Problem: Weber 5F6A with very low output!

[erndawg]

Ok!
I've downloaded VA wich turns my laptop into both signal generator and oscilliscope.
I'm ready to try the signal generator and take measurements on speakers and fender test points.

//Jibe

The reason I recommended an old CD/MP3 player, is that in case you have a high enough unwanted or unexpected DC voltage on a point you want to test, you won't feel too bad if the CD/MP3 player gets smoked. Bear in mind that a real signal generator will have a DC blocking cap on its output. If you use the VA application, you should decouple the output from your laptop via a blocking cap.

[erndawg]

The RCA connector from the chassi to cabinet gets smoking hot. That is the output from the OT.
How come? Is it really supposed to get so hot you almost can't touch it.

NO. Your output connector should not get hot at all. I thought you disconnected the 2 and 4 ohm taps and ran straight to a 1/4" Switchcraft?

What exactly is this "cabinet jack" you speak of? Sounds like that could be the problem. Get rid of that, and wire directly to a single 1/4" jack.

Make sure the green OT wire gets soldered to the lug on the jack that corresponds to the speaker cable plug tip.

[jibe]

I did disconnect white and yellow.

It's wired like so:

Green from OT to RCA jack in chassi, black to chassi ground RCA ground to chassi ground, from RCA to 1/4" Switchcraft jack in amp cabinet where the speaker cabinet connects.

I touched the RCA the other day when doing my experiments and it was hot, more than I expected.

I guess I can bypass the RCA connector and go from OT to switchcraft. That would take another part out of the equation.

I'm on my way now to some work on the amp. I'll get back with progress.


PS. I thought of the danger of using my laptop as signal generator, I'll have to make sure there are no DC when I plug it in, for now I don't have a cap to use. DS.
//Jibe

[jibe]

Update:

Before I started to rewire to bypass the RCA connector I thought I would measure for short. I used the "beep" function on my meter and behold. I got a beep when touching tip and ground. I disconnected the OT lead from RCA the beep went away.
I tried from tip of the OT cable to ground and: BEEP!!!!
I've got a beep from all 3 secondarys coming out of the OT. My immediate response to this is BAD.
This is not supposed to happen? Right? This is really, really bad?
I didn't even get started with todays experiments, I packed up and went back home to report my findings instead.

What do you make of this? Beeping from Secondary output to ground is bad? Short?




//Jibe

[Diablo]

I would disconnect secondary leads of OT and check each lead to ground for resistance. If either one is not infinity, you have a shorted OT. If the OT secondary leads are connected in the circuit correctly, one lead connects directly to ground and the other lead is connected in parallel to the output speaker jack, and the negative feedback resistor to the presence pot and then to ground.

Your measurement of continuity test with the OT wired into the circuit showed a "normal test".

[loudthud]

The secondary leads of the OT will have a very low DC resistance. Even the 8 ohm tap will probably be below 0.25 ohm. This is why I suggested disconnecting the transformer to ohm the connector.

[jibe]

Ok, I'm not sure I get this. When OT is connected, touching the sleeve and tip of my RCA connector makes a "beep" and that's not a bad thing? I was sure I had a short there.

I guess it's back to work tomorrow and start with testing the resistance from lead to ground of OT to start with. Everything is already disconnected and ready for that.
If everthing checks out fine, I'll go forward with my testing and probing that was planned for today.






//Jibe

[Diablo]

Ok, I'm not sure I get this. When OT is connected, touching the sleeve and tip of my RCA connector makes a "beep" and that's not a bad thing? I was sure I had a short there.

//Jibe

That's not a bad thing. If it didn't make a beep, that means your OT secondary winding was open. As Loudthud pointed out, the resistance of the OT secondary winding is very low, and one lead is connected to ground. One side of your RCA jack is also connected to ground. Look at the Weber schematic.

[erndawg]

I used the "beep" function on my meter and behold. I got a beep when touching tip and ground.

The "beep" function (continuity test) will beep for any resistance less than 70 - 200 ohms, depending on the meter. That is a pretty rough check.

As the others mentioned, the DC resistance of the OT secondaries is way less than 1 ohm.

The only way to properly test an OT (other than declaring dead/failed any winding that is Open), is to measure inductance. If your meter has an inductance scale (many do not, some do, most techs have an LCR meter in their arsenal) let me know and I'll look up the inductance values for a 5F6A OT.

[jibe]

What would that look like on my meter if I have?




//Jibe

[erndawg]

What would that look like on my meter if I have?

You would generally have ranges of 200 uH (micro Henry), 2 mH, 200 mH (milli Henry), 2 H, 10 H (Henries). A "Henry" is the unit of Inductance.

[jibe]

Update:

Installed two 220k B+ bleeders, worked fine, drained the system within 30 secs. Does this lower B+ somewhat? Seems I'm back to 420 B+.
What to do here? Do I have to make changes because of the bleeders?

Bypassed RCA jacks direct to switchcraft speaker cab output.
SUCCESS, PROBLEM SOLVED!!!!!!
Nice clean powerful sound, not 45 watts I think but nice.
B+ is low 420 and bias voltage -40, whats up with that? How come it changed
so much? Had 470 B+ and -45.7 bias the other day.

It was the lousy tin RCA jacks supplied with the kit. After examination I can honestly say that those jacks aren't worth sh*t.
The tip made of tin breaks if you so much as breathe on them. I need a selector switch and a sturdy robust RCA Jack if I want to be able to switch impedance.

Didn't have time to reset everything, had to go home, both my girlfriend and my youngest son got sick today, he's only 8 weeks.

I have to rebias, but before that I wonder if there's any modifications to take care of before I do.

Questions:
loudthud mentioned 100k feedback resistor if 8ohm output, is that so? Why?
100k = 8, 56k = 2, what about 4?
Tubes: What to use instead of the supplied chinease tubes, both preamp och power.
Caps: What changes can be made here? Read something about orange drops, seems a common mod. Good idea? Bad? Others?
Anything else?

I made it!!!!! (With a lot of help from you guys ), I made my own 59 bassman It's actually working
Thanks a million, you are all fantastic for taking the time and effort.





//Jibe

[loudthud]

OOPs. I was wrong about the 100K. 56K would be vintage correct for an 8 ohm tap, 27K for a 2 ohm tap. 39K is about right for 4 ohms. In amps where there is an adjustable output impedance (tap) the feedback is usually connected to one of the taps before the selector switch. If the value is too low, the power amp could become unstable at some setting of the Presence control. You can experiment with the value but if the amp starts to sound sick, you could have gone too low. The higher the value, the less your Presence control will work so a happy balance should be sought.

[tubeswell]

So it sounds good with a plate voltage of 420VSC at idle aye? I thought it would. Even tho the Fender Scheme is 50 years old, 420 can still sound good when the bias is right. Well done!

[jibe]

It sounds good, yes! But it still don't put out what I thought, still low ouput. But this time it's a punchy nice fender sound, maybe a bit bass heavy, but I can't say it's about 40 watts. Maybe 15-20.
I played it all the way up to 8-9 on the volume in the little cabin I work in.
I can't play my Laney LC30 II, past 4-5. Do you think the low B+ could be a factor here?
When I lowered the bias voltage last time, B+ went up, but I can't lower bias voltage any more. Maybe it's just time to bias, see what B+ ends as. I'm just not sure these tubes are the ones I want in my amp. New tubes, don't know wich just yet, and orange drops are replacements I'm thinking of, was hoping for a bit on input on that. Or maybe I should play for a while and let it grow on me.




//Jibe