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 Post subject: Re: Tube down TC15 Build
PostPosted: Sat Oct 19, 2013 10:10 pm 
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I expected some glitches due to the 2x12 combo but the damn thing sounds great. Thanks for the help.

Personally my luck has been not so good with the EF86's I've purchased. Sound fine but eventually rattle and hiss which is too bad. I'm on the hunt for reasonable NOS for certain.

Good info on the bypass cap and I think I'll give it a try. I've got a couple of 10uf 63v caps. I figure that should tame some hiss at least. Bleeds through when using ABY and playing Ch 2. Goes away if I turn down Ch 1. but I like using both channels. Great flexibility.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Sun Oct 20, 2013 11:20 pm 
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Thanks, Stephen. I never thought of that. I was thinking of trying a 10uf Mallory I have. I find that when the tube is "healthy" I can us a bit less on Ch.1 gain anyways. More gain is just giving more noise anyways and I've got plenty of drive on tap.

Playing in a group or at volume most of the time doesn't matter but when playing clean or quiet on Ch.2 the rattle and hiss come through from Ch.1. It has been noticed by a fellow player and unfortunately my reputation compels me to make adjustments!

If I turn down the volume on the EF86 it's almost gone but then I can't switch to it on ABY which is great to be able to do especially since Ch.1 seems to like my homemade boost/distortion drives great with humbuckers. Fellow players seem to also appreciate that EF86 sound which seems to be a different kind of magic and I'm hooked.

I still love my mixed speaker 2x12 combo though and am on the hunt for decent NOS EF86 that'll hopefully survive better especially dangling down behind the speakers. Tried a RFT from tube store (which sounded great) but my combo ate that too! Waiting for them to get some NOS back in stock before I try again. If I can tweak things to help before 'investing' in more tubes I'll be happier.

Didn't mean to double post. Didn't flip page.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Tue Oct 22, 2013 1:22 pm 
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Did you use the silicon ring provided in the kit?

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 Post subject: Re: Tube down TC15 Build
PostPosted: Tue Oct 22, 2013 10:22 pm 
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You bet. I then moved onto socket isolation, different o-rings, high temp silicone and lastly doubled up heat shring tube on the tube. I manage a heavy duty repair shop so I got ideas and supplies to work with. There's lots of info on the internet related to noisy tubes and I think I tried most of the stuff that makes sense.

If it was just hiss or something like that I might start looking elsewhere but the physical rattle (that I can reproduce with gentle tapping of the tube with a chopstick) leads me to believe I'm dealing with mechanical noise. Whether its the tube construction or my combo killing the tube I haven't determined yet. Seems to be more common with newer production tubes in this application as well. If all goes well maybe I'll get a good available tube but its nice to be able to minimize the potential of future noise as well. Besides, its nice to be able to replace any tube eventually and get most your original sound back if you like how a certain type sound.

It doesn't make the amp unplayable, just quirky. Unfortunatley nobody I know has a functioning EF86 amp I can borrow a tube out of either.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Tue Oct 22, 2013 10:53 pm 
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Look this over. http://www.guitargear.net.au/discussion ... ic=37811.0


Also:

https://taweber.powweb.com/store/chassis/chord2.html

Scroll down a bit, the part you want is listed as "9 pin shock mount".

Look at the pic, you can build your own. The socket itself is mounted to its own little sub-chassis with rubber grommets then the sub-chassis (really just an oversized washer) is mounted to the main chassis with springs on the mounting bolts. There's a lot of wiggle room in the assembly, that's what keeps the EF86 quiet.

You could mount the socket to a small square of sheet metal then suspend the square of sheet metal under the main chassis with four little springs.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Wed Oct 23, 2013 12:44 pm 
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I use a NOS bugle boy in my tube down TC15, and have never had a problem...I just use the rubber ring. Rock solid. Expensive solution, but it sounds great.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Wed Oct 23, 2013 10:12 pm 
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tinnitus wrote:
I use a NOS bugle boy in my tube down TC15, and have never had a problem...I just use the rubber ring. Rock solid. Expensive solution, but it sounds great.


I like the Bugle Boy as well. Great tube and tone.

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 Post subject: Re: Tube down TC15 Build
PostPosted: Wed Oct 23, 2013 11:46 pm 
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Thanks guys for recommendation.

