Odd normal vol channel..

[stokes]

Way too much info there.Lets keep this simple.Put all the tubes in the amp,turn the AC mains on,if the light doesnt glow bright,and I suspect it wont,turn the standby switch to the play position,at this point the bulb may glow bright for a second as the caps charge up and then dim.If this happens you are good and the culprit was the old PT.If, when you switch the standby to on,the bulb glows full you have a short.Pull the power tubes one at a time.If the bulb dims when you pull the first tube,put it back and pull the second and see if the bulb dims as well,if so pull the other one and the bulb will dim further.90% of the time any short will be in the power supply.I wouldnt worry about the caps holding a charge,that is what they are supposed to do,I am going to guess that when you saw the 100v's there were no tubes in the amp,but anyway it is a good sign-if any of your filter caps were "leaky" or "shorted" you would see no volts on those caps as soon as you shut it down as the volts would drain imediately thru the "leak" or "short".I'm sorry but I just dont see in your last two posts where you describe the limiter as glowing full,indicating a short,so re-do the check as I just described.I could be wrong,but I think you are expecting that the light should glow bright and then dim every time,it will only glow bright for a split second when the caps are first hit with the dc.Tests performed immediately after may not produce the bright light again as the caps will still have a small charge.

[The Captain]

Apologies for too much info Mr. Stokes! (I do try and keep concise- badly obviously).

**Results with both switches flipped: All tubes in= bright lamp. Pull either power tubes or both= lamp dims**

My query is the lamp when bright. I expected to see a fully shining 100w. I see only 1/4 of this shine when bright (as if the bulb was say a ~20watter). It significantly drops from this when dim. (If my explanation here is not clear, imagine a rotating dimmer switch: my bright is ONLY at 4 on the dial, my dim is 1 on the dial. Id assumed my bright would be max 10/ dim to be 1). Hopefully I can dismiss this concern/ these are normal findings..

Thanks Captain.

[Steve Conner]

Hmm, sounds like your old PT was the problem, then. The results with the new PT sound like the amp is working correctly now. The lamp won't light fully with all the tubes in: it only lights fully if the amp is shorted out somehow.

If you're worried that the amp is still faulty and will kill the new transformer, you could try taking the old dead transformer to someone who can examine it and tell you how it died. For instance, if the heater winding is burnt out, maybe you need to check your heater wiring for shorts, etc.

[stokes]

Trying to describe exactly what brightness levels you will see is difficult to do.I get different brightness levels from different amps.I just checked a 5E3 I have on the bench,which I know has no shorts and I actually get no light at all,not even dim,whereas if I plug my MKII Boogie,which is also working right I get some light,but not what I would describe as bright.I cant positively say your amp has no shorts based on what you are saying,as Steve does,I also cant say Steve is wrong,as I cant see the light levels you are describing.If the light gets considerably brighter than it is with the mains on and the standby swith off when you flip the standby to on,I have to think there is a short somewhere.After warm-up when the standby is flipped to the on position,the light will get a small bit brighter,and possibly get very bright and settle down to about the same level as when it is in standby mode.If you are unable to make a definitive call,I would say the fact that you now have a 1amp fuse in the proper position will protect the PT if you plug it directly to the main outlet (no limiter),the fuse will blow if there is a problem.You said in an earlier post that you had 100v on the filter caps half an hour after turning it off.This is a good indication that the caps are okay,as I explained earlier.Other considerations pertaining to the power tubes would be:the tubes themselves,cathode resistor and bypass cap i.e. the cap could be shorted or the bias resistor could be shorted or too small to bias the tubes properly,and it is simply a case of the tubes being biased too hot.

[The Captain]

Ah ok- if it was definitively a usually bright 100w bulb I must see, then I'd have concerns. As there's not it seems Im a bit lost again.. BUT although I was 98% sure at this point I had a short (as only when both 6v6s pulled did the lamp dim) still hooked up to limiter, I warily just plugged the f*&%r up...

ITS ALIVE! Ive my amp back it seems GREAT! unless I still may have a short- surely not if it works though? Im inclined to use the amp with the limiter/100w for a 'safety barrier' now, but only if there is any sense in the idea-? Is there anything else I need check too to be sure? I so hope this PT wont pop again or it WILL go out the window for sure!

[stokes]

The fuse would blow if there was a dead short.If it is a case of something drawing too much current,but not enough to blow the fuse,you will notice the PT getting very hot when you use the amp.We are not talking about it getting slightly warm,that is okay,but if it gets very hot.I would not recomend playing the amp while connected to the limiter,it is for diagnosing only,use it plugged in normally and put your hand on the PT from time to time.If it doesnt get very hot after about 20-30 minutes,you should be okay.I would check the current draw on the power tubes to be sure they are okay.I would say 22 to 28ma's would be okay,depending on your plate volts,if they are any higher you may want to tweak the cathode resistor.

[The Captain]

I think Im there Mr. Stokes (at long last, 110 posts!)- so a VERY big thanks for your help and patience on this thread. Hopefully I wont be along with any more gremlins soon. Lastly, could you just remind me how to check power tube current? the chassis seems normally warm, but Id like to do as many checks to minimise any chance of this PT popping.

Cheers, Captain.

[stokes]

To check the current draw you can use a milliammeter,put the red lead on the CT of your OT and the black lead on the plate of one power tube,this shunts the current from the OT to your meter.Another way would be to check the voltage drop across the cathode resistor and do the math.
When you say the "chassis seems normally warm" I assume you mean the PT seems normally warm,if not check the PT not the chassis for excess heat.

[The Captain]

I'll try that Ma MM check tmrw Mr. Stokes. I gave the beastie a good run today. PT seems to remain normally warm, & looks to be a bit better quality so fingers crossed.. Ive a Jensen C12N in now which suits way better (cheers MJWB): that bassed-out sound gone.. great. I found the legendary overdrive too, albeit at vols I can't use unfortunately but NOW I see what the fuss is about! I kept playing it for hours (clean only as I got a complaint from 500yds away with it overdriven! but the clean is very sweet). So thanks for spurring me on folks; it been worth all the effort. Captain

[stokes]

Glad to hear you are finally happy with the sound and performance of your amp.I have to wonder if the problem with the sound was the bad PT all along.

[The Captain]

I cant say for sure as I was eager to replace skr with the C12N at same time- but it sounds much better, perhaps a bit better quality PT? Id like to add a gain footswitch (68k to ~22k) or a MV so Im trawling for info on these ideas.

Anyway Im glad to say all's finally achieved- here she is with my diy case:
http://i102.photobucket.com/albums/m...Picture284.jpg



Captain.