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BIAS switch question. If I wired my bias switch exactly like it is in the document colored diagram (which it is), it looks like the switch is up (as pictured in the document) for 6L6 and down for 6V6. This would mean that the switch is up toward the open side of the chassis and that would be the 6L6, and pointing it down toward the closed side of the chassis would be 6v6. Is this correct?

I want to know for sure before I power it up with the 6v6 tube. I have my dim light bulb limiter wired and ready, but I want to make sure that if the switch is pointing up toward the open side of the chassis that this is the 6L6 position-- so I would point it down for the 6v6 test.

If you wired the switch the same as the layout shows then, looking down at the chassis (same as looking at layout) then the switch should be up for the 6V6 position (toward you). Well at least that's how mine is. You can verify this by checking with an Ohmeter, if you put one probe of the meter on the grounded side of the 750 Ohm resistor and the other probe on Pin 8 of the 6V6 socket, then in the 6V6 position you should get 750 Ohms and if you flick the switch to the 6L6 position it should read lower (like 300 and something Ohms or thereabouts, from memory ).

Snowy

This is very helpful information. Thanks so much!!

Today I double checked the components by checking them against the colored diagram on both the website resource page and the one that came with my kit. I also checked my components using Snowy's thread [http://www.trinityamps.com/phpbb/viewtopic.php?f=16&t=3188]. I then checked the wiring of the rotary impedance switch against the thread for installing this switch for EL 34 (and other tube) use [http://trinityamps.com/phpbb/viewtopic.php?f=16&t=2919].

I next checked for connectivity. I did find one connection that was troublesome and so I resoldered it (this was the blue wire from the bias switch to pin 8 on the power tube socket--that is a little bitty hole); it is good now.

Next post will be about burning it in with the dim light bulb limiter. Then hopefully putting the tubes (6V6 and 12AX7) in, connecting the speaker, and taking first voltage measurements.

Interesting you mention the Dim-Bulb Current limiter as I also used one on my amp builds, here's how I used mine.

I use several different wattages of bulbs. I start low with 15W ... then if all is safe, I move up to 25W .... then 40W ... 60W ... 100W. If there are no arcs and sparks or smoke on any of the in-between bulbs, by the time I get to the 100W bulb, I feel comfortable that I'm good to go and I then plug the amp straight to the wall as normal and start taking measurements in the amp and comparing them against stated "standard" values in the documentation.

I know some people just use the one bulb, but the interesting reasoning behind the progressive wattages, as I was taught, is that the smaller wattage bulbs have a higher internal resistance which constricts the flow of current. The larger the wattage, the lower this internal resistance and therefore more current is allowed to flow in the amp. So by starting with the low wattage bulbs, you start the test with minimum current flowing through the amp. If there is a wiring problem, the potential damage is greatly contained. So I gradually move to more and more current flow (higher wattage bulbs) until there are no bulbs and you are running straight from the mains.

Anyway that's how I was taught to use it and it's worked well as an insurance policy for my new builds. .


Snowy

Thanks Snowy.

Good news, BAD news . I did the gradual dim bulb current limiter and it was fine. I started with 25 watts, then 40, 60, 75, 100w. When I turned on the TRAMP the 25 and 40 watt bulbs would glow for a second and then dim down. I read that this is normal. So then I plugged it straight into the wall; turned it on and the pilot light came on. Next I started to measure the VDC voltage on the first power capacitor (the second one over, which is actually the first in order of power). That was trouble! It pegged and fried my multimeter. It was set on 1000 vdc. Meter is shot.

There is no smoke, no smell, and I got power and no obvious short .

But I need a new multimeter to proceed.

Check the multimeter's internal fuse first.

That all sounds very odd though.

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Thanks kurtives. I did check the multimeter's fuse and it is okay, but the readings are all screwed up. None of the settings work in it, it just desplays a -1 constantly, even in ohm mode.

Is what I described about the dim light bulb test normal? That the bulb will only glow lightly if there is no short, That is what I read --that if htere is a short that the bulb will light up like it is plugged straight into the wall. My test bulb only glowed very lightly and that only at the lower wattages.

That's right, if there is a short the bulb will glow at full brightness and stay bright, just like it was plugged straight to the wall. Your dim-bulb start up test sounds normal to me, a bit of initial inrush current makes it glow a bit brighter and then it quickly drops to a dimly lit bulb as the circuit settles.

Did you try replacing the battery in your meter, sometimes a dodgy battery can screw up the readings.

Snowy

Good news! I bought a new multimeter and took first measurements. They look within the ball park.
I measured without tubes or speaker and here are the first measurements:

First capacitor (second one over) reads 440vdc
VRM B+ measured at positive side of C12-- VRM at idel = 40vdc
VRM measured at MAX = 430vdc

VAC across two red twisted wires = 640vac to 645vac [measured across the two red lines where they connect to the two diodes on the eyelet board]
VAC across two green lines=6.4vac [measured across the two outer posts on the first terminal]

Power tube socket measurements without tube:
pin 2 = 3.1vac [[Edited:: I originally wrote pin "1" in error and have now corrected that to pin "2" in my edit.]]
pin 7 = 3.1vac

Preamp tube socket measurements without tube:
pins 4&5 = 3.1vac
pin 9 = 3.1vac

How do these look to you guys?

Hope you mean pin 2.
Pin 1 should read 0V as it is grounded.

Those all look correct.

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Yes, I meant pin 2. I will go back and edit that. Thanks for being careful and observant!

