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Old 22nd June 2009, 05:09 PM   #21
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You might also try cleaning the tube pins (not socket) very carefully with a very fine emery board.
I use a toothbrush soaked with WD40. It works on some of the nastiest tubes that I have found.

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I don't think a 12AX7 will work.
Nope. I tried them. The CCS will force 10 mA through the input tube which makes a 12AX7 very unhappy. Some 12AU7's will work but the volume will be low.

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I checked my guitar amp and it uses 12AX7's...
Some guitar amps (Fender) use a 12AT7 in the reverb circuit.
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Old 22nd June 2009, 08:34 PM   #22
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Default Re: Simple SE static

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Originally posted by oldmanStrat

I now get random static at a fairly low level. It comes and it goes. It literally sounds like an old radio tuner in between stations. It also seems to be getting progressively worse over time.

I'm thinking that maybe my input tube is going bad?

thoughts?

Some years ago I was re-working a poorly sounding p-p amp with exactly the same problem of medium wave noise gradually coming and fading for no reason. By chance I disconnected the global nfb loop and the noise vanished. Changing the front end tube made no difference but the noise went when the earthing layout was changed.
The sec winding from the output tranny was earthed in such a way that the loudspeaker current went via the input stage grounding. ! NO.
This problem is sim to the LS return in ic amps.

Check it !

richy
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Old 22nd June 2009, 09:00 PM   #23
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Default Re: Re: Simple SE static

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Originally posted by richwalters



Some years ago I was re-working a poorly sounding p-p amp with exactly the same problem of medium wave noise gradually coming and fading for no reason. By chance I disconnected the global nfb loop and the noise vanished. Changing the front end tube made no difference but the noise went when the earthing layout was changed.
The sec winding from the output tranny was earthed in such a way that the loudspeaker current went via the input stage grounding. ! NO.
This problem is sim to the LS return in ic amps.

Check it !

richy
I did my best to follow the assembly for the grounds in George's description... but if it was a ground problem, would it take 6 weeks to show up? The amp was dead quiet to start, and only over the last week has it been a problem child.

I found a 6201 ! The leads are pretty icky, but I'll see what I can do to clean them off.
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Old 22nd June 2009, 10:22 PM   #24
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Put in the 6201 and its been running for over an hour....

The demon has been exorcised!

I pretty much knew right away - the heaters on the "new" tube glow brighter than all of the others, where the 12At7 I could barely make out the heaters at all, even with the lights out.

Thanks for all the help!
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Old 22nd June 2009, 11:17 PM   #25
rknize is offline rknize  United States
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The EH 12AU7s I have in my preamp also have dim filaments compared to RCA and some others I've put in there. The Sovtek 12AX7LPS was the same way IIRC.

EDIT: just want to point out that dim filaments aren't necessarily indicative of a bad tube. Glad you figured it out, though!
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Old 23rd June 2009, 01:30 AM   #26
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Default Re: Re: Re: Simple SE static

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Originally posted by oldmanStrat
I found a 6201!
It looks like a GE. That should be a nice tube. I have a small stash of Hewlett Packard labeled GE 12AT7. They were the first driver tube I used in my Simple SE.

Glad you've got the problem solved.
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Old 23rd June 2009, 02:20 AM   #27
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Quote:
Originally posted by oldmanStrat
Put in the 6201 and its been running for over an hour....

The demon has been exorcised!

I pretty much knew right away - the heaters on the "new" tube glow brighter than all of the others, where the 12At7 I could barely make out the heaters at all, even with the lights out.

Thanks for all the help!

I think you'll find that a good 6201 sounds better than most USA made 12AT7A. Amperex, Mullard, and Telefunken make particularly nice sounding examples of the genre. (ECC81/12AT7A) Also look for E81CC/ECC81 types from Philips MiniWatt, Fivre, etc. Nice..
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Old 23rd June 2009, 03:24 AM   #28
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EDIT: just want to point out that dim filaments aren't necessarily indicative of a bad tube. Glad you figured it out, though!
Yup, which is why I resoldered the socket.

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It looks like a GE. That should be a nice tube.
The only markings on it were 6201 (and below) USA with a triangle.
There might be quite a few gems in this collection, but I'm sure there are as many duds. Although I did find a tube (if you can call it that) that was labeled Edison - and looked like a relay. Thats a keeper just because it looked cool.

I'm glad the static is gone too!

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I think you'll find that a good 6201 sounds better than most USA made 12AT7A.
My 12AT7 was an EH, which I'm pretty sure is soviet?

Running all night now. No issues. Back in SSE heaven
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Old 23rd June 2009, 04:24 AM   #29
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Quote:
Originally posted by oldmanStrat
My 12AT7 was an EH, which I'm pretty sure is soviet?
Russian, nowadays. They're made at what used to be called the "Reflektor" factory (now ExpoPUL?). ElectroHarmonix is one of many of New Sensor's brand names. They are the ones that bought the "Tung-Sol", "Mullard", and "Svetlana" brands here in the US. They are generally of good quality...I haven't really had any major issues with them.

I haven't noticed much difference between the AT7s I have tried in the SSE. I have an NOS RCA, some JAN tube (Philips I think), JJ, and one of these surplus Mullards that have been floating around the vendors lately. I also have a Shuguang that was used during bring up, which looks like a copy of the RCA. The reason is probably the CCS, as George has mentioned, which forces the tubes to operate similarly. I keep the JJ in there because it was cheap and readily available. I'll save the NOS tubes for an amp that cares.

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Originally posted by oldmanStrat
Running all night now. No issues. Back in SSE heaven
How sweet it is. How's that TSE coming?
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Old 23rd June 2009, 05:28 AM   #30
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[QUOTE]Originally posted by oldmanStrat
[B]Put in the 6201 and its been running for over an hour....

The demon has been exorcised!


Microphonic Tube, nuff said
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