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Hey guys (and girls if you're out there)!

I'm pretty new to amp building and indeed this is my first build.

I went down to Stephens' last Sunday to pick up the ol' 5e3 and also got to see his wonderful shop. Such a wonderful man with a very nice wife, dog, and cats

Well a few days ago I started the build and it was much easier than I had imagined it to be... things came together quickly and before I even know it I had installed the eyelet board and soldered all the components together. Feeling very excited and not finding any batteries to get my multimeter working, I decided to just turn her own to see if I at least get some sound out of her... and indeed there was sweet beautiful sound I switched through all the channels and tried both output jacks... everything was fine... except for a strange hum.

I played around for maybe 5-10 minutes and then turned her off because I don't have the appropriate speaker yet and I was plugged into a 4ohm 6" fender crap speaker.

I turned it on again immediately after turning it off to ensure that everything was fine, but unfortunately that was not the case. There was no sound coming from any of the channels. When I switched it to standby there was a hum, but turning standby off it was dead silent.

I kept fiddling around, turning it on and off and checking my connection when suddenly it came alive again! All inputs and outputs worked but when I turned it off and then on again it was the same situation. No sound! Just a hum on standby.

I found an analog multimeter laying around and took some measurements with it. I'm not exactly sure how to read it so I'm gonna give you guys two different readings, one using the v-ma and the other using dBs (it says ACV10 in red)...

ACV10 / dB

v5 - 18 dc (8/2) - 19ac (4/6)
v4 - 20dc (3) 15ac(8)
v3 - 15ac(8), 19dc(3) 18dc(4)
v3 - 12dc (1,6)
v1, 16ac(3), 20ac(6)

V-mA

v5 - 150dc (5,2) - 175ac(4,6)
v4 - 200dc (3), 125ac(8)
v3 - 100ac(8), 175dc(3), 150dc(4)
v2 - 75dc(1,6)
v1 - 175ac(3), 200ac(6)

These measurements were made while the amp was on standby. If I turn standby off then I the same voltage readings on V5 but zero on everything else.

Really hoping you guys can help me out here! I've checked all my connections and everything is wired like the layout has suggested... so I'm pretty much out of ideas on what to do next here.

Sounds like an intermittent connection. The trouble might be a flaky standby switch but more likely it's a bad connection somewhere on the B+ line after V5. Sometimes cold solder joints can look OK. You have to look very carefully, often with the aid of a magnifying glass. A good solder joint will be fairly shiny and the solder will have flowed well onto all the wires and terminals.

Next time it stops working leave the standby switch closed and take a voltmeter and follow the B+ from V5 to the standby switch. If the switch and its wiring is good you should see the same voltage on both terminals. If that's good go on to R22 and R21. The voltage will be lower after the resistors but it should still be there. Wherever you stop reading voltage, there's the trouble.

Your voltage readings seem low. You should read around 400 volts DC at pin 8 of V5. All the B+ readings should be done with the meter set to DC volts.

Of course, be very careful when probing around inside a live amp. Clip the meter's negative probe to the chassis and hold the positive probe with one hand and the other hand in your pocket.

Another way to find bad connections is to prod or tap them with a wooden stick (a chopstick works well). Do this with the amp live and again keep one hand in your pocket.

Best of luck finding the problem.

Thanks for your reply Mitch. It's not working at all actually.. it only worked twice.

I got my digital multimeter working and these are the measurements I got. It was set to 750V ac:

v5 - (797 (8), 796 (2), 344 (4), 345 (6)
v4 - 785 (3), 702 (4), 43 )8)
v3 - 781 (3), 700 (4), 43 (8)
v2 - 226 (1), 3(3), 337(6), 5(7), 138 (8)
v1 - 303 (1), 2(3), 321(6), 2(8)

seems like everything is twice what it should be!

I also realized this morning that I didn't have a bridge cable on pin 4 going from V3-V4. After doing this I no longer hear a hum when it's on standby. I'll take another close look at the solder joints to see if I can find something. If anyone has anymore suggestions please keep them coming!

also, the standby switch is working in reverse... I took these measurements while the amp is on standby. if i turn it on then there is zero voltage all across v1-v4 and it acts as though it is on standby. i checked the wiring many times and it is as it should be on the v5 / 5y3 socket.

