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I recently laid out a board for a custom 15 and decided to apply the design to the TC-15. It shortens wires, reduces jumpers.

Can you spot the changes? There are 6 of them.



I had some chokes lying around so I installed one to see how it sounded. MY very first 15 had one. You'll notice there is no 1K5 power resistor across the 32/32 can cap.

Now to get lbet to test it out and bgroup too.

Eventually this amp will have the VRM circuit installed.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Ah, Coco, ever the perfectionist! One of your great gifts, to be sure! But OK, I struck out! But didn't sleuth thru the schematic or layout diagram, so what did I expect to find? I only built one TC-15!

Using the choke reminded me of a question I've meant to ask you or others on the forum: What changes in sound are you hearing with the choke instead of the resistor? Also, I think you recommend minimum values for the choke, but I have an unused one from another project. Would going higher on the henries and current capacity be a problem? Mine is a Hammond 158Q, 5H/150mADC.

Second question: Since the EF86 channel is higher volume at most settings than the 12AX7 channel (assuming I wired everything correctly), is there any simple way to boost volume (not gain, which is already high enough) in the 12AX7 preamp circuit, so that switching between the two channels is a bit more equalized in volume (not necessarily gain)? At present, to do that I have to run the EF86 channel preamp volume pot really low, since the master volume needs to be set fairly high to get good volume for channel 2. I realize the TC-15 was designed more as two amps in one than a switcheable amp, but just trying to think outside the box. Not a complaint, this amp is wonderful as is.

These questions may be better for another place on the forum, but your revised design stirred my curiosity.

Best,
Jim

Your choke is fine. Replace the 1K5 5W with it if you want. I used 5H 90 ma.

Look for a tighter, stiffer sound. More attack, less compression. I'm going to give it some good testing and report back. I guess it could be another switchable option.

I'll give the other question some more thought. As always, it usually takes some experimentation to confirm it.

I'll reveal all later on the changes.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Aha, I found my problem! Not a circuit design problem at all (I should have known). My short jumper wire bridging pins 1 and 7 on V2 had broken at one end. I started wondering if I had a problem somewhere in the preamp circuit for channel 2, separate from the EF86 channel which had much more power. And voila, there it was, looking perfectly fine until I touched the ends of the jumper and found the sneaky little devil entirely broken loose.

Thus I was not getting the benefit of the second half of the 12AX7 (V2) amplification - V2a plate disconnected from V2b grid. My amp has now come alive! Fantastic, rich sounds now from channel 2, and though I haven't AB'd it yet, I suspect the overall volume match between channels 1 and 2 when switching is very close now. Sorry for the spurious question earlier today.

Thanks, Coco, for clear cut schematics and layout diagrams.

Jim

Good stuff. It does get sneaky at times. I was listening to my new one with lbet playing it [he took it away as he usually does for a gig & more testing] today and didnt detect any real difference in level.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I'm always up for testing! Bring it on!!

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Brent Bodrug
Producer-Engineer/Songwriter

www.slyfichapel.com

Lbet came over on his way to a gig.

Once we got things set up on the TC-15, (gain, crunch/munch) andtunes the LP, there was some very interesting sonic observations made using a a freshly built 212 V30 'low boy' cab.

The Celestions V30 212 has a sound of it's own with additional sonics not in the program material. This is the main difference between the Tone Tubbys. This confirmed to me that the TT are hi-fi guitar speakers for sure.

But, the rig must have been good becasue he took the 212 and TC-15 away to play atthe gig.

Now looking for feedback from him and the return of the gear!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Stephan, the new layout looks clean and tidy. Will it fit the board I purchased last week ? If so can you post a new layout diagram ?

Marc

Looks like you've moved the electrolytics around to more logical locations, instead of having them all at the one end of the board.

I've been working on a compact, Hoffman-style layout to try to fit into a narrow Hammond organ amp chassis. Work in progress:



It'll be on a much narrower board than the diagram suggests, probably 2". 22uf radial electrolytics at both ends, and a 32/32 cap can. The donor amp had a choke, but I've been unable to find any specs for it. I may try hooking it up. I'm going to wire the power tubes like the Trainwreck Rocket clones I've been seeing photos of on ampgarage.com.

Same size board, differnt location of parts. I'll post it after we complete the testing and once the remaining boards are gone, will change add the new layout to the resource section and start shipping.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks, that sounds resonable.

Marc

Okay, I will bite:

On the EF86 channel:
Its hard to tell from the photo – too small and blurry, but it looks as if maybe a resistor/cap have been added in series around the EF86 tube. Are you adding on to the C31 (0.01uf) or the R35/C30 (2k2/25uf) pair?

C18 (22uf power supply cap) moved closer to V1TB plate.

“Boost/Cut” switch added to selectively place/remove the cathode bypass cap on TBV1.

C17 (22uf power supply cap) moved closer to V2TB

R21/C12 cathode biasing resistor/capacitor moved to outside edge of the board. This puts the bias resistor in an easy to mod location, and further removes the requirement to place the 22k resistors so close to the standoff mounting screw. Cool!

R9 (220k) moved to a perpendicular orientation (so as to align in parallel with the corresponding R11 (100k) divider from the TB tone stack). This allows you to remove the wire jumper (blue wire).

There, I think that is six.

Interesting:
Stephen:
I am curious why you did not also move C40 over to the 330k plate for the EF86?

Also, I assume that you ran ground wires from C18/C7 back over to the power supply ground?

Finally, care to elaborate on the tweak at the EF86?

Most importantly, did you perceive any benefit to the changes you made, e.g., to the power supply filter cap relocation?

If it makes a difference, those of use with the head cab can likely reposition those caps using some well placed terminal lugs.

Best regards
Tom

Pretty good job Tom.

You got 5 but I also move the EL84 cathode res/cap pair to the end of the board and I made no change to the EF86.

I wanted to move C40 over to the 330k but it was going to push the interconnects too far over and one of my objectives was to shorten these.

The amp sounded the same as before (another objective) but mechanically, it went together a bit cleaner.

In the newest chassis, I have also moved the ground to the front of the chassis leaving plenty of space for VRM some day and cleaning it up some more.

Thanks for the nibble!!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Gotcha.

At first glance, I thought that you may be kicking around the idea of adding a switchable network on the EF86 side to provide a boost switch for that channel, since you have a boost for the TB side.

I had sort of envisioned that the second cap on the right was made large, e.g., 22uf and was wired in series with a large resistor, e.g., 100k or so that parallels R35/C30. I also envisioned changing the current cap C30 to something like 0.47uf. Then, you add a switch that selectively shorts out the 100k so that you have a "boost" of sorts.


Tom