BE50 build... Problems

[Jaymz77]

OK guys here are the pics you requested.
Its a bit messy from fault finding, but not too bad.


On a side not, my new 1987x arrived today and my first impression is WOW!
1, because its DAMN loud and 2, because it sounds awesome, it just screams AC/DC.
I mentioned in an earlier post that i made a dummy load with an aux speaker out for testing purposes. Anyway, after an unsuccessful attempt to use a passive volume control in the effects loop (it sounded like crap) i used my dummy load as a power soak so i could really push the amp for power tube break up. It lasted about an hour of noodling and 15 mins of ROCKING before burning out. LOL
Its all good, i knew it would. I just wanted to test the amp properly. I have spare parts to fix it.

[Jaymz77]

Another

[Jaymz77]

Another

[sluckey]

I don't see any obvious boogers.

[shooter]

Here’s my basic steps, IF the amp powers up without flaming out;

A)   measure VDC at power tube(s) cathode and plate (if your meter can handle it)
B)   calc max plate to make sure I’m not frying my PA tubes.

NEXT

1.   measure The power rail DC from after the rectifier to V1, recording each taps VDC value.  Your power rail looks to have 5 taps
2.   measure VAC at the same (5) points, record values.
3.   measure VDC at the plate, grid and cathode of each tube.

Once I have these and know they are “close enough for now”

I plug in and see what sounds come out

If it’s screaming cats, or WOW, because I have a scope, I inject a signal, measure each plate starting at V1, playing with knobs as I “pass them” to see the tubes response, gain and distortion.

Once I have all that info, I scratch my head, tweak parts n pieces till I get stuck, then come here and ask for help, or smile with a big-ol grin and pester the cats and wife with guitar noise!

[Jaymz77]

Thanks for that, I'll try all of that from scratch.
It a real head scratcher because the power supply circuit is fairly simple, not many components yet it is humming like all hell.
The only things I haven't tried (that I can think of) is:
Not a good enough earth through the PT mounts.
PT primaries are dual 120's hooked in series for 240. Perhaps I didn't place the joined wires carefully enough.

Otherwise I'm out with of ideas.

[Jaymz77]

Ok guys, I've had a bit of progress
Its a little bit embarrassing but its not entirely my fault either.
When i bought the transformers, Phil from Heyboer face me the pinouts in an email, i then copied and pasted that email into a word doc for keeping.
As you know, when you cut and paste things, the formatting doesnt always come out as you want. I thought i had corrected it at the time, so that it was clear and easy to read. Obviously not.
I had the OT centre tap and one of the secondaries back to front.
The way it sits on the page after i printed it and stuck it on my pin board in the garage, makes it a bit un clear. When i connected it up, all i looked for was which one was the centre tap (obviously the other 2 go to the output tubes).


So that was the source of my hum. It still has a very faint hum, but within what i would call normal but possibly fixable.


So onto the next issue.


Immediately after resolving that, the amp started squealing. I pulled all the tubes one at a time and in various combinations. It only seems to do it when the PI tube is in. Also, it varies with the presence control. Worse when presence is low/ off, and basically gone when presence is on 10.


Any suggestions with that one?
Thanks

[Jaymz77]

Phil from Heyboer *GAVE* me the pinouts in an email.

[Jaymz77]

Actually, don't worry, Squeal gone.
It was crossed OT primaries.


Now onto the preamp noise...
Last time i checked it was somewhere around V2 i think.

[sluckey]

Alright!   

[jojokeo]

How about a few pictures of the amp? This way we can see what the heck is going on. Especially mistakes in layout, lead dress, and grounding. Not to mention a plethora of other possibilities as you continue to keep finding...

[shooter]

Nice work, don't be afraid to just swap parts in the effected area, you're deep into the fun part now

[Jaymz77]

Pics have already been posted.

[jojokeo]

Pics have already been posted.

Sorry, didn't see them before maybe from my phone but in any event I see numerous ground points of many various parts of your circuit of all your sections using the chassis as a ground plane? You have ground loops in an amp design where this is a highly important aspect. Not surprised to hear there's some preamp hum/buzz as likely parasitics too? These will change as frequencies and signal voltage changes...you will see in time once you get through and spend some time playing it? Good luck.

[Jaymz77]

The issue with the ground points is a fair call.
The problem is the schematic does not resemble the pics I have taken as far as grounding goes. It will probably be a game of trial and error.

The pics show the backs of the pots grounded. I always thought that was bad...

[jojokeo]

You did a fabulous job in planning and building everything except a "grounding plan" which is right up there with component placement and lead dress IMHO. The only other thing that caught my eye was the relays' positioning near other components especially the inputs one which is most highly sensitive low level high Z area of the entire amp.

BTW, you can do things to help the grounding situation as it's "not too late" here. Play the amp for a while and see how things go. If you notice any further issues or something nags at you then you can approach the remedies later, and also be much more fresh and determined with a good plan going forward. Attacking it now could lead to further frustrations and doing things hastily. Not sure what you've read regarding the various grounding schemes but it's worth checking and reading them all in the meantime. Especially Merlin's - it takes several readings minimum to digest everything, and when you think maybe you've got it no problem, there's subtleties there that still could catch you by surprise. I'd gone through several builds before finally getting the hang of it all.

[Jaymz77]

Thanks for the kind words.
The "general" layout is the same as a BE100. If anything ive compressed it slightly. I've also designed my own chassis and I positioned the board a little too close to the pots and input. I'm also starting to get concerned about the way the OT secondaries run between v3 and v4.
At the moment the amp is not running well enough to plug a guitar into. There is some sort of oscillation going on I think. One channel is worse than the other 2.
I was concentrating on the hum first, and now that is fixed I'll work through the amp from the other end.
Cheers

[shooter]

There is some sort of oscillation going on I think

fwiw
I've had a couple builds with parasitic osc., the low freq ones tended to sound like I had tremolo (when I didn't), the higher freq ones tended to sound like hissing.

[Jaymz77]

I think mine is low frequency. There is no real hiss. In fact it gets worse when I plug a cable in.
It sounds like when you ground the tip of the lead. That sort of thing anyway.

[shooter]

it gets worse when I plug a cable in

most amps get worse when you do that, kinda like an antenna for noise.
once you've checked/fixed any grounding schemes, without a scope, the listening amp is a good tool, inject a signal at the input, listen at each stage, hear where things go south, well in Australia, I guess north

[Jaymz77]

Nah it's still south to us. I think it's around v2