50W 3rd gen build - troubleshooting

[gonzomode]

Hi all!

my name is Josef and I'm from Regensburg, Germany. I found this forum a few weeks ago and since then I lurk around here whenever I can find some time..
I build the 50w 3rd gen ODS from the files section- my first amp ever . It was quite challenging but also a really interesting journey. I want to thank everyone here, without you guys I would not have been able to build such an amp.
Now the situation is as follows:
I followed the schematic/layout but with an effects return added. The light bulb limiter test was succesful, no smoke etc. So installed tubes and set the bias- everything fine until now. The cleanchannel is working and sounds really serious.. all switches and pots are working except manual/pedal. The Fet input is far behind the normal input in volume and doesn't sound musically at all (did martin mannings method to set FET bias and had 9,2v at the drain). Also the channel-switching isn't working, I guess there is an error somewhere with the relayboard.. It is a 12v relay without regulator, just like the schematic.
Voltages are B+1 = 451v; B+2 = 448v; B+3 = 424v; B+4 = 281v; B+5 = 274v.
Please feel free to comment if there is something obvious, Im looking forward to any advice
Thank you-
Josef

[xtian]

First ever amp build?!? Wow! Are you also the guy who says, "gosh, I never played a violin before..." and then plays a Paganini solo first time?

I mean to say, really great work. Your lead dress is very nice.

About the switching, can you confirm your 12vDC supply is working? Does the relay get energized when you flip the channel switch?

[drew]

Very nice build.

Relays are like Kryptonite to ampgarage members.

[gonzomode]

Thanks xtian and drew, to be honest I built a TAD 5e1 kit an a bunch of pedals before but thos is the first ‚real‘ amp I built from scratch. There are some minor things I feel a bit unconfortable with but overall its ok.

There is no clicking or something when i flip the channel switch. Also there are 22v at the relay coil

[Lothy]

There is no clicking or something when i flip the channel switch. Also there are 22v at the relay coil

That's way to high for a 12 v relay. I built a #124 a few months ago and I use a 12 V dc power supply kit from Tube Town for the relays. And I tested them, before I wired them up.

https://www.tube-town.net/ttstore/tt-ki ... -12-v.html

Maybe the polarity is wrong, but get the voltage down first, before you filp it.

BTW: I live close to Nuremberg. Maybe there is a chance to make a little Dumble session!

Cheers
Gerhard

[rootz]

This is a great looking build, especially for a first time. Impressive!

That relay supply voltage does not tell much. It depends when you measure that. Is that with the od engaged? Loading the relay transformer will drop a few volts. And where did you measure? At the relay?

Have you confirmed that the od switch works and grounds the relay coil?

You could do a quick test to see if the relay is working. Ground the switched end to the ground bus with clip leads. Clip one side to the switches side of the coil, the touch the ground by or chassis with the other. You should hear the relay switch.

[rootz]

There is no clicking or something when i flip the channel switch. Also there are 22v at the relay coil

That's way to high for a 12 v relay. I built a #124 a few months ago and I use a 12 V dc power supply kit from Tube Town for the relays. And I tested them, before I wired them up.

https://www.tube-town.net/ttstore/tt-ki ... -12-v.html

Maybe the polarity is wrong, but get the voltage down first, before you filp it.

BTW: I live close to Nuremberg. Maybe there is a chance to make a little Dumble session!

Cheers
Gerhard

Voltage is not necessarily too high Gerhard. There is no regulator and when disengaged the relay transformer is unloaded. So you can expect a higher voltage.

You are right about polarity. The diode could be in reverse. Make sure the diode cathode points to the relay transformer, the anode goes to the switch/ground. When the relay is engaged, the diode does not conduct. Only when unpowering The relay it does to suppress the back EMF of the relay.

[rootz]

One last note about coil voltage. The Finder 30.22.9 can take quite a beating in the respect. There is a diagram in the datasheet that shows the coil can take more than twice the voltage when operating 40 degrees Celsius above ambient. Not that you should want that, but even if there really is 22v when engaged, I’m positive it should work and not instantly kill the relay.

