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Can someone tell me what I did wrong????

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#141
will33 said:
As usual...party pooper. :D

Hey, at least I got more right this time than last time. :)

I'm admittedly no expert on transformers, but what happens on the primary side (which I guess if you're juicing it backwards would be a secondary of sorts) with respect to Pauls comment about voltage having nowhere to go?

Purely for my own educational purposes here and nothing else.
Click to expand...

It does have somewhere to go - it'll dissipate through the balance resistors on the two section B+ (plate supply) filter cap.

Potentially the high voltage reflected on the primary could take out:

Power tubes
Plate B+ filter cap

...but if it had, he wouldn't be getting sound out.
 
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#144
aborgman said:
It does have somewhere to go - it'll dissipate through the balance resistors on the two section B+ (plate supply) filter cap.

Potentially the high voltage reflected on the primary could take out:

Power tubes
Plate B+ filter cap

...but if it had, he wouldn't be getting sound out.
Click to expand...
So couple of resistors spec'd for a high voltage, but very low current circuit, being hit by lower voltage (35 volts on 4 ohms is around 300 watts, less ohms means less voltage needed to get there), but higher current signal?

Dummy loads for big amps are big things with lots of resistors and the get hot. Here's hoping those resistors you're mentioning act more like fuses.


I appreciate the time you're taking to tech it out...really. I know it's a bad thing to do what the OP did, but don't always get the details of what it will destroy, and why, and where in the circuit some part will be small enough to just blow open and stop it from going any further.
 
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#146
Jeez, this thread is a trainwreck!

I agree with what others have said - this amp is a ticking time bomb and when, not if, that OT goes down it will likely take out other expensive things along with it. Power tubes and possibly speakers.

If someone brought me this amp to look at, I'd tell them they made a HUGE mistake, and I'd immediately be emailing Heyboer to get a new OT.
 
#149
will33 said:
So couple of resistors spec'd for a high voltage, but very low current circuit, being hit by lower voltage (35 volts on 4 ohms is around 300 watts, less ohms means less voltage needed to get there), but higher current signal?
Click to expand...

A couple of resistors spec'ed for 2 watts (resistors generally aren't specified in current or voltage, but power dissipation), seeing a significantly HIGHER voltage with almost no current....

The primary will see ~20x the voltage of the secondary - so if you jack 35V into the "secondary" side, the primary will be seeing about 700V.

Funny enough - that is a pretty NORMAL voltage for that node in a SVT. The plate B+ runs at about 700V in an SVT.

The B+ stacked cap is rated at 900V (450V per section).

At 700V the balancing resistors each dissipate:

P=I*V, I=V/R, therefore P=V^2/R

P = (350V)^2/220Kohm = 0.55W per resistor. They are rated at 2W continuous and can probably handle 5-10W for short bursts.

It would take more like 2000V to kill the resistors, and the 900V cap would die LONG before you got to that point.
 
#150
Rickenbackerman said:
Jeez, this thread is a trainwreck!

I agree with what others have said - this amp is a ticking time bomb and when, not if, that OT goes down it will likely take out other expensive things along with it. Power tubes and possibly speakers.

If someone brought me this amp to look at, I'd tell them they made a HUGE mistake, and I'd immediately be emailing Heyboer to get a new OT.
Click to expand...

Well... that is definitely what I'd do if I was running a repair business for profit.

If it were my amp... I'd look for burn marks on the PCB, I'd check for noisy B+ (potential pi filter cap failure), and I'd load test it on a dummy load at full power. If everything checked out - I wouldn't touch a thing until something went bad.
 
#151
aborgman said:
Well... that is definitely what I'd do if I was running a repair business for profit.

If it were my amp... I'd look for burn marks on the PCB, I'd check for noisy B+ (potential pi filter cap failure), and I'd load test it on a dummy load at full power. If everything checked out - I wouldn't touch a thing until something went bad.
Click to expand...

But since some of the magic smoke escaped (likely from OT secondary winding insulation, yes?), assuming it passes a bench test now doesn't necessarily mean it won't blow up catastrophically tomorrow.
 
#152
aborgman said:
A couple of resistors spec'ed for 2 watts (resistors generally aren't specified in current or voltage, but power dissipation), seeing a significantly HIGHER voltage with almost no current....

The primary will see ~20x the voltage of the secondary - so if you jack 35V into the "secondary" side, the primary will be seeing about 700V.

Funny enough - that is a pretty NORMAL voltage for that node in a SVT. The plate B+ runs at about 700V in an SVT.

