#002 - my journey begins

[Richard1001]

Noted in regards to the solder going through. To be honest this is my first time going PCB and I find it a bit nerve racking, due to the fragility and lack of flexibility. I bought some 0.7mm solder to minimise time and heat at the lugs and tried to be more "in and out", but maybe should have kept the heat a bit longer. I still prefer turret followed by P2P eyelets I think.

The brown boards are very well made and in my experience can be soldered with enough heat to let the solder flow. The tracés are very thick copper and don't come of the board. The bushes going through the board are also very strong high quality.

[Bombacaototal]

Found the issue!!!!

It was a bad 12ax7 in the dry mixer tube. I replaced it and attached the amp with master at max.

Who would guess my NOS Sylvania was busted

Thanks again to everyone for the help

I am glad to have shared the issues as well given the contributions from TAG allowed me to make improvements in the amp

[rccolgan]

congrats!!!

[talbany]

Awesome!. Great attention to detail!..Love it!
That's a lot of work for a single channel clean amp huh? I am not really a big fan of long delay spring reverb but 002 has to be one of the best/lush/chime-ridden reverbs ever attached to a guitar amp IMO. Now if you can just keep it from being too noisy your all set! Your Tube Screamer will never sound boxy again ..Fantastic amp!!

Enjoy

Tony

[Bombacaototal]

Awesome!. Great attention to detail!..Love it!
That's a lot of work for a single channel clean amp huh? I am not really a big fan of long delay spring reverb but 002 has to be one of the best/lush/chime-ridden reverbs ever attached to a guitar amp IMO. Now if you can just keep it from being too noisy your all set! Your Tube Screamer will never sound boxy again ..Fantastic amp!!

Enjoy

Tony

Thanks Tony, I appreciate your compliments

Yes, 7 tubes plus the filters is no joke, lots and lots of work but well worth it, as this is probably my favourite amp I have build/played as of yet.

[Bombacaototal]

Just wanted to update you all in a couple things I changed. I settled on 47pF on bright and 11pF on the "MID" switch, both mica

I didn't like the mid switch as a presence cap, and 1uF was way too much for this amp, probably 0.1uF non polarised would have been a better fit

[Bombacaototal]

Weirdest thing just happened. I was turning the amp on and off a few times to swap pre amp tubes. In one of the times I turned it on I heard a hum, which was not very loud but it was clear enough, then a click/pop and after that no more sound going through. I took the amp out of the shell and noticed that when I turn the mains ON, with the standby engaged, there is a click sound (attached). At the end of the clip you can hear me turning the amp off via mains.
The fuses did not blow, I have a mains and a HT one. I do not see or smell any burning or smoke

I have replaced the standby switch as I read this could be one cause but no avail

Anyone has had something similar? Any ideas on where to start? Could it be a bad power tube?

[professormudd]

Can it be one of your filament pins arcing with a neighboring pin?

[Richard1001]

Most likely there is a component or connector with a alternative path for high voltage to cross (flashover) Either due to compromised isolation, dirt or defect.

When you have a flashover for instance on a tubesocket due to a spike in voltage, the spark can create a carbon trace which in turn makes it easyer for voltage to cross. So it will keep happening even when the spike in voltage is no longer present. Inside a transformer a flashover could weaken the isolation, again making it easyer for the voltage to cross a second time. Most problems occur in the tubes themself. Contamination inside the tube or on the spacers and/or deformation of the electrodes due to heat / errors in production / etc. Ofcourse flashovers could occur anywhere where big diffrences in potential exist in conductors near each other.

You could darken the room, put the amp on and see if you can find anything flash when the click occurs.

[Bombacaototal]

Hi Richard and Matt, thank you both for the contribution. I think it is indeed an arcing tube. I did have an incident the day after I fired it up, whereby I removed the MM probe sleeve to measure the bias and then forgot to add it back when I went to check the plates, the result as you can imagine was plate and filament connecting, a big spark and fuse gone. That incident left a dark stain on the socket which I cleaned up, but in retrospect I should have replaced the socket back then. I have ordered new sockets and will go through the replacement and report back. I hope this didn't create other issues, as right after this happened there was no more signal coming through. But one thing at a time. I will report back as soon as I have replaced the socket

[Bombacaototal]

Just giving some upates. I have replaced the socket which had the issue. After pulling the tube out I noticed it was a bit rattling so I removed it from the stach and I have only the 2 central power tubes connected now (with mistaching the impedance 4ohms into 8 ohms load for correct primary).

