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Messages - Theors

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Tubes and Hybrids / Re: Help Diagnosing Reverb Drive & Return Circuit?
« on: November 24, 2015, 01:02:36 AM »
Well...thank you so much for the "Tip of the Return Circuit" hum test! This is a used amp that I've had for some time now. It seems that the return circuit was reversed! The outside of the RCA cord, just touching it, gave a hugh hum! The tip...nothing. Well I knew that was wrong! So I soldered it correctly AND I think it's working like it's supposed to....meaning, what I thought was normal reverb effect was waaaaay outta whack! Never able to turn the POT up more than 3 or 4. After realizing the original tank "Accutronics Reverb Tank 9AB1C1B" has a decay time of 1.2 to 2.0 secs (short), it seems to be working like it should. I just hope it didn't damage any components of the reverb circuit. The new tank I got has a decay time of 1.75 to 3.00 secs (medium). So buying I new tank without isolating the problem wasn't a total lose :loco Thanks again......

Tubes and Hybrids / Re: Help Diagnosing Reverb Drive & Return Circuit?
« on: November 23, 2015, 05:17:47 PM »
The amp works just fine. I'll do the "touch tip test" this evening and get back with results. The PCB is clearly marked "RD = Drive" and " RR = Return"

Tubes and Hybrids / Help Diagnosing Reverb Drive & Return Circuit?
« on: November 23, 2015, 08:22:42 AM »
Straight to the point......eliminated Foot Switch....replaced both RCA wires from PCB to the Reverb tank....replaced Accutronics Reverb tank....connected a speaker to the Reverb Drive wire, the results were a low uncontrollable guitar sound. Volume/Master or Reverb POT made no change to the guitar signal during this test. What's my next move?
My Amp is a Tube Works RT-2100. The date on PCB is 1991.
The problem is the Reverb effect suddenly dropped to approximately 10% of it's potential.
Attached is the Wiring diagram I obtained from this SSAmp forums.

Any help would be greatly appreciated. Thank you.

Thank you g1, I feel a little bit better after looking at the Jack schematic page  :-\

Reading back......your post all makes sense now! I guess "I is just too slooooow :duh" Thanks for the "edumacation" J M Fahey.
And I did find those exact jacks online if ever needed. :dbtu:

1) thanks drgonz for the schematic  :dbtu:
2) 13.7V DC???  OUCH !!!!!!!!!!
3) I see you are sleeping with the enemy  :o
Don't get the full picture yet, but the schematic shows what looks like an "input in use" sensor circuit, not sure if it's some kind of mute or it enables some function, but there you have 2 x  22k resistors connected straight to jack ring pin leaf contacts and on the other end to "CA" .
Said ring pins are grounded if nothing is plugged in, you'll have current passing through the 22k resistors.
If you plug into any of both inputs, one 22k resistor gets open and you halve passing current; if you plug in both, you fully stop current there.
That can be detected for some function I mentioned.
The only "CA" I find (you might find others) is on the emitter of "Y" 2N5401 , to the right bottom of the tubes area, which is also connected to the power supply node "C+" , which happens to be .... +13.7V  :trouble

Now those +13.7V shouldn't be a problem because if:
a) nothing is plugged in, 22k resistors get shorted to jack ring legs , so 0V there.
To boot, jack tip legs are also grounded, as an extra security layer.
b) you plug into 1 or 2 inputs:
the jack tip contact gets ungrounded, and signal gets into the preamp.
c) the jack ring contact also opens, current through 22k resistors stops, some function is triggered.
You have +13.7V 2 mm away from signal contacts, but it "SHOULD" be no problem, meager 13.7V can (should)  not be able to jump 2mm of air or PCB material .
I guess either the jack is damaged, has bent leads, whatever, or resoldering shorted nearby contacts or leaf switches are worn or bent or PCB is contaminated , and now those 13.7V cxan contact the *audio* pins.
They travel backwards to your guitar and make a scratchy mess.

So I would replace those jacks, while out clean the PCB area very well, I'd use Isopropyl alcohol because it dissolves both grease and salts (Big Brother does not let you USA kids to buy 94% ethyl alcohol ;) ) and recheck that DC voltage dissapears.