The B+ stacked cap is rated at 900V (450V per section).

At 700V the balancing resistors each dissipate:

P=I*V, I=V/R, therefore P=V^2/R

P = (350V)^2/220Kohm = 0.55W per resistor. They are rated at 2W continuous and can probably handle 5-10W for short bursts.

It would take more like 2000V to kill the resistors, and the 900V cap would die LONG before you got to that point.
Click to expand...


See...this us why I asked.

Thanks.
 
#153
The smoke most likely being from insulation on the windings, it would take a high temp. (high power) test over an extended period of time to see if the insulation was still doing it's job, and doing it for extended periods of time under stressful conditions.

IMO, the "simple test" would be like testing a speaker with one watt and thinking you know how it's going to behave with 200 watts.

Or testing a transmission on the rack in the shop and thinking you know how it's going to behave pulling a heavy trailer up a steep grade in the summertime.
 
#154
Rickenbackerman said:
But since some of the magic smoke escaped (likely from OT secondary winding insulation, yes?), assuming it passes a bench test now doesn't necessarily mean it won't blow up catastrophically tomorrow.
Click to expand...

Even if none of the magic smoke had ever escaped - passing a bench test now doesn't necessarily mean it won't blow up catastrophically tomorrow.

If it can pass a full power bench test without failing catastrophically, the chances that it will fail catastrophically due to whatever he did are relatively low... and SVT output transformers are expensive.

If the SVT was powering life support equipment - I'd go ahead and replace the OT just to be safe. Considering it's just an amplifier though (and the OP appears to have a backup/2nd amp)... I'd be inclined to run until/if it fails instead of going with a $400 prophylactic treatment.
 
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#155
will33 said:
The smoke most likely being from insulation on the windings, it would take a high temp. (high power) test over an extended period of time to see if the insulation was still doing it's job, and doing it for extended periods of time under stressful conditions.
Click to expand...

Actually the most likely failure would be arcing in the secondary - so a full power test is necessary, but it is unlikely to need a long term power test.

will33 said:
IMO, the "simple test" would be like testing a speaker with one watt and thinking you know how it's going to behave with 200 watts.
Click to expand...

Nah - the simple and accurate test is just to disconnect the OT and test it with a Megger. It'll be quick, easy, and it'll tell you if you have insulation degradation.
 
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#157
aborgman said:
Even if none of the magic smoke had ever escaped - passing a bench test now doesn't necessarily mean it won't blow up catastrophically tomorrow.

If it can pass a full power bench test without failing catastrophically, the chances that it will fail catastrophically due to whatever he did are relatively low... and SVT output transformers are expensive.

If the SVT was powering life support equipment - I'd go ahead and replace the OT just to be safe. Considering it's just an amplifier though (and the OP appears to have a backup/2nd amp)... I'd be inclined to run until/if it fails instead of going with a $400 prophylactic treatment.
Click to expand...


Also makes sense, assuming it's not going to take down more expensive stuff with it.

Except...what's all this prophylactic stuff? Certainly that can't contribute to the feel of this legendary amp, but make seem rather cold and impersonal.
 
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#158
Dredmahawkus said:
thats exactly who I called watertown!
Click to expand...
Without exchanging an actual name, how can you be sure you're both speaking about the same tech? Is Watertown really that small?

OP, don't be slack (like not unplugging one amp from a cabinet when using another amp) and get your SVT checked out. I have to agree that if it produced smoke, something is wrong in there and waiting to fail. If it's in the OT you don't want to mess around with it, it will already be an expensive repair without taking down any of the other amp systems.
 
#159
Theres like 4 tube amp repair places in MA! and the one in Watertown is the best he has been there since the 70s.
I just got the micro amp yesterday for a back up....and it wasnt really slack I used to have 2 GK cabs a mbfusion and a mesa 400 all tube.....I had 2 speakons on to each cab coming from the mbfusion and 2 1/4 cable coming from the tube amp...into 1 cab each. I didnt know about daisy chain until recent...I didnt think it was a big deal to have 2 amps plugged in as long as only 1 was on.....I knew 2 8ohm cabs going into 1 amp was 4ohms.....but I had no idea I couldnt do that! till this morning! I hooked the new amp up last night with a speakon....and played it for like 4 hours! no problem at all....it wasnt until this morning when I wanted to see how much headroom the backup amp had that I saw the smoke when I was really pushing the micro a wisp of smoke came up.
 
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