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 Post subject: New TC-15 is Born
PostPosted: Thu Jul 15, 2010 10:38 pm 
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A bit of a change from a stock TC-15 on this one. I added a few mods and changed a few component types/values.

I went with Orange Drop 6PS caps as I have used them a lot in recent builds and quite like them, the similar Trainwreck Rocket also used these caps. 1W carbon film for everything else basically except plate loads which are 1/2W CC.

I did add a few mods to the build. I have played a few TC-15 before this build so I knew what the amp had to offer, wasn't modifying blindly. I should note all the mods I have done are either switchable or tune-able for a 100% stock circuit. So really my mods are "adds ons" to an already great amp.


Mods:
- Choke/Resistor switch. This three way switch functions as a switch that selects either a choke or resistor for the PSU with the middle position being the standby function for the amp.
- Reverb! Add one tube reverb circuit to channel two (non-EF86 channel, TB channel). Single mix control to control reverb level/strength. Medium decay reverb tank mounted in the head cabinet. Reverb is foot-switchable.
- Cascaded/Parallel switch. On Channel 2 the first tube parallels the two triodes. I am using a 3PDT switch to either select the two paralleled triodes or cascade the two triodes for a bunch for gain and sustain. When the triodes are cascaded there is a 70% increase in gain. In cascade the sound should be pretty smooth and rich sounding.
- Phase Inverter limiter mod. This is a trim pot in series with the “tail resistor”. This trim pot controls how clean or dirty the signal is after exiting the phase inverter and is passed on to the output tubes. Ken Fischer of Trainwreck Circuits often did a similar mod to this.
- Mid trimpot to adjuct the mid range on Channel 2. This will probably be replaced at a fixed resistor in time.
- Decrease the bright cap on Channel 1 and increase caps on rotary switch. Fuller tone with less highs. I only play single coils so this was something I needed to do.



Pics...

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If you wanna see more pics I have a shi t load in my photobucket. Most are progress pics. http://smg.photobucket.com/albums/v610/ ... s/?start=0



And my mini review...

The tones are great. Lots of versatility with the Parallel/Cascade switch. Parallel is much cleaner than cascade and a bit fuller and thicker. The Cascade mode it basically an overdrive mode, so sweet with lots of bite and gain.

The Choke/Resistor switch. The resistor mode has a bit more girth and underlying grind to it. Choke mode the sound is a bit tighter and focused, a bit cleaner. The choke runs all the voltages higher.

Reverb sounds amazing, I was stunned at how well the single tube reverb worked out. I did have to change a PSU dropping resistor to get the voltage up (290V) on the driver/tube but that was the only tweak from my original plan. The reverb is nice and full not spanky and in your face like BF reverb. When the reverb control is dimed you have a nice full sounding reverb which I like. I am not a fan of the BF Fender dimed reverb, it's much to intense for my tastes.

Still haven't fiddled much with the PI or Mid trimpots so I can't comment much there.

The Crunch/Munch switch which selects different primary windings on the OT provides two unique tones. In my prior experiences with the TC-15 I thought one mode was just brighter than the other. Not the case. Both the highs, clarity and gain differ between the two modes. I have no favorite as of now, they are both really unique and fun to play on.

Great harmonics, sustain and feel to both channels. Have already cranked the amp up and let it go into harmonic feedback while holding a note, sounds great.


More to come as I play more and the amp/speakers burn in...

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 Post subject: Re: New TC-15 is Born
PostPosted: Fri Jul 16, 2010 9:21 am 
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What, all that and no effects loop?

Nice, I'd like to hear the reverb some time.

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 Post subject: Re: New TC-15 is Born
PostPosted: Fri Jul 16, 2010 11:13 am 
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Quote:
- Cascaded/Parallel switch. On Channel 2 the first tube parallels the two triodes. I am using a 3PDT switch to either select the two paralleled triodes or cascade the two triodes for a bunch for gain and sustain. When the triodes are cascaded there is a 70% increase in gain. In cascade the sound should be pretty smooth and rich sounding

I eventually did this same setup with my "Chimp" SE amp a while back...although mine has a gain pot between the stages (functional only in cascade mode). Did you incorporate any caps &/or resistors in your switching, or does it use the same setup for both modes? I'd love to see a diagram if you have the time & inclination. :)

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 Post subject: Re: New TC-15 is Born
PostPosted: Fri Jul 16, 2010 12:57 pm 
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^^No room :bugeye:

^I don't have a formal drawing at the moment. I have a really rough sketch of the circuit on what looks like a beat up paper napkin.

The cascade/parallel switch is a 3PDT, it switches all active elements of the tube. When in cascade mode plate, cathode and grid components are added. Cascade uses components in such a way that there is more gain than the proceeding stage but some signal is cut before hitting the second stage grid (following?). The cascade mode is voiced in such a way that a bunch of highs are cut yet there is still tons of bite. This is done with the coupling cap and a cap bypassing the plate load resistor.

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 Post subject: Re: New TC-15 is Born
PostPosted: Fri Jul 16, 2010 2:14 pm 
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Quote:
^^No room :bugeye:

LOL - yeah...TC-15's front panel is plenty busy enough as it is. I didn't have a lot of room either, so I went with stacked pots. I found a cool rear/outer knob & detent washer for a Jazz bass at Angela Instruments. The detents limit the available in-between settings on the 2nd stage, but it keeps me from accidentally noodging it when I tweak the 1st gain level (front/inner knob).....& it makes a cool clicky sound when I twiddle it.
:happydance:

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 Post subject: Re: New TC-15 is Born
PostPosted: Mon Sep 06, 2010 1:33 pm 
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Did some tweaking on the EF86 channel last night. That channel seemed a bit too "hard" (stiff) for my single coil tastes. I recently got a Tone Tubby and that helped soften it up but it needed something more. At first I thought it had too many highs and needed bass but after lots of playing I decided that wasn't the case.

