BE50 build... Problems

[shooter]

i thought that would damage the OT.

the source for the OT is the '34s, so it's doing nothing with tubes out

[Jaymz77]

I can confirm that i can hear the PT humming with ALL tubes removed.
Its not super loud but i can hear it.

[shooter]

Its not super loud but i can hear it.

is it the same "loudness" as with tubes in?  probably wrong rabbit hole since your fuse isn't blowing, follow Steve, i'll watch

[Jaymz77]

Yeah i would say so.
If there is any difference it is so borderline that its hard to say 100%

[sluckey]

It would be nice if you could provide a schematic of your actual build.

Since you eliminated the preamp tubes as the source of hum, we need to concentrate on power supply and power amp. The voltages you measured on the output tubes don't tell anything about the current flowing thru them. Put a 1Ω resistor between cathode and ground on each power tube. Then measure the voltage across that 1Ω resistor. It will be less than 1 volt so set your meter to read millivolts. What reading do you get on each tube?

[Jaymz77]

Unfortunately i don't have a schem of the actual build.
All i can say is that it is the same except for the power supply section. I have ended up with a 1987 power supply up until the choke, then after the choke it is per 100w schem.
I don't actually know if i have any 1ohm resistors. Ill check my stash and if i do, ill do what you said. I could always put my DMM in line i guess... I do have clamp probes for the dmm.

[Jaymz77]

OK,
both output tube cathodes level off at about 46mA, but will very slowly creep up to about 51mA, at which point i stopped measuring after a couple of mins.
If i max the master they will jump to about 55mA.

[Jaymz77]

It is absolutely KILLING me that NOTHING i do changes ANYTHING

[shooter]

troubleshooting is kinda a meditative thing, the more frustrated you get, the more gremlins smell it and invade!  hang in there, you have 40yrs to catch up

I believe your readings so far are close, but wait for conformation.  Could you get a freq reading after the choke, anywhere in the PS, post choke.

[shooter]

EDIT:  Also, this is probably a wild HARE, but can you pull R53 or R52 (per schematic you referenced), then put the 34's in n power up, hum still there?

[Jaymz77]

Pulled r53, hum still there. Preamp noise gone tho, but no signal either.


Ive never been a good fault finder, i get frustrated too easily. Even when constructing a high rise building, if i have problems my tendency is to rip it out and start again.


I just read a thing on the Aiken page that said the OT secondary common should not be grounded to the chassis, so i tried lifting that so it only went to the sleeve of the speaker jack and the hum became worse.


I don't believe i should be able to hear the PT at all. Even if i rip it out and sit it on my bench, wire up the primaries and leave the secondaries hanging loose i can still hear the PT humming.

[sluckey]

Sometimes PT just hum. Laminations may be loose and are vibrating. Try tightening the bolts that hold the PT together. If that won't stop or minimize the humming, then there's probably nothing you can do about it.

Is the PT hum as loud as the hum we are chasing?

[shooter]

Even if i rip it out and sit it on my bench, wire up the primaries and leave the secondaries hanging loose i can still hear the PT humming.

so now, is it a problem or normal?

Preamp noise gone tho, but no signal either.

Removing the R, removed power to the PRE.

[Jaymz77]

Sluckey, sitting on the bench? No but it sounds the same. When i hear it through my dummy load with headphones, it sounds louder.


Shooter, it hasn't changed. I just said that to make the point that there is inherent hum in the PT. I actually haven't done that with this PT, i did it with the previous one. But when i wired the new one in the problems were the same, so I'm assuming this one would do the same thing.

[PRR]

> troubleshooting is kinda a meditative thing

Zen and the Art of Motorcycle Maintenance

https://www.amazon.com/dp/B0026772N8

www.arvindguptatoys.com/arvindgupta/zen-motorcycle.pdf

[Jaymz77]

Ha ha ha,how did you know I'm a bike man too?

[Jaymz77]

I'm starting to think I might have to redo the whole layout

[shooter]

there were 3 books, (well 4 counting the Bible), that had a major effect on my life's path, Zen and the art of motorcycle maintenance, Siddhartha, and hitchhikers guide to the galaxy.

I might have to redo the whole layout

don't look at the amp as a whole, look at it as the sum of it's parts.  The focus has been on the PS, based on hum.  I think, (needs conformation) your DC part is good, same with the DC part of the power amp section.  there's still the AC part, the connections part, the values part, yadeda

[Jaymz77]

Well, it's still humming away.
What do I do?

[silverfox]

>
www.arvindguptatoys.com/arvindgupta/zen-motorcycle.pdf

 Dangerous and provocative information of a type one only discovers from life if they choose to be aware of self and surroundings.

silverfox.

[Jaymz77]

Anyone got got anything other than zen for me?

[shooter]

i followed a 1987 power section. Problem solved. However, i then had unwanted noise.

I wasn't watching to close for this part.   Did/do you have any guitar sound? 
how loud is the current hum?, could you say put the guitar on 5 and make the hum go away?  have you built a listening amp?, maybe we can figure out what parts are good.  with PA tubes in only, did you measure AC volts on your power rail?  (normal should be a few VAC after the reciter, going down to mV AC by the final tap.)

[Jaymz77]

I can get some guitar signal through it, but it's not great. That is a different problem ken I think.
The hum does not change with volume. The preamp noise gets worse with a lead plugged in.

What do you mean by a "listening amp"?.