Ticking is still present. There is no sound. I checked filaments voltages and they are fine althoug they seem to oscilate. Plates voltages seem really low, at around 200V?

C- was really high like -511V. I could not measure the bias mV, it was negative and going all over? Maybe something in my bias circuit?

B+ before the standby (2x47uF) was in the 200V range as well. It actually strats at 274 and keeps going down to even around the 100's

I strated measuring the bias board. HT from PT is getting 335V into the board on both cables (which is fine), but I only have about 150V out after the 6 diodes. It actually went up to 250V after start up then it started falling towards the 100s. I heard a "zeuuawm" (like a light saber) sound through the speakers and turned the amp off. That same sound happened last time followed by a small pop before the amp stopped working

Without the power tubes there is no ticking sound. The HT is giving 345V on each side. Out of bias board is at 390V and -48V on the other side of the 10uF bias cap

[bepone]

problems with the Ub+ to the ground. diodes healthy? need to remeasure them. capacitors looks new, otherwise will be suspicus for internal short circuit to the gnd.. unfortunately, need to remove all consumers, all wiring to the amp from the Ub+ line, leave only rectifier and capacitors with discharging resistor on them (220k ohm 2w) and start the amp only with rec. and caps.
if voltage is ok, then need to add only output section, without PI, and preamp-
step by step,one by one, other consumers (tubes in preamp) need to be connected to Ub+ line, and when start the problem, there is short, long job, but systematic. in max half day is possible to repair the amp, which is at the end very fast, tommorow amp will sing like new.

[Bombacaototal]

Some further testing. It is weird but it seems that regardless of the standby position I seem to be getting voltages all the way to the Tonestack plates.

Without the power tubes I measured all the voltages too and they seem low, plates and B+ at 380V (originally my amp had 420V -still lower than usual but we covered that already).

I measured the 10uF bias cap with the cap meter and it seemed fine

Thanks for the contribution bepone. I have used the amp for 3 months with no issues. Can an internal short appear just like this? Any tips on how to test the diodes?

[Richard1001]

It was not clear to me the amp still didn't work at all.

I don't understand your voltages. You say you measure -48V on the 10uF bias supply cap, but there should be something around -380 V or so to feed the CF cathoderesistors.

If you mean -48 on the powertube grids, this should be fine.

If the B+ supply was 420V normaly under load (with the amp on), It should be higher (450 -460) on standby / without powertubes. Only 380V unloaded could indicate one side of the rectefier diodes is not working. Essentialy only having a half wave rectifier.

It could also be high resistance in the mains wiring / mains switch or HV supply center tap ground connection or filter caps ground.

What is the B+ on the preamp plates in standby? Does IT drop? How fast?

[Bombacaototal]

Many thanks for the help Richard, and sorry if I was not clear. Let me try to clarify.

I have replaced the "most likely" arcing power tube socket and the amp still doesn't work. Well, it turns on, it has the LED light working and the heaters and all, but it was still giving the ticks sounds and had no sound going through the speakers.

On the 10uF I had measured the C- with two power tubes and got something like -511V. Without the power tubes I just measured again and it is slowly incresing from -70V to -90V and so on. Keeps increasing but super slow. B+ (called B+ Stby1 at the pcb board) is now at 365V. I think indeed there is an issue with my bias board and thanks for pointing to one side of the rectfier diodes. How can I verify this?

The standy switch makes no difference to the voltages on the preamp plates, it does not drop at all. Bear in mind this is the second standby switch I fit in

How can I investigate the high resistance in the mains wiring / mains switch or HV supply center tap ground connection or filter caps ground?

As far as the filter caps ground, I have two as per layout, and one of them shares the 470K, 100R of my previously arcing tube socket (not sure if it may have impacted)

I also measured between the first filter cap and the OT primary at the power tube socket and I get 24ohms