Cecelius2

TUBE TROUBLES I inserted the 6V6 and the ECC83s that came with my kit, and I plugged in the 8 ohm speaker. I selected the 6v6 on the bias switch and the 8 ohm position #2 for the rotary impedance switch.

Both tubes glow in what looks like a normal level HOWEVER, there is a very loud HUM when the volume and the power levels are turned up even half way--too loud. There is also no signal; when I insert a guitar cable and touch the tip, there is no sound, only the constant hum.

PREAMP TUBE has bad voltage readings
pin #1= only 147vdc
pin #3= 1.6vdc
pin #6=NOTHING, no voltage
pin #8=NOTHING, no voltage

Other voltage readings:
At the 750 ohm 5w = 29 vdc
at + side of the 33uf500 capacitor = only 290vdc

6v6 power tube voltage readings:
pin #3 = 397vdc
pin #4 = 390vdc

[EDITED: I am editing this paragraph because I checked the ecc83s preamp tube and it is good;see next post. I will adjust the following to smallest font as there is no strikethrough available.] Does this mean the preamp tube is bad? It is getting it's voltage as the heaters are working (see earlier post)
I can try another preamp tube, but before trying that I want to hear what you guys suggest. I don't want to damage my other preamp tube (spare that I have lying around) if you think it is something else.

I just tried the ecc83s that came in my kit and put it in a preamp and it IS WORKING--so the tube looks okay..

It must be a problem with my wiring or a component. What should I do to trouble shoot the voltage issues?

Here again are the readings:
PREAMP TUBE has bad voltage readings
pin #1= only 147vdc
pin #3= 1.6vdc
pin #6=NOTHING, no voltage
pin #8=NOTHING, no voltage

Other voltage readings:
At the 750 ohm 5w = 29 vdc
at + side of the 33uf500 capacitor = only 290vdc

6v6 power tube voltage readings:
pin #3 = 397vdc
pin #4 = 390vdc

Not sure what to do. Glad you guys are here to help me trouble shoot this. Any suggestions on how to proceed?

Cecelius2

Just double checked and resoldered the preamp eyelets. Still get the same readings. I did notice that I get the 290vdc reading at the base of the dark brown 220k carb comp 1/2w resistor, but that nothing is measurable on the other side of that resistor.

I am going to go to bed and get some rest and hope that you guys have some advice tomorrow.

All those voltages are good and right where they should be minus pins 6 and 8 on the preamp tube.

First check that the 220K resistor going to pin 6 is indeed good and you have continuity from the eyelet board to pin 6. Next check that you have a wire from pin 8 going back to a resistor on the eyelet board and that the other end of that resistor is grounded (check your jumpers).

Loud hum suggests you may have missed a ground connection or a jumper is missing somewhere.

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I can't really add anything other than what kurtlives has suggested, unfortunately my electronics troubleshooting knowledge is fairly basic. Sounds like you did the right thing resoldering the preamp connections, I'd now go back over the layout methodically and check every ground connection, including the jumpers marked with dotted Green lines on the layout.

On the other side of that Brown carbon Comp 220k resistor I think there should be about 330 - 340 Volts coming from a jumper connected to the Positive side of the last 33uF cap C6, maybe you can trace back that way and check. So if you are getting nothing across the other end of that CC resistor, connected to pin 6 of the 12ax7 then I think that CC resistor is worth checking out, as kurtlives mentions (maybe it's failed - open circuit).

I know from reading various builds a few people have been caught out missing the sneaky Power Ground wire that runs under the board from the Grounded side of C12 over to the Power ground point.

Snowy

Thanks kurtives and Snowy. I am going to the electronics supply store to get a new 220KK comp Cap 1/2w resistor. I pulled it and measured it, and it was correct and right on the measurement. HOWEVER, when I put it back in it still showed 297 on one side and nothing on the other side. I double checked its connectivity to the + side of the 33um500v cap. It shows connectivity and has the same voltage on that side of the resistor, but absolutely nothing on the other side.

I also checked the connectivity/conductivity from EVERY preamp eyelet lead from the eyelet back to the associated preamp pin. Everything shows connection.

I then placed my multimeter black/ground clip on the chassis and went methodically and checked the ground connection with every component that touched the green ground wires. I also checked the jumpers across eyelets to make sure they show connectivity.

I also checked all the leads from the eyelet board to the potentiometers. I resoldered those tiny, itty bitty posts on the 'Tude" and "Fat" connections and confirmed that they show connectivity/conductivity to the eyelet board.

Everything seems to point to the 220k CC 1/2W resistor as it has voltage on one side and absolutley nothing on the others side.

QUESTION FOR YOU GUYS--I do notice that the input jack signal (copper wire) shows conductivity to the ground. I checked the schematic and it shows that the jack has within it a connection from the input to the ground post and internally grounds the copper hot signal wire. I would have thought that this would cause the hum?


I think I am making progress, but I am not certain. I have not lost hope.

If you can't get a "carbon comp" from the electronics store (I know my local one doesn't stock those) you can just use any 220k 1/2 watt Carbon Film to continue troubleshooting, as far as I know the "Carbon Comp" spec was just to add a little Mojo.

Snowy

You can't measure resistors/caps when they are in circuit, your readings won't be accurate. Things are in parallel with each other, caps are charging/discharing, etc. Your resistor is fine.

The reason you have voltage on one side of the resistor but not the other is because of something on the no voltage side of the resistor. Either that wire is broken, or the cathode resistor/section is messed up.

Post some pics of the preamp area.

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