[Richard1001]

I see you are using a 1M2 with 33K to ground at the input of the overdrive tube. Even if the relay is working, your sound would still be clean when switched to overdrive.
The input signal becomes too low with this resistor combo to produce any overdrive. Try 330K instead of 33K to ground to get some overdrive. Or put in a 500K pot temporeraly to dial in the best sounding resistor value.

[norburybrook]

ah relays they've been the one consistent problem area in builds for me

make sure your relays aren't polarised ones is my advice then they will always work with the layouts posted. If you've bought polarised relays , which is easy to do by mistake, certainly with the OMRON mini relays then you'll have to work out which way round the polarity is. It's written on the diagram underneath the relay but it's actually showing from above, so it's backwards...if that makes sense. confused the hell out of me


edit: I see you're using a finder relay not sure if they are polarised or not. I'll leave my post in case someone is searching for relays and issues in the future.

M

[erwin_ve]

I see you are using a 1M2 with 33K to ground at the input of the overdrive tube. Even if the relay is working, your sound would still be clean when switched to overdrive.
The input signal becomes too low with this resistor combo to produce any overdrive. Try 330K instead of 33K to ground to get some overdrive. Or put in a 500K pot temporeraly to dial in the best sounding resistor value.

It is the basic od entrance for 2nd and 3rd gen, I never encountered any problems for overdrive tones.

[Richard1001]

Strange, with the 1M2 and 33K to ground the voltage of the second stage into the overdrive stage is divided by something like 37. So 37 volts in the 1M2 resistor gets you 1 volt out on the other side. I tryed it in my amp and mostly got clean sound exept with everything on 10. With the most used 220K / 100K pot the signal is divided by 3 with the pot on full. In my amp this makes a huge diffrence, thats why i sugested 330k for the same 1/3 division. But maybe i did something wrong.

[gonzomode]

Thanks to all for your help so far. The OD is working now, the switch had no ground connection . I measured 22v at the relay and about 17v when it's engaged.

I ended up playing it for an hour or so before I realized the alligator clips are still inside the amp this amp is just.. wow.. it's exactly what I was looking for and it has a good amount of gain too.

So what can we do about the FET? Can I simply change the 22k resistor? What about the voltages, they seem a bit low on the preamp side compared to the layout.

BTW: I live close to Nuremberg. Maybe there is a chance to make a little Dumble session!

Great idea, Gerhard. We should do that for sure


Thank you

Josef

[gonzomode]

ah relays they've been the one consistent problem area in builds for me

make sure your relays aren't polarised ones is my advice then they will always work with the layouts posted. If you've bought polarised relays , which is easy to do by mistake, certainly with the OMRON mini relays then you'll have to work out which way round the polarity is. It's written on the diagram underneath the relay but it's actually showing from above, so it's backwards...if that makes sense. confused the hell out of me


edit: I see you're using a finder relay not sure if they are polarised or not. I'll leave my post in case someone is searching for relays and issues in the future.

M

Thank you for your effort Marcus, there is never too much information on a thread like this i think By the way your 2nd gen build thread already helped me a lot .
Most people seem to use Omron relays; the reason I used Finder was my local supplier and it has the same pinout as the Omron.



I have a couple of questions but first I want to point out that I have difficulties in describing things, phrasing questions etc due to my limited english skills so I hope you can get my point anyway..

My voltages are now

house power 230V(measured)

B+1 454V
B+2 452V
B+3 428V
B+4 285V
B+5 277V

plates:

V1 191V/186V
V2 200V/195V
V3 304V/306V
V4,V5 451V
bias 40mA


I have 8.5V on top of the 10k resistor, this should be ~20V in order to get the proper operation point of the fet, am I correct?
I assume i have to change the 22K resistor IF the voltages of the rest of the circuit are ok. OR should I use the 240V tap of the PT to bring down B1-3 and then B4 and B5 up to match the voltages on the layout?


Edit: Tubes are TAD 6l6GC, TAD 7025 and Philips Miniwatt ECC81

Josef

[gonzomode]

A quick update: got it all working now and I'm very happy with the result. I like the FET a lot so I'm thinking about making it switchable..
I will post some pictures as soon as I have a cabinet.

Josef