funny voltages on my rocket

[beasleybodyshop]

UPDATE: So i wired the IEC backwards. Yeah, that will give some wierd voltages

Still, here are my preamp voltages with power on and standby OFF, preamp tubes only installed, with SS rectifier in the socket.

seem really high to me. Is this because of the SS recto? I didnt think my voltages would be that much higher...

[beasleybodyshop]

Could some of these voltages be because i have no tubes in and standby is on? Didn't want to throw in preamp tubes only to have them blow with 100+v on the heater.

[M Fowler]

Your always going to have high HT voltage readings without the tubes installed but 120V on a 6.3v filament supply is not good.

[beasleybodyshop]

Your always going to have high HT voltage readings without the tubes installed but 120V on a 6.3v filament supply is not good.

Mark, i wired the IEC backwards. The results were....shocking to say the least! I have my preamp voltages listed now at the top of the post.

[Bob S]

The fuse holder should be wired up with the hot lead furthest from the cap.
Saves you from getting zapped when replacing a fuse.
I always double check heater wiring with a magnifying glass for shorts & cold solder joints.
Not because it's the main thing I screw up
I'd check heater supply voltage at each socket.
It'll be high with no tubes installed - 7vac or so.
If it's good I'd plug in pre tubes & check voltages again.
Be safe,
Bob

[beasleybodyshop]

Preamp voltages with preamp tubes installed NO power tubes:

[Reeltarded]

The fuse holder should be wired up with the hot lead furthest from the cap.
Saves you from getting zapped when replacing a fuse.


Be safe,
Bob

^^^^^^^^^^ STICKY:

Your UNloaded voltages will settle somewhere around 20-25% higher with the si diode rec so I can't say your unloaded voltages are much more than expected but doing it different makes you a little uneasy, don't it!?



Have you a rectifier tube? maybe run start up with a tube, then swap when you get comfortable.

[beasleybodyshop]

The fuse holder should be wired up with the hot lead furthest from the cap.
Saves you from getting zapped when replacing a fuse.


Be safe,
Bob

^^^^^^^^^^ STICKY:

Your loaded voltages will settle somewhere around 20-25% higher with the si diode rec so I can't say your unloaded voltages are much more than expected bit doing it different makes you a little uneasy, don't it!?



Have you a rectifier tube? maybe run start up with a tube, then swap when you get comfortable.

Woah, didnt know it would bump it up like 20 percent! If that is the case then this is looking good considering.

380V B+ did not feel very good. Jesus. I printed a big IEC cable pinout diagram and taped it in front of my workbench. somebody up there must love me haha.

I have a sovtek GZ34 laying around here somewhere, guess I could toss it in and see what gives. I didnt have a set of cheap EL84s to test, just the expensive ones I ordered, didn't want to blow those up!

[Reeltarded]

Just for your own comfort check it with the tube but it looks pretty close from here.

You need some startup tubes. That is a coin toss I hate to make even if voltages look good. A new amp might do something stupid 20 minutes into that first wailing test with a guitar plugged in or even 3-4 hours. Actually, if they sound good i might leave them in for months. hah

and with more coffee let me correct my above post because I meant unloaded voltages being unexpectedly higher but when loaded it's more like 10-12% with SI vs tube.

[didit]

Hello -

I keep a handful of 20W 10K ohm power resistors used to provide reasonably close dummy load when testing a repair or firing up a new amp. On an express or liverpool style a pair in parallel gives you 5K @ 20W, which is enough to pull down power rail from the center tap of the output primary. Then once that looks good, load up with preamp tubes and you'd get fair measure of idle voltage down the chain. If you have scope and signal source you can even check/diagnose the preamp before risking it all with power tubes etc.

FWIW.

Best ... Ian

[beasleybodyshop]

Hello -

I keep a handful of 20W 10K ohm power resistors used to provide reasonably close dummy load when testing a repair or firing up a new amp. On an express or liverpool style a pair in parallel gives you 5K @ 20W, which is enough to pull down power rail from the center tap of the output primary. Then once that looks good, load up with preamp tubes and you'd get fair measure of idle voltage down the chain. If you have scope and signal source you can even check/diagnose the preamp before risking it all with power tubes etc.

FWIW.

Best ... Ian

So i think what your saying is wire in a pair of 20W 10K resistors in parallel between the OT CT and the standby switch? And this will give me approx. "loaded" voltages that I should expect to see when i install power tubes?

[didit]

Hmm -

Not exactly. I (very carefully) clip the load to ground and then B+1. But if you wanted to test upstream of the standby then clip to the positive (+) end of your first pair of power filter caps.

I do this starting with the power off and filter caps checked they're fully drained. And then (very carefully) using a pair of alligator clip leads. I usually put some tape or tie-downs in to make sure nothing will move and short while testing.

I have to underscore very carefully as this messing somewhat recklessly with the highest voltages inside the amp.

Best ... Ian

[beasleybodyshop]

Ok i think i get it. Basically your just shunting some of the load to ground with a big ol resistor.

Yes, careful is the word. Last nights event was kind of a scary moment.

[beasleybodyshop]

Picked this up today from an old ham radio guy ive recently made friends with. "Here" he said "I have ten or twenty of these and they arent doing me any good sitting in a box" !

[Reeltarded]

WHAT A JERK!

You, not him..