Experimented with increasing the screen voltage on the EF86. The layout calls for 2M2 but most are using 2M (I did anyways). I played around with resistors in parallel. Increasing the screen voltage increases the compression and touch of the stage. I went as low as 600K for the screen resistor, at that point it sounded like I was playing with my Dyna Comp plugged in front, lots of compression.

In the end I went for 2M in parallel for a combined resistance of 1M. The compression increased and I find it softer and more lively with my strats. Just seems easier to play through, but that's me.

Anyways, was thinking. Would I be stupid to use a mini toggle switch to select different resistors? That would be a pretty HV I'd be switching. That being said the Crunch/Munch switch has some big voltages being thrown across it.

2M screen resistor:
Supply node - 348V
Screen - 85V

1M screen resistor:
Supply node - 341V
Screen - 119V

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 Post subject: Re: New TC-15 is Born
PostPosted: Tue Sep 07, 2010 4:47 pm 
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Here is the finished amp in it's cab I got from Trinity. Like usually a very nicely built cab with a solid tolex job (tolexing isn't easy!). The reverb tank barely fit, you can see how tight it is around the OT. It fit by mili meters.

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 Post subject: Re: New TC-15 is Born
PostPosted: Tue Sep 07, 2010 5:54 pm 
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Incredibly there was no extra noise from the proximity of all that gear inside that head. A sweet reverb addition indeed! Nice job!

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 Post subject: Re: New TC-15 is Born
PostPosted: Wed Sep 08, 2010 2:19 pm 
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Close up of wiring to reverb tube socket.

Attachment:
TC15_reverb_ 0011.jpg
TC15_reverb_ 0011.jpg [ 173.25 KiB | Viewed 12202 times ]


Close up of wiring to Tank In/Out jacks.

Attachment:
TC15_reverb_ 0031.jpg
TC15_reverb_ 0031.jpg [ 187.85 KiB | Viewed 12202 times ]

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 Post subject: Re: New TC-15 is Born
PostPosted: Wed Sep 08, 2010 4:07 pm 
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If anyone wants a copy of the reverb schematic I can post it. It's quite simple and easy to implement.

Here is the cascade schem
Image

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 Post subject: Re: New TC-15 is Born
PostPosted: Wed Sep 08, 2010 5:05 pm 
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kurtlives wrote:
If anyone wants a copy of the reverb schematic I can post it. It's quite simple and easy to implement.


That would be great to share here.

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 Post subject: Re: New TC-15 is Born
PostPosted: Wed Sep 08, 2010 8:10 pm 
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Hey whats the matter... I think one of your wires isnt exactly 90 degrees to the rest :)

Looks good. WHat EF86 did you use?

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 Post subject: Re: New TC-15 is Born
PostPosted: Thu Sep 09, 2010 4:35 pm 
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:o :D

I got a used old EF86, was cheap and tested fine. It seems it is an Aprex. I haven't heard too many good things about new production EF86s so I went with an old one.

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 Post subject: Re: New TC-15 is Born
PostPosted: Thu Sep 09, 2010 6:23 pm 
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Ask Stephen to try one of the ones I brought down. They are really nice - to me anyhow. Amperex, but not bugle boy. No noise at all however, even if you bang on the head.

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 Post subject: Re: New TC-15 is Born
PostPosted: Thu Nov 25, 2010 4:22 pm 
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re: reverb schematic: yes please!!


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 Post subject: Re: New TC-15 is Born
PostPosted: Tue Jul 26, 2011 3:39 pm 
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What fianl values were used for:

- Phase Inverter limiter mod trim pot in series with the “tail resistor”.
- Mid trimpot to adjuct the mid range on Channel 2. This will probably be replaced at a fixed resistor in time.
- Bright cap on Channel 1 and increase caps on rotary switch.

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 Post subject: Re: New TC-15 is Born
PostPosted: Tue Jul 26, 2011 9:10 pm 
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Couldn't find my notes, opened it up...


5K trim with 1W 1K in parallel all that in series with a 720R 1W. This makes up the PI "tail". ~ 950R

50K trim for the mid control ~ 13K

Contour: 22nF, 10nF, 4.7nF, 2.2nF, 1nF, 360pF
Bright cap is 150pF

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 Post subject: Re: New TC-15 is Born
PostPosted: Sun Oct 02, 2011 7:00 am 
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Just finished my first build. The notes and drawings made it so easy to build, it fired up first time, no noise no smoke! Great sounds, distortion on CH 2 is really nice. Running all NOS tubes mullard in V1, V7 and the rectifier. Using a Telefunken in V3 and a sylvania in V2. V4 & 5 are national EL84's never heard of them but they sound good so.... The clean channel sounds excellent, but I'm thinking of trying the cascade mod you've described to get some more gain. My main aim in building the amp was to get a better understanding of how an amp works and how to tailor it to my needs. I want to use a pot to control the gain in cascade mode. Would 1M be about right?
Posted some pics, let me know what ya think.


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 Post subject: Re: New TC-15 is Born
PostPosted: Mon Oct 03, 2011 3:51 pm 
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Sounds like a fun plan! Amp looks good!

1M(A) would work, but for a bit more control and a tone that is not over the top I'd try 500K or 250K. 1M is ideal here but will give tons of gain.

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 Post subject: Re: New TC-15 is Born
PostPosted: Mon Oct 03, 2011 4:59 pm 
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Thanks! Enjoyed the build, looking forward to trying some of your mods!


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