I like the idea of mechanical suspension and other attempts have obviously failed at least with new production tubes (which I've spent enough money on already).

Stephen, that product is right up my alley as far as designing my own. The combination of springs which can be tensioned to suit and some small hydraulic o-rings for screw isolation can't hurt. I'll see what I can come up with.

Curious though, if chassis reinforcement or steel chassis would be different. Nothing wrong as is very nice chassis but have to wonder if long aluminum chassis doesn't have a certain amount of vibration transfer in my case. I'm still blaming the tubes and don't want to shake any more though. The RTF going bad kinda made me think I might want to take some steps before stuffing another tube in.

One positive though is now I have a few different tubes to play with for different sounds even if they make a little noise. Bugle Boy seems to be popular out in web land for EF86. Wish tube store had them. I like dealing with them as I'm a big Canada guy for buying stuff.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Thu Oct 24, 2013 9:00 am 
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There will be vibration transfer. Did you use some closed cell foam between the chassis and cabinet in an attempt to isolate it somewhat.
Whatever rubber or material is used is going to have to be soft enough to dampen vibrations in the 50 to 5000 Hz range. Maybe a combination of spring and rubber is the trick? Sounds like a good project for an engineering class!!

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 Post subject: Re: Tube down TC15 Build
PostPosted: Thu Oct 24, 2013 9:35 pm 
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I was thinking a kind of foam donut under the socket and using the machine screw/spring idea to put tension on. Probably wouldn't even need the springs which makes it easier. I would just need to make a small plate to attach the socket to and have four screws to hold it down.

That would provide mechanical isolation from the chassis. I'm not certain but I would still think that sound pressure (layman's term) from the speakers could still be a factor. Won't know until I try.

I did play the amp with the chassis on the bench on a towel and the cab on the other bench when I was first working a couple of buzzes out of the unit. I put the chassis back in with some thin sticky back foam where it contacted the wood (front too) and slid a bit of tolex in the chassis corners at the back before putting the chassis back in which got rid of all of that.

Still looking for a tube.

Question off topic though. I kind of remember now that, as the chassis was sitting tubes up on the bench, was it just me or did things sound different when I played it this way? Do tubes care whether they are pointed up or down? It was kind of a 'not quite warmed up yet' sound. I remember even putting a shirt over the amp to cover the chassis opening to see if it made a difference.

Amp designers must go nuts figuring these things out!


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 Post subject: Re: Tube down TC15 Build
PostPosted: Thu Oct 24, 2013 9:50 pm 
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In as much as the tube may run hotter, it may sound different. But physically, no difference and I don't think electrons care!

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 Post subject: Re: Tube down TC15 Build
PostPosted: Thu Oct 24, 2013 10:49 pm 
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Thanks for confirming it's possible I wasn't imagining things. I wasn't really worried about tying the two together but cool to know!

I only really care about the musical electrons anyways.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Wed Dec 04, 2013 3:02 am 
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After much research, reading (including previous topics on this forum) I have a plan. I went so far as using a c-clamp on the chassis to play with vibration and have come up with the issue being twofold. One is too much gain on EF86 (hiss). I can post my results when I've finished tweaking. Second is just plain old speaker hammering on tube. I have a new idea for this once my NOS amperex tubes arrive. I'll post once I have results.

Had my semi-pro buddy up to play amp the other day (plays modern and heavy) and loved the responsiveness and tightness of amp and would like to try recording some tracks with it so I want to get rid of rattle. He'd never really played an EF86 before and like most of us that have fell hard for it.

Still love it.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Mon Dec 16, 2013 2:30 am 
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Alright. I smartened up my EF86 mounting with some better O-rings on screws and socket. I found some NOS amperex bugles boys so I put that in and it sounds great. Still had some noise so I slid some shrink tube on the tube, put the damper O-rings on and then went a step further and put a piece of that foam insulating wrap around the whole works and it seems to help quite a bit. It aint pretty but function before form right.

I was looking at some other similar schematics and was still thinking of using some other values other than the 330K/2.2M combination. I see that 270K/1.5M and 220K/1M were popular and assume this would pull some of the gain back a bit. I've got quite a collection of 1/2watt Metal Film resistors and was curious if this would be a good place for them. These old tubes seem to have a little more hiss to them and thought that might help. Sound great though.


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 Post subject: Re: Tube down TC15 Build
PostPosted: Tue Dec 17, 2013 12:19 pm 
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BCB wrote:
Alright. I smartened up my EF86 mounting with some better O-rings on screws and socket. I found some NOS amperex bugles boys so I put that in and it sounds great. Still had some noise so I slid some shrink tube on the tube, put the damper O-rings on and then went a step further and put a piece of that foam insulating wrap around the whole works and it seems to help quite a bit. It aint pretty but function before form right.

I was looking at some other similar schematics and was still thinking of using some other values other than the 330K/2.2M combination. I see that 270K/1.5M and 220K/1M were popular and assume this would pull some of the gain back a bit. I've got quite a collection of 1/2watt Metal Film resistors and was curious if this would be a good place for them. These old tubes seem to have a little more hiss to them and thought that might help. Sound great though.


Did you try reducing the 25uf cathode bypass capacitor?

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 Post subject: Re: Tube down TC15 Build
PostPosted: Wed Dec 18, 2013 12:07 am 
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Sorry Stephen, I didn't try that yet and I may have gotten a little wrapped up in the resistor idea. I like to try one thing at a time so I can confirm if something actually made a difference. Capacitors always seem to have such a variance in tolerance (20% seems to be normal) and it seemed to be a little easier to do the math with resistors and none of the other schematics I looked at ever lowered the cap value but I think the theory is sound. I will definitely try that and let you know the results as I said I would!

I really appreciate the input and you're patience with me. You will be the second to know.

Merry Christmas!


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 Post subject: Re: Tube down TC15 Build
PostPosted: Mon Feb 17, 2014 11:11 pm 
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So I went a bit of a tangent and installed a VRM and decided to try that before messing with gain on Ch.1 just to see. My issue is really the mechanical noise off of the EF86 which isn't a big deal till it comes time to mic the amp.

It works like a dream and I play it plenty. If you mix a bit of VRM and Master Volume there is even more playability in this amp. I plumbed it in right off of the standby switch and then into the cap can. It's great for micing as without the speakers hammering the EF86 I get quite a bit less noise.

Did raise questions though of course.

If I wanted to just control the B+ of the PI and output only wouldn't I have to add another 1.5K cement resistor just for the pre-amp? If the OT B+ comes before the 1.5K across the cap-can and the output and PI are on the other side then to get my pre-amp B+ unmodified I'd be losing the 1.5K (and cap) if I took the pre-amp B+ from the standby switch. Would this be OK?

I noticed that with the VRM turned down the 12AX7 channel is much quieter compared to the EF86. Think dropping the cathode bypass cap like you mentioned before would apply more now? I was thinking 10uF would that be enough you think?

On a different note, "TC1530" looks interesting. Nice to see you guys aren't ONLY moving on to newer things. This is a great amp and has lots of room for modifying!


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 Post subject: Re: Tube down TC15 Build
PostPosted: Tue Feb 18, 2014 1:14 am 
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Yes, you will need to make changes to the voltage balancing resistors to get to the same voltages as pre-VRM. This will take some math and some experimenting. You also need two diodes to prevent voltage interaction as well.
I prefer to scale the whole amp, but would like to hear how yours works out.

As soon as we get some extended feedback form the owner of the 1530, we do plan to make it an available kit option.

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 Post subject: Re: Tube down TC15 Build
PostPosted: Tue Feb 18, 2014 9:40 pm 
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It works too well wide open to be messing around there just for balancing at lower volume in my application.

The whole amp scaling works pretty good and I'm quite happy with the results.

I had the diode thing figured but it just looked to me that I was trying to get three different wires from two sources (one VRM and the other straight B+) and was curious where the best place to really split these apart. There is great schematics for sIII and tramp but nothing for TC15 and thought I might be smart enough to figure it out.

I should really stop fiddling with my main amp but its too much fun. I might need another one, eh!

Thanks again Stephen!


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 Post subject: Re: Tube down TC15 Build
PostPosted: Wed Apr 02, 2014 9:50 pm 
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I see, that you had a great deal of trouble.
I just ordered the tc-15 and plan to
Do the tube down combo version too.
I want to use all wisdom here to prevent microphony.

This is going to be 1/12 combo.
I want to also install partition board between the speaker and
Chassis to decrease vibration of the upper part of the
Cabinet. Is it worth ?
Anyone used anti vibration tube mount?

Thanks guys.
Looking forward to this.


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