Here are some readings with no tubes:
v5- 362(4,6)
v4 -03(2,7),
v3 - 03(2,7)
v2 - 03(4,5)
v1 - 0

pics:

Re-read the last post by mitch m, ESPECIALLY the qouted part below!



HTH,
Gene

I see some solder joints that bear close inspection, particularly on V1, V3 and the input jacks.
My $.02,
Gene

Thanks for the input gentlemen. I'm not exactly sure what "B+" readings are. Readings made on the tube sockets?

I won't be able to work on this the next 2 days as I'll be away from home but will get back to it asap.

Can't wait to get this working!

B+ is the high voltage that feeds all the tubes. The name comes from the early days of radio when most electronic equipment ran on batteries. It's direct current so any readings taken with a meter set for AC volts can't be trusted. Set your meter on DC volts!

The B+ run is marked on the schematic. It starts at pin 8 of V5, goes through the standby switch then on to the output transformer center tap. Then it goes through R22 and feeds the screen grids of the output tubes. It also goes through R21 and on to R13 and R14 which feed the plates of V2. And it goes through R7 and R8 which feed the plates of V1.

The amp is on standby when the standby switch is open. In that case there should be no B+ anywhere and the DC at the rectifier will read low because the filter capacitors aren't in the circuit. The amp should run normally when the standby switch is closed.

And yes, some of your solder joints could be improved!

Thanks Mitch! You have been so helpful. So just to reiterate things, when the switch is facing away from the 'standby' emblem, the amp should be silent? When I get home I'll add some solder to all the joints and take another measurement in DC Voltage and repost.

Standby is Off (hi voltage to tubes) when down. I.e In same position as when the Power switch is On.

The manual has a good section on startup. I suggest you start from there.

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

Good news guys!!!

I got back home last night and re-soldered some connections. I had left my jj5y3 on my table and it rolled off and fell on the floor. It didn't shatter but some filament inside came lose, so this morning I went and got myself a Sovtek 5y3 GT (couldn't find any JJs). So I turned the amp on and I got a wonderful hum suggesting that the signal flow is coming through. I did all the measurements and they do come in correctly except for pin7 on v2. This part was a bit strange...

As I reached pin7/v2 I got a low voltage reading of 02VDC and then the signal suddenly died. When I took it out I saw there was a crack right by pin 7. I think this may have to do with the fact that it was very difficult to get in there and I had to really wiggle it back and forth with pressure to get it to fit. Luckily I had another sovtek 12ax7 laying around and I put that in there.

However, the issue remains:

I am still only getting 02VDC where the voltage chart is suggesting I get 18.

What do you guys think should be done about this?

Also, Pin 8 / V2 is giving me 44 where the suggested reading is 50. I have read that the readings can vary about 10volts... should this be of any concern?

One more thing. When I try to measure pin 6/v2 i get some crazy noises and I feel like I shouldn't be touching the multimeter there. Is that normal?

Are the parts that are marked with the dashes on the voltage chart not supposed to be measured?

This is OK.

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

You are going to induce a little noise when you touch the plate or grid of a tube, a pop, click , loud or not - something. But crazy noise, not too sure what that is ...

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

What about getting just 02 vdc at pin7/v2? i read somewhere that the reading at this location can be unpredictable because the multimeter changes the way the tube is operating?

well i'm literally hearing a squeal happening inside the amp with no speaker connected...

So is the amp working now?

Voltages depend on the AC line voltage which can vary from place to place and the time of day. They also depend on the tolerance of the parts. Usually anything within 10% of the expected value is OK in a guitar amplifier.

Pin 7 of V2 is the grid. You can't really measure the DC voltage at a grid because there isn't any grid current. It will just read close to zero. If the optional 470k resistor is installed in series with V2's grid (shown as the dashed line on the schematic) you might read 18 volts on the end that connects to C6 and R12. My Tweed doesn't have that resistor so I can't say for sure.