The smell of resistors in the evening

[moggi1964]

R16 to be precise.

Was measuring the two caps C11 and C9 and C11 I could get close to 175V but the other would shoot up to over 350V (brought up via Variac).

I swapped the 5842's around and it stayed with the channel so it seems not to be the tubes.

R16 then smoked so I shut down.

Any advice? What could cause 350V at C9?

I should add that B+ and B- are within expected range.

 

[moggi1964]

Anyone?

 

[jan.didden]

Well it's unknown what it is you are talking about, so it's a bit hard to say something sensible.

 

[JP]

Sounds like a bad 10M45 - drawing excessive current.

 

[JonSnell Electronic]

Resistors too small wattage?

 

[Frank Berry]

Give us a clue. A schematic would be good.

 

[moggi1964]

Sorry, I thought I had mentioned it was the TSE I was building.

JP; thanks, I have ordered a replacement as I thought that might be a culprit.

Jon, checked the resistors match the Part List.

Being doing some measurements comparing resistance across resistors and they seem to match on both sides (R16 slightly off now that it smoked).

I'll start by replacing the 10M45 and see how that pans out.

 

[JP]

Does that channel red plate the 5842?

 

[moggi1964]

Yes it does JP!

You are on to something here I can feel it

 

[JP]

Yep, the 10M45 is a goner. Unfortunately, that 5842 may be as well. I'd replace R16 as well - I never trust them after they've been overheated.

 

[moggi1964]

Have two 10M45's and two R16's coming (best to be sure, right!) and just bought a new pair of 5842's on the bay.

The old CCS is proving a pig to remove, I think I need a second set of hands so will attempt that tonight.

Thanks JP

 

[jan.didden]

Just cut it off and remove the stumps one by one...

 

[moggi1964]

Now why didn't I think of that!

Thanks Jan, saved me a bunch of time and frustration.

 

[moggi1964]

So I discovered that some solder had run down one of the legs (picture soldering underneath with the CCS hanging upsidedown) and had managed to form a bridge between two legs (too much solder I guess).

Won't make that mistake again.....hopefully!

 

[jan.didden]

Won't make that mistake again.....hopefully!

Ohh but you will - I've done if more than I like to admit.
But then you develop a habit to look for that sort of thing first

Most diy-ers transition from 'that part must be broken' to 'what could I have possibly have done wrong here' within a couple of years

Jan

 

[moggi1964]

LOL

Well the parts are replaced but now I am getting weird numbers from B+ and B- and they are on runaway.

I need to spend some time checking through the changes I made and then I'll start a new thread if I cannot resolve the issues. Be a couple of weeks though before I can get to it.

Thanks for all your help everyone.

 

[moggi1964]

So managed to get B+ and B- in check but when measuring C9 to ground and C11 to ground (with rectifier and the 5842's in place) I am getting runaway high voltages where I should expect to get something around 175Vdc.

Up till that point the checkout was going to plan.

Suggestions on what to check are welcomed.

Thanks.

 

[JP]

You'll get high voltages until the tubes start to conduct. Mine takes ~30 seconds or so to stabilize, then you adjust from there with the trimmer.

 

[moggi1964]

I am using a Variac and getting well over 200Vdc and rising at only 70Vac on the Variac.

I'm worried about letting it run on or increasing the voltage.

Will R16, and it's equivalent on the other channel, blow before anything else does? If so, I'll risk it

Thanks JP.

 

[JP]

I see nearly full B+ at initial power on - on my monster EML 520B TSE, that's 520VDC. No problems.

Remember that you're also starving the filaments using the variac = less emission = less current the tube can pass. This means the condition will last longer.