This is what tip and ring means, applies both to plugs and to matching contacts in jacks:

By the way the amp schematic has tip and ring jack contacts drawn the wrong way, tip (wherev 68k resistor go)  should be drawn the furthest away from the sleeve/ground contact, and ring between them ... as it physically appears in a plug.

And the input sensing circuit is also wrong: as drawn, whether 22k resistors are grounded or not , voltage at 2N5401 transistor does not change, since it comes straight from the nominal "+15V" OpAmp supply (actually +13.7V) called "+C".
Those errors make me lose trust in that schematic.
It may be close enough as a general idea but each part should be checked/matched with what's actually on the PCB.
Of course, the amp works or they wouldn't have sold so many but the schematic is iffy.

Thank you Enzo,... just completed the straighten of all bent tongs and used ohm meter to confirm proper positioning (and visual too) with and without cord plugged in. The amp is clean as a whistle (and down & dirty). Hummmm....TRS jack? Tip-Ring-Sleeve jack I'll remember that for sure!!! :)

I feel the need to explain my stupidity. Cleaning the pots I can do and have done before.  But when I decided to fiddle with the input jacks I had no idea that they were the type of muting jacks or whatever. Nor was I even familiar with that type of input jack. Little did I know the headaches and frustration I would create for myself by trying to adjust the tension by pushing on the tip and the sleeve tongs. Since the Jack is basically enclosed in plastic and soldered to the board the damage is not visible to the eye. Still, even when I removed the Jack from the board and looked inside I didn't understand why two tongs were touching the tip of the cord! Because of my lack of knowledge on what to look for in this type of input jack I just looked at it for hours on end. But when I finally posted a picture of what I was looking at, that's when "g1" said, "Those jack switches look to be bent in a way that prevents the switching function to work properly". What?...jack switches? Good lord! It was staring at me right in the face! Of course!...I pushed on that tong which bent that piece over which now touches the tip! BINGO! How stupid can I be!
Well, A picture is worth a thousand words. I know I would have never discovered this on my own.
Thanks a million to all of you! I definitely learned something.
Jeff O

Note to self...DON'T "JACK" WITH AN ALREADY WORKING JACK!!! Especially a fairly complicated one!
Sorry guys. Thank you so much for your patience and help!

I think I might have found the culprit. Thanks to g1's remarks. Out here on my phone, pouring over the pictures of the disassembled jack, I can see that the (CA) contact is bent back which allows it to touch the Tip! I don't think it's supposed to! It should be in the (G) position until disengaged by the Sleeve of the cord!!!!
(I feel like Gene Wilder in Willy Wonka!!!)
I shall bend it back this evening to confirm.
The (CA) should never touch the Tip in the first place!!! Wahoooooo!!!!!! guys think I'm crazy? Or got it solved?

I wouldn't be considering the jacks at all but since I did fiddle with both of them in an effort to snug up the fit.

Great...if it's that simple. Can you recommend a website where I can order replacements? And what type I should order? I can solder new ones on. It's worth I try


more pics

The (CA) has the 22k resistors on each jack which contacts each jack Tip. The (I) has two 68k for both jack Tips. Checking ohms while the resistors are on the board, the 22k’s read 22k. The 68k’s read 34k. But the 68k’s off the board read 68k each.

Correct. Both (CA) and (I) touch the Tip.

I’ve attached pics of the jack. Disregard the large Red & Black wire used for a simple 2 wire jack.

I’m going to try and describe what I see as the schematic of the input jacks:

When cord is inserted,
•Red(I) contacts Tip.
•Black(G) contacts 3 surfaces: 1-Sleeve 2-Ring 3-Becomes disengaged from Red(I) when cord is inserted.
•Purple(CA) contacts Tip also. (yes it's dedicated right to the tip)

68k inline with Red(I) Tip
22k inline with Purple(CA) Tip

Can anybody draw it? Is it different from what the schematic shows?

Also Enzo, I think I get what your saying about transistor Y. Isn’t that the voltage amount that was showing up at the tip of my cord? Bad transistor?

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