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Does anyone have any idea how I can install a choke on my TC-15?

I assume it goes in place of my 32+32uf electrolytic cap but the cap has 3 connections and the choke has 2.

Any guidance is much appreciated.

Why would you want to put a choke into the TC-15? The cap has to stay in there in any case.

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Great tones come in small glass jars!

Good question.
I heard that a choke provides a more refined tone and less flabby in the bottom end, since it provides more current.

Sorry if my questions seem out there, as I am a noobie (with an EE background), but I love the idea of experimenting with Trinity's awesome design.

If you want to stiffen up the supply, and tighten the response, put in a choke. IMO it's not required but go to the Resource forum and pull the TC15 docs. The schematic shows you where to put the choke.

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

It depends on where you place the choke. If you place a huge, fat choke (200mA rated) in the main B+ line after the first filter cap, it may help stiffen up the amp. If you place it in the screen grid supply, it will actually make the amp more saggy and loose, like a vintage Vox. If you just want to tighten up the amp's bass, then increase the value of the EL84s' cathode cap to anything between 1000uF to 2200uF. Then also increase the cathode resistor to 180 ohms, to prevent the tubes running too hot with the big cathode cap.

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Great tones come in small glass jars!

You can replace the 1K5 5W resistor with a choke. Inductance = 4 H, 90mA(DC).
See schematic notes: viewtopic.php?f=12&t=859

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

That's what I did and it worked fine for me. I used 50mA though, still more than enough.

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FWIW

I have compared a choke without a screen dropping resistor in series, also with a dropping resistor in series and then with just a dropping resistor, no choke. Made it switchable for direct comparison.

The sound with the choke was more harsh and brittle, less organic or musical you might say. It was somewhat better with the choke and resistor, but the resistor alone was the best by far, with the same resistance.

You will see a screen voltage increase with the choke alone because the choke will only be around 100+ ohms, so check voltages after doing this. 20 to 40 Volt increase is what I saw with the choke alone. To offset this, just put a resistor in series with the choke that equals (Choke + Resistor) the total resistance of the screen node resistor that provided correct screen voltage before.

I did not see any benefit in the choke but it's cheap if you just gotta try it, or you want that raspy sound.

Another sideline.... screen resistors have the same effect on sound as the aforementioned choke, so I leave those out too, by making sure screen voltage is below plate voltage by an acceptable margin. This is controlled at the screen node dropping resistor. 20 to 40 volts offset works for me.

The 100ohm output tube screen resistors in the TC-15 are low as most want to go as a failsafe and have minimal sound effect, but it is there. 100 is better sounding than the usual 470 though and I imagine that's why the TC-15 has 100s.

How did it sound with the choke in this position?

Would you also want to add a resistor in series with the choke, to get back to 1K5 and retain the same B+ out or is the B+ gain so little as not to worry about it at that point?

Thanks

I dont if I put a choke in. The B+ does increase a bit, maybe 5 volts or so.

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

Bit more open and clear sounding. This was apparent at higher volumes, low volumes it was hard to tell. Voltage does increase a bit, so I guess more gain theoretically right?

Sounds good to me. Not better or worse than the resistor, just a different tone. It was something I wanted to try.

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http://pdfelectronics.com

A few points...

High voltages rarely ever harm tubes, despite what the specs say. Excessive power dissipation is what damages tubes or shortens their lives, whether anode or screen grid dissipation. The main danger with high voltages is the potential to cause excessive power dissipation. There is ultimately a point where arc-over starts to happen inside a tube, but you have to go to real stupid high voltages for that.

It is essential to have screen grid protection resistors, when you have a screen grid supply with a filter capacitor (like in most amps). This is because when the amp cranks, the filter cap will dump a load of current into the screen grids, so they go to the edge of melt-down, especially on transients. A lot of vintage amps use a 100 ohm value, but IMO that's too low if you want to preserve your tubes. I would never use less than 1k with any EL84 amp. See the comments in this EL84 review by Randall Aiken - http://www.aikenamps.com/JJ_EH_tube_tests.html I've also just finished repairing an amp for a customer, which had 100 ohm screen resistors. The EL84s were pretty much ruined and one was red-plating. Needless to say I put in 1k screen protection resistors to help protect the new set.

A choke also has a current limiting effect and can help protect screen grids. The fundamental action of a choke is to fight changes in current through the choke. So when screen grids start to draw more current on a transient, the choke will rapidly drop the voltage seen at the screen grids. The result is to make an amp compress more, with a softer attack and a looser feel - like a Vox AC30. Larger screen resistor values also make for more compression, although not as much typically as with a choke. Just for refernce you may like to compare these schematics from an AC30 and a Matchless Lightning with the TC-15's:
http://www.schematicheaven.com/voxamps/ ... weramp.pdf
http://www.schematicheaven.com/newamps/ ... htning.pdf

There is no reason for an amp to sound brittle or harsh with either a choke or adequately sized screen resistors. There are thousands of EL84 amps out there which have awesome tone, and which aren't melting down their screen grids. One of the amps I often gig with has 1k3 resistors going to each screen grid (just what I had handy at the time), and has a tone as smooth as butter. If an amp sounds harsh or brittle once you've put in sensible screen grid protection measures, then that indicates that a problem elsewhere in the amp has been unmasked. Possibly even just poor quality power tubes.

There are inevitably a lot of subjective opinions about what screen protection resistor value sounds best. I've even come across one guy who swears by his 2k7 screen grid resistors. He's an experienced blues player, and I so don't argue with him.

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Great tones come in small glass jars!

Respectfully speaking, everyone likes something different and that is fine. But switch those socket mounted, screen resistors and chokes installed at the screen node, in and out of the circuit with a switch, almost on the fly and see what you hear.

As long as all concerned voltages are acceptable the screen voltage stays below plate voltage, during hard use it will be fine. That issue is easily taken care of before screen resistors, at the output tube sockets. Just take a look at an original Fender 5E3 circuit and some others that get along just fine without screen resistors. That is not to say that I would never use them if I liked the way the amp sounds. They are just one piece of the puzzle.

The choke is just as subjective and a matter of preference. I still believe the sound is better without them in this amp. I will say that a Bandmaster sounds great and uses a choke

In my testing, Tubes and other variables were not changes only the switch positions. Voltages and red plating were closely monitored as well. Choke alone, at the screen node yielded plate and screen voltages almost equal, choke and resistor in series yielded the same voltages as the screen node resistor alone due to the same resistance applied.

Calculations and theory give you a great place to start and most good information is backed up by circuits that last, but your ears are the final judge. People regularly run amps out of spec or close to the edge, to get the sound they love.