away from the chassis should help too.

Have you considered wiring the 2 speakers in your cab in series rather than parallel?  Two 8 Ohm speakers in series will turn your cab into a 16 Ohm cab.  Then if you add another 16 Ohm cab on the other speaker output that will give a total nominal impedance of 8 Ohms.  The trick is ensuring that the additional cab is 16 Ohms.  Wiring a 16 Ohm in parallel with something other than 16 Ohms will give some unusual nominal impedance values.

Cheers,

Crusty

Hi Crusty, yes I am aware of the change on the wiring to vary the omhs of the cab. It is something real easy that I have not done, most by laziness, my bad... thou where I am using the amp right now even the half power setting is loud, so adding another cab (wich I'd love) is not a practical option by now.
I am even waiting for some parts to install the VVR3 instead to tame the volume a little. Maybe having this mod done may allow the use of another cab, just for projection of the sound.

It would be appreciatted if you post some pictures of the ruuber and the baffle. You can never tell when the EF86 is going to be picky...
Regards!
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Crusty_old_rocker
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« Reply #11 on: November 27, 2009, 01:17:45 AM »
I have been looking at the VVR circuit and am interested in the mod.

Are you installing it in place of the master volume or as an additional control?  Are you scaling the entire amp or just the power stage.  I have only been able to find a schematic for cathode biassed amps that scales the entire amp.

I'm not sure.  If I installed the mod as an extra control, I'd probably put it on the back of the chassis.  If I was sure that it was going to perform perfectly, then I would just take the master volume control out of the circuit and put the VVR in its place.

Cheers,

Crusty
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alwalt
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« Reply #12 on: November 27, 2009, 05:27:58 PM »
Well, scalling only the power tubes was just beyond my understanding, at least based on the instructions Dana sends. Nik was so kind of trying tyo guide me trhough it, but I believe I will do the whole amp mod instead. I will probably take out the MV control (wich I don't like at all) and use that place for the VVR.

The only use for the orginal MV I found was for bedroom level practice. But it doesn't do any good in terms of taming the amp at gig or  band practice. I hope the VVR makes a difference...

Cheers!
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hywelg
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« Reply #13 on: November 30, 2009, 10:14:29 AM »
Quote from: alwalt on November 27, 2009, 05:27:58 PM
Well, scalling only the power tubes was just beyond my understanding, at least based on the instructions Dana sends. Nik was so kind of trying tyo guide me trhough it, but I believe I will do the whole amp mod instead. I will probably take out the MV control (wich I don't like at all) and use that place for the VVR.

The only use for the orginal MV I found was for bedroom level practice. But it doesn't do any good in terms of taming the amp at gig or  band practice. I hope the VVR makes a difference...

Cheers!

With the London Power version you really do need a master volume (he calls it Drive Compensation) since as you lower the B+ the tubes behave differently and you will overdrive them progressively earlier. On mine you have to turn th DC and PS down together otherwise it all turns to mush.
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alwalt
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« Reply #14 on: November 30, 2009, 08:45:39 PM »
Quote from: hywelg on November 30, 2009, 10:14:29 AM
Quote from: alwalt on November 27, 2009, 05:27:58 PM
Well, scalling only the power tubes was just beyond my understanding, at least based on the instructions Dana sends. Nik was so kind of trying tyo guide me trhough it, but I believe I will do the whole amp mod instead. I will probably take out the MV control (wich I don't like at all) and use that place for the VVR.

The only use for the orginal MV I found was for bedroom level practice. But it doesn't do any good in terms of taming the amp at gig or  band practice. I hope the VVR makes a difference...

Cheers!

With the London Power version you really do need a master volume (he calls it Drive Compensation) since as you lower the B+ the tubes behave differently and you will overdrive them progressively earlier. On mine you have to turn th DC and PS down together otherwise it all turns to mush.


Yep. The same with VVR. Dana at Hall Amplifaction told me that the MV on the DC30 may work, but he would suggest a PPIMV mod. I also asked him a little help with the "only power tubes" mod, but he would not give me any more info that a pdf much too generic for my knoweldge (wich is little) in this matters.
Nik indeed, explained me better the whole concept, but also made me realize that the "power tubes only" mod was a little more complicated in terms of instalation on the DC30, as I needed to mod a couple of things more, not only add a couple of caps and resistors (as the "whole amp" mod would requiere only).
 At least, that's what I could get from his kind explanation!
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