36w First powerup HELP!

[macombaland]

I checked my voltages and they seem to be screaming! Any guidance would be greatly appreciated. I am using the 36W GDS/Heyboer Transformer Set. I used the layout from the downloads section. If I missed something (which I probably did) let me know.

V1 12ax7
1. 315v
3. 1.4v
6. 436v
8. 2.8v

V2 12ax7
1. 147v
3. 1.4v
6. 455v
7. 376v
8. 147

V3 12ax7
1. 425v
2. 244v
3. 388v
6. 433v
7. 344v
8. 397v


the EL84's
all have 56v on pin 3
550 on pin 7
460 on pin 9


BTW, on first powerup the gz34 flashed. Needless to say, that was probably bad. Should I replace it?

[scottva59]

I had about 380v as a B+ using a 36 watt GDS set and a SS recto w/ no sag resistor. Your B+ is way too high and probably too high for your Cap ratings too.

[krx]

How is your rectifier wired? I'm guessing you may have inadvertently made a bridge rectifier rather than a full-wave, which would explain the really high voltages. Another possibility is that you've hooked up the PT incorrectly for your wall voltage.

[nyazzip]

i'd hold off on replacing the rectifier untill you can find out what else is wrong, unless you're SURE it is toast. i had a rectifier doing some arcing once and it survived
post some pictures if you can

[57chevy]

I'm thinking it's impossible (maybe?) to get 550vdc from that PT. Can you use another meter?

[macombaland]

How is your rectifier wired? I'm guessing you may have inadvertently made a bridge rectifier rather than a full-wave, which would explain the really high voltages. Another possibility is that you've hooked up the PT incorrectly for your wall voltage.

i wired it exactly like the layout in the downloads section

[krx]

I'm thinking it's impossible (maybe?) to get 550vdc from that PT. Can you use another meter?

On that note, your EL84 tube plates should be glowing like crazy at those voltages...

[darkbluemurder]

V1 12ax7
1. 315v
3. 1.4v
6. 436v
8. 2.8v

V2 12ax7
1. 147v
3. 1.4v
6. 455v
7. 376v
8. 147

V3 12ax7
1. 425v
2. 244v
3. 388v
6. 433v
7. 344v
8. 397v


the EL84's all have
56v on pin 3
550 on pin 7
460 on pin 9

Hi,

These voltages are too high. Can you please post the voltages you get at pins 4 and 5 and 9 on the 12AX7? That would help in determining whether you wired the power transformer's primary section correctly.

Cheers Stephan

[macombaland]

Hi,

These voltages are too high. Can you please post the voltages you get at pins 4 and 5 and 9 on the 12AX7? That would help in determining whether you wired the power transformer's primary section correctly.

Cheers Stephan

Ill check those when I get home. Here is how I wired the PT

[krx]

Ill check those when I get home. Here is how I wired the PT

What's the wall voltage in your country? If you've got 220-240 at the wall and you're hooked up to the 120V tap, that would explain why everything is so high.

[macombaland]

I'm in the US so its 120.

[macombaland]

could a blown rectifier cause the high voltages?

[krx]

could a blown rectifier cause the high voltages?

If the rectifier's blown then it's not rectifying anything, so no. Did you check your heater (AC) voltages yet? Also, you're measuring everything else in DC, right? And are your EL84s glowing like crazy?

[macombaland]

If the rectifier's blown then it's not rectifying anything, so no. Did you check your heater (AC) voltages yet? Also, you're measuring everything else in DC, right? And are your EL84s glowing like crazy?

I checked the heaters and they are at 3.25v. (Across pins 4,5 to 9 is 6v)

Yeah, I try to turn it on then do my measurements very quickly because the EL84 are getting ready to blast off.

[krx]

If the rectifier's blown then it's not rectifying anything, so no. Did you check your heater (AC) voltages yet? Also, you're measuring everything else in DC, right? And are your EL84s glowing like crazy?

I checked the heaters and they are at 3.25v. (Across pins 4,5 to 9 is 6v)

Yeah, I try to turn it on then do my measurements very quickly because the EL84 are getting ready to blast off.

The mystery deepens... I was expecting those heaters to be off. Try measuring the 290 taps (AC) off your PT. If you're getting ~290 there, then the problem must be in the rectifier/rectifier wiring. If you're getting something way higher there, then the PT is the problem. You can make this measurement without any tubes plugged in for safety.

[macombaland]

From each 290 tap to ground I get ~290, across both 290 taps I get ~610

[krx]

From each 290 tap to ground I get ~290, across both 290 taps I get ~610

Not your PT then. Hmmm... Are you sure you followed the schematic exactly in wiring up your rectifier?

[macombaland]

Ive gone over it again and again. The 290 legs go to 6 and 4. 5v and 0v go to 8 and 2. Maybe Ill go over my solder joints tonight.

Should I be careful about putting a new rectifier in?

[krx]

Double-check the ground on the 290-0-290 center tap. It seems that somehow you've either made a half-wave rectifier rather than a full-wave rectifier.

The heaters and PT look good, so the problem must be in the rectifier section. I guess there's a slim chance it's the tube? Never seen anything like that happen though -- much more likely the wiring.

[macombaland]

Just to be sure, pin 1 on the gz34 doesn't need to be connected?

I want to be sure that when I put another rectifier in it wont blow.
I guess I am curious about what an amp generally does with a bad rectifier tube?