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PostPosted: Wed Sep 06, 2006 12:56 pm 
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Holy Ghost
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Should I have a load on the output during testing? It occurred to me last night that I probably should. I have something I can rig together. That could explain the smell.


RULE # 1 - NEVER operate a tube amp without a load.

I hope it stodd up to the abuse.

The rest looks good ! :D

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Last edited by coco on Wed Sep 06, 2006 4:17 pm, edited 1 time in total.

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PostPosted: Wed Sep 06, 2006 1:53 pm 
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Yeah, I thought so. Maybe you should add that to the instructions for dummies like me. :oops:


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PostPosted: Wed Sep 06, 2006 3:41 pm 
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It's in the Power Up section, but I guess it's not obvious enough.

Is it still working now, with a load connected?

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PostPosted: Wed Sep 06, 2006 3:44 pm 
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Some DO NOTS

• Never, never, never run the amp without a speaker plugged in. This can cause major damage.

• Do not flip the power switch off, and then back on rapidly. This can cause power supply damage.

• Never replace a burned out fuse with a bigger-amperage one. Remember - there was a reason the first one burned out, usually protecting something more expensive. Putting a bigger fuse in will just ratchet up the power level until something really vital burns out. If the second equal-rating fuse pops, turn it off and get a tech to look at it.

• Never ignore signs of high heat inside - a wisp of smoke or a burning smell is NOT normal.

• Your amp produces lots of heat, and will continue to do so even if you block the fresh air vents. Blocking the vents will overheat the amp and you may have to get some very expensive repairs done.

• Never ignore a red glow other than the small orange ends of the filaments. A red glow over a large part of the internal plates of the output tubes means they're about to melt. If you notice this, shut it down and get a tech to help you find out what it wrong.

Some DOs

Add another speaker into the "external speaker" jack; a mismatched speaker load won't kill it, while an open circuit (disconnected speakers) may do so.

Overdrive the stuffing out of it. Tubes are very forgiving of massive overdrives, unlike solid state stuff. As long as they tubes don't overheat or stay overdriven for long periods, it's not fatal.

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PostPosted: Wed Sep 06, 2006 5:40 pm 
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I'll try it again tonight.

While we're on the subject, how should I turn it on and off? Should I let it warm up or cool down in standby? Or is standby just for when you won't be using it for a while?


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PostPosted: Wed Sep 06, 2006 8:14 pm 
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To turn the amp on, flip the standby switch to standby, and then turn the power switch on. Leave it this way for 30-60 seconds, and then turn it to normal operation. This gets the heaters hot before the main power supply comes up.

To turn it off, simply flip the power switch to "off", don't use standby. This lets the still-conducting tubes bring down the high voltages in the power supply.

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PostPosted: Wed Sep 06, 2006 11:50 pm 
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B+ is 349V. I'm going to connect it to a speaker now....


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PostPosted: Thu Sep 07, 2006 12:24 am 
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...well, faint sound on the TMB channel, and no sound from the 18W channel. Here's an update on my voltages:

B+= 349
Heaters= 6.5 (pin to pin)

*V1*
1= 151
3= .86
6= 152
8= .83

*V2*
1= 160
3= 1.32
6= 252
8= 159

*V3*
1= 207
2= 45
3= 63.5
6= 202
7= 44
8= 63

*V4*
3= 8.9
7= 322
9= 308

*V5*
3= 8.8
7= 316
9= 308

They're all low, but in the ballpark. Anything look off to you? Thanks again.


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PostPosted: Thu Sep 07, 2006 12:44 am 
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Location: 31°45'32.69"S 115°46'51.29"E Perth, Australia
synthetic wrote:
B+ is 349V. I'm going to connect it to a speaker now....


I don't quite understand, have you been running the amp without a speaker or other load connected? If you have it's not beyond the realms that you have fried the OT.


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PostPosted: Thu Sep 07, 2006 1:23 am 
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I ran it without a load for about 5-10 minutes. So yeah, I might have to replace the output transformer. Tonight I built an 8 ohm load to use during testing. It's my first amp project, if you couldn't tell.


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PostPosted: Thu Sep 07, 2006 3:13 am 
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That's a bit sad. I have never been a great fan of dummy loads, I prefer to use an old 8 Ohm speaker as it gives you the opportunity to solve hum, motorboating, crackling issues as well. I have a rough speaker cabinet with a dispensable speaker in it on my bench for this purpose. Until you are sure of your OT status you are not going to get much further, your voltages are in the ballpark as you say so the next thing would be to get her singing.
Good Luck
Nigel


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PostPosted: Thu Sep 07, 2006 7:46 am 
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Voltages look respectable but the voltages at V4,5 do seem low, compared to your B+ (which is right on). This could be due in part of the OT problem because they are connected to the OT primary.

OT Doesn't sound great. :(

Fully Disconnect the OT primaries & secondaries and measure the resistance on the primary from each side. Measure the reistance on the secondary from common to each lead. Note all the values. If any are zero, it's toast.

More extensive OT testing can be found at Guitaramplifiermagazine.com

http://www.guitaramplifiermagazine.com/ ... chtip.html

If it all proves to be bad, I have single OTs here in and will help get you going.

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PostPosted: Thu Sep 07, 2006 10:42 am 
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I'll check it tonight. Hiss goes up as I turn up the volume, would this happen if the transformer was bad?


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PostPosted: Thu Sep 07, 2006 11:02 am 
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Who brought the marmalaide? Because we got toast. 0 ohms between any of the secondaries. Kids, let this be a lesson to you.

I guess I'll be contacting you about another output transformer. At least it wasn't an expensive part that I smoked. :roll:


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PostPosted: Thu Sep 07, 2006 11:23 am 
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What was the resistance on the primary from each side?

I'mm gonna measure a brand new one for reference and post it

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PostPosted: Thu Sep 07, 2006 1:24 pm 
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It was around 610 ohms from end to end and maybe 300 from middle to end on the primary side. From any of the secondary wires to any of the others it was 0 ohms.

I'm less bummed about the money than the wait to get the replacement. :(


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PostPosted: Thu Sep 07, 2006 3:58 pm 
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It was around 610 ohms from end to end and maybe 300 from middle to end on the primary side


Appprox 300 on either side of the primary center tap?

I"ll measure a new one later on. Watch this space for an update..

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PostPosted: Thu Sep 07, 2006 9:31 pm 
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Output Transformer Resistances:

286 ohm - brown to CT on primary; 339 blue to CT on primary

On secondary approx 10 ohm from each tap to black (common)

Looks like the secondary is fried.

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PostPosted: Fri Sep 08, 2006 7:57 pm 
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Hey Synthetic

I'm a first-timer right there with you. Don't give up hope. It's really very exciting to see it through. It will happen.


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PostPosted: Fri Sep 08, 2006 9:54 pm 
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I'm less bummed about the money than the wait to get the replacement. :(


Help is in the mail - EXPRESS! :D

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