I come to grovel and beg for assistance, voltages low!

briane · Post by **briane** » Wed 04/04/07 8:42 pm

dont wanna jump in too hard here since you all have so much going...but...

I had one build where the voltages went down to near zero when I hooked the power section up to the pre-amp. Turned out I was working off a schemo where one polarized cap was not marked for polarity...and I had it reversed.

instant ground. Not to mention there were not voltages on that capon the schemo, and using a 25v across 450v also did not work too well. Good way for sunn to protect their design....

This really sounds like a reversed cap, a blown cap, or just live voltage going to ground to me. It all seems to make sense.

Keep with it man, your almost there!

rollingelbow · Post by **rollingelbow** » Fri 04/06/07 11:46 am

Hey everyone.. seems like i am closer to solving this one. I gave a repairman a call who is located 4-5 hours from here and he gave me a few ideas. I was getting low voltages off my diodes back to standby switch and therefore having low voltage through the rest of the amp.. now, because my red/yellow wire through the .5 fuse and to ground kept blowing, i was not getting the right voltages through the filter caps. He suggested i try using alligator clips to see what happens when i run a ground wire from where the red/yellow wire connects to the fuse so that i could ground it. I did that and my voltages went up.. this is a non master volume amp and what i heard was a steady loud hum through the speaker. With a guitar I can play but it is just distortion that comes through... really loud punchy crunchy distortion.. and then I saw a bit of smoke around the last output tube. Any suggestions as to why that fuse would blow? Is it now too MUCH voltage? Should i use the two primary taps that have around 330 AC each rather than 360 AC?

Clueless in Seattle... ( Ottawa ) ..what an easter gift if i could get this bad boy working..

Cheers!

Chubsman · Post by **Chubsman** » Fri 04/06/07 12:26 pm

Did you read my last post?

rollingelbow · Post by **rollingelbow** » Fri 04/06/07 1:19 pm

woops sorry guys, i totally missed your posts.. i was over zealous in my reply and had not seen any posts for some reason.. if you guys want to pop over at some point to try to A. blow it up together, or B. get it working, i'd totally beup for it.. in the mean time I will do what you have suggested and go back through this bad boy. I am also mobile and can go nearby as i am about 5 minutes drive from Bacchus..

Thanks fellas!

Chubsman · Post by **Chubsman** » Fri 04/06/07 1:54 pm

I feel you are going too fast...
Go slow... look at the layout... can you send me that layout
stevocurran@hotmail.com

Any underboard wires missing?
Jumpers.
Grounds.

rollingelbow · Post by **rollingelbow** » Fri 04/06/07 1:55 pm

Interesting, that 1987 design is very similar until the filter cap stages where i have this standup board and the connections get routed a little differently.. the design doesn't seem as concise as what you have posted. I have attached what i am working with... it gets extremely crowded when you see it in person.Also, looking at the schem and layout, those are indeed two 220 k resistors.. strange eh?

rollingelbow · Post by **rollingelbow** » Fri 04/06/07 1:58 pm

Sent you a note via hotmail, thanks.. it will come from ppolenton@hotmail.com

rollingelbow · Post by **rollingelbow** » Sat 04/07/07 2:50 pm

Alright back to the board after discussing the problem offline with Chubsman.... I think we know that the general problem is somewhere around the power section, we've got that .5 fuse blowing and who knows why.... maybe we can get something shakin before the weekend is out..Any other ideas?

icd · Post by **icd** » Mon 04/09/07 9:50 am

rollingelbow - is there any update on the mystery of the too low voltage ? I'm waiting for the next exciting installment ...

defy · Post by **defy** » Wed 04/11/07 10:56 pm

Dear Mr Elbow,

Patience. Are you still blowing fuses? You can make a simple current limiter from an ordinary light bulb. This will allow you to power up the amp at least, the light will glow brighter as more current is drawn, but the fuse will stay intact! It is perfectly safe for your amp.

Your cct voltages will be reduced from their true readings but it will allow you to see them "relative" to one another.

Having chased my own tail on many occasions with a variety of faults i can almost guarantee yours will be the simplest of faults...eg a dry joint, missing earth, reversed connection, etc.

Just slow down and be methodical - trust yourself, you will find it. Then there will be laughter and beers, and that particular type of fault will never catch you out again.

Patience, Grasshopper, patience.

defy · Post by **defy** » Wed 04/11/07 10:59 pm

Dear Mr Elbow,

Patience. Are you still blowing fuses? You can make a simple current limiter from an ordinary light bulb. This will allow you to power up the amp at least, the light will glow brighter as more current is drawn, but the fuse will stay intact! It is perfectly safe for your amp.

Your cct voltages will be reduced from their true readings but it will allow you to see them "relative" to one another.

Having chased my own tail on many occasions with a variety of faults i can almost guarantee yours will be the simplest of faults...eg a dry joint, missing earth, reversed connection, etc.

Just slow down and be methodical - trust yourself, you will find it. Then there will be laughter and beers, and that particular type of fault will never catch you out again.

Patience, Grasshopper, patience.

rollingelbow · Post by **rollingelbow** » Thu 04/19/07 11:12 pm

No nothing new gents.. I finally just brought it in to the amp tech.. he was working mon-wed in the music store and then works on the amps thurs and Friday. Haven't heard anything yet. I am hoping he can find the issue soon... I haven't a clue. That and i am feeling the itch to build something again. Something with a cleaner layout. Would love to build one of those JCM800's. But for now, we sit and wait. I was just tired of going through it myself..... I'll def let you guys know once i know.

icd · Post by **icd** » Fri 04/20/07 1:50 am

Bunch of us going blue down here ........ Will be interesting to hear the solution to the problem.

rollingelbow · Post by **rollingelbow** » Sun 04/22/07 11:19 pm

No kidding... you and me both. I still have heard nothing. Maybe it truly cannot be solved? We shal see.. i am gonna have to call the chap this week if i have not heard something.

rollingelbow · Post by **rollingelbow** » Mon 04/23/07 5:37 pm

Supposed to be solved by Wednesday folks... but that was before he's even had a look at it. Its an "estimate". We shall see if the tech can navigate through my spaghetti plate wiring

mchauck · Post by **mchauck** » Mon 04/23/07 6:48 pm

I can't wait!!!

(taking a Xanex)

BH

rollingelbow · Post by **rollingelbow** » Wed 04/25/07 11:46 am

Ok friends.. are you ready for this...

It was a BIAS problem. The thing was running way too hot and therefore popping the fuse. This si what I suspected but was unable to troubleshoot for myself due to lack of experience but also because i didn't want to go deviating from a design which obviously is somewhat "off" from amp to amp. Might be due to transformers that come with the kit being diff who knows... So a few resistors needed changing and presto, in business.

Other problems which i new the solution to were oscillation (just had to switch output wires between output tubes). There was one weak solder joint on my volume pot as well that i just missed. But she's running and the clean sounded quite good to me in the shop so I am happy with that. Couldn't crank it because it is a non master volume but we shall see tonight what happens.

Next on my list is to learn to bias amps.. thanks to everyone that participated in this witch hunt!

Chubsman · Post by **Chubsman** » Tue 05/01/07 2:43 pm

How was the tech and how much did he charge?

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I come to grovel and beg for assistance, voltages low!