Ceriatone Forum

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

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...

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.

I am probably going to get the valves from Bob at Eurotubes. What are the JJ EF86 valves like?

Cheers,

Crusty

Microphonic...... Can't get past 3-4 on the dial.

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

I am going to be using these too:

http://www.tuberings.com/

Cheers,

Crusty

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

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...

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!

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

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!

I think also that the DC-30 also needs some serious consideration for cooling. Mine has a heatsink and very small fan which thanks fully is almost inaudible. I believe its the same for most cathode biased amps. Fixed bias are eaiser to do aparently.

Is your fan powered from the amp itself?

Yes, not quite sure where from, probably heater supply. You'll guess I didn't install PS myself ;D

Yep I guessed that!
But you served as witness that it works fine on the DC30...
Have to do mine, let you know how it goes!

Crusty keeps us informed about your amps!

Regards!

Started building today.

All is very straight forward.  The first few solderings were a bit shabby (out of practice) but it soon came back to me.

The quality of the kits is great for the money with just one exception - the power indicator (jewel lamp) has to be the cheapest and nastiest one I have ever seen.  I will be getting some good quality ones with a blue jewel for the amps.

We just did a lot of the fiddly stuff today, soldering the jumper wires and resistors to the tube sockets before installing them.  I have just twisted the wires for the heaters to leave them overnight, so they stay twisted.  Also paired up and twisted the PT output cables.   So, everything is ready to install the PT and lay the heater wires.

We picked up extra cable ties to keep things neater in the amps.

My friend the luthier is a degree qualified engineer but has never really done anything much with electrical.  It's great explaining to him how a tone circuit works and he just loves the physics behind the valves.  It's awesome being able to explain a diode, triode and pentode to someone who immediately understands it.  Our valves arrived from Bob at Eurotubes and my buddy has take the GZ34 home with him just to look at it.  I remember when I enjoyed just looking at valves.  I used to love cracking open the dead ones to see the guts of them.  They really are very cool devices.

Anyway, this exercise has put me back in touch with my teenage years.   It's great getting back into electronics (analogue style), I am remembering stuff that I assumed I must have forgotten over the years.  I think back to doing work experience at school with a TV repairer (yes, back when TVs were full of valves).

I'm loving it!

Cheers,

Crusty

you were luckier than me then! I started learnig some very basics of tube electronics ... a couple of years ago, when I first bought the DC30. And even then, during the 1st year I did not even open it to see the guts. Now days I found how passionate can it be!

Hi Alwalt,

Well I finally got around to finishing one of the amps.  We'll be double checking and firing up the second one next weekend.  Then it's on to building the cabinets.

I have an issue with this first one (don't know if it's a characteristic of the amp until I finish the 2nd) but there is a high pitched squeal at around 12kHz that kicks in at around 30% volume on both the 12AX7 and EF86 channels when the master volume is >50% or bypassed.

Although it's hard to tell at the frequency, it sounds like a sine wave and the frequency shifts slightly when the volume level is changed.

Given the nature of this squeal appearing within the preamp stage and the fact that it comes in when increasing the volume on either preamp channel when the master volume is up suggests to me that this is some HF feedback.

I'd appreciate any suggestions on how to track this down and eliminate it.

I already tried different EF86 valves from JJ EF806 to a few mesh plated Mullards that I have and it's still there, so it's doesn't appear to be EF86 related.

Cheers,

Crusty