Just fired up my 69 100 watt kit but blowing HT fuse

redozzman · Post by **redozzman** » Wed Feb 21, 2007 11:46 pm

I followed the procedures on the step by step instructions. My initial readings were 3.31 vac on pins 2 and 7 on outputs and on down the line. I went to the next step bias voltage was fine and was getting and I was getting 515 dc voltage. On to next step. My readings were good I then installed pre,s readings look in line. next power tubes. Flip stanby no sound. then pin 3 was getting no readings and ht fuse blew.

WHere do I start?

rockstah · Post by **rockstah** » Wed Feb 21, 2007 11:53 pm

hard to tell from the pictures - i cant seem to make out how your power cord is wired. recheck how the switches and diodes are wired.

HIn · Post by **HIn** » Wed Feb 21, 2007 11:59 pm

[quote="redozzman"]I followed the procedures on the step by step instructions. My initial readings were 3.31 vac on pins 2 and 7 on outputs and on down the line. I went to the next step bias voltage was fine and was getting and I was getting 515 dc voltage. On to next step. My readings were good I then installed pre,s readings look in line. next power tubes. Flip stanby no sound. then pin 3 was getting no readings and ht fuse blew.

WHere do I start?

Are you using slow blow fuses. had the same problem when I used fast blow fuses. If that doesnt work then my next thing to check is output tubes

Take care
Dan

redozzman · Post by **redozzman** » Thu Feb 22, 2007 1:43 am

Sorry, those pics were taken before I wired the power cable in.

THe fuses are the ones that came with my kit. THey are not slow blow. I am not getting any readings on pin 3 of power tubes. I have added a new pic with the power cord installed

Here is a pic of the power cable,

Also is 3.31 high for VAC on pins 2 & 7? I thought that was ok?

I just replaced the fuse and started over when I went to measure pin 3 the voltage was at 531 and climbing so I fliped the standby back off.

Guitar Adjuster · Post by **Guitar Adjuster** » Thu Feb 22, 2007 9:02 am

The 2 10K Metal Ozide resistors in the middle of the board are suppose to have a jumper tying them together? Check you diagram again.

redozzman · Post by **redozzman** » Thu Feb 22, 2007 10:08 am

Great find. I did not put the jumper there. Would that cause me not to have any sound coming out? I will have to correct that. Thanks

I also found another problem, I did not have a jumper on the snubber caps and I had the choke, ot, and lead from the fuse tied to the same lug as the snubber caps. I will have to move those three wires under the board to the empty lug above the 1n4007 diode. I remember being a little confused in where the ot, and choke wires went at in that process.

I'm curious if not having the jumper on the 2 10 k resisitors would not alow bias voltage when tubes where in? and not put out any sound?

I hope this cures my problems.

Thanks for looking things over.

redozzman · Post by **redozzman** » Thu Feb 22, 2007 1:37 pm

Here is the latest

Here are my readings on the pres, with only preamp tubes installed.
V1
1. 180
2. 0
3. 1
4. 3.25
5. 3.25
6. 231
7. 0
8. 2
9. 3.25

V2
1. 188
2. 0
3. 1
4. 3.25
5. 3.25
6. 319
7. 188
8. 189
9. 3.25

V3
1. 248
2. 226
3. 342
4. 3.25
5. 3.25
6. 236
7. 28
8. 43
9. 3.25

EDIT 2:53 pm

Update: A few words of advice to the paint by numbers guys like myself. Make sure the selector switch is clicked into place. The reason I was not getting any sound was due to the fact that the selector switch was not seated correctly on the 16 ohm setting.

The second word of advice: when reading Bias current on the 1 ohm resistors on pin 8 maker sure that you meter is set to millivolts(DOH!)

My amp is up and running, is very quite and sounds great, let the tweaking begin.

ChuckLogan · Post by **ChuckLogan** » Mon Mar 05, 2007 2:28 pm

Is this problem resolved?

I had the same problem then had to use slow blow. . and kind of fixed the problem. If you are still having the problem connect your meter across the fuse and measure peak current accross it while you are playing.

On my 50 Watt I never see anything above say 0.299 Amps and the fuses are rated at 0.5 Amps. But keep in mind that 0.299 A will flash a fast acting 0.5 rated fuse . . at least radio shack fuses.

Also you could look at lowering your bias setting as the bias value directly affects the current the H+ fuse sees. I was at 85% of max for that tube now I am done around 70% and the H+ fuse is holding. The sound difference was neglible at best.

Hope that helps.
Cheers

Metropoulos Forum

Just fired up my 69 100 watt kit but blowing HT fuse

Just fired up my 69 100 watt kit but blowing HT fuse

Re: Just fired up my 69 100 watt kit but blowing HT fuse