I have just sat down at my desk at work on Monday morning. I'll try measuring the ac on the power rail tonight.

I'm actually thinking about buying a 1987x. Obviously to use but also for reference material. Ive never actually owned a Marshall yet I'm trying to clone them...

[Jaymz77]

Ken? Bloody auto correct

[shooter]

What do you mean by a "listening amp"?.

since you don't have a scope, a listening amp will let you walk through the signal path to find out where bad things start.  do a search here and you'll find how to make one.  that should nail down your preamp noise. 
with all tubes in a complete DC and AC voltage readings from each PS tap will help isolate the HUM.

Ken? Bloody auto correct

??

hang in there

dave

[Jaymz77]

Cheers mate.
I'm going to buy myself a cheap scope to make this and future things easier to locate.

[Jaymz77]

Ok,
so you mean to get voltage readings from both sides of the HT? I have 252.5vac none side and 253.5vac on the other side.
I took a reading from after the rectifier and read 462vdc, but i also read 2.3vac in what i assume is ripple.
To have 2.3vac at that point, is that normal or are the diodes possibly dodgy?


Cheers

[Jaymz77]

To test the filtering i just temporarily connected another 100u cap across the existing one, the hum definitely got lower in volume.
Kind of suggests to the dodgy rectifier diodes argument doesn't it?

[shooter]

read 462vdc, but i also read 2.3vac in what i assume is ripple.

2.3VAC seems good at the rectifiers.
do the same after the choke, after R53, after R43, after R34.  Those are your PS rail taps, often denoted as A,B,C, etc.  measure, (both DC and AC), with all tubes in, nothing plugged into the input.

[PRR]

> 253.5vac
> after the rectifier and read 462vdc

Does not sound right.

You actually have one 506V winding. If the _caps_ are good, this should give 708VDC(!!) at light load. 462VDC is SOOO far down it suggests the caps are not peak-catching.

> 2.3vac in what i assume is ripple.

Anything near 5% ripple at first cap is very reasonable and not a problem. You have less. Suspiciously less.

However most meters will NOT correctly read ripple riding on top of large DC.

I don't know BE50. Is this really a Seven Hundred Volt amplifier?? Or have you picked a way-wrong PT?

[Jaymz77]

You know, I better double check those numbers tonight. I could have had a brain fart.
It is a 350 0 350 Tx, and I bought it from Heyboer. I spoke with Phil and told him what I was trying to do. This is what he suggested.
At the risk of saying something you already know, there is no such thing as a BE50, only a BE100, as far as I know. I am creating my own BE50.
I am using a Fluke 117 dmm and in my experience these seem to pick up ripple even when I don't want them to. No other dmm I've used does it.
So maybe the caps eh? I wonder if my original power supply setup caused this. As my earlier posts say, I originally had the ps set up as per 100w and got instant red plating. I was reading 500 and something volts on the plates, maybe 560 or 570. The caps are 500v rated.

Cheers

[sluckey]

It is a 350 0 350 Tx, and I bought it from Heyboer.

That PT puts out twice as much voltage as you need for a full wave bridge. It is meant to be used with a full wave conventional rectifier.

In your other thread you said you converted to a conventional rectifier. Did you just forget to update the layout?

[Jaymz77]

Yeah exactly, just hadn't updated the layout.
I actually updated it last night. When I get home tonight I'll post it.

[sluckey]

OK, thanks. We were about to chase down that rabbit hole again. There's a lot of relevant info in the other thread. Do you want me to combine the two threads so no one has to chase info between the two threads?

[Jaymz77]

Yeah , probably a good idea.
Sorry, I am a bit naive when it comes to general forum etiquette.

[shooter]

want me to combine the two threads

awe man, now I got to find my reading glasses

[Jaymz77]

Just on a side note guys... I came to thinking in the weekend and realised that here I am trying to build Marshall clones (my first was a successful 2550) and I've never actually owned a genuine Marshall!
So I fixed that last night and bought a 1987x. I justified it to myself and my mrs by saying that I needed some reference material for my hobby builds... worked a charm!
Can't wait to receive the beast.

[shooter]

Can't wait to receive the beast.

bonus, with all you've learned here, you can fix it when it arrives broke

[Jaymz77]

Why would it arrive broke?

[sluckey]

I've merged the two threads about this amp.

I'd like to see the updated layout and also some high rez pics of this build. Especially the power supply end of the board. I'd like to see where the PT wires are connected now that you have modified the circuit to use that PT with a full wave conventional rectifier.

[shooter]

Its the Aussie way

Why would it arrive broke?

American humor, now go get pics for Sluckey

[Jaymz77]

Yes sir.
I am at work. I'll post them when I get home

[Jaymz77]

Here is that updated layout. I don't think I've missed changes.

[Jaymz77]

Oh and i just checked those voltages again.
Just as i suspected, i had a brain fart last night. The voltages are 352.5 and 353.5 on the HT, not in the 200's like i stupidly wrote.
B+ at the rectifier is correct though.

[Jaymz77]

Bump

[Jaymz77]

Testies testies one two three

[sluckey]

pics pic pics

[Jaymz77]

Oh crap...
It is per revised drawing. I'll get some tonight. Not sure how much new information they will give but

[shooter]

volts DC and AC from each PS tap

[Jaymz77]

By ps taps do you mean the power transformer secondaries?
Shouldn't there there be zero dc on the power supply taps?
As far as ac goes there is 352.5